p0300 code. NEED URGENT HELP!!!

[spivey94]

the engine seems to run ok in park and neutral and when at higher rpms when in drive, but when its at idle in gear it misfires really bad. any ideas???

1998 GMC Yukon 5.7l

 

[SunlitComet]

leaking sparks, cloggy injectors or vacuum leaks. what is rpm in park and in gear idle?

---------- Post added at 06:10 PM ---------- Previous post was at 06:09 PM ----------

 

[spivey94]

In park its like 700 then in gear it goes to around 500 or so

 

[BattelWagun]

700 seems a little high.(I'm not sure though if its out of the acceptable range though) I would check for leaking spark/clogged injectors too.

 

[SunlitComet]

and a vacuum leak for sure with those numbers. Also keep in mind if it was that low in gear the PCM should have boosted it with IAC(Idle Air Control) valve so it may be be stuck or plugged. Test it and find out. It may be that the IAC valve is the cause of your problems. It also boosts the rpm when A/C compressor is engaged.

 

[spivey94]

Ill definitely see if that's it. Could it be the egr valve? I've read up about it and a few sights have said that.

 

[BattelWagun]

It's a possibility that it could be the EGR, but that won't cause misfires as much as it would roughen up the idle and create issues under low throttle situations. My advice is to park the truck in a dark place (like a garage), get a spray bottle and fill it with water, the pop your hood and spray down all of your ignition system. Don't soak it, just mist the water onto it, if there is any spark leak you will see it (like little blue lightning bolts pretty much). if nothing shows up, post back here and we can go to the next step.

also, are all your ignition components GM parts?

 

[SunlitComet]

Or MSD?

 

[spivey94]

No mad quite yet wifey wont let me. I just put the msd off road ignition in my wrangler with the Mallory distributor. So that was my monthly allowance lol.

 

[BattelWagun]

Or MSD?

There goes sunlit flaunting his new ignition haha

 

[SunlitComet]

And it is still in the box too.

 

[spivey94]

alright so i went to a friends shop today and he ran a test and said the misfires were in 1,3,5, and 7 cylinders. what could be causing that?

 

[SunlitComet]

That is the the entire left cylinder bank. Unless only those injectors or spark system for that side is malfunctioning, I would look into a damaged converter or head damage. Hit up an exhaust shop for a back pressure test. It should be cheap and check the left bank plugs and post pics here for diagnosis.

 

[spivey94]

i did have an issue with a coolant hose quick disconnect on that side and when it blew out is when all this started, what could that have done possibly?

 

[SunlitComet]

the quick disconnect is on the right side of manifold not left. Only thing I can think of with that is perhaps the residual coolant is deteriorating spark wires or something.

 

[spivey94]

O ok I didn't know if it was left side looking under the Hood or from the drivers seat. Now I sound really dumb! Well I guess ill start replacing plugs and wires then huh?

 

[SunlitComet]

inspect them first.

 

[BattelWagun]

I don't think its the ignition, I'm thinking heads or cats

 

[gpracer1]

I would check the driver side O2 sensor and wiring also.
Does it do it when cold, or only when the engine is warmed up?

 

[spivey94]

gpracer1, it pretty much does it all the time and now it has started to smoke after i changed my plugs, wires, rotor, and cap. i was told to check the EGR valve so i pulled it off but i really dont know exactly what im looking for.

---------- Post added at 02:45 PM ---------- Previous post was at 01:52 PM ----------

well from everything im seeing from the radiator gurgling back into the resevoir to the white smoke, im beginning to believe its a head gasket!