I know there are generaly no after market chips for the 4 cyl motors, but has anyone tried geting a chip from another car that's a bit heavier? The 4 cyl's were used in an awfull lot of other GM cars some of wich are a couple hundred pounds heavier. Would seem like a heavier car would need a stronger setup in it's chip.

The number of chip choices is probably limited knowing GM, but there should be at least a couple HP in one of them.

Ogre, I realize that you're probably looking for a performance boost, but as you are no doubt aware, there are many GM chips (PROMs) that can be used to alleviate driveability problems. My 2.5L ‘87 with the 5-speed has always had a problem with detonation at around 2500-3000 RPM. This engine is designed to operate with regular grade gas, but even higher octane fuel doesn't eliminate this problem.

My research into this has turned up Pontiac Service Bulletin #89-6-65 entitled Multiple Driveability Concerns For 2.5L Engine. It addresses the following conditions for the 1987-88 Fiero:

1) Hard hot engine restart
2) Intermittent higher than "normal" idle
3) Spark knock (detonation)
4) Code 42

There are two tables listing replacement PROMs in this bulletin. One table deals with the hot engine restart problem, the second table deals with the other concerns.

So for example, my current PROM I.D. is #9562. The replacement PROM listed for my application is I.D. #3501, or part #16143453.

If anyone wants to know what the replacement PROM is for their 1987-88 Fiero, just post in this thread- the year of your Fiero, auto or manual, the current PROM I.D., and which of the four driveability concerns listed above.

You may need a scanner to identify the PROM in your car. I'm not sure if it actually says on the PROM or not. Ogre, do you know?

I haven't bought the replacement PROM yet. I'd be interested to hear from anyone who HAS replaced their PROMs according to this or any other Pontiac service bulletin. Did it help?

mines an 87 auto tranny with item 3. :)

can you email me that? I haven't read that one yet.

You can get a code scanner now for about 150$us. I'm getting one soon I think. I sick of guessing at it. the scanner also lets you check things in real time as far as I know. I have to look at it more.

there are alot of GM roms. I think the lable that is on the rom is not it's spare part #, but I'll have to look.

some of the GM codes and which computer you have are listed here http://www.cruzers.com/~ludis/ more general info can be found here http://efi332.eng.ohio-state.edu/diy_efi/

Ok, Ogre, it's on it's way. It's split up into three attachments.

Patrick, Thanks.

That TSB was Very interesting. It was especially interesting to see that the hot start problem also required replacement of the Fuel Pickup, and pump, as well as a few other things. I'd say they found either the pumps were bad, or that the system is vapor locking. Hmmmm rubber bumpers.... to keep the fuel tank from whacking the hell out of the pump maybe?

Cliff and I have been discussing some additions to the site. Cliff, I'll forward this to you, This is a real good one. While it doesn't specifically help pre 87 cars it's still a good one to put up, and it might even be related to all the hot start problem thread. never know with GM.

Hey, glad to be of service. :)

Pat,my Fiero is an 87 with a 5spd,problum# 2 intrmitant higher than normal idle. A few times the accelorator stuck under hard acceleration!! Is that from the same problum? Feel free to email with answer. rossfirth@netscape.net Thanks.

Hi Ross,

Without knowing your current PROM I.D., I can't tell you for sure what the replacement PROM is. There's a chance that it's the same as mine, but then again it may not be.

Having the throttle stick under hard acceleration is not one of the problems that a replacement PROM will cure. It sounds like something is binding in your throttle linkage. Unless you like to drive REAL fast, you had better find the problem.:)

With my Fiero, the high idle problem occurred when I restarted the engine after it had already been warmed up. The damn thing would "idle" at 3000-3500 RPM for about a minute. People would look at me like I was some kind of a jerk! Before I found out about these replacement PROMs, I cured this problem by installing a switch on my console that is wired into the Idle Air Control valve on the throttle body. It's the IAC that controls the idle speed, and my switch prevents the IAC from cranking up the idle speed when I don't want it to.

When you own a Fiero, it helps to be innovative. :)

hahahahhah!!haha,Pat thats exactly what would hapen to me!!!Evrey one whithin two city blocks would think I was acting like some kind of Punk Racer!!And you cant drive away becouse the idle only goes down when youre sitting still!!heheeheee. Tell me what PROM solved youre problum becouse it sounds identical. TAKE CARE!!

he can't tell you till you get the prom code with a scanner. there are a bunch of them, and it Does matter which one you started with.

Ross, you're not reading my posts thoroughly enough. :)

As I stated earlier, and as Ogre has reminded you, I can't supply you with the replacement PROM I.D. for your Fiero unless you supply me with your current PROM I.D.

I also stated earlier in this thread that I haven't replaced my PROM as of yet.

Again, as I also stated earlier, it was the switch that I wired to the IAC that solved my problem with the high idle speed. However, I wouldn't recommend trying this procedure without replacing the PROM first. Not only could changing the PROM fix the high idle speed problem, but it could also cure any detonation problems, etc. that one might have. I installed the switch before I found out about these updated PROMs.

Glad you got a laugh over my comment about feeling like a jerk. What used to embarrass me the most was that some people probably thought that I was trying to impress them with the sound of this little put-put 4-banger.:)

well..... I went and got an ECM scanner. 150$us. This is Not your basic code reader. It does real time scanning and has a 2 line LCD to display things on.

I'm gonna play with it over the next day or 2 and let you all know how it works.... be interesting to read the prom ID w/o pulling the console. Maybe I'll figure out why it stalls sometimes when I'm backing up.......

If someone would read the chip from the 4 banger and send me the image in binary format, I can take a look at it. DO NOT READ AN 84 OR EARILIER ROM!!! It could be the S81 chip and it will be damaged by reading it. The 85 and up should be fine. Likely a 2732.

I have the V6 6869/7170 down pat.

terryk, you've certainly been digging through the archives!

I'm curious, what is it you'd be able to do with this information?

I always suspected that the(prom)was funky from the way that my 4cyl car was so very sensitive to timing;I couldn't describe the timing unless it were to be in minutes,degrees were of another magnitude to that motor.When I finally got it to where it wouldn't ping,but still ran well,I marked the distibutor,first got a cap with brass contacts,not aluminum,so I wouldn't have to endure that so soon again.
Ogre,when looking for replacement chips,look at the differing intake manifolds also;they're different per chassis I recall;chips will be different based partially on this factor as well.
Got my car running as well as I believe it could without internal changes by raising the fuel pressure a bit(one turn on the regulator),and a little adjustable resistance(pot)soldered,inline to the temp sensor,this afffected things a little different than the pressure change,and was a more minimal effect as well.Had to run premium also.
Oh,the idle air valve settings are critical to running also,had to try a few settings to get it right.
Good luck

This is an old thread...........

I'm not too interested in changing the 4 cyl prom..... It was more of a musing. After changing the thermostat to 180F, and locking the fan on, I don't have any more pinging even in dead traffic. The car has picked up some power as well. There's another thread, or three, about that tho........

After a fair amount of research,,,, Most of the 4 cyl proms are close to maxed for the engine they are on. With the exception of some service proms that correct specific problems, no one makes any after market proms. Part of the reason is that the 4cyl is gennerally perceived as weak, and part is because they don't think there would be any volume.

I have found a couple places where ECM data is available in quite a bit of detail. Including a good amount of Fiero specific data. The general feeling is that there isn't allot that you can do to the 4 Cyl PROM that would increase performance. On the other hand, some things like Idle spark advance could be changed, and that might make the engine idle better. I don't have time to fool with it, Plus I don't have the data for the 87 which is far diferant from the distributor motors.

Hey theorge does my 1986 2.5 5-speed fiero prom come with a FREE pac-man game inside were I could hook it up to my ATARI?LOL J/K

Agreed. There is no "con-o-liquid dragster" changes for the eprom. GM does a dang good job of tuning. Except for turbo engines, there is no hidden power to be had.

About the best you can do is get all of the the power all of the time, but considering the age of the ECM, it is unlikely there is any torque management, so even that is not going to happen.

You could add some spark, bring the fan on temps down (if they are ECM controlled), remove the rev and speed limiters, maybe lean it out a bit for more power. Things like that.

Terry, if you are able to modify the timing, I think that there might be some interest in what you are proposing. Earlier in this thread, I had mentioned that my ‘87 2.5L has a problem with detonation between 2500 and 3000 RPM. I also mentioned in a different thread about DIS ignition that the idle timing was way too far advanced. This is a quote from that thread.

"On the ‘87 2.5L, the timing at an idle as set by the ECM is supposed to be 38 degrees BTDC. This seems unbelievable to me, but I've heard this from several reliable sources. This would explain the relatively rough, uneven idle, and the high emissions at an idle. The only reason this engine ever passes a smog test is because the "cat" has to work furiously to burn up all the raw fuel leaving the engine. I was able to see the proof of this myself when I had my Fiero smog tested immediately before and after a new cat was installed with NO other modifications done to the engine. The difference in emission levels was amazing. My 2.5L happens to run very strong, so I don't believe that there is any other problem contributing to the rough idle and emission levels."

If you're interested, the entire thread can be found here:

http://212.206.1.44/ubb/Forum2/HTML/000412.html

As I was discussing with Ogre in that thread, GM makes a replacement PROM which supposedly eliminates the detonation problem and the high idle speed, etc. However, this replacement chip does nothing to address the problem of the way too far advanced idle timing.

What would you be able to do?

Let me look at the thread and see what is happening.

I don't have a 2.5L prom, so if some can read it, I will look at it.

6864 or 748 ECM? The 748 would be easier to work with.

I *think* they are TI 2532's. Hope they aren't fusables!

We can go offline with this if you prefer. It might get boring to some.

yep, they run it pretty high in the 86.

Again, what is the ECM part number we are talking about?

1226864 or 1227748?

Don't take the continuation of this thread off the forum please.

DIS idle advance is also high..... around 30 deg.

All the proms I've seen are 2700 family, or their equivalent fuse/mask unit. I have an extra 85 prom here some place..... All GM proms used in Fiero should be readable on standard hardware.

I can tell you part of the ping problem in the 2.5 is definatly temperature related. Try the simple change to a 180F thermostat, and locking the fan on. (Locking the fan on is pretty much a requirement below 45-50mph) The 180 stat keeps the engine around 190F, instead of the 210-220F the 195 leaves you at. this gives a bit of performance boost, and it's less than 10$.

Sorry, it's a 27C128. Code and calibrations.

Cailbrations run from C000-C7D2. Code starts at C7D9.

The spark is about 30 degrees at idle. I haven't figured out if there is an extension table for the spark. It does look like there is a base coolant spark advance adder.

So what is the question? 8^)

Terry

Ok, final comment on this thread.

Changing the spark table is not the solution. GM set the advance that high for a reason. Keep in mind that both timing and IAC is used for idle stability (makes it smoother). That's why you sometimes see the timing mark moving around at idle.

Are you guys sure you don't have dead or clogged EGR's? That would be the first thing I would look at.

Terry

Well Terry, I'm glad I didn't bother trying to decipher that information you emailed me. It might as well have been in Greek.:)

I replaced my EGR with an aftermarket unit that uses "washers" with different sized holes to make adjustments with. I couldn't swear to the fact that it has ever worked properly.

most after market EGR's use the washer. I usually paint the area the washer rests in with some high tack, or "supper 300", permatex, then stake it acording to direction. That makes sure it doesn't leak around the outside edges.

I had oroginaly replaced my EGR because I was having intermitant wierd codes in the ECM. Plus the old one was just in bad shape. One thing you want to watch out for is that if the new one came with a plastic elbow on top, is that the elbow isn't leaking vacuum.