Missfire Ugh.... 5.7 Vortech

tblake · #1 01-11-2010, 11:51 PM

1997 K1500 4x4 350 110,000 miles. Running good, drove 30mi to work, parked 8 hours. Left work, started it, started fine, ran good, driving home came to a rid light, stopped and felt a missfire.

RPM's lower than 1000 in park and drive, you can feel the missfire. Its a dead miss. Get the RPM's above 1000, miss goes away, completly.

No SES light, Ignition parts all new within the past few months. Distributor cap and rotor both delphi, Denso brand wires, delco 41-993 plugs.

I didn't have a chance to check it out when I got home because it was dark. I just dont know.

Hoping I didn't crack a piston in half or something....

Any ideas to check?

spunbearings · #2 01-12-2010, 03:30 PM

fuel pump?

J-Ri · #3 01-12-2010, 05:26 PM

Low fuel pressure should be OK at idle and be very short of power on acceleration, doesn't hurt to check though.

My first guess would be a dirty MAF sensor, pull it apart and spray it out with intake cleaner. Just be sure to let it dry completely before plugging it back in, liquid hitting the wires can damage the sensor. Blow drying is OK, just hold the tip a few feet from the sensor, don't want to damage it.

tblake · #4 01-12-2010, 05:27 PM

THanks guys, its a rhythmic miss if that helps. I'm thinking I sucked my LIM gasket in causing a vacuum leak into the crankcase.

I will diagnose tomorrow and report back.

spunbearings · #5 01-14-2010, 03:42 PM

lol wow those gaskets must have a timer on them

danielsatur · #6 01-14-2010, 03:45 PM

Yep!
Plastic, rubber, and seals are going to fail.

tblake · #7 01-14-2010, 05:35 PM

Problem could still be my LIM gaskets, but looks like one of my plugs fouled out with oil. I really need to change my valve guide seals. It is just too darn cold out in MN. Especially to be messing with tiny parts like valve spring locks when your shivering.....

laxman21 · #8 01-14-2010, 09:24 PM

Is that what's causing the plug to foul out? How do you know. My 7 plug fouls all the time,

tblake · #9 01-20-2010, 10:22 AM

What is yours fouling out with? Oil?

laxman21 · #10 01-20-2010, 11:37 AM

Quote:

Originally Posted by tblake

What is yours fouling out with? Oil?

Yep..oil

spunbearings · #11 01-20-2010, 01:44 PM

i had problem like this on my 4.3 the one plug looked like someone dipped it in bearing grease and the other had a hot plug. it never smoked or smelled like antifreeze though.

spunbearings · #12 01-21-2010, 03:35 PM

any update?

tblake · #13 01-23-2010, 07:11 PM

Yep, Fixed. That grey ashy residue on my 1-3-5-7 bank plugs (mainly 3 and 5) must have been gas. A day after I got home from it missfiring, I started it, and it took about 5 seconds of cranking for it to start. My code reader showed a P0303 pending and thats it. (go figure) I checked fuel pressure and during prime, it jumped up to about 60psi but dropped off to 0 within a few seconds. Peeked inside the UIM through the throttle body with a flashlight and saw liquid pooling on the passenger side (gas?). Yesterday I replaced the fuel pressure regulator along with new UIM gaskets and a new failsafe thermostat. Truck has never ran so good. Fuel pressure holds, and truck starts WAY better. No more shutter at idle, and no missfiring.

Only thing I can think of is maybe my FPR had been leaking slightly for a while. Then on my way home from work let go, and dumped all 60+ PSI of fuel pressure into the port runner for cylinder number 3 causing the dead missfire at idle.

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