black smoke from exhaust
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Launching!
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From: Hereford, Tx (near amarillo)
black smoke from exhaust i was wanting to know what my problem was with my 94Z A4. you see it has a rough idle and when i get on it at about 3500 rpms it cuts off and throws a large puff of black smoke from the exhaust and it doesn't pull from then on i have to let off the throttle. i just changed the fuel pump, the opti and plugs and wires. the wires are good. would it be the fuel pressure regulator. i think it has the stock one still on there. i have a cat on there. my SES light is throwing these codes. DTC 29, DTC 32, DTC 44. i don't mind the light on but does this have to do with my problem? sometimes it will work fine without cutting out but most of the time it cuts off and throws smoke at 3500-4000 rpms. would this mean that i'm running lean or rich? need help ASAP.
DTC 29 = Secondary Air Injection
-check the secondary air injection system for an open circuit in the wiring
DTC 32 = Exhaust Gas Recirculation (EGR) failure
-Check the vacuum source and all vacuum lines.
-Check the system electrical connector at the ECM/PCM and EGR valve.
-Replace the EGR valve.
DTC 44 = Lean Exhaust
-Check the wiring and conectors from the oxygen sensor to the ECM/PCM
-Check the ECM/PCM ground terminals
-Check the fuel pressure
-Replace the oxygen sensor
These are taken from my repair book. Do you have aftermarket headers on the car. I would get a fuel pressure guage on the car and make sure that is okay.
Mike
-check the secondary air injection system for an open circuit in the wiring
DTC 32 = Exhaust Gas Recirculation (EGR) failure
-Check the vacuum source and all vacuum lines.
-Check the system electrical connector at the ECM/PCM and EGR valve.
-Replace the EGR valve.
DTC 44 = Lean Exhaust
-Check the wiring and conectors from the oxygen sensor to the ECM/PCM
-Check the ECM/PCM ground terminals
-Check the fuel pressure
-Replace the oxygen sensor
These are taken from my repair book. Do you have aftermarket headers on the car. I would get a fuel pressure guage on the car and make sure that is okay.
Mike
Thread Starter
Launching!
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Joined: Sep 2006
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From: Hereford, Tx (near amarillo)
it's all stock 94 Z A4 with a high flow cat with the LM. it has the OBD1. would the o2 sensor make that much of a difference? is the EGR valve hard to replace. and i think the AIR Pump is messed up anyway. i keep on blowing up the fuse in it and i got tired of replacing it so i left it off. we hooked up a guage to it and it was about 25 psi at idle. and when i would give it gas it would just stay there i t would not climb.
TECH Fanatic
Joined: Jan 2005
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From: St. Augustine, FL
fuel pressure is 25psi? that sounds low.
also, o2 sensors could be telling the engine that it is lean when it is not. That would make it dump gas in there making you actually run very rich (black smoke?)...
also, o2 sensors could be telling the engine that it is lean when it is not. That would make it dump gas in there making you actually run very rich (black smoke?)...
Make sure you are checking your fuel pressure correctly, unhook the vacuum line thats on the FPR to simulate WOT. I'd say you have bad o2's. Replace them anyway, since they are part of our scheduled maintence.
TECH Fanatic
Joined: Jan 2005
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From: St. Augustine, FL
I could be wrong but, I dont believe the EGR would have anything to do with your issue. Its only a vacuum operated valve that will let a small bit of the exhaust gas enter the back of the intake manifold. If your already throwing codes and not using your AIR pump your not emissions legal so, you could consider removing and blocking off the EGR stuff.
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Verdad Gallardo TECH Fanatic
Joined: Jan 2005
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From: St. Augustine, FL
"How EGR systems work The EGR valve recirculates exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process by several hundred degrees, thus reducing NOx formation." -taken from this web page
I've looked into this before and in my limited understanding of it, the EGR will reduce the combustion temps some (although that link suggests 100's of degrees) and keep the pollution down.
I've read that some cams will have enough overlap to handle the EGR completely on their own. Any one know more about that?
I've looked into this before and in my limited understanding of it, the EGR will reduce the combustion temps some (although that link suggests 100's of degrees) and keep the pollution down.
I've read that some cams will have enough overlap to handle the EGR completely on their own. Any one know more about that?
Also, with this Engine, the EGR helps bleed off the Cylinder pressures during Engine running. The stock Cam is the cause of this, the profile of it doesn't allow the pressures to bleed off. The LT4 Doesn't have stock factory EGR, cause the Cam is different.
