VERY Rich, Please Help! - Stumped
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VERY Rich, Please Help! - Stumped
1990 L98 350 TPI
730 ECM/Howell Custom PROM, MAP Sensor
Painless Wiring Harness
Ran fine for 2 years and then this:
Problem:
Motor is running VERY rich, I'm talking fuel dripping out the tailpipe, tons of fuel vapor out the exhaust, black smoke, and if you stand behind it, it will hurt your eyes. I think rich is an understatement, because I believe the injectors are simply stuck wide open. As you can imagine, the plugs are fouled, if you pull them out and turn them over gas will pour out. It is rich in all cylinders. I've actually managed to get the motor running by cutting the fuel pump off, I can floor the pedal to enter clear-mode in the ECM and it will stumble to life and idle around 400-500 rpm. You can see the IAC motor open up to keep it running. Once in closed loop it detecs a rich condition and meters back the injectors, albeit not enough. For a while I was able to cut the fuel pump back on after it was started and keep it running normal for a while. If I try to start it with the fuel pump on it will just totally flood the motor. At this point, I can't get it to run at all anymore.
What I've tried:
*) I have used DataMaster to monitor the engine running conditions and main sensor inputs. Unfortunately, all sensor inputs are within resonable spec and nothing is obviously bad. TPS, MAP, IAC, RPM, 02, etc....all checkout with "normal" values. I verified the TPS by hand with my multi-meter.
*) I tested resistance between injector pins and all injectors came back with 16.8 ohms, or very close to it. I checked to see if any of the injectors were shorted to ground but that was not the case. I tested the harness and the ground side is indeed grounded(i believe it is supposed to be). Since the 730ecm only has one injector driver I assume that the reason it is rich in all cylinders is because it batch fires them all. The computer for some reason is wanting to dump tons of fuel in!
*) I put a fuel pressure guage on the fuel rail, after i turn the ignition on the fuel pump primes and the rail goes to 38psi. I can watch it blead-off down to about 20psi and it seems to stay around there. Is there some safety valve to protect the pump from starting under pressure??? Hoping an injector was stuck open I pulled the fuel rail off of the vehicle and pressured the rail on my workbench with the return line capped. I used compressed air and brough it up to 60psi. It held fine for over several minutes. Is this an accurate test to see if an injector is mechanically stuck open? I can only assume pressure is pressure. Thinking that it may be shorting out while installed onto the mainfold I re-installed the fuel-rail and pressurized it again with air and it holds pressure again. I need to pressurize it some more with ignition on, etc....
*) I replaced the ECM early on because of the quirkyness of the issue. It didn't help the situation. I've double checked my wiring and there is not a short in the harness that I can see. I did a very clean job with the painless harness and seriously doubt it is a short with that.
What are the inputs to the computer that tell it to fire, is it possible my PROM has gotten screwed up? I do weld on this vehicle often. Please help!
730 ECM/Howell Custom PROM, MAP Sensor
Painless Wiring Harness
Ran fine for 2 years and then this:
Problem:
Motor is running VERY rich, I'm talking fuel dripping out the tailpipe, tons of fuel vapor out the exhaust, black smoke, and if you stand behind it, it will hurt your eyes. I think rich is an understatement, because I believe the injectors are simply stuck wide open. As you can imagine, the plugs are fouled, if you pull them out and turn them over gas will pour out. It is rich in all cylinders. I've actually managed to get the motor running by cutting the fuel pump off, I can floor the pedal to enter clear-mode in the ECM and it will stumble to life and idle around 400-500 rpm. You can see the IAC motor open up to keep it running. Once in closed loop it detecs a rich condition and meters back the injectors, albeit not enough. For a while I was able to cut the fuel pump back on after it was started and keep it running normal for a while. If I try to start it with the fuel pump on it will just totally flood the motor. At this point, I can't get it to run at all anymore.
What I've tried:
*) I have used DataMaster to monitor the engine running conditions and main sensor inputs. Unfortunately, all sensor inputs are within resonable spec and nothing is obviously bad. TPS, MAP, IAC, RPM, 02, etc....all checkout with "normal" values. I verified the TPS by hand with my multi-meter.
*) I tested resistance between injector pins and all injectors came back with 16.8 ohms, or very close to it. I checked to see if any of the injectors were shorted to ground but that was not the case. I tested the harness and the ground side is indeed grounded(i believe it is supposed to be). Since the 730ecm only has one injector driver I assume that the reason it is rich in all cylinders is because it batch fires them all. The computer for some reason is wanting to dump tons of fuel in!
*) I put a fuel pressure guage on the fuel rail, after i turn the ignition on the fuel pump primes and the rail goes to 38psi. I can watch it blead-off down to about 20psi and it seems to stay around there. Is there some safety valve to protect the pump from starting under pressure??? Hoping an injector was stuck open I pulled the fuel rail off of the vehicle and pressured the rail on my workbench with the return line capped. I used compressed air and brough it up to 60psi. It held fine for over several minutes. Is this an accurate test to see if an injector is mechanically stuck open? I can only assume pressure is pressure. Thinking that it may be shorting out while installed onto the mainfold I re-installed the fuel-rail and pressurized it again with air and it holds pressure again. I need to pressurize it some more with ignition on, etc....
*) I replaced the ECM early on because of the quirkyness of the issue. It didn't help the situation. I've double checked my wiring and there is not a short in the harness that I can see. I did a very clean job with the painless harness and seriously doubt it is a short with that.
What are the inputs to the computer that tell it to fire, is it possible my PROM has gotten screwed up? I do weld on this vehicle often. Please help!
Last edited by onetontj; Sep 3, 2004 at 08:08 AM.
Thread Starter
Junior Member
Joined: Dec 2001
Posts: 24
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When I turn the ignition on and prime the fuel system, the pressure falls quickly(eventually gets to 0). I have done many hours searching here and find this is a symptom of the holley afpr, i just put it on thinking I had a bad stock one.
When I test the injectors for a short to ground, they check out fine. When I check the harness I get two different things. With the ignition off I get 14.0ohms to ground on the pink wire. With the ignition off I get no short.
The pressure not holding could be a couple things but why is it running so rich!!!
When I test the injectors for a short to ground, they check out fine. When I check the harness I get two different things. With the ignition off I get 14.0ohms to ground on the pink wire. With the ignition off I get no short.
The pressure not holding could be a couple things but why is it running so rich!!!
Last edited by onetontj; Sep 3, 2004 at 06:12 PM.
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