89 Camaro computer readings different from TR?

T

ThikStik

My sleep apnea is winning
Joined
Mar 27, 2002
I apologize for a foreign posting, but a very similiar car (ecm) is giving crazy #'s that ive never seen. Its a 89 IROC tuned port. Tps when key on gives a good reading .52 on up. Then with motor on, the reading is .19 to 1.3 volt. And the o2 reading is stuck at .445, but o2 cross counts show perfect. Code does give tps too low, and o2 sensor malfunction. All is new including ecm, and old ecm did same thing, except o2's were correct. Wiring ohms out fine also. Grounds are fine. Has anyone seen this in this generation of ecms? Ive never seen it in a TR. On my 87 GN, for comparison, I did pull the o2 wire off while scanning, key on, and it also just sat at .445. So it would seem the iroc has a dead o2, or open wire, but neither is bad.

Sorry again , but there is 0 info on the pertinant boards.
 
Chuck, its you! Havent seen much of ya around here lately. Well, i had my buddy post on there and it is devoid of any input on the old Cambirds, and the TR guys know their old computers well. Shame...his car is a real beast, very flat tork on a 350. Ill try that tho, thanks. BTW-Are you still flowing f i?
Thanks
 
ThikStik said:
I apologize for a foreign posting, but a very similar car (ecm) is giving crazy #'s that ive never seen. Its a 89 IROC tuned port. Tps when key on gives a good reading .52 on up. Then with motor on, the reading is .19 to 1.3 volt. And the o2 reading is stuck at .445, but o2 cross counts show perfect. Code does give tps too low, and o2 sensor malfunction. All is new including ecm, and old ecm did same thing, except o2's were correct. Wiring ohms out fine also. Grounds are fine. Has anyone seen this in this generation of ecms? Ive never seen it in a TR. On my 87 GN, for comparison, I did pull the o2 wire off while scanning, key on, and it also just sat at .445. So it would seem the iroc has a dead o2, or open wire, but neither is bad.

Sorry again , but there is 0 info on the pertinent boards.
Click to expand...

The '7165 ECMs are known for being intermittent. Same with the MAFs used on those engines. Try the tap test. With the engine running rap on the case of the ECM. If the engine stumbles or changes in any way the ECM is bad.

Can do the same with the MAF sensor. Rap on it with the engine running at idle.

I realize that you mentioned that the grounds are fine. The EFI harness is grounded to the engine via bolts on the backs of the heads. I think that they are on both sides of the engine. Check those to make sure that they are clean and tight.

RemoveBeforeFlight
 
Thanks...he insist that grounds are fine..you know how that goes. Thing is, before the old motor came out, the tps did this exact thing except no code. And the ecm was a different one. The o2 staying locked at .445 and open loop seem like it may be running off calpack. But i thought the tps in calpack mode would read like 2.5 volts. Nothing adds up except for ecm being loony or a lack of full power to it. Theres soo little info, i wish i had pin outs for testing. Thanks, we'll tap test.
 
ThikStik said:
Thanks...he insist that grounds are fine..you know how that goes. Thing is, before the old motor came out, the tps did this exact thing except no code. And the ecm was a different one. The o2 staying locked at .445 and open loop seem like it may be running off calpack. But i thought the tps in calpack mode would read like 2.5 volts. Nothing adds up except for ecm being loony or a lack of full power to it. Theres soo little info, i wish i had pin outs for testing. Thanks, we'll tap test.
Click to expand...

ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227165/

With the ALDL working the ECM is running from the PROM. If it were in limp mode then the ALDL link would be dead.

RemoveBeforeFlight
 
RmbFreflght,

You are the man...thanks very much! Thats more info than he ever found on other boards. I knew some one with class on the TR board would come thru.
First off, i will plow thru these schematics to find where the 3 volt memory is.
Thanks again.
 
I found pass. side grounds going to firewall, nice and tight, but wanted to go to head. So did change that....no help at all. Next step is to check for raw 12v at ecm. i just cant see how the voltage at tps changes with key on VS engine on.
 
Yes, but only with key on. Start and its down to 1.9. The 5v supply also feeds the air valve (nw removed) and the mat sensor according to the schematic that RmvB4flight supplied. Thing is, this car doesnt have a mat that ive found. So i stilll dont see how in the h#$% a 5v supply goes down to 1.9 just because car is running. If those wires were touching something, then how do they magically do it when engine turns on? Again, ecm has been rep. CEL + tps too low. O2 signal frozen at 450.
Only thing ill check later is the main feed 12vand gnd to ecm, and maybe continuity of tps wires. Im sure thyll be dead on. Car is a beast so ecm has to be running maf, etc. Idle hunting and low end balk is main symptom. Drives amazingly considering. Im sure its hurting mpg.
Thanks
 
Once you've proven the 12v into the ECM suppose I'd isolate that 5v rail at the ECM to prove to myself its a downstream load.
 
with the key on and scan tool hooked up, move the wiring on the tps. I had messed up tps reading on my iroc that really screwed with things. It ended up being bad wires on the tps plug. If this ends up being the problem you can still buy a pigtail from GM and wire it in.
 
Man, its just wacko...everything reads fine with key on, engine off. Then turn engine on, and volts go down, but will try wiggiling. Otherwise i did find that the o2 sensor was on wrong wire...dont know what connector it was on , but now the o2 is alive and ecm is getting into closed loop. Also did a pin out of most important wires, and all grounds and hot wires going to ecm. Of course, all just fine. He had a 305 in it that had 0 drivablility issues with this same tps hijinx, now this hot 350 only has some balking in low speeds. It scats otherwise with perfect wot. So i just dont know how the ecm is reading throttle corrrectly to even drive as well as it does. Again, ecm has been changed. Only wild card is this...sometimes his tach will jump and engine will burble a tiny bit when it happens. Also, he hit a bump and it made headlights barely go dim , so i want a complete check of wires to starter. Wires to starter are tight and he has repllaced ign swithc...no change. thanks, i will wiggle those tps wires. Hell, i may put acetylene on them!
 
T/b shaft worn out?
W/ no airflow the tps may be gtg..
Start the engine, the airflow is causing the t/b shaft to wobble around?
 
Interesting thought. Thing is, its like half voltage. Ill look for that nevertheless. Hey Chuck, is ethanol hard on injectors/inj tubing?
 
ThikStik said:
Man, its just wacko...everything reads fine with key on, engine off. Then turn engine on, and volts go down, but will try wiggiling. Otherwise i did find that the o2 sensor was on wrong wire...dont know what connector it was on , but now the o2 is alive and ecm is getting into closed loop. Also did a pin out of most important wires, and all grounds and hot wires going to ecm. Of course, all just fine. He had a 305 in it that had 0 drivablility issues with this same tps hijinx, now this hot 350 only has some balking in low speeds. It scats otherwise with perfect wot. So i just dont know how the ecm is reading throttle corrrectly to even drive as well as it does. Again, ecm has been changed. Only wild card is this...sometimes his tach will jump and engine will burble a tiny bit when it happens. Also, he hit a bump and it made headlights barely go dim , so i want a complete check of wires to starter. Wires to starter are tight and he has repllaced ign swithc...no change. thanks, i will wiggle those tps wires. Hell, i may put acetylene on them!
Click to expand...

Can you post everything that has been done to the car?
 
Sure..thanks
He had a 305 with headers and cam , no custom chip. And it had no drivability issues and the tps did the same thing. Now it is a 350, LT 4 cam, ported heads, hogged out tpi runners, custom chip...very strong runner with 300rwp/365tk. Trans=6speed. I always blamed the ecm, but a rebuilt one does same thing. I notice that the a.i.r. valve has 2 connections that are fed off the same 5v wire that feeds the tps and his air valve is removed. But dont see why that would affect the tps in any way. Those connections are not grounding out.etc. Ecm does give a tps code as theres no setting it....set it at .52 key on/engine off just makes it .19 when engine is on. The o2 was plugged into some wire with exact weatherpack as o2 has. It is towards firewall and it is now unplugged, and i dont know what it is. It shouldnt affect the tps. There is a speedo box that takes the place of the original T-5 speed sensor since its now a 6 speed. When checking ecm pin-outs, i didnt crank motor and look at 12v feeds, as there are several and i dont know which one is a main power feed. But im wondering if there is a 12 v sag to ecm when engine is on which drags down the tps voltage. I doubt it tho. All pins are clean , no past trauma, etc. Very similiar system to tr's. I dont see why it runs as well as it does with the wacko tps readings. thanks
 
I'll get my gm service manual out when I get home and list the flow chart and checks for you. List all SES codes you have at this point.
 
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