Misfire/stuttering issue

[raptorforme93]

What's up guys, It's been a while since Ive posted. Just been super busy all super and recently moved up to North Carolina and am attending Nascar Technical Institute and building race cars! Some know I was rebuilding my tranny and had a few problems with that but I got it all situated and have been loving it, going nice and strong. Recently in the past two weeks the hoe has developed another problem though and it seems rather tricky. I'll try to describe as best I can with all details, feel free to ask specific questions.

Basically I have an intermittent misfire or skip throughout the whole RPM range. It doesn't do it when I first fire the truck up, regardless if the engine is already warm or still cold and I drive for 5 to 10 minutes and then it will start to misfire predominantly under stress. It doesnt seem to do it at all if Im just free reving the engine but under a load it does. It's not constant and it doesnt backfire or make any noise, my engine sounds very clean and tight.. There is a good lack of power at all times it seems now and there are not any engine lights on at all with any codes but I havent had a good scan tool on it yet. It's really noticable at stop when its in gear. When not skipping, it idles very smoothly and purs but when it starts skipping you can really feel it rumble and shake. Also, when the TC is locked up over 50mph and it skips you can reallyyyy feel it skip, kinda jerks you forward for a split second.

Thats all the details I can think of, feel free to ask more and I can get a video of it if you guys think it'd help. Where do I start diagnosing this thing?? What are some things I can look at and start testing? I havent done anything to the truck at all except put new spark plugs in when it first started skipping (they were pretty damn bad). Thank you guys and I look forward to being on the forum more often now!

 

[dsteele]

You said you put new plugs in it, but did you change the wires too? In the past I've had vehicles skip around like that that needed a new wire or two. Look at the wires and make sure that there are no burns or cracks in them or the boot. Sometimes you can go out at night and lift the hood while it is running and see some sparks if there are.

 

[SunlitComet]

I am thinking weak spark so check your misfire history, make sure the CEL operates because you should have had an indication by now with those problems, and inspect all the ignition parts for damage or arcing.

 

[raptorforme93]

Would wires make sense since it doesn't always do it and it's worse under a load? And how can I ensure the cel is working? It always has in the past but I also figured that I would have seen something from it by now but there hasn't been anything. I'm having my friend scan it at tire kingdom tomorrow though

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[dsteele]

Mine would do it more under a load than any other time. When I had a firebird if I accelerated it would kind of bounce around and feel like it's jumping in and out of overdrive while accelerating.

 

[SunlitComet]

Official functional check: cel on with key on and then out with engine start.

 

[raptorforme93]

Thanks guys, found the culprit. How do the contact points get the corroded? Put a new cap, rotor, and wires on and it runs like a top now! Super smooth Thanks again!

---------- Post added at 12:18 PM ---------- Previous post was at 12:16 PM ----------

Looks like the cel isn't working though.. need to get that figured out

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[raptorforme93]

How often and likely is it that the cel light burns out? I know it was working when I put the dash back in after replacing the heater and evaporator core

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[SunlitComet]

rarely but like any bulb it could happen. Always do a bulb check at every start cycle to see if a warning light somewhere is out. Oh and if you blow out another cap with the same corrosion stuff in view when removed you may be due a new dizzy. I blew out a delco, bwd, napa and msd in 15 months time and said screw it time for the new MSD dizzy. Such a lovely part.

 

[raptorforme93]

I put in a new head unit today and checked the instrument lighting while I was at it and turns out the cel light was burned out, no wonder it never came on. Lol. I'll keep an eye on my cap and see how it does in a few months, thanks for the heads up and thank you guys for the help!

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[JDWX]

For anyone reading this at a later time, if you've tried the above and still have issues.... Pop the distributor and examine the teeth on the drive gear for wear like getting knife edged. .

I chased a slowly increasing random miss for a couple years! Swapping plugs/wires cap rotor quite a few times, lol.. It would actually seem "help", but as any part wore out of spec a bit, it would slowly get worse and throw the random misfire code. Often it seem mostly around 2000+ rpm under slight acceleration, while in TC lock up, like highway usage. I was almost figuring the converter clutch was chattering as that was when it was noticeable. Popped the unit out, saw knife edging, swapped the distributor with a reman and fixed it. Amazing it never occurred to me previously.