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I have a stock, no mods 1989 Camaro 5.0, TPI 5-speed. The idle is not as smooth as my other TPI cars. Its not hunting, or surging & the car actually runs & drives pretty good, but idle jumps around over 100 rpms & its enough to see the tach needle move & I can feel it sitting in the car.
Has "newer" injectors that were installed by the previous owners service center.
What I have done so far:
I did a simple test on all 8 injectors using 100 5ms pulses & all of them dropped the same amount of fuel pressure in the rail over that time, started the pulses when the pressure dropped to exactly 40 & repeated. each injected dropped the pressure to 19.5 - 20 psi So pretty close imo. Not a perfect test, but best I can do without removing them.
Used Vaders write up on setting minimum Idle speed & that greatly improved the cold starts, but the rough warm idle is still there.
I also swapped the MAF from my 1987 & it didn't change anythingl. No difference, So I think its safe to say the MAF is ok.
Here is the data stream when at full temperature. Anything on these images look suspect?
I can make better ones, or if there are some that would be helpful to group together over shorter times just let me know.
thanks for any ideas
Also, the cooling fan had kicked in while saving the data, thats why the temperature is shown as dropping.
Last edited by F-body-fan; 08-06-2023 at 05:51 AM.
I realize this is just what the ECU thinks is happening. If there is something I should pull right from a sensor let me know.
Once the engine cools down I might do a compression test next.
Last edited by F-body-fan; 08-05-2023 at 01:30 PM.
Can you datalog in tunerpro rt ?
Is the cts dropping in that image ?
I have an older snap on solus pro that I am currently using. I have never used Tunerpro rt. I'm kinda old school
I do have a snap on verus edge that can do so much more & It has a labscope if I need to tap some reference wires directly.
But unfortunately I don't have an OBD1 cable for the scanner, otherwise I could post some much better logs
I logged the RPMs again today from a cold start & it appears to be smooth at the initial elevated idle, but as soon as it comes down to 1000rpms its already fluctuating, just cant feel it in the car because of the higher engine speeds As soon as it drops down to 750rpms that's when you can feel it & see it on the tach / data log.
On a positive note, I have to mention again how after resetting the minimum air & TPS the cold starts are just fantastic. No sputters or hesitations & the car is really running great overall.
Just this nagging idle issue.
Last edited by F-body-fan; 08-06-2023 at 07:14 PM.
So I believe I am on the trail of the culprit. I found the initial timing was set at 8 degrees not 6. So I backed it off to 6 degrees & while checking my adjustment, I noticed it would randomly advance another 6 degrees for a split second & come back to 6. This is with the timing advance disabled. this did of course effect the idle quality each time it happened.
Is there any condition that would tell the ECU to do that? Or should it not move at all when bypassed? Only thing I can think of is the knock sensor, but that should take timing away, not add.
Then for testing purposes, I turned the base timing back even lower to 5 degrees with the advance still disabled, then unplugged the iac & it just idled steady as could be.
Bad ECU?
EDIT: I just found I can jump the timing from 6 degrees to 12 degrees by just slightly opening the throttle, or moving the TPS sensor arm. This is while the timing advance is disabled. it will stay at 12 degrees at any RPM above idle & only comes back to 6 if I release the throttle completely. Normal? or Abby Normal
Last edited by F-body-fan; 08-09-2023 at 07:49 PM.
So I have been picking away at this & pretty much have it straightened out. I found a few things that were collectively making it problematic. What has been most helpful is I brought the 89 GTA home as a reference, & also to "borrow" parts from two rule some things out.
Two main culprits were the aftermarket ignition module adding limp mode timing while the ecm was in control & not in limp mode. Replaced that. Also replaced the plugs, wires, cap, rotor & took a compression test. This seems to have helped a little, but its negligible. Compression was perfect. all cylinders are at 168-170 PSI.
after all of this, the car really ran & drove well, but still just the little "roughness" when the idle would come down to 750. What was getting past me this whole time is whenever I disconnected the spark control bypass wire, the idle would be dramatically smoother. As soon as the ECM takes control and advances the timing, roughness comes right back. So I decided to swap ECM's with the GTA, (but with the original prom). no change, Then decided to pull some timing out of it. pulled it back to 2 degrees initial timing. Plugged the ecm control back in & noticed a big improvement in idle quality. So I am scratching my head on this one. Really wasn't seeing any knock counts when initial was set at 6 degrees, with exception to a few erroneous ones at start up.
Then questioned the timing mark. Decided to check TDC with my spark plug hole piston stop. No issues there either, the mark on the balancer is within 1 degree of true TDC. So what gives here? Is it possible this prom is just giving a bit too much timing at 750 degrees. it sure is happy with a little less.
I will check to see how much advanced the timing it has at idle & what it is all in & see what you guys think about it. maybe I need a different or custom prom?
Last edited by F-body-fan; 08-20-2023 at 11:33 AM.
Initial timing is currently at 2 degrees. while ECM controlled & 750rpms ECM is adding 21 degrees giving me 23 degrees total
data log says 26 degrees which would be accurate if I had the spec'd 6 degrees initial.
With the timing at full end of its curve, the ECM is adding 32 degrees giving me a total of 34,
data log says 38 degrees, which again would be spot on accurate if I hadn't pulled 4 degrees away.
So assuming this data is normal, I either need to live with losing 4 degrees of timing, or find out if there is another prom that would change the timing curve a bit
if the timing at idle is below 20 degrees its very smooth
26 or more, its starts getting rough
Thoughts? 26 degrees does not seem unreasonable to me.
Just wanted to say I appreciate you detailing your troubleshooting techniques and results. There are far too many threads on here that have an issue and then don't have the corrective actions taken. Odds are that somebody will have this issue in the future and your efforts now will help them.
Thinking about this a bit more, I decided to pull the ecm timing control once again, & manually advance the distributer at idle to see what happens. It started to get rougher right around 23-24 degrees, & very noticeable at 26. More than 26 its starts getting crabby.
so to me, this confirms this engine does not like this much timing at 750rpm's 22 seems to be the edge of where its still pretty smooth. So, I went back to 2 degrees base & plugged in the ecm control again.
Seems odd to me, this is a completely original car with 54K miles on it. It does have an aftermarket cat converter on it, but I don't see how that would effect anything. Also fresh 91 octane fuel.
Now I am being a bit fussy here, so I am not talking about an engine that's shaking the paint of the fenders. But its enough where you can see the tach fluctuate & you can feel it in the car..
How does the car run overall with 2 degrees of initial timing? I have a similar issue with my 89 L98. I think part of my issue is the AC compressor kicking on and off too much. I adjusted the AC pressure switch and reset IAC and gained some ground but not quite where I want it yet.
Runs great, but might have lost a tiny bit of zip based on my rump dyno.
Unplug the ESC wire & see how your idle is, that should tell you right there if yours is doing the same thing. I also have an 89 GTA L98 & that car is as happy as can be at 6 degrees initial.
same with my 87.
08-05-2023, 12:59 PM
