Ive had a problem for the past 2 monthes thats been getting worse.

The problem started with the engine revving higher than normal at idle and giving me a code 15. The coolant temp sending unit was replaced, and the engine ran well for a month.

2 weeks ago I decided to change the plugs and wires (they needed it fairly bad). Put in Bosch Platnum plugs and 7mm wires. The car then gave out a code 51 after 20 miles. Today I replaced the prom with one from GM (stock) and I also replaced the ECM.

The car doesnt give any codes out now, however when on the throttle hard or even semi hard (even in neutral), it bogs down and even stalls in some circumstances. When the throttle is lightly applied (ie, taking 15sec to get up to 45MPH), it hums all the way to the redline (if I push it that far). Another issue after replacing these is that black smoke now comes out of the back. Not blue smoke Im sure. I have 2 large spots on the driveway that sit under the tailpipes now.

My question is...I know blue smoke is from oil passing into the combustion chamber, however what is this black smoke? Seems like the car may be missing at low RPMs too.

Im no mechanic, however I do enjoy working on the car myself. The car has 175k on it and is only driven 80miles per week.

91 v6 3.1L Automatic.

Any suggestions would be appreciated. timing? although why would the timing differ just swapping the ECM? Ive heard some plug wires may not be able to handle the heat of the passenger side exhaust. Can this be the answer?

please, im frustrated at this point.

 

Black smoke=too much fuel.
Don't know much at V6s, but if it has a MAF, check the elec connector. If it has a MAP, check elec connector and vacuum hose condition. Coolant temp sensor can do it too.
Check fuel press regulator vacuum line for fuel inside.
Check fuel press.

The sensors should throw a code if reporting abnormal conditions.

 

thanks for the reply...now that its dark, I can actually see the spark at the end of one of the wires. Front most passenger side plug...the hardest one to get to. Would this be a cause for all the problems?

thanks for the input again. Im just frustrated at this point.

 

ok, I reseated the plug wire and the car seems a little better. Drove it 4 miles and no 'bogging down'. Are these plug wires junk? They dont seem to 'seat' on the plug like others.

I purchased Borg Warner 7mm standard set (obviously the set designed for the car).

Any suggestions on 'good' wires? Im taking these back tommorrow.

 

Any reinforced wound-carbon core with silicone outer insultaion should be good for a street vehicle. Brass terminals are usually the mark of a better quality wire set, or you can make your own set.

As for the other problems, do an archive search for "Bosch" and "plug", and see how many "problem" threads are turned up.

 

Those wires should be ok.
With new wires, you may have to push fairly hard to get them fully seated.
You should feel a "snap" when they are fully seated onto the plug.
If these are "angled boot" wires, look up inside them to confirm the recepticle is oriented correctly.

 

swapped the wires out this morning. Same thing is happening. Still getting alot of fuel into the engine. Its idling high (right at 1250).

I dont know how to check the fuel pressure, however could this be from the O2 sensor?

Im just out of thoughts here.

 

Yipe, 7mm wires? I ran on a set of those once while my MSD 8.5mm's were being replaced; my motor ran like crap.

Do everything here first: https://www.thirdgen.org/techbb2/sho...hreadid=162251

 

thanks for all the info guys, turned out to be a cracked coolant sensor. Go figure. $25 for the part and an hour to put it in...Im ready to roll again.

BTW...awsome forum here.