So as some of you know i developed a nasty inconsistent missfire the other day. I have already changed my plugs (autolite 3923's) and my cap and rotor. Still no improvement. So today i did a compression test and got 175-190 on all 8. I also check fuel pressure and holding a steady 49 psi. I swapped out my coil for a spare one i had and no change. I have just about run out of ideas. The only thing i havent tried is driving around with the fuel pressure gauge to see if it cuts out.

I would think that if i had a broken valve spring that the miss would be constant and that if the dizzy shaft gear was worn then it would run like **** all the time if it would run at all.

My plenum does appear to be leaking a little bit but no pools of oil in there. I do hear a noise when it misses that almost sounds like a ping, but its not loud enough to be certain. I guess i can pull the o2 sensor and see if thats helps but i dont see any of the clogged cat symptons.

 

Sounds like you should try the o2 thing. Can't hurt at least.


Also check your Plug wires thoroughly. I had a misfire appear out of nowhere in my '95 not long ago. It was so bad I thought I blew a head gasket and lost compression in one cylinder or something. Turned out to be a plug wire arcing out on the exhaust manifold.

 

could be a dirty injector... occasionally getting clogged and causing a miss

 

yeah tonight im going to mist everything down with water and run it to see if i see any "lightning". The only other thing i can think off is maybe my injectors are dirty or a leaking brake booster, but my brakes seem to operate just fine and i dont hear a leak.

Ohh an BTW it only seems to do it with a load on it. It may be doing it in park or nuetral but its to light to tell. Also when I changed the plugs they were all clean, no residue, so my plenum is not leaking very bad at all. And if i had a broken valve spring, cracked valve seat, or a sticking valve the compression test would have shown it right? or do i need to do a leakdown test?

 

Does it do it regardless of engine temp? Or, just when it's cold? Just when it has warmed up??

 

Engine temp does not seem to matter. If i dont find a leaking plug wire tonight then i am going to pull the injectors and check them. And the injectors on my motor are red, i have never seen factory red injectors. Should i suspect that these are aftermarket?

 

No, the last few years (2001 for instance) had red injectors.

 

Good to know. I dont recall seing red injectors on my last 2001 though, but it was a 318. Maybe they were different.

 

So i pulled a sample of fuel from my truck and its pretty yellow. looks a bit like mountain dew. So i hoping that this is all just bad gas. I took it on a short drive and ran it kinda hard and it was definitely pinging which will happen with bad gas. I wont know for sure though until i get some fresh gas. at least i only have 1/4 tank in it now.

 

Throw in some 89 octane, and a bottle of techron.