Ok, here's the deal and it's starting to upset me.

I own a '92 M6 (Car in sig with mods in sig)

Once in a while, the car will seem to have a bad miss in a cylinder. If it starts, it'll stay on for a little bit and slowly work it's way down the RPM band until it shuts off. It's sounds like a miss whenever I drive it. And on top of it, when I crank the car over (without it starting) a good bit of white smoke comes pooring out. Now, to me it seems like this is the motor (WHICH I JUST HAD REBUILT) but the odd thing is, it only does this whenever the car is having problems starting. I also have a code 33 which is a Map Sensor code.

Now this, from the little knowledge I've had, is what I can come up with:

1. I probably have some sort of internal leak which I'll check with my machine guy and do a leak down test (cause for white smoke)
2. One or both cats are clogged.
3. My "Opti-Crap" just bit the dust and I've been bitten by the bad-luck fairy.

Questions I have :
Does an excessively rich condition cause white smoke? As in a leaking injector in a cylinder.
Do clogged cats on a LT-1 seem like a cylinder missing and causes the car to die? Also a hard starting condition? ( I have to keep my foot on the gas while cranking for it to start sometime)
What does a failing MAP sensor do? And does it fail due to boost?
And the last and most important question of them all..........

WHY ME? Just kidding.... Why would this be intermittent?


Sorry for all the questions, but I'm hoping that I'll find some help somewhere. I'm pretty sure someone has been through the same ordeal that I've been through and could shed some light on this subject for me.

Once again, thanks in advance to all the forum members that reply.

 

Make sure your ignition wires are not the cause of your miss. In a completely dark garage, run the engine and look for sparks from the wires to ground. You will need to let your eyes adjust for 5-10 minutes and get your face down there to check every inch. I had a miss occationally that was solved when I changed ignition wires.

Pay particular attention to the ignition wire (correct name is high tension lead) that runs from the coil over the top of the water pump down to the Opti-spark. Its sort of below the throttle body. Mine was pretty tight to the water pump housing and was experiencing lots of sparks.

If most of the wires are sparking, it may be a good idea to change them as well as the spark plugs or at least check the plug gaps.

 

Mez,
Thanks, I'll probably end up pulling all the plugs to check them ( they have less than 1k on em) as well as checking for any arcs.

Once again thanks for the info.

 

If you have access to a scanner, determine if the car is going to open loop, at idle, and if the miss is occuring while in open loop. If so, it could be a rich injector which should show up as a fouled plug (though it might take a couple of hundred miles before you can get a decent read on the plugs).

 

The plug I did pull was "BLACK" which does prove that it's running rich. I'd like to go to a stand alone GEN VII DFI in the near future, but I'm trying to make sure nothing is wrong with the motor itself. I don't want to start buying parts and realize there are other prior existing problems. So any ideas about the white smoke?

Thanks again

 

Fluffy dry black is too much fuel meaning the injector is rich or leaking. If you don't have a fuel pressure guage and an injector tester, it's a little difficult to tell if it's leaking or maybe just sluggish due to gum and varnish deposits. You can try this method, though to see if its leaking: Put the plug back in and turn the ignition on for a minimum of 2 seconds. Do this a couple of times, waiting 10 seconds after you turn the ignition off before turning it back on. This will ensure maximum pressure at the rail. Pull the plug back out. If it's wet, then you can be certain the injector is leaking. If it's not wet, that doesn't mean the injector isn't leaking because if the intake valve is closed, the fuel is still sitting in the manifold. To test further, disable the fuel pump, remove the injector harness and pull the plug wire. Turn the engine over. It's probably going to start, so be ready to turn it back off. Pull the plug again. If it's wet, the injector is leaking. If not, cleaning the injectors may improve performance. Bottom line is that you're going to have correct it before you do any mods. Hope this helps.

 

Check your WIRES. I had a miss that almost sent me in to the nuthouse. First it was fuel pressure dropping off... then it kind of went away with fresh plugs and a fuel pump. It wasn't entirely gone however. We put different wires on...see ya later. My mechanic to simulate a short/wet condition soaked the wires then fired the car. You could see the one plug wire arcing like mad. My miss was under load. Part throttle it ran perfectly.

Try that and let us know how She does. Remember to breathe! Don't let this stuff get to you.

 

Sounds like a head gasket. What is your fuel system and injectors?

 

The if it starts it slowly works it way down and dies sound a lot like my opti problems. I'd hate to think this was what is wrong with yours, but that's what mine did when I bit the dust.

 

I'm currently running 36lb/hr injectors
ATI's FMU
ATI's external IN-Line fuel pump
Stock '92 ECM with chip tuning by Exotic Muscle

I'm going to start pulling stuff off tommorow and hopefully come up with something. Thanks to everyone that replied and gave me some basis for my tear down.

I'll post tommorow with what I come up with.

Thanks