348 fuel mixture issue

Hello fellow 348 brotherhood. I have just completed an extensive major 30K engine out maint program on my 1990 348ts. After reassembly I had a few issues with a fuel leak and I inadvertently had reversed connections on the oil pressure transmitter. Once these items were rectified the engine is running very rich on all 1-4 cylinders. At first I thought maybe a bad injector ? Upon removing the new spark plugs, all four plugs on the rh (1-4) cyls were black with soot. Any ideas as to why this would occur ? I was going to swap the Motronic brain boxes next left to right and see what happens..... Any advice would be appreciated, thanks. JGW

 

Just curious, How did you know it was rich? Was it sputtering or running funny, is it when cold or hot or both?

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Starts and immediately revs up to 4000 rpm then idles down running rough. Smells of fuel and will eventually slow down and stall. Pulled all the plugs and 1-4 are black with soot. Major isp included everything from new clutch, flywheel repack, valve clearances, water pump etc etc. Replaced problem cam drive bearing, corroded coolant fitting and all the common issues. Intake was removed, injectors, oil pan, chain case, drive shafts rebuilt, susp bushes all replaced all wishbones repainted, sway bar mounts, calipers and brakes.... Everything I thought needing attention was completed. If only it would run ?

 

Forgot that also the throttle movement has little effect due to rich fuel mixture...

 

Sounds more like an ignition problem.

 

You have done too many things to easily identify the culprit. I think you have to go back to square 1 and ...

1. Check fuel pressure
2. Check vacuum leak
3. Check idle controller
4. Check o2 sennsor
5. Check MAF

 

Chances of 4 stuck injectors is slim.
If IAC is bad it would not idle well at all.
Vacuum leak typically means lean condition but I'd check that regardless.
Fuel pump going bad typically means not enough fuel.
Bad FPR could be it but they typically fail to deliver not deliver too much but its possible if its stuck wide open somehow.
Water temp sensor would affect the car when hot.
I'd swap the MAF's and O2 sensory to the other side and see if the problem moves to the other bank. I'd bet on one of those 2.

 

You've got a bad connection somewhere, MAF, TPS, anything which can affect fuel.
There are also some other good ideas in the last few posts too.
This is exactly why I am getting rid of those old Motronic clunkers.

I can't wait to eject those clunky old things to the garbage from my 348. Modern ECU is the clear answer for reliability, performance and of course huge flames from the exhaust on over-run!!

 

Reversed connections on the oil pressure transmitter and ...?

Otherwise, I would first check the simpler possible causes of one bank running rich which are:

1. Vacuum line to the FPR not connected or broken (no vacuum on the FPR causes increased fuel pressure, vacuum reduces it)
2. Bad connection on the coolant temp sensor or bad sensor (open circuit)

 

Thanks guys, I will tomorrow investigate further. I must have done something as the engine ran fine before and the car has only 14K miles. Also I replaced both coolant temp sensors "while I was there" and I don't think they would affect cold start mixture regardless. I can't even run it long enough to warm it to operating temp as it eventually will die. It's like in the old days if you ran a warm engine on "full choke" I'm thinking something simple must be the culprit......

 

Regarding my previous post about the oil pressure, I was just commenting on a few snags I had after the engine/transaxle was reinstalled. I replaced the spade connector on the wire to the oil pressure transmitter when I had the intake manifold off due to a frayed wire and inadvertently reconnected the two wires in reverse to the transmitter. On first start attempt I noticed the oil pressure guage was off scale. Once I reversed the connections at the transmitter the oil pressure was reading normal.

 

Maybe it's simpler but based on the above and other things you have said, I would be curious of a few things.

First, do you have any way on that car to view fuel trims? Not sure if it has air injection but a bad check valve there or compromised seal at the head to exhaust manifold, anything that could introduce outside air into the exhaust system would give the o2 false input resulting in the ecu adding fuel (positive fuel trim) until o2 reads stoich. If that happened under the condition that outside air influenced o2 feedback, plugs on that bank would show rich (as it would be at that point)

Next, maybe do a compression test and compare bank to bank. If the rich bank had retarded intake cam timing that would reduce low rpm volumetric efficiency (and cranking compression) to the point of a rich condition based off the base map. (but should be compensated for eventually by negative fuel trims).

 

Coolant sensor, MAF, Front o2's should be swapped 1 at a time. And T-belt timing off on 1 side can do that. All that being said, check for bent out pins at all the sensor connectors first. GL

 

I would not not swap the coolant sensors I would just replace them both, quite cheap, if a sensor is bad you have to do a painful job twice.

 

My car is all packaged up in storage, otherwise I would go take a look. Pull the vacuum off the FP reg, and see if it gets wet while running. Then shut it off and stare at it and see if it starts dribbling. The diaphragms don't always just blow out. Give it 15 min and see what happens. If the exhaust cam was off it would do what you describe also. Just thinking out loud. Those coolant sensors can be checked with an ohmmeter to see if they match at any temp. I would not buy new ones. If it was OK before the overhaul, odds are high that it's something you did. I wish your car was in my shop. GL

 

Just a though. OP said it does it at start up. That would mean open loop and O2 sensors and CTS aren't in the loop so unlikely they are the issue. MAF is a possibility.

 

I thought of that. CTS's are immediately in the loop. So are MAF and TPS. Ambient air temp to a lesser weighting. But, if the O2 is disconnected or grounded on some cars it still makes a big difference. FCA products. Dodge, Jeep etc. Open loop won't go Stoichiometric but some need that half a volt feedback just because. Turn the key on and check for .5v on the Black wire just for grins.