New member and new owner here. Would like to start out by saying how helpful this forum has been. I have learned a lot in a short time. Background is that CV19 cancelled all of my 14 year old sons summer camps and activities. I wasn't going to let him sit inside all summer, so I set out to find him a summer project. He loves cars and has been asking questions so I figured a car project would be great. And yes he saw Leroy and started googling images of buggyed out corvettes, so a project was born. Found a 1985 not far from home. Been sitting several months. It was going to be their project, but it never happened. A new battery and fuel pump later, we drove it home for a $1000.00. Took it straight to my mechanic to do a quick check and we agreed to replace injectors, FP regulator, plugs, wires, set timing, change fluids. It ran really strong for a few days. We were cruising around the neighborhood one evening and it suddenly started to run rich. Strong smell of gas, black smoke and wouldn't accelerate. Limped home and have not figured it out yet. Went through several MAFs, replaced IAC, ESC module, O2 sensor, coolant sensors, etc. New ECM, new TPS, etc. Engine cant find idle, rich black smoke, car wont accelerate past 30. Scanner shows a code 43 and says bad circuitry or faulty ecm. Goes into closed loop. IAC is hoovering around 145, which I know is wrong. Idle is about 1000. No detectable vacuum leaks. Engines runs same with IAC unplugged and when ESC is unplugged. Any thoughts would be great. At this point I feel as though it is a ground issue somewhere.

 

Check fuel pressure with a gauge, see what is happening with the regulator. 36-40psi with vacuum attached and 50psi or so with vacuum off.
See if any fuel is present in the vacuum line attached to the fuel pressure regulator. If so, time for another regulator.
When I started my 86 project the car had been sitting for years. My injectors were stuck open I had the same symptoms. Mine was so bad that the oil level was going up every time I ran the engine there was so much fuel going into the intake. Check your oil level.

 

Welcome aboard. If you know your IAC counts, I see you are collecting data which is always helpful.

Just remember new doesn't mean good. Still needs verified.

Do your normal checks. As said above, verify fuel pressure, timing, perfrom a min idle set procedure if it runs well enough, verify CTS is providing accurate information, same for the MAF.

What injectors did you have installed? 85s run injectors rated at a lower pressure IIRC. Some injectors need tuning help.

Further information on current condition will help, don't bank on what has been replaced. New parts are less reliable than pulling slightly used parts. When it comes to being that rich usually it is a stuck open injector, bad MAF, bad CTS, or bad 02 sensor. I wouldn't throw any more parts at it until you have some hard data. Have you pulled plugs to see if one or two cylinders are behaving differently than the rest?

 

Thanks for the reply. Fule pressure is just as you stated above. FPR was replaced, and it is still working as it should, no leaks or fuel smell. All plugs are soaked with fuel and ****. Fouls our after 20 or so minutes of letting it run. I have a couple sets of plugs and just keep cleaning them and swapping them out. Yes, fuel in oil as well, but wasn't going to change it until I figured out the issues...Thanks again.

 

Thanks for the reply. Yes, all of the above. It doesn't run well enough to adjust min. idle. 85 model actually uses a 24lb injector. All new Bosch injectors. All plugs are fouled after 20 or so minutes of idle and short drives, soaked with fuel/****, I just keep an old set, clean them and swap them out until I figure something out. It ran great for a few days, and then just fell apart. Thanks again for the response.

 

Bosch Injectors are known to need Voltage offsets adjusted in the tune. This usually causes rich idle... but not this rich.

If you have fuel in the oil I would be having the injectors tested. Here is one you can do yourself... Crimp return line, hook up the fuel pressure gage, turn key on to prime but don't start the engine, crimp the feed line after you see pressure come up, turn key off. If you lose pressure quickly, something is leaking in the fuel rail. Considering what you are saying, the only path for the fuel to get into the oil is through the injectors into the cylinder.

Another test you can do is using a noid light, you can check for pulses while it is running at each injector socket. There is a potential here that you have an issue in the wiring based off the description " runs fine after we do something and then later it doesn't". Sometimes it is grounded hanging the injectors open and other times it isn't and runs fine. Does jiggling around the harness effect anything? I could see the IAC having to open to try and keep up when the fuel is flooding the engine.

The only thing that confuses me here is that you say it will go into closed loop and idle at 1000RPMs. Does it do that all the time even when you are experiencing issues or is that when it is running OK?

 

Thanks for the reply. I rebuilt the entire fuel rail & FPR so that I could test the system properly to ensure that I wasn't loosing fuel through an injector. Even deleted the 9th injector. System tests fine and holds pressure. No external leaks either.
The injectors all ohm out the same and you can feel them pulsing when you touch them. Base PW(ms) stays around 7.0. I have read that is acceptable. Moving the harness around doesn't seem to make a difference.
What baffles me is that it runs the same with the ESC module disconnected. And disconnecting the IAC valve doesnt make any difference (maybe when its unplugged it stays open?).
Idle really never changes after the engine is started. Open loop or closed loop it hoovers around 1000rpms. As bad as it is running, I'm scared to idle it down until I figure out the fuel issue.

 

Well, just reasoning it out, if you have fuel in your oil it has to be getting in there through the cylinders. I don't see any other path.

Where does fuel enter the cylinders...intake manifold

How could fuel get in the manifold. Injectors and FPR.

If your FPR vacuum hose doesn't have fuel or smell like it and you have solid pressure, you can eliminate it.

This leaves the injectors. The ECM is either telling them to dump too much fuel, The ECM has lost control of the circuit and they are hanging open, or a failure where one or multiple injectors are hanging open.

There are other oddities about the 1000RPM idle with the IAC and ESC unplugged. That sounds like a vacuum leak, but then you would be lean not rich.

ECM telling the computer to dump too much fuel for the condition is going to come from the CTS, 02, or MAF. Well, a faulty ECM could be the issue too. Intermittent issue could be a result of wiring issues to any of the sensors or sensors with faulty internal circuitry that isn't always in a "bad" spot sometimes giving the proper signal and sometimes not. Could also be it can't control the new injectors, but I don't see voltage offsets or a few extra #'s causing so much fuel in the cylinders that it is getting into the oil.

If the ECM has lost control, that goes back to the harness being grounded and the injectors just hanging open, full flow, all the time.

Obviously, the injector failing open is just that.

Puzzling for sure.

 

Thanks KyleF. I agree that its something in the circuitry. The ECM is reading the senors (using a Snap on MODIS Scan tool), but I don't think it is making the proper adjustments. Replaced ECM, no changes in conditions. At one point, everything worked great together, until it didn't.
I could idle the engine down some, but it won't matter at this point. I'm going to continue checking all the wires. Thanks again.

 

Idk if we're looking at the same thing but my bpw at idle hovers around 2-3ms '90 vert. At 7.0ms would that be like dumping twice the amount of fuel???

Not familiar with MODIS but coincidentally on an '85 if you add the 10k resistor between A-E while scanning, that will drive your rpms up to a 1000 and perhaps the IAC will follow @ 145 that's usually where the ecm will park it for crank start. I know the CTS is new but is it reading correctly? Also, are you running any type of capacitive discharge ignition devices like an MSD box? Friend of mine was and it caused a pig rich condition as the car warmed up. Watching BLMs climb to 108, I flashed 15% fuel from the idle cell and it seemed to like it as BLMs dropped to 128 then started to climb to 108. Flashed another 15% but this time the engine stalled and couldn't get it to start again. Yanked the MSD and everything returned to normal.

 

Exactly, seems like something is telling the ECM to dump fuel.



As far as I know, on a 85, there is no other option to read data but by entering ALDL mode, which tells the ECM to idle the engine at 1000RPMS, it does this with the IAC and ESC. This is an issue if you only have symptoms at idle, but he is still rich at 1000RPMS. So, no matter what scanner is being plugged in, it should be giving the 10K resistor to get the 160 Baud data stream. I know the later ECMs could also do the 8192 baud stream with the right equipment, but I don't think the 85 supported this.

I really want to say an MSD should not cause this. I think you know it shouldn't, but with any change point there is always the possibility of disturbing something during install, installed improperly, settings not right, or a bad unit that can cause unexpected problems. Sometimes you have to remove things and take a few steps back and add them back in one at a time to isolate the issue. Not to get stuck on the MSD, but many of us are using these boxes with no issues. So, I don't think it would be an issue of having a Capacitive Discharge box in and to itself. However, in this light, if you do have some modifications to the car such as an MSD box, you may consider removing them and seeing if the problem goes away. Aftermarket components have just as many opportunities to fail as components put in by the factory.

 

Thanks stew. Yeah, don't know why they are being told to dump so much fuel. Code 43 is known as the knock sensor code. So yesterday I replaced the knock sensor, it made no difference. I think today I am going to drop the ECM and start checking all the connections, especially the grounds. So far as aftermarket equipment, this car is bone stock, Hard to believe I found a 35 year old corvette that still had all the smog equipment, factory exhaust, factory radio, etc. The car has been neglected, but not molested. Thanks again for the input.

 

Thanks again Kyle. Today I hope to pull the computer and start checking all the connections, especially grounds. A new knock sensor did not make the code 43 go away. I'm going to keep trying.

 

If you don't own a FSM, you can follow the logic tree at this link:
https://www.corvetteforum.com/forums...post1600002941

 

It would really be great to have access to a good scanner to be able to see what is going wrong in your system. I have an older OBD1 code reader and those are close to useless on problems like this. Find something that can access your data live.

 

This is great information, I never knew the FSM was this detailed, I am ordering one right away. But now I've got a new problem (which may be the same problem). My scanner has lost communication with ECM, then it will regain communication. But when is is communicating, I get no codes and the car runs better, When I stop communication, car falls apart again. I'm not imagining things. Car obviously runs better when being diagnosed. I'm thinking my new computer may have taken a crap. Thanks again for all the help!!

 

Well, new computer is now communicating with Scanner, but it still runs like crap, same as before. Pig rich and cant find idle.
No codes
After it warmed up and went into closed loop:

RPM = 1025
02 (mv) = 760
Integratr = 68
exhaust oxygen = rich
tps(v) = 0.54
Block Learn = 108
IAC Position = 115
Coolant = 189
MAT temp = 106
MAF(gm/Sec) = 39
Base PW(mS) = 4.8
A/F Learned = yes
ECS Counter = 0
Knock = 0

Where to go from here?

 

As I mentioned in post #11, it's the 10k resistor that your scanner uses that places the ECM in diagnostic mode which in turn makes you think the engine runs better when the scanner was hooked up but like crap when you couldn't connect. You had to change the ECM??? Ahhhh anytime I change parts and it brings up the opportunity to upgrade...never mind. I'm kinda stumped here too which led me to search and read a few '85+corvette+rich problems. One thing that came out was to check the functionality of MAF burn off relay. Check not change...