I just put a new engine in my 88 z31 it has run great until today when I started it and it is running rough. It's like it's not firing all 6 cylinders. When it's running it has white smoke from the tail pipe and the exaust smells like gas. It was running great yesterday and had no exaust smoke either. Could it not be getting spark? I am kinna stumped so any help is appreciated.

 

Start with the basics...
-Check ecu diagnostic codes.
-Read spark plugs.
-Check compression.
-Check fuel pressure.
-Check MAF / CHTS.
-Check color of oil.

 

Tried all of that stuff. The ecu gave code #23 the plugs are good. My only concern is the fuel I feel like the pressure is down but I'm going to get a gauge to see what it atcualy is. It runs great if you let the fuel pump cut off and then fire it up but after about 10 seconds it starts to run rough

 

Code 23 sends you to the throttle valve switch and circuits. Did you check out your switch operation and the throttle position sensor? They have to work right. Check your manual at page EF&EC 63. Also check for loose/dirty/corroded harness connectors and clean them.

 

Checked the TPS and it was good and also it was replaced when the engine was put in only 2 months ago

 

white smoke generally means blown head gasket. Car will run regardless of TPS

 

Okey so here's an update. I checked and all cylinders are getting spark and the ECU is no longer reading any problems. I'm thinking it might be a fuel issue. When you first start the car it fires up fine and then runs for about 3 seconds before it runs rough. Maybe it's not getting enough pressure? I am trying to get ahold of a pressure gauge so I can check.

 

Okay I started it this morning and it ran great until the engine warmed up. Anyone know what this means?

 

Rough idle when warm could be a sensor sending bad or no information to your ECU. Sensor diagrams etc begin on EFEC-3 of your service manual.

 

could be the chts. could be O2 sensor. there were different sensors used on different years. easy way to check unplug O2 sensor and drive around until everything warm. if no die you know the answer. if no change time for a chts. be sure the egr isn't stuck open. stick a finger up there and see if the diaphragm gives and returns.

 

Okay so I changed the chts and got a new catalytic converter because a friend of mine had had the same problem and it had been the cat. I also tried unplugging the O2 sensor and running it but it didn't help. I'm going to check the erg valve today.

 

Just did self diagnostic and got codes 12, 23, and 42

 

Okay so I replaced the ECU and it made no difference. I took out a plug today and they are black. Could it be the AFS?

 

codes fairly useless at the age of everything. it isn't an afs those are on s130. you have a MAF there is a diagnostic procedure in the FSM. you need a VOM and some jumpers. Have you checked your fuel pressure? Have you checked the vacuum at idle? If you are still getting white smoke you got a blown head gasket.

 

The smoke is gone and the fuel pressure is good. It's getting worse the car will bearly start now. I checked the timing and it is good. How do you test the MAF?

 

Okay never mind about how to cheek the MAFi found it

 

The O2 sensor was apparently the problem. The car is running the best it ever has. Probably because I replaced almost all the sensors. But thanks to everyone for the help.

 

I drove my 88 for months with the O2 unplugged. Didn't even know it. Only on an obdII car would you be able to tell the difference.