Miss-firing and backfire

[samandw]

My car recently started miss-firing and sputtering. It started happening intermittently under moderate (but not high) boost, and now happens at anything over a 1.2-1.4 TPS voltage. It pops, seems to backfire, and misses badly. Pulling it down a gear usually helps a bit to smooth it out, and it seems to idle ok, just a little rough. At one point I couldn't get the car over 35 mph going up a slight grade on the freeway.

We noticed the crank pulley seemed to be wobbling and got about a 1/4 turn out of the bolt, but it didn't make a difference with the sputtering problem.

I noticed pulling the fuel pressure back seemed to help the problem. I took a screwdriver to each injector and to my ear and could plainly hear each injector firing. I also noticed a "brrrrt" type sound on tip-in enrichment (as expected?).

If I brake boost the car, I can almost get it to build boost and then it goes "POP" and almost dies. I plan on swapping out sensors/coil pack this week to see if I can find the culprit, but thought I'd post to see if anyone had a similar experience. . .

Thanks!

 

[TurboMonte 2]

Check your crank sensor, make sure you have 0.025" clearance on ALL THREE ring portions & that none are bent. Need use flexible feeler gauge--NOT TYPICAL METAL ONES that won't fit in curvature properly. Use several wall thicknesses of plastic soda bottle, credit card (temp'y ones you get unsolicited in mail...).

 

[blkrs86]

I had similiar problem and check everything until I was so p.o. I quit working on it for a while.Then I broke down and bought a ls1 and translator and it runs so awesome I'm back in love with it again.I don't like to put parts on unless I know they are bad and the maf didn't seem bad but what a huge diff. it made.Just something to think about.

 

[231Turbo]

fuel pressure? 02 readings under wot?

 

[samandw]

I don't have a fuel pressure guage but I believe the baseline was 43 psi.

I can't get it to WOT, so I don't know what the O2 readings are.

One of my GN buddies is on vacation so he let me burrow some parts of his car to diagnose my problem. . .and I'm 99% sure it's a broken crank sensor. Mine wiggled at the plug connection and his was rock-solid. I'm going to check the clearance on the pickup fins tonight and maybe swap in his crank sensor. Is it possible to bend a crank-pulley? I ask cause it still doesn't seem to run perfectly true, but that could be just my imagination.

Thanks all :biggrin:

 

[231Turbo]

I don't have a fuel pressure guage but I believe the baseline was 43 psi.

I can't get it to WOT, so I don't know what the O2 readings are.

One of my GN buddies is on vacation so he let me burrow some parts of his car to diagnose my problem. . .and I'm 99% sure it's a broken crank sensor. Mine wiggled at the plug connection and his was rock-solid. I'm going to check the clearance on the pickup fins tonight and maybe swap in his crank sensor. Is it possible to bend a crank-pulley? I ask cause it still doesn't seem to run perfectly true, but that could be just my imagination.

Thanks all :biggrin:

good luck