random cylinder misfire

so i driven down the highway and i'm tryin to pass this old ass man up so i can get off the highway. well at about 50mph the car starts shaking. i let off the gas to see if it will stop and it did. so i gave a gas again a lil and it accelerated fine. while all of this was going on my check engine light was flashing and stayed on. i erased the code and it came back up, and now its doing it a lot worse. like 35-45 when i give it gas hard. now i've owned the car for 2 years of that 2 years i had brand new motor installed. not jus new to me but brand new. when i bought the car the fuel gauge did not work, i was told that i would have to replace the fuel pump$500 at he dealer. well i still havent replaced the fuel pump and im starting to think that pump is starting to go out. if someone can help me out, i dont want to replace the pump yet cause i dont have to $200 to buy the pump and installing is not a problem i'll be doing that. gotta love the access panel in the back.

i've poured sum sea foam into the throttle to clean the injectors and it still does it.


i need help so i can unlock my new motor with less than 1k mi

sounds like a plug or wire. Not a fuel pump issue.

How old are wires? That would be the first thing I'd replace.

AA wrote:

How old are wires? That would be the first thing I'd replace.

If they are old, yes I would replace them. If not you can check them with an Ohm meter, see if one is drawing too much, if more than one then I would replace them also. Normally a bad wire will misfire under a load, not a bad plug though?

I had a cracked spark plug that worked fine except under medium load.

Just got the code for random misfire (P0300) on my way back from school.
While driving the trac off light kept turning on and off, but the car was acting fine. i turn into my neighborhood and the SES light starts flashing at me. I pulled it over and turned it off to prevent damage. The car was still running fine and never felt like it missed a beat. I limped it home with the SES light and trac light on (around the block). pulled in to check the codes and the only one that is relevant is p0300. (also a P0140 for not having a cat or rear O2)
I am about to pull the plugs and wires but they are literally only a few weeks old.
What else can cause the random misfires? I also have a new-ish LQ4 MAF sensor and N* TB with new sensors.
Cam sensor or crank sensor? wouldnt they also set a separate code?

Thanks,
Matthew

How many miles on the car??

150k, most stuff in it isnt that old.

I had random misfires, .
Replaced my wires first, no change....
a new set of 104's took care of it

front 104's still look new, and they should since they have 1,358 miles on them. wires were done at the same time and i used acdelco.
i'm about to pull the rear plugs as soon as the motor cools down some, but i dont expect to see anything wrong with them either.

what sensors can throw this code? anyone with a FSM?

I was getting this code while the lim gasket was bad. replaced today, code gone.

hmm, i know i've been loosing some coolant (a cup or 2 over a couple months) and it's about that time. any way to verify that is the cause?

The plugs are not white/ashy, burnt or wet.

i planned on doing the lim at the same time as the rockers, i may have to move that deadline up some...

You could have your oil analyzed. That would not confirm the cause of the misfire but could verify if the coolant that is disappearing is in the oil, or not.

http://www.blackstone-labs.com/
If you sent them a request for the kit it will arrive quickly and as soon as they get it back they will email the results. You could have the results back in a week or so from today.

Bert

I was able to actually hear the leak and hunt it down with a broom handle, though I know that's pretty shade-tree, and not the recommended course of action.

The job itself was about 6 hours for me, replacing valve cover gaskets, as well as lim sc and tb.

$100 for gaskets, FI O rings, EGR delete kit, and the lock tight.

i think it is leaking into the cylinders and burning off. i occasionally get white smoke on cold start ups.
i have been meaning to send out my oil (already got the kit from them), but havent had the extra $$.

james, where did you order the LIM from? i want the new aluminum one, but the one on rockauto doesnt specify material.

I'm unaware of the different types, but I ordered the gasket through the dealer, part number
89017405 for lim
24503648 for TB
24503911 for SC

ok, i cleared the code and put all the plugs and wires back. So far the code is gone and the car ran great on 3 WOT runs. hopefully it was just a loose wire or a fluke electrical thing.
i'll post up again if it comes back. thanks for everyones speedy help!

You can get the latest generation metal intake gaskets GM P/N 89017825 (set) from ZZP or direct from dealer.

Rickw wrote:

You can get the latest generation metal intake gaskets GM P/N 89017825 (set) from ZZP or direct from dealer.

Felpro actually has a nice aluminum set now. Any auto parts store who carries felpro should have it. O-reillys I work at has it in stock. There's no reason they would be any better than gaskets from GM or zzp but they might be easier to get hold of depending on you situation.

I had the random misfire code on my car and it was running poorly. it would shake and dog out under a load. my problem ended up being a coil.

HOW do u check the coils, I have a digital meter !! ????

AZANC1995 wrote:

HOW do u check the coils, I have a digital meter !! ????

Disconnect them and measure resistance across the secondary, and between primary and secondary. (I will explain).

Secondary resistance is the "tower" side. IIRC it should be 5000 to 7000 ohms.

Primary resistance is the side that sits flush on the ignition module. IIRC it should be a an ohm or two, almost a dead short actually. I mean, check it to see that it's not open circuit (high resistance) but don't wig out if it measures an ohm or so.

Between primary and secondary should measure virtually infinite resistance, an open circuit. If not then wha-la you have a fried coil. I understand they don't taste any better with mustard & ketchup, so you need to replace.

Problem is that even if the coil secondary resistance is ok the coils can still be bad because you could have a bad primary winding (which is why to check the primary) or the insulation could be failing. Problem there is that bad insulation does not always show up as spark leakage that can be seen.

By the way - be sure all the plugs are gapped evenly at 0.060" -- because mismatched plug gaps will unbalance the DIS coils and cause rough idle problems and miss. NEVER over gap sparkplugs in the Riv's (or for that matter any other GM DIS) ignition system to "prevent fouling." You will cook the coils... I guess you could say that a coil that does not work won't foul the plug (ha ha).

And never mess with it with the engine running, DIS secondary voltage can kill you.

These may be helpful, read 'em before you start (won't take long):

http://home.comcast.net/~fierocave/gmdis.htm

http://www.ehow.com/how_4912368_check-coil-packs-voltage-meter.html

this is with ign. on or off ??