spitting fuel and misfiring

hercman · October 10, 2006

Ok here's the story.

Truck is a 98 with the 5.7L with approx. 98,000 miles on it.

Truck is throwing P0300. Multiple cylinders misfires

Engine barely runs. Pulled plugs and several plugs on both sides of the motor are fuel soaked the rest are real black from carbon. Also raw fuel is being spit out the tail pipe.

So here is what I have done so far

Changed out the fuel filter, distributer cap, rotor, wires, plugs, and front O2 sensors. No change the new plugs look just like the old ones after a couple of minutes. I then unplugged the MAF sensor and the engine started firing on more cylinders and would idle at about 1k.

I have a MAF on order.

Is there something else I should be looking at? A friend of mine suggested something like the fuel injector spider or something. But with fuel in the cylinders it just doesn't make sense to me that it might be a fueling problem.

Any help would be great.

GM-Tech · October 10, 2006

Sounds like possible plugged cats.

hercman · October 10, 2006

Wife told me today that when it started acting up she needed to add coolant. I had topped it off the week prior. What I thought was alot of fuel coming out of the pipe was actually a little fuel from the misfire and lots of water. The pan I used to protect my friends garage floor confirmed this after the truck sat over night.

Today I noticed after I put the MAF in that there was enough water coming out of the tail pipe to soak your hand after about 10 secs.

At this point do you think I should go ahead and change the intake gasket first and see if that takes care of it or should I reconnect the wiring (i started to remove things out of my way to pull the intake and would be easy to reverse if you think the cats are the big problem) and disconnect the cats and see what happens?

I'd hate to break into seals if I don't need to.

GM-Tech · October 10, 2006

You wife told you it acted like you need to add coolant on startup? Exactly what does that feel like? No offense meant but does your wife know anything about the mechanics of a car?

I'd disconnect the pipes at the manifold first. It's relatively easy and doesn't cost anything but some time. Otherwise, you're just guessing and I can't tell you what else might cause your problem without a bit of diagnosis.

hercman · October 10, 2006

I guess I mispoke lol. She knows her way around an engine compartment. When the truck started acting up she changed all the ignition components and checked all the fluids and noticed the coolant was low.

I drove the truck home and idle sucked but from 1800 rpm and up (never went over 2200) the motor smoothed out and produced enough oomph to limp it the last 20 miles home.

Tomarrow I'll reconnect my wire harness and and stuff and disconnect the exhaust and see what happens.

hercman · April 17, 2007

Problem was a bent valve. Caused by build up from a leaking manifold gasket.

luthor · May 12, 2007

Good to know that you already diagnose the cause of your problem, please do post more on how it goes and how you are planning to fix your problem because my friend has the same problem he also thought it was his GM fuel injector spider and he is planinng to make a replacement on that part... I guess I have to phone him tonight to tell him that it could be his vent valve and try checking both the valve and the manifold gasket... Thanks and Goodluck...