Mark VIII Spitting & Sputtering ??

[Don Pfau]

Well I want to be able to run at CAROLINA THUNDER on Sunday but the Mark started spitting and sputtering a just a little about a month ago. So I took it over to Barrys last week and they changed the plugs and cleaned the air filter and said it was running great. I picked it up and it started doing it worse than ever. I took back and we worked on it all day. It has good fuel pressure even when it starts to doing it. Replaced the O2 sensors and didn't help. First cleaned and then replaced the MAFS and didn't help. Replaced the crank sensor and again no help. PS It shows no codes as if all is well ?? Plus when it starts to spit and sputter the air/fuel gauge goes full lean.

 

[mossbergman]

Hmm bad coil or coil pack depending on which car of yours it is. Mine sometime does this too and that's what I suspect it is, just haven't gotten around to it. My buddies cobra did the same thing too and a coil fixed his

 

[Don Pfau]

The Supercharged 93. It seams to run fine and normal at WOT but spits and sputters at times while cruising and stalls at times when idling.

 

[mossbergman]

Same here. When I air it out it seems to do better in the higher rpm ranges. My has lots of trouble idling when it acts up. Very intermittent..

 

[chargerxr]

Possibly a bad TPS sensor. I seen them do that before and not set a code.

 

[PenGun]

Water can do that kind of thing to an ignition.

 

[Chadly]

I had a similar problem on my last cross country drive. I got to Arkansas and it was sputtering pretty bad but fine at wot. I tested the TPS and it was bad but also had codes for O2's. Easy enough on a gen 2 but might be a PITA on a 93.

 

[98lincmk7lsc]

Vacuum leak?

 

[Jacksun]

Iac?

 

[driller]

Plus when it starts to spit and sputter the air/fuel gauge goes full lean.

Must be fuel related? I would think if it was spark, it would go show rich?

It seems to me the only clue is something that is air/fuel related in closed loop. Of course that leads to a lot of suspects, much of which you have replaced. The TPS can be the problem though.

This is what I hate about the EEC-IV. Not enough parameters for proper diagnostics.

 

[thaywood]

Vacuum leak?

That's where my money's at. Had a similar issue with the '97 LSC and the '97 Cougie. Vacuum leaks both times.

 

[Psychostang]

Do you have a chip on the car. If so, I would remove the chip and see if it returns to normal. IF that doesn't help, try a new computer. IF you have proper pressure and the car runs fine at WOT, I would say that there is something wrong in the control system. Specifically fuel injector pulse width. You have already changed components that would effect the fuel injectors, so It can only be the chip or computer.

 

[chris2523]

its got a blower. pulling the chip is probably a bad idea.

 

[Psychostang]

Doesn't mean anything, while idling or in steady state cruise.

 

[NoLimit95]

Possibly a bad TPS sensor. I seen them do that before and not set a code.

My first thought when I seen this thread.

 

[Don Pfau]

Thanks, We checked with carb cleaner and could not find any vacuum leaks. It does have a SCT chip and has a 511 pcm failure code but it always has had that and we just thought it was because of the chip. When the chip is remove the code goes away so I still think that. We didn't try running it with out the chip but I will try that. We disconnected the EGR valve and it was a little better but thats not it. The fuel pressure drops as so as you turn it off so there is a bad valve in the fuel pump but I drove it with a fuel pressure gauge on it and the fuel pressure was always good even when it ran bad ?? Rechecked all the spark plugs and they all looked good. Both O2 sensors have been replaced. We tried changing the ignition module but it was no better. I'm going to try the TPS like suggested and then maybe the stock coil packs. Thanks again everyone. PS I'm taking it to the drag strip like it is as I'm now satisfied it is still running properly at WOT.

 

[NetKeym]

I'd have to agree with the previous post that it's not spark-related because you should be running rich, not lean with a spark miss. If the gauge shows super-lean when it sputters, the ECM should be cranking on the fuel with O2 signals like that.

Did you try a simple thing like a fuel filter? One time my car was running funny, I checked the fuel pressure and it showed right up there where it should. HOWEVER, when I pulled the fuel filter, I couldn't even blow through it and it was full of black crap! It's a cheap and easy thing to change.....

 

[BIG ROLLER]

Some good info here. Subscribed.