My ‘86 GT failed AirCare in two categories. I was rather shocked to see how bad the Driving CO was.

I have a custom chip installed with the EGR deleted. I currently have a 195 thermostat installed. The coolant temperature was 220 before I entered the testing facility. The cat is an aftermarket one that looks like it hasn’t got a whole lot of miles on it.

New ACDelco O2 sensor and the ignition system is basically all new as well (except for the wires) - ACDelco ignition module, pickup coil, MSD Blaster coil, Accel distributor cap and rotor, NGK UR5 plugs gapped to .060" and the timing was set at 10 BTDC with the A and B terminals jumpered.

Motor appears to run fine, idles smooth at 800-850 RPM. Possible lack of power though from mid to high RPM.

Here's my readings. I've added the Allowable readings to the image at the top of the columns. Notice the last time it's been through AirCare! (The car was in storage for six years before I bought it.)



Any suggestions as to why those particular readings are so high?

I have WinALDL, but to tell the truth, except for very basic things I don’t understand what to do with the info.

Seeing the results above, what should I be paying attention to and/or recording with WinALDL?

[This message has been edited by Patrick (edited 10-31-2008).]

Driving HC is real close. EGR might help that, tho my 86 did well without it. the plugs are gapped too wide. should be .45, regardless of the coil. I would only up the gap if it had a real msd box firing it.
I would regap, check your timing also, then do a leakdown test on the fuel rail, tho I doubt it is the problem as idle would also be high.
May want a new o2 sensor also, as one sitting that long may have gotten gunked up with rust. Lat but not least is the cat, if that is funked up, it won;t burn off the extra HC's.
How soon is this being done after sitting? the gas tank cleaned and loaded with fresh gas? has it had some good runs to let it blow out any crud still in it?

Thanks for the response, tjm4fun. I'll cover your questions below:

Driving HC is real close. EGR might help that, tho my 86 did well without it.
Actually, I’m surprised my NOX readings are so low without the EGR.

the plugs are gapped too wide. should be .45, regardless of the coil. I would only up the gap if it had a real msd box firing it. I would regap.
I looked up a lot of posts here in the archives before I decided to gap the plugs at .060". It seems that the wider gap is rather common when it’s just the Blaster coil which is being used. I might hold off re-gapping those plugs until I hear some more feedback on this as I’m not all that keen to pull those front plugs for awhile.

check your timing also
Timing is 10 BTDC. (Edited original post to indicate this.)

then do a leakdown test on the fuel rail, tho I doubt it is the problem as idle would also be high.
I was wondering about that myself.

May want a new o2 sensor also, as one sitting that long may have gotten gunked up with rust.
The one I took out was quite rusted, but a new ACDelco O2 sensor was installed a week ago. (Edited original post to indicate this.)

Last but not least is the cat, if that is funked up, it won;t burn off the extra HC's.
I know it’s impossible to tell from simply looking at it, but as stated above, the cat looks good. It’s a newer style hi-flow design. I’ve heard that fellas in my local Fiero club have passed the emission test with ‘87 and older Fiero V6s without a cat, so I was hoping the condition of my cat would be a moot point. One concern I do have though is whether or not the contents of the original cat are currently plugging the muffler. One reason I’m suspicious is that I don’t feel the engine has a whole lot of mid-range to top end power. The engine is smooth, it just doesn’t seem to get up and go above 3000 RPM or so. This is my first V6 Fiero, so I’m not familiar with how they should go. I guess a simple solution would be to have someone else who IS familiar with V6 Fieros drive the car and see how it compares with their own (and/or I could try theirs).

How soon is this being done after sitting? the gas tank cleaned and loaded with fresh gas? has it had some good runs to let it blow out any crud still in it?
I bought the car in early spring, and although I haven’t driven it much (as I’ve been working on it), it’s had about five tankfuls of gas through it including one tankful with injector cleaner added. The gas tank was never drained and/or cleaned, but the fuel filter was replaced after the first tankful. It’s been out on the freeway several times for good runs.

As I say, the engine appears to run just fine as far as staring up and driving around town goes. I’m just surprised though that when it kicks down into second gear on the freeway at 50-60 MPH that nothing much happens except for intake noise. The engine is not rough at all, it just doesn’t seem to pull much at medium to high revs. I don’t know if this is related to the engine failing the emission tests or not.

Can't remember, have you check the fuel pressure before. Running lean can cause high NOX also.
In fact High NOX is usually only caused by lean running or bad CAT.
Maybe a faulty MAP?

What are your INT and BLM running. Running lean would account for most your readings.

Is your exhaust system tight and not leaking?

You said the EGR was eliminated. How was that done? Any possibility the cover used is leaking allowing air in..

Have you done another log you can share?


That's my 2 cents for today..

[This message has been edited by Dodgerunner (edited 10-29-2008).]

Ok, just thought I'd hit the obvious. log a run after the engine is warmed up with winaldl. log everything, it;s not that big.
then put it on one of those file sharing sites and link it here, we can take a look at it.

rapidshare.com is easy to use and allows 10 downloads of the file.

Rory, I’ve responded to your points below:

Can't remember, have you check the fuel pressure before.
I’ve never had it checked.

Running lean can cause high NOX also.
In fact High NOX is usually only caused by lean running or bad CAT.
The NOX reading is very low. It’s the Driving CO reading which is almost six times the allowable limit!

Maybe a faulty MAP?
Would WinALDL show this up?

What are your INT and BLM running. Running lean would account for most your readings.
Sounds like a look at some WinALDL readings is in order!

Is your exhaust system tight and not leaking?
I have the dreaded “tick, tick, tick” coming from the front exhaust manifold. It’s worse when the car first starts up, then after about a minute it all but disappears.

You said the EGR was eliminated. How was that done? Any possibility the cover used is leaking allowing air in.
My EGR tube was cracked. So I blocked it off at both ends. I’m pretty sure it’s not leaking as the idle speed is perfect. (However, I will admit that there’s an awfully high pitch sound that comes from somewhere on the engine. It’s not all that loud, but I’ve been suspicious of a slight vacuum leak.) I then had a custom chip burned by a local fella (in this forum he’s known as Watts) which instructs the ECM to only “look” for the EGR if the engine temp approaches some unattainable temperature. Basically the EGR has been “deleted”.

Have you done another log you can share?
Yes, I have several.

That's my 2 cents for today...
Oh, you can’t go away for the whole day quite yet. I still need your help.

Oops got the allowable mixed up with what was...

Here is some food for thought. So high fuel pressure maybe...IE running rich...

[This message has been edited by Dodgerunner (edited 10-29-2008).]

This is a datalog from last week. It was taken before I cooked my ignition module and re-built basically my whole ignition system. However, the car was running fine and I wouldn't think the readings would be a whole lot different than what they would be now.

The file is downloadable from Here.

If I go out today in the GT, I'll save another datalog file.

Thanks for feedback anyone might be able to supply.

You are definately running rich. First, get your EGR working again. It helps a lot more than you think with emissions.
You failed the driving HC not the idle. EGR should only open under driving conditions.

Something else you can check is your cat. After your next drive, jack up the back of your car, put some jack stands under it and measure the temperature of the exhaust pipe before the catalytic converter and the cat itself. If you catch the cat quick enough, then it should be 400-600 deg when operating. If it is the same temperature at the exhaust pipe just in front of it, then your cat is bad and you need a new one.

Doug, thanks for your feedback.

quote Originally posted by Doug85GT: You are definately running rich. First, get your EGR working again. It helps a lot more than you think with emissions. You failed the driving HC not the idle. EGR should only open under driving conditions.

I’ll connect the EGR again if need be, but I’m sort of reluctant to do so as I’ve paid for and installed a custom PROM with a few tweaks done to it, including the deletion of the EGR.

I’m waiting to hear back from the fella who burned the PROM to see if he has anything to say about these readings.

quote Originally posted by Doug85GT: If you catch the cat quick enough, then it should be 400-600 deg when operating. If it is the same temperature at the exhaust pipe just in front of it, then your cat is bad and you need a new one.

What is used to measure the temperature?

To check for a leaking injector, connect a pressure gauge to the shrader valve at the end of the fuel rail.
Turn the key on to prime the system. Turn it off and let it sit for a few seconds. Turn it back on again. Then off. The system should charge to ~ 35-40 lbs, and should hold that pressure for quite a while. If you can see the pressure bleed off in a short period of time, there is a leak of some sort.
If you don't have a pressure gauge, try this. Make sure that the system is primed, and let it sit for a few minutes.
Take a pointed instrument (like a small screwdriver) and depress the shrader valve. Fuel should squirt up hard enough to hit the bottom of the open decklid. Obviously, you don't want to do this while the engine is hot. Be careful that you don't spray yourself in the face.

Also, nobody has mentioned this...
Hook up your WinALDL and look at the coolant temperature that the ECM is seeing with the engine at operating temp. It should be very close to what the gauge is reading (even though they are both read by different sensors.)
If the ECM thinks the engine is cold, it will cause the engine to run excessively rich.
The temp sensor that reports to the ECM is the one that sticks straight out, horizontally, from the end of the intake manifold, pointed towards the right side wheel well. It's well hidden, under the wiring harness and other stuff.

quote Originally posted by Raydar: Be careful that you don't spray yourself in the face.

Heh heh, thanks for the warning. I don’t have a pressure gauge, so I’ll try the screwdriver test.

quote Originally posted by Raydar: If the ECM thinks the engine is cold, it will cause the engine to run excessively rich.

One of the few readings I understand with WinALDL is the coolant temperature that the ECM sees. Coolant temps appear to be hunky-dory. When I had the 180 thermostat in (with Rodney’s low temp fan switch), the temp would definitely level off once the reported temp reached just over 180. Now that I have the 195 thermostat back in and the stock fan switch, temps are reaching up to 220 (and maybe a bit higher).

Thanks for the tips Raydar, much appreciated.

[This message has been edited by Patrick (edited 10-30-2008).]

The best thing to measure the temperature with would be a lazer pyro guage. That way you don't have to actually touch anything hot. If that is not available then you could use a meat thermonitor. Don't tell the wife you are doing this and make sure you clean it off very well after you are done.


You are going to have one heck of a time passing emisions without a working EGR. The ECU does not measure emissions coming out the tailpipe, it measures the oxygen level and determines the A/F ratio based on that. The ECU wants to maintain 14.7 A/F while cruising and at idle.

The EGR system works by inserting the inert exhaust gasses into the intake charge. This has two effects:

1. The exhaust gasses displace the incoming air. That means there is less oxygen to burn therefore it takes less gas to burn it. You get a leaner burn.
2. The exhaust gasses also heat up the incoming charge. Hotter air expands so the same volumn that goes into the combustion chamber is leaner. This also leans out the burn.

The end result is you burn less gasoline as the same A/F ratio because the space in the cylinders are filled with inert gasses. When you turn off the EGR system, then the intake charge is more dense and it is 100% air rather then air + exhaust gasses. This takes more gasoline to burn that mix at the same A/F ratio. It also means more HC are going to the catalytic converter and at a certain point, they go through the cat because the cat can only burn so much at a time. The end result is you have too much emissions coming out and you fail the emission test.

You can try to correct for this by leaning out the cruising A/F ratio. That will help to a certain point but if you go too far, your engine will start to knock and you will lose performance. If you keep going lean to clean up the emissions and your emissions will actually increase and you can damage your engine.

Just for referrence, here is a nice A/F chart with affects on emissions:

quote Originally posted by Doug85GT: The best thing to measure the temperature with would be a lazer pyro guage.

Oh yeah, like I've got a couple of those in the ol' toolbox.

Doug, I certainly appreciate the detailed description of the EGR process.

I originally deleted the EGR because my EGR tube was cracked when I bought the GT. Several members of my local Fiero club have deleted their EGRs, using a custom burned PROM, and they've all been able to pass the emission tests here. (Apparently the readings are more stringent for the 88's, so EGR deletion won't work on them, but '87 and older is supposed to be a gimme.)

Obviously there's a chance that something else is going on with my engine (besides the EGR deletion) that is causing these high readings, so I'm not willing to concede (yet) that the EGR deletion alone has caused my test failure. However, having said that, I was able to come across a good EGR tube so I now have the option of installing it and going back to using my stock PROM.

I drove over to my Dad’s last night so I ran WinALDL on the way there. I’ll get the file off the laptop and make that datalog available here shortly. I’m hoping someone who understands these readings can have a boo at it and see something worth investigating.

Ok, I just got back from seeing my mom at the hospital and have looked at your last log.

Well it does say your rich. When you can see the O2 hang on the high end you know it's fairly bad.

You need to do that leak down test. If you don't have access to a gauge check with a parts store. Most have a loaner you can use.

Also you said you have the tick from your front exhaust. An O2 works by comparing the ox in the exhaust with the ox in normal outside air. IE it uses the air around the outside of the O2 sensor and compares it to what is in the exhaust. If you have much exhaust leaking near the O2 it's going to compare bad outside air to what is in the pipe and read incorrectly.
(Just an tip..some people think they will do something nice and put some sealer on the wires of the O2 to keep water off. The sample air is allowed to leak into the reference side of the o2 via the wire and insulation. So if you cover the wire with silicone or grease it can't get it's reference Air and hence messes it up..) I actually saw this done once.

Anyway one with the log. Your MAP looks a little high at idle. I'm use to seeing mine at 30 or a little below when I'm idling at 900. Would like to hear what others think.
You MAT also seemed to keep raising. Don't know what your air temps are like there but seem to be picking up a lot or heat from somewhere. Guess you drive was not above 34 so would not be moving as much air... just noticed it..

[This message has been edited by Dodgerunner (edited 10-30-2008).]

quote Originally posted by Dodgerunner: Ok, I just got back from seeing my mom at the hospital and have looked at your last log.

Rory, I hope your mom is okay. My dad is 88 (and my mom has passed away ), so I know what it’s like to be concerned with a parent’s health.

quote Originally posted by Dodgerunner: You need to do that leak down test. If you don't have access to a gauge check with a parts store. Most have a loaner you can use.

I’ll probably try the “screwdriver” fuel pressure test that Raydar mentioned. I’ll try to prevent being shot in the face with gas.

quote Originally posted by Dodgerunner: You MAT also seemed to keep raising. Don't know what your air temps are like there but seem to be picking up a lot or heat from somewhere. Guess you drive was not above 34 so would not be moving as much air... just noticed it..

This particular set of readings were taken from a cold start and a slow drive through city streets in rush hour traffic with lots of traffic lights. I noticed both the Coolant Temp and the MAT showed 55 degrees at the start of the readings which I suspect is a positive sign that they both matched each other. And it actually was 55 degrees or so outside at that time. However, I touch upon this again later on...

quote Originally posted by Dodgerunner: Anyway one with the log. Your MAP looks a little high at idle. I'm use to seeing mine at 30 or a little below when I'm idling at 900.

You know, more and more I’m beginning to suspect my muffler is clogged with the remnants of either the current cat or the original one. When I was re-doing my ignition components a few days ago and revving the engine by hand while at the back, it seemed to me that I could see fine white "dust" of some sort flying out of the exhaust tips. Hmmmm.....

The day my GT left me stranded (as reported Here), I was revving the heck out of the engine on the highway to get it good and hot for the emission test. I was driving on the highway mostly in second gear (with a 3-speed auto). Perhaps the contents of the current cat (which was sitting for six years before I bought the GT this spring) have broken up and are now choking the muffler? Hmmmm.....

I found something awfully interesting Here. What do you guys think?



In ALDLView, I put my MAP readings over top of my RPM readings. I see several examples I believe are similar to what this fella is discussing. I'm not trying to jump to conclusions, but I'm getting a little excited.

Let’s look at the situation:

1) Failed emission test with high readings for HC and very high for CO in the Driving part of the test, but the Idle readings were quite low and well within limitations.

2) Car starts fine, idles fine, accelerates smoothly, but it’s absolutely gutless at mid to high RPM.

3) Fuel economy is terrible.

4) Saw clouds of fine white “dust” flying out of the exhaust tips while accelerating engine at the TB by hand.

5) Perhaps a little too much heat being produced in engine compartment as reported by the MAT sensor.

6) MAP sensor readings are a little high, and seem to mimic problem addressed by fella in article I linked to.

Okay, I’m very interested in getting some feedback on all this.

[This message has been edited by Patrick (edited 10-31-2008).]

Could very well be it. Here is another link that fits with what you found.
http://ca.autos.yahoo.com/m...onverteranswer2.html

You can try the screw driver fuel test but I believe that is not as valid as using an actual gauge.

Everything you've posted (driving: high HC, very high CO, low NO_x) confirms that the engine is running very rich except at idle. I've looked at the logs you posted, and it's clear from the BLMs that your ECM knows that the engine is running rich and is trimming fuel back to correct it (BLMs less than 128), but 120 is as low as the BLMs are allowed to go. An exhaust manifold leak usually results in high BLMs, so that's not likely to be the problem.

Since your HC and CO are well within limits at idle, that pretty much rules out a leaking injector or excessively high fuel pressure. You say that the timing is set to 10 degrees BTC; I presume that you set the timing properly (with the ALDL A and B pins connected), didn't you? Severely retarded ignition timing is another possible cause of the readings you got.

It does appear that the exhaust system is the most likely suspect at this point. But before opening it up and/or spending a lot of money on it, I would strongly suggest that you stick the stock PROM back in your ECM. GM did a very good job on it, and a "custom chip" can't be helping matters here. To isolate and fix the problem, you need to eliminate as many variables as possible. Be aware that running excessively rich for very long is also likely to burn out your catalytic converter, due to the higher than normal heat released as it tries to oxidize the excess HCs and CO.

[This message has been edited by Marvin McInnis (edited 10-31-2008).]

Marvin, you’ve brought up some excellent points. Much appreciated.

quote Originally posted by Marvin McInnis: Everything you've posted (driving: high HC, very high CO, low NOx) confirms that the engine is running very rich except at idle. I've looked at the logs you posted, and it's clear from the BLMs that your ECM knows that the engine is running rich and is trimming fuel back to correct it (BLMs less than 128), but 120 is as low as the BLMs are allowed to go. An exhaust manifold leak usually results in high BLMs, so that's not likely to be the problem.

I didn’t know any of this stuff. Very interesting. Thanks for the schooling!

quote Originally posted by Marvin McInnis: Since your HC and CO are well within limits at idle, that pretty much rules out a leaking injector or excessively high fuel pressure. You say that the timing is set to 10 degrees BTC; I presume that you set the timing properly (with the ALDL A and B pins connected), didn't you? Severely retarded ignition timing is another possible cause of the readings you got.

Yes, I was wondering about the fact that the idle readings were well within tolerances. Thanks for confirming my suspicions that the injectors are probably not leaking. I think I’ll check the fuel pressure though just out of curiosity as the car had been sitting for six years.

Yes, the ignition timing was done with the A and B pins jumpered. Heh heh, that much I know how to do.

quote Originally posted by Marvin McInnis: It does appear that the exhaust system is the most likely suspect at this point. But before opening it up and/or spending a lot of money on it, I would strongly suggest that you stick the stock PROM back in your ECM. GM did a very good job on it, and a "custom chip" can't be helping matters here.

Keep in mind that I went this route in the first place with a custom PROM because my EGR tube had cracked. Other fellas in the local Fiero club swear their V6 Fieros run fine (if not better) without EGRs as long as the EGR has been “deleted” in the PROM. If it turns out I’m not happy with the fuel economy with this modification, I may go back to using the EGR system and the stock PROM. However, I don't believe there's anything definitive to indicate that my big problem here is actually related to not running an EGR.


Now for something incredibly relevant to this discussion...

Anybody who’s had an interest in what’s been discussed in this thread has GOT to have a look at This recent thread!

Now, is that relevant or is that relevant?

[This message has been edited by Patrick (edited 10-31-2008).]

Ah ha !!!

Progress today. I got the cat off and it's plugged solid. Surveying this mess, I can't believe the motor could even run.

Don't know for sure at this point if the muffler is affected or not, but looking at this current cat (it's not the original), I've got my fingers crossed that the muffler is okay.

I'll post some pictures looking in both ends of the cat. It's quite interesting...

Here's the entire contents of my cat in the bottom of a bucket...



I put the gutted cat back on and started her up... What a difference in sound!

Didn't get a chance to drive the GT yet after getting the exhaust back together. However, judging from the sound, it should go a heck of a lot better.

While I had the cat off, I took the opportunity to have a look at my front exhaust manifold from underneath. Well, I found the reason for the slight "tick, tick, tick" sound coming from it. The bottom bolt is broken off on #2 cylinder. That's a chore for another day (next spring).

Next step is going through the smog test again. That'll probably be next week. Reports to follow.

[This message has been edited by Patrick (edited 11-06-2008).]

I filled up my gas tank as soon as I drove the car so I could work out what kind of mileage I was getting while the cat was plugged.

Are you ready for this...

9.4 miles per gallon.

I will say that the GT feels a WHOLE lot healthier now. Sounds much better too!

How soon before you retest?

quote Originally posted by Hudini: How soon before you retest?

When I failed the smog test I was allowed to buy three months worth of insurance. In order to buy insurance again, the car needs to pass the test (or in certain situations get a waiver).

I may as well take it through sooner rather than later, but I want to monitor a few more WinALDL datalogs beforehand to try and make sure that everything is running correctly. So I'm hoping when I upload and link to another datalog that the helpful braintrust here will have a quick peek and give me some feedback.

I’ve uploaded another WinALDL log Here which was taken last night on a short 10-15 minute drive back to my place (which means the engine wasn’t absolutely cold when the log began).

Since my last log that I linked to earlier, I’ve unclogged the cat and the car goes a heck of a lot better! (I’ve also put the 180 degree thermostat back in, just in case anyone might wonder why the temperatures are different than last time.)

Please download it and have a quick look if you understand these numbers. My concern is that the engine might still be running a bit rich. I’d appreciate some feedback on this before I take another run through the smog test. Thanks.

Patrick- Thanks for this thread. Very interesting. Good luck with retesting !

quote Originally posted by sjmaye: Patrick- Thanks for this thread. Very interesting. Good luck with retesting !

Oh, you’re welcome. I was hoping it would be informative.

I, in turn, thank those of you who've been kind enough to offer advice.

We’re almost done here (I hope). I just need to have my latest WinALDL log looked at and analyzed by a couple of you smart cookies.

Well the BLM now is staying down closer to normal.
However you O2 is acting different. If you look at you rich/lean graph it should be a smooth saw tooth. You can see yours is jerky.
That is due to the fact you O2 quits switching at times. It stops often at idle.
Might be due to the cat being gone that it cools off quickly and stops working. You might also put your 195 stat back in and see what affect it has on the O2.
Have to run, will look more later..

[This message has been edited by Dodgerunner (edited 11-17-2008).]

I'm happy that you've apparently found your problem.

One suggestion that I'll make...
I have heard of 2.8s passing the smog test with no cat, but with no cat and the 180 stat, I think it'll show high HC and/or CO. (Too rich.)

quote Originally posted by Dodgerunner: You might also put your 195 stat back in and see what affect it has on the O2.

Ah, interesting observations on the O2 behavior! Thanks Rory!

Yes, please have a more thorough look if you get a chance.

quote Originally posted by Raydar: I have heard of 2.8s passing the smog test with no cat, but with no cat and the 180 stat, I think it'll show high HC and/or CO. (Too rich.)

Excellent point, Raydar.

I had switched from the 195 to the 180 thermostat just prior to removing my cat and unplugging it. My engine compartment seemed to be getting a little warm, and I guess that stands to reason when the cat was plugged and the engine was working hard just to force the exhaust out of the system!

But yes, I was thinking myself that putting the 195 thermostat back in for the smog test might be a good idea. Heck it might be a good idea to leave it in because my gas mileage still seems lousy (although not nearly as bad as when the cat was plugged).

A question for Rory or Raydar or anyone who might be knowledgeable - It’s a custom PROM that I have installed. A local fella burnt it for me and the main reason for it being done was to delete the EGR function. He also did a couple of “tweaks” such as enable power enrich mode (which as I understand it only kicks in at a relatively high TPS value). I’ve been driving the GT rather gently, mostly because one of the exhaust manifold bolts is broken off and I don’t want to blow the gasket right out of there. However the gas mileage is still lousy, and I appear to be running somewhat rich. The fella who burned my PROM has offered to burn the PROM again with the only modification being the EGR deletion. Would this make a noticeable difference in my WinALDL readings and/or my gas mileage? Or would I simply lose a bit of high end performance if/when I do decide to put my foot into it?

What I find very interesting is what happen at time 150 to 200. Your tps is at idle but the INT is at 165 to 170 for a long time.
Then 575 to the end it does a similar thing. Any idea what was going on at those times.
The INT seems to be saying that there is not enough fuel and it's trying to add a lot more at idle. Crazy...

quote Originally posted by Dodgerunner: What I find very interesting is what happen at time 150 to 200. Your tps is at idle but the INT is at 165 to 170 for a long time. Then 575 to the end it does a similar thing. Any idea what was going on at those times.

This was a relatively tame drive home at night with little traffic but lots of stop lights. Judging from the MPH, I can only imagine that I was sitting at a long stop light between 150 and 200. From 575 'til the end, I was going downhill (from a stop light) about seven blocks before I turned the corner and came up the lane to pull in beside the house (corner lot) and park.



What do you think is happening, Rory?

[This message has been edited by Patrick (edited 11-17-2008).]

quote Originally posted by Patrick: ...A question for Rory or Raydar or anyone who might be knowledgeable - It’s a custom PROM that I have installed. A local fella burnt it for me and the main reason for it being done was to delete the EGR function. He also did a couple of “tweaks” such as enable power enrich mode (which as I understand it only kicks in at a relatively high TPS value). I’ve been driving the GT rather gently, mostly because one of the exhaust manifold bolts is broken off and I don’t want to blow the gasket right out of there. However the gas mileage is still lousy, and I appear to be running somewhat rich. The fella who burned my PROM has offered to burn the PROM again with the only modification being the EGR deletion. Would this make a noticeable difference in my WinALDL readings and/or my gas mileage? Or would I simply lose a bit of high end performance if/when I do decide to put my foot into it?

Power enrich mode is part of normal acceleration. It causes more fuel to be injected and (generally) more spark advance, at higher RPM and larger throttle openings.
It sounds like he probably set it up to kick in at a lower RPM, or with less throttle.
Either way, it should cause you to use at least a little more fuel.
If he doesn't mind experimenting, you ought to ask him to burn you a standard (but with EGR disabled) chip.
Do a little comparison testing between the two.

Having the EGR disabled will also cause it to use a bit more fuel.
With the normal (enabled) EGR function, the spark is advanced a bit, and the fuel is (I think) also leaned out a bit.

You also mentioned engine heat. A blocked cat will cause the underhood heat to skyrocket.
A friend of mine had a V6 5 speed SE that, when the cat plugged up, actually boiled the fluid in the clutch slave.
He had no power and no clutch.

All of the tuning stuff is as I understand it. If I have misspoken, I trust that someone (Dodgerunner?) will correct me.
He's been into it much more in depth than I have.
I won't even venture a guess as to the high integrator values.

[This message has been edited by Raydar (edited 11-17-2008).]

quote Originally posted by Raydar: Power enrich mode is part of normal acceleration. It causes more fuel to be injected and (generally) more spark advance, at higher RPM and larger throttle openings. It sounds like he probably set it up to kick in at a lower RPM, or with less throttle.

Raydar, I know nothing about this stuff, so I'm only repeating what I was told by the fella who burned the PROM. If I remember correctly, I'm pretty sure he said the power enrich mode was disabled on the factory PROM for this application, and one of the tweaks he did was simply "enable" it. Is there more than one kind of "power enrich mode"?

Another local club member has told me that the power enrich mode doesn't usually kick in until the TPS/throttle plate is at least 70% opened. Comments?

This discussion is good. We'll get to the bottom of all this yet.

[This message has been edited by Patrick (edited 11-18-2008).]

quote Originally posted by Patrick: Raydar, I know nothing about this stuff, so I'm only repeating what I was told by the fella who burned the PROM. If I remember correctly, I'm pretty sure he said the power enrich mode was disabled on the factory PROM for this application, and one of the tweaks he did was simply "enable" it. Is there more than one kind of "power enrich mode"? Another local club member has told me that the power enrich mode doesn't usually kick in until the TPS/throttle plate is at least 70% opened. Comments? This discussion is good. We'll get to the bottom of all this yet.

I'm pretty sure it's enabled. I'll have to check a few of my files when I get home from work.