After searching all the threads about splicing in the harness, there isn't really a step by step available. It looks like I have more of the harness than most start with, so I have a few questions.

I have everything up to the back of the speedometer cut out of the car. All the sensor plugs, grounds, etc have been removed, not cut.

Where are all the connections to the C203 and C500 made? Are they spliced in? The wires entering the 3 computer plugs from the caddy dash?

The only wires I have removed so far are to the air bag sensors (the yellow plugs)

The other threads mention re-pinning the connectors, but mine are still complete. Other than shortening or lengthening the engine sensor wires, deleting wires not used, and routing everything, what else is there to connect?

Need help from the 4.9 masters!

------------------
1988 GT Wingless Fastback 5 Speed Purchased 8-4-07


1986 GT (Soon to be 4.9)
1992 Deville (Soon to NOT be 4.9)

Billiard Ball Shifters For Sale! https://www.fiero.nl/forum/Forum4/HTML/038696.html

I am not a master at this, in fact I have not even finished mine yet. But I used nearly all of the wires in the engine wire harness and lengthened then to go to the C500 and C203. That is it.
You can use a stock Fiero engine wire harness (may be best?) or just use the C203 and C500 with the wires cut as long as possible. Then use a good wire diagram to connect the Caddy wires to the Fiero connectors.




This is the thread I used to do my harness.
https://www.fiero.nl/forum/F...2/HTML/079246-4.html

I did cut every single wire in this harness and splice them together. I wanted the harness to be "stealthy"
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[This message has been edited by Rickady88GT (edited 05-15-2008).]

I'm one step behind you. I am just about to take the harness out of my caddy and start as well. I'll be keeping a close eye on this thread. If when I get caught up I'll add anything I can.

I'm looking for what to actually connect. I understand that I have to connect the C203 and C500, but what to I connect it to? What wires from the caddy go to the fiero harness? Isn't there only a few wires that are needed to go to the fiero? It looks like everything else is stand alone from the caddy except for gauges, fuel pump, etc

Not an expert, but have done a couple...

First, see my post here: https://www.fiero.nl/forum/Forum2/HTML/079246.html

Second, do you have the C500 and C203 pinouts (note: these are for the most part the same, but there are some differences in the years)?

Your choice, but I prefer to cut the bulkhead connector outof the 4.9 harness (the big gray connector in your picture). Next I connect all the wires up to the motor and lay out the wiring along to block and feed the now cut ends through the Fiero's firewall (label each group of wires for which sensor they go to and bundle them up as you go). Then you can install the C500 into the bay, run the wires to the 4.9 where they came from on the original motor - examples: C500/C2 goes to the temp sensor (green wire), C500/E2 goes to the starter, C500/C3 goes to the TACH connector on the distributor, etc. Same goes for the C203, examples: C203/J feeds 1 bank of injectors, C203/K feeds the other bank, etc. The C500 and C203 wires are either spliced into the 4.9 harness (C203/J is splice to the injectors common feed wire) or go directly to that part (C500/E2 goes directly to the starter).

I then remove the drivers seat and sit on the floor facing the ECM. Working one plug at a time and using the ECM pinout diagrams, from Rockcrawls site, start splicing each sensor/item group of wires to the ECM (shortening or lengthing as needed) - example: grab the injectors wires, the common wires go the C203 (typically red and white wires) and then take the rest of the wires and splice them to the correct plug. At this point I just match wires colors, but specifically: cylinder 1 wire (BLK) goes to ECM connector C11. The connectors are labeled on the blue parts of the plugs, the row marked with an A, B, C, etc and the pins number are labeled as well as which is 1.

I find it helpful to tie the wires up that you are not working on up to the right of the ECM so they are out of the way of the group that you are working on.

Always cut wires to the max length you can, they can always be shortened

[This message has been edited by Mickey_Moose (edited 05-15-2008).]

quote Originally posted by Carver1: After searching all the threads about splicing in the harness, there isn't really a step by step available. It looks like I have more of the harness than most start with, so I have a few questions. I have everything up to the back of the speedometer cut out of the car. All the sensor plugs, grounds, etc have been removed, not cut. Where are all the connections to the C203 and C500 made? Are they spliced in? The wires entering the 3 computer plugs from the caddy dash? The only wires I have removed so far are to the air bag sensors (the yellow plugs) The other threads mention re-pinning the connectors, but mine are still complete. Other than shortening or lengthening the engine sensor wires, deleting wires not used, and routing everything, what else is there to connect? Need help from the 4.9 masters!

Looks like you have a great start already. Use the diagrams Mickey posted and just start working one wire at a time. You'll get there before you know it. Re-pinning the connectors is optional. You'll probably only have to remove some wires since there are a few that cant/wont be used in a fiero. If you have specific questions, and you will, just ask. There are a few out here that can answer them for you.

You going with a custom chip? What can be done in the chips has changed a bunch in the last couple years and can make wiring much easier. Good luck.

[This message has been edited by Fieroseverywhere (edited 05-15-2008).]

quote Originally posted by Fieroseverywhere: There is one other printing error I found in the diagrams. It involves the fuel injector connector. The Coolant temp sensor is NOT wired into that connector as it shows in the diagram. There is actually only one 10 wire connector for the injector. 8 injector wires and 2 power. I will try to post the diagram out of my 92-93 service manual. Its much better and the wire colors and pins are the same. I can e-mail you a copy but cant seem to post it. Its in PDF format so maybe someone more computer savy can tell me how to post it. Anyone?

I'll take an email copy I'll PM you my address.

quote Originally posted by Carrluvr: I'll take an email copy I'll PM you my address.

I tried to reply to the PM but I get an error message that says I have been banned from this forum.

EDIT: Which, thankfully, is not the case. Whew! E-mail sent. It includes all diagrams needed from 92-93 deville/fleetwood/sixty special FWD versions only. Page 3 of the file is the one I'm talking about. You will see the difference immediately. You might also notice that there are 2 different wires that say they are blk/lt blu (C15&D14). This is not a typo. My 93 harness actually had 2 of the same color wires. The pins in the injector harness connector are still the same as listed on the diagrams posted by Mickey. If your harness is from a 91 they you may have a blk/red wire in place of the one going to C15 (injector #4).

[This message has been edited by Fieroseverywhere (edited 05-15-2008).]

That email would be great! carver1@gmail.com

quote Originally posted by Carver1: That email would be great!

E-mail sent.

I can post it if you email it to me (I can post in in either format: PDF file or as pictures).

BTW - thanks for point out the other error with the temp sensor, I never paid all the much attention to that part of the diagram
since I use a different temp sensor and it does not really apply. I mostly used the first 3 pages plus my written page along
with the C500 and C203 lists.

You are also correct about the 2 injectors that share the same wires colors (not with all 4.9, but some) - you should mark those
wires before you cut them - otherwise you will have to meter out the wires from the plug that connects to the injector to see which
is which.

[This message has been edited by Mickey_Moose (edited 05-16-2008).]

quote Originally posted by Mickey_Moose: I can post it if you email it to me (I can post in in either format: PDF file or as pictures). BTW - thanks for point out the other error with the temp sensor, I never paid all the much attention to that part of the diagram since I use a different temp sensor and it does not really apply. I mostly used the first 3 pages plus my written page along with the C500 and C203 lists. You are also correct about the 2 injectors that share the same wires colors (not with all 4.9, but some) - you should mark those wires before you cut them - otherwise you will have to meter out the wires from the plug that connects to the injector to see which is which.

E-mail sent. I think you'll like this one. I wanted to send it to you anyway.

I'm using a 3 prong temp sensor and the 91 Deville PCM. I have 2 of the wires running to E11 & E16. Then I have the third wire going to the C500 pin C2 which if I'm right is sending the signal to the temp gauge, but that leaves C500 pin D3 with a wire hanging out of it. On the Fiero this would go to the Coolant light indicator, do I just not connect that, or am I missing something?

Thanks,
Darren

This is great information. After I complete the harness, I plan on doing a full write up with all the info I can. Maybe we can get this knocked out for everyone that needs a harness, but doesn't have $700. Thanks for all the info. Keep it coming!

------------------
1988 GT Wingless Fastback 5 Speed Purchased 8-4-07


1986 GT (Soon to be 4.9)
1992 Deville (Soon to NOT be 4.9)

Billiard Ball Shifters For Sale! https://www.fiero.nl/forum/Forum4/HTML/038696.html

quote Originally posted by Darren's 87 coupe: I'm using a 3 prong temp sensor and the 91 Deville PCM. I have 2 of the wires running to E11 & E16. Then I have the third wire going to the C500 pin C2 which if I'm right is sending the signal to the temp gauge, but that leaves C500 pin D3 with a wire hanging out of it. On the Fiero this would go to the Coolant light indicator, do I just not connect that, or am I missing something? Thanks, Darren

Correct.

Coolant sensor with temp gage: black wire - E11, yellow wire - E16, green wire - C500/C2. C500/D3 left unconnected.

Coolant sensor with no temp gage: use the stock 4.9 coolant sensor (2 wire) and connect as original (to E11 and E16). To connect the temp light you can use the head temp sensor (not all all 4.9's) and connect this to C500/D3 (C500/C2 left unconnected).

quote Originally posted by Fieroseverywhere: I will try to post the diagram out of my 92-93 service manual. Its much better and the wire colors and pins are the same. I can e-mail you a copy but cant seem to post it. Its in PDF format so maybe someone more computer savy can tell me how to post it. Anyone?

The "Fieroseverywhere" service manual (in PDF format) can now be downloaded from here: 92-93 service manual.

[This message has been edited by Mickey_Moose (edited 05-17-2008).]

quote Originally posted by Mickey_Moose: The "Fieroseverywhere" service manual (in PDF format) can now be downloaded from here: 92-93 service manual.

Thanks!

-Connect a tach wire to the coil. I used an extra caddy coil power connector for this. I shaved off the piece of plastic that keeps it from being used on the tach side. Soldered up the white wire from the C500 and was done.


Can you take a picture of what you mean on this part? I'm not sure if I am missing a connector on the distributor or not.
Still unsure of how to connect the tach wire to the coil.
Also unsure of the heavy pink (on an 87) ignition wire E3 from the C500. How do you hook this up?

quote Originally posted by Darren's 87 coupe: -Connect a tach wire to the coil. I used an extra caddy coil power connector for this. I shaved off the piece of plastic that keeps it from being used on the tach side. Soldered up the white wire from the C500 and was done. Can you take a picture of what you mean on this part? I'm not sure if I am missing a connector on the distributor or not. Still unsure of how to connect the tach wire to the coil. Also unsure of the heavy pink (on an 87) ignition wire E3 from the C500. How do you hook this up?

The heavy pink wire from E3 is your coil power wire. The white wire from C3 also connects to the coil. It is your tach signal wire that eventually goes to the tach. Aparently the diagrams posted above dont have listed. I'm working on adjusting the diagrams for use in a fiero. They both plug into the coil near the top of the dist cap right next to each other. If you take the coil cover off you will see where the wires go. The dist cap should be marked with which one is which. If its not a delco cap then it might not. The wires coming out of the coil should be red and white also. It may have red and yellow wires if the coil's not original.

The connector you need (x2) should be in your wiring stuff somewhere but may not since its not actually part of the engine harness. It will only fit into the power side in its un-modified state. Its an 18" section of pink wire with a single wire white square connector on one end and a single wire black round connector on the other end. (hehe, hows that for a description? ) The wire probably has some loom on it. It may be in your pile of wire. I'm sure you have one. Find that connector and you should know exactly what I mean. I just used a second one from the junkyard and cut off the plastic ridge that kept me from using it on the tach side.

I'll just tried to get my dad to take a pic for me but he wouldn't do it since it's raining. Guess he's afraid he might melt, but I know he's NOT that sweet. I'll post it as soon as he sends me the pic. The car will be on the road "officially" next weekend. Then I can take all the pics you want or need myself at that point. If you need I can grab you a couple of those connectors from the yard this weekend, modify the one and send them to you.

[This message has been edited by Fieroseverywhere (edited 05-22-2008).]

quote Originally posted by Fieroseverywhere: I just used a second one from the junkyard and cut off the plastic ridge that kept me from using it on the tach side.

...actually, you can grab the tach connector from any HEI distributor that just happens to have one versus modifing the BAT connector. I forget the
specific models that I grab them from, but they could be anything from trucks to F-bodies (anything with a tach and HEI).

Just an FYI: the 4.9 uses a HEI setup, so your looking for the same type of distributor/cap - easy to spot.

[This message has been edited by Mickey_Moose (edited 05-23-2008).]

Heading out to pull a part in the morning, I should have no problem finding the part, I just have been wondering if I was missing something where it says tach and Batt on the distributor.

Thanks for all the help. I hope to have it running either sunday or monday.

Darren

quote Originally posted by Mickey_Moose: ...actually, you can grab the tach connector from any HEI distributor that just happens to have one versus modifing the BAT connector. I forget the specific models that I grab them from, but they could be anything from trucks to F-bodies (anything with a tach and HEI). Just an FYI: the 4.9 uses a HEI setup, so your looking for the same type of distributor/cap - easy to spot.

Yea. I tried that but didn't have any luck. The yard I frequent is pretty inconsistant with the exception of the 4.x caddys. Probably a better idea for others though. Good call.

[This message has been edited by Fieroseverywhere (edited 05-23-2008).]

quote Originally posted by Mickey_Moose: Ok, for some reason I was motivated to scan in my wiring notes (this is all I use - left orignal size to keep it readable). Note: credit to Rockcrawl as this is where the original diagrams came from before I scribbled all over them.

Tim, thanks to you and Rockcrawl, I am going to attempt to reverse engineer my wiring harness so I can produce an as built drawing to help me trouble shoot a problem I am having. Your hand scribbled notes are priceless, I just have one question...what significance, (if any) does the purple highlighter have?

Once I complete my drawing, I'll post it here as it might help the next person, but I have yet to see an end-to-end drawing of a 4.9 harness.

Ya know I had to go all the way out to the Cadero list just to find my way back to this thread. So here is a bump and gets added to my fav's list. Doing a total re-wire on my 4.9 while I am moving it from the 85GT to the 87GT chassis.

------------------
85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

quote Originally posted by Capt Fiero: Ya know I had to go all the way out to the Cadero list just to find my way back to this thread. So here is a bump and gets added to my fav's list. Doing a total re-wire on my 4.9 while I am moving it from the 85GT to the 87GT chassis.

...or you could have just used this one: https://www.fiero.nl/forum/Forum2/HTML/098096.html

quote Originally posted by Mickey_Moose: ...or you could have just used this one: https://www.fiero.nl/forum/Forum2/HTML/098096.html

I sent him there yesterday on Caldero

Trying to make sure I am up to speed here on this 4.9 harness.

In the picture below, all of the wires that go from the 4.9 engine to the large gray connector, those all stay as they are, right? Basically, if the wire/connector goes to the 4.9 engine in the Cadillac, the same wire/connector goes to the 4.9 engine in the Fiero.

Mickey_Moose says that he cut out the gray connector and fed the wires through into the cabin of the Fiero.

Do you just splice the wires back together in the interior of the Fiero where the gray connector once was, just without the gray connector?

Then take the 4.9 harness in the interior of the car and plug them into the 4.9 computer that you took from the donor car? The picture below lists the 3 connectors as "To computer."

Or am I way off on this?

[This message has been edited by Sir Ken (edited 07-29-2009).]

I removed the large gray connector, (C225) from the Caddie harness. I am in the process of building a harness right now for my swap . Basicly the things needed to run the Caddie are still needed. The Fiero C203 still needs to be there, and wired to the Caddie engine to do the same function. Run the AC ,Temp Gauge etc. The same thing with the Fiero C500, alt wires, back up lights etc.

I removed the gray C225 from each half one wire at a time and soldered them back togeather in my kitchen. It was cooler in the house than sitting in my shop with it 108* outside. I also learned each and every wire in the process as I checked each wire with an ohm meter and labeled them at the engine connecter end. Now that I have seen how much extra wire I have, I dont think I would do this that way again. I am gonna have to remove the excess and reconnect them again. I think just once would be better, and less chance of making a mistake.

Remember just deal with one wire at a time. There are about 50,( just a guess), wires in the Caddie harness needed. Less if you are donig a stick shift swap. About 22 wires involved with the Fiero C203/C500 harness, (counted just now).

I suggest if you can not read and understand wiring diagrams do not try this. None of this is rocket science. There are plenty of good knowledgeable members here on PFF to help you out if you hit a road block. I have read and followed every 4.9 thread I could find here. After labeling, soldering and removeing the Caddie C225 from the harness, when they are talking about C26 or A09 in these threads I understand what the are discussing much better.
Joe Crawford

[This message has been edited by josef644 (edited 07-29-2009).]

...and that's what I am doing, asking questions. So, if I may continue...

The wiring harness from the donor computer to the Cadillac 4.9, do those wires stay as they were removed? Other than maybe lengthening or shortening them to suit your installation.

Everything in the picture below that is surrounded by yellow, does it stay the same up to the plugs that go into the donor computer?

Thanks in advance.

quote Originally posted by Sir Ken: The wiring harness from the donor computer to the Cadillac 4.9, do those wires stay as they were removed? Other than maybe lengthening or shortening them to suit your installation. Everything in the picture below that is surrounded by yellow, does it stay the same up to the plugs that go into the donor computer? Thanks in advance.

Not entirely the same. The caddy has several systems that are not used in the fiero (computer command ride, heated windshield, ect). Your install may have other things also that you choose to use or not use. The part you surrounded in yellow is what you need to do the job. The center connector (big grey/blue one) is the caddy C225. You can use it or not. Its deffinately much easier if you do not. I chose to re-pin it and use it in my install as a engine quick release.

The wires for the PCM connectors do not change position. Some wires will need spliced in at the connectors, others can be eliminated completely.

At the engine you will probably use all of the engine sensors. Of course if you choose to eliminate AC, cruise, auto trans, emmissions, ect you can add/remove wires as necissary.

The minimum of what you need to do this swap...

Fiero C203 connector
Fiero C500 connector
All 3 caddy PCM connectors (1 green, 2 black)
Engine sensors/connectors (minus the 2 wire temp switch connector)
ALDL connector (fiero or caddy)
3 wire temp sensor connector (92 cavalier, ect)
Tach wire connector (from any GM car with HEI ignition and a tach in the dash)

If you have these then the job can be done. The more wiring you keep from the original harnesses the less you will have to add later. Most wires will be shortened from the stock caddy length. Remember to switch out the caddy oil pressure sender for an 88 fiero one. Hope this helps.

[This message has been edited by Fieroseverywhere (edited 07-29-2009).]

I have all of the donor 4.9 engine compartment harnesses. I also have the harnesses for the original 2.8 Fiero harnesses. To make the 4.9 run, I need the the donor 4.9 computer to make the 4.9 run, right? The 4.9 doesn't run off of the 2.8 computer does it?

I guess I am not as smart as I thought I was. I guess I need someone to explain it to me like I am a 2 year old.

I have read all the threads I could find on this subject but it's not clicking. I have the time to do all the splicing but I just want to do this right the first time. I certainly don't have the $700.00 to buy the plug-n-play.

To try and simplify things just a bit. The combining of the 2 harnesses needs to be looked this way. First you are using the Caddy harness to run the engine (and Trns if you are going Auto) and connecting parts of the Fiero harness to the Caddy harness to interface the Caddy engine and ECM to the Car (Fiero).

I built my harness somewhat differently ( My 3.4 DOHC also) by first delooming the harness then laying the harness on the engine and connecting all the sensors, From this point I then decide how I want to route the wiring. You have to keep in mind that there will be 2 ends to the harness coming off the engine (it will end up looking like a Fiero harness). The first will run up to the bulkhead pass through, this will have the ECM connectors and the wires that need to attach to the C203 connector in the cab (this end should be about 3 feet long to allow placing were it won't be near the exhaust). The second other end will be the C500 connector in the engine bay Passenger side.

I then start with one wire and lengthen or shorten as necessary. I use cable ties to keep the growing bundles in order.

You will need one C203 connector with 6 inches of wire, One C500 Connector with 6 inches of wire. and one Fiero Bulkhead pass thru connector. You can get these from your current Fiero harness. The pass through connector does come apart it is hot melt glued together just take your time.

After you have the harness running the way you want it you can then reloom the entire harness and remove the cable ties as you go.

I now that it sounds so simple! I have found that it is easier for me to end up with a nice harness by doing it this way.

My Caddy harness has worked from the first turn of the key, I had 2 minor issues with the DOHC harness 1 solder joint that broke, and one sensor that was wired backward.

Good Luck don't let it scare you and keep good wiring diagrams right to hand

Joe Sokol

------------------
85 SE Daily driver with a 3.4 DOHC build underway
88 Formula/GT 4.9 Allante Intake (My Baby)

quote Originally posted by Mickey_Moose: Correct. Coolant sensor with temp gage: black wire - E11, yellow wire - E16, green wire - C500/C2. C500/D3 left unconnected. Coolant sensor with no temp gage: use the stock 4.9 coolant sensor (2 wire) and connect as original (to E11 and E16). To connect the temp light you can use the head temp sensor (not all all 4.9's) and connect this to C500/D3 (C500/C2 left unconnected).

Does anyone happen to know what the Injection Technology harness is doing regarding the coolant temp sensor? I've got the Injection Technology harness in my
car, but it's simply connecting to the stock Caddy (2-wire) CTS, yet my temp gauge is working fine. Is it possible they're splitting one of the 2-wires on
the stock 4.9 CTS to get signal to both the gauge and the ECM? Alternatively, is it possible that the engine runs decently well with improper or no signal from the CTS?

The reason I'm even asking is that I'm trying to chase down a cold-idle problem (the 4.9 won't idle till it's warmed up a bit). Other than that the car runs great with lots
of power. The only other possible "symptom" I'm seeing is that the gas mileage seems like it may be a little low given my driving style/route (~22 mpg on nearly all rural
highway with a light foot except in one ~200 yd stretch), but not totally out of step with what others are getting. Just for comparison, on the same route, same driving
style my stock 6.0L Trailblazer SS gets ~19-20 mpg (which is significantly higher than what other stock TBSS owners report --> 14-17 mpg).

On paper, from the EPA mpg numbers for the '94 Deville 4.9L which is 16/26 mpg, I would have thought the 4.9/4T60E in a Fiero would have gotten closer to 30 mpg
as some are reporting.

quote Originally posted by BigGuyTinyCar: Does anyone happen to know what the Injection Technology harness is doing regarding the coolant temp sensor? I've got the Injection Technology harness in my car, but it's simply connecting to the stock Caddy (2-wire) CTS, yet my temp gauge is working fine. Is it possible they're splitting one of the 2-wires on the stock 4.9 CTS to get signal to both the gauge and the ECM? Alternatively, is it possible that the engine runs decently well with improper or no signal from the CTS? The reason I'm even asking is that I'm trying to chase down a cold-idle problem (the 4.9 won't idle till it's warmed up a bit). Other than that the car runs great with lots of power. The only other possible "symptom" I'm seeing is that the gas mileage seems like it may be a little low given my driving style/route (~22 mpg on nearly all rural highway with a light foot except in one ~200 yd stretch), but not totally out of step with what others are getting. Just for comparison, on the same route, same driving style my stock 6.0L Trailblazer SS gets ~19-20 mpg (which is significantly higher than what other stock TBSS owners report --> 14-17 mpg). On paper, from the EPA mpg numbers for the '94 Deville 4.9L which is 16/26 mpg, I would have thought the 4.9/4T60E in a Fiero would have gotten closer to 30 mpg as some are reporting.

not sure about the injection technologies harness....

you should be getting 28-30 mpg on the highway, 20-22 mpg in the city, and 24-26 mpg with mixed driving, but onlyif you have a properly tuned chip, properly working O2's, and the power steering input has 12v+ running to it

I'm not sure about the 4.9 - does the engine temp affect the ECM like in the 2.8 - has to reach a certain temp to go into closed loop? I ask becuase I believe Tim's car has historicaly ran "cool" meaning I don't think I have ever seen the temp gauge above the first tick mark on the gage! Wondering if a hotter t stat may help? Just shooting from the hip.

Pat

Thanks guys.

quote Originally posted by katatak: I'm not sure about the 4.9 - does the engine temp affect the ECM like in the 2.8 - has to reach a certain temp to go into closed loop? I ask becuase I believe Tim's car has historicaly ran "cool" meaning I don't think I have ever seen the temp gauge above the first tick mark on the gage! Wondering if a hotter t stat may help? Just shooting from the hip. Pat

Hey Pat, you're correct about it running cool. I wondered about that too. Although, if the Injection Technologies harness is not using the proper signal
to drive the gauge, that could be the reason...i.e. maybe it only LOOKS like it's running cool.

[This message has been edited by BigGuyTinyCar (edited 02-02-2011).]

quote Originally posted by katatak: I'm not sure about the 4.9 - does the engine temp affect the ECM like in the 2.8 - has to reach a certain temp to go into closed loop? I ask becuase I believe Tim's car has historicaly ran "cool" meaning I don't think I have ever seen the temp gauge above the first tick mark on the gage! Wondering if a hotter t stat may help? Just shooting from the hip. Pat

Yes. As most GM vehicles do. The temp in question is 180 degrees. The PCM needs to see a coolant temp reading of 180, good switching the O2 sensor (indicates that its warm enough to read properly), and a ~60 second time delay must have passed. Then the PCM will switch to "closed loop" mode and start adjusting fuel based on O2 readings.

Check out that T-stat. These engines seem to run best with a 195 degree one in my experiance. If that doesn't do it try disconnecting your temp gauge and see if that doesn't help a bit. Its not common practice to "T" one temp sender wire to run both the gauge and feed the PCM. This may bring about issues but I'm not positive.

The part numbers for the newer 3 wire CTS are in micky's wiring thread. You'll need to wire in a new connector for it and run that extra wire also if you decide to go this route.

You got a scanner? If so you can confirm what the PCM is reading for temp.

[This message has been edited by Fieroseverywhere (edited 02-02-2011).]