I've found lots of answers on this forum, but I need a little help with an issue before I proceed. Any input would be appreciated.

1985 Camaro IROCZ 305 TPI. Recently began experiencing a hesitation at idle, along with rich fuel smell from exhaust and the occasional pop in the intake. The fuel pressure is good, fuel pump relay replaced, fuel injectors have been replaced with the correct replacement injectors. HEI and distributor cap have also been replaced. Timing is also correct. Today I decided to unplug the advance wire to the distributor and the hesitation went away. I have also had the inline fuse to the fuel pump blow on multiple occasions recently. Would the car be experiencing an ECM issue? I wanted to get some input before I attempt replacement of the ECM.

 

This may sound ridiculous but I'd start with checking and cleaning all the grounding points. Some major connections are behind the engine on the heads, hard to get too but sure get corroded and loosen up over time. I can't imagine the ECM causing these problems. Do you have access to a scanner?

 

That's actually what I was doing when I saw the advance wire that goes to the distributor. Decided to unplug it and see how the throttle responded. Was kinda shocked it made such an improvement. I only checked a couple of grounds that I could reach easily. I do have the cable to be able to hook up my laptop and run Tunerpro, but i don't have much experience with it.

 

You confirmed fuel pressure is good, and your injectors were serviced. Now remove the vacuum line from your fuel pressure regulator, and face it towards an area where you can see the end of the line from the drivers side door. Reaching in through the opened window, turn the key in the On position w/out starting the engine and watch for fuel trickling out of the end of the vacuum hose at the same time during engine prime. If you don't see any, then start the engine, and give it a few minutes and wait for it. If any fuel makes its way out of the end of the vacuum line then you have a ruptured diaphragm in the regulator housing and it needs to be replaced. Provided your fuel pressure is in fact good, and your injectors are in fact good, and with no ECM codes being prevalent, it can't really be anything else... unless another sensor is skewing data and you're unknowingly locked in Open Loop. Disconnecting the distributor wire did nothing other than effect your SA. If anything, pull the plugs and check to see if one or two of their electrodes is toast. That will affect your air/fueling as well...

- Rob

 

Thanks for the replay Street Lethal. I failed to mention that I did replace the diaphragm when I replaced the fuel injectors. I'm going to go thru the other ground locations on the heads and see if that helps the issue. Hopefully its a ground wire issue causing the ECM and fuel pump wiring to blow that fuse.

 

If you're running Rich (which is what you mentioned) it won't be the fuse, and if there are no SES lights it isn't the ECM. Unless you are mistaking a Lean scent for a Rich scent in the exhaust (you mentioned popping in exhaust, that is a Lean condition not Rich), then it has to be in your combustion chamber. However, if you are Lean, which is what I am thinking due to the popping in the exhaust you mentioned, then it is something entirely different. Grounds in the head ground the bank, not an individual injector (Batch Fire). If the engine starts and idles, but has a scent in the exhaust and occasionally pops, that is something else, not a ground. Check plugs and for vacuum leaks.

- Rob

 

Will do.. thanks for the input, Rob! I will check for vacuum leaks and take a peek at the spark plugs. These are the things I was hoping people would suggest as they are pretty easy things to check before doing something like replacing the ECM.

 

Trust me, do not replace your ECM. It's not that. I know it is very hard to analyze an engine by trial and error, but your best bet is to get it datalogged. Example, a simple Coolant Temp Sensor that is reading wrong (they go bad in time) might tell the ECM the coolant is 100* F when it is really 150*F. This will not trigger an SES light, however your AFR is stuck at 13.5 AFR (Open Loop) and not the 14.7 (Closed Loop) it needs to be. This alone will cause a Rich scent, and stumbling...

- Rob

Edit: Incidently, a dead O2 sensor will cause the same issue as the CTS example described above...

Get it datalogged.

 

Do you have any suggestions why unplugging the spark advance wire would cause it to smooth out and run so much better? As soon as I plug it back in, it goes back to the major hesitation. Cold start with it plugged in, I get the hesitation and the idle is erratic. 500rpm to 1500rpm. Once it warms up, the idle will smooth out, but the hesitation remains. Unplugging that wire smooths out the idle and the hesitation.

 

When you break the Loop of ECM control, it causes the engine to run on predetermined and fixed values, similar to a carburetor system. The ECM monitors your spark advance in relation with your fueling through O2 correction. When you break the Loop (Open Loop) you are forcing the engine to run in a fixed state with no correction, so it somewhat feels better, but not as near as efficient. With no SA control, you are basing your timing off of a fixed setting in the ignition module (default)...

- Rob

 

A lot of this stuff has been explained over and over again, decades ago, but I see you are new, and I don't mind taking the time. If you are unknowingly stuck in Open Loop, you are idling at 13.5 AFR. When you hit the go pedal, you are going to have hesitation from it being too Rich. You are also going to have a surging idle because the RPM wants to go higher due to the increased fuel, but the TPS is forcing it to go lower, thus the game of tug and war ensues. You need to get it datalogged if there is more to the story, because you didn't mention surging or erratic idle in the beginning. A datalog will underline what it is immediately. Without one, then you will have post after post of possible causes until you eventually find the culprit.

- Rob

 

It seems so odd that so many systems going through the ECM have gone bad at once. The car ran alright on the pad and around the building but had trouble when hitting third (automatic). The cooling fan is not working and the gauges do not work. Could it be the ECM and how do I check it? The big question is what works on the auto.

 

Mine is not shifting from second into third but going into neutral. I have been busy traveling to Denver for work. Will be up there all next week. Should I take it to a transmission shop?

 

#1, Your ECM controls exactly one thing and one thing only on your transmission, the torque converter clutch. If your having ANY other trouble with your transmission beyond the "lockup" feature of your torque converter, it ain't the ECM's fault.

#2, While the ECM does control the fan, there is also a temperature switch screwed into the cylinder head that will turn on the fan if the ECM doesn't, so if it runs to the point of overheating with the fan never coming on, it isn't likely the ECM is to blame here either.

#3, And lastly, the ECM is not in any way whatsoever in control of your gauges, three strikes and your out.........