Misfire Under Light Load Driving Conditions

[Kyle1911]

Hi,

 

I just did a tune up on the ole beast...

 

Replaced the Distributor rotor/cap, and put new Accel wires and NGK iridium plugs.

 

Motor has 192k km on it, idles perfectly and accelerates hard with no noticeable misfires.

 

It is mainly at cruising speeds, where I am hardly on the gas. It feels like one or two cylinders are misfiring.

 

 

What should I check for?

 

I read somewheres else that none of the wires can physically touch eachother. Since these wires are bigger than the stockers I didn't think it would be an issue to remove the clips that hold them together directly after the distributor. Since with my nissan I never had that issue. Could that be the problem? I thought it would happen at all times not just under light load.

[j.roffel]

I've never heard of that before, and usually just throw those clips away cause I break them.... Can't think of what else it could be, but I'm pretty sure its not the wires touching....

[Kyle1911]

yeah I didnt think it was probable either. What should I look for?

[dietz4ibanez]

About 2000 miles ago I was having the same problems! I put a scanner on my truck and I had cylinder 3 and 6 that were mifiring/backfiring on low rpms.

I looked at the distributor gear on the bottom of the distributor and the teeth were worn down to as thin as a razor, so I replaced it and it runs great now... My truck has about 191k...

 

 

Hope this helps let me know how it comes with getting the problem fixed.

[Kyle1911]

About 2000 miles ago I was having the same problems! I put a scanner on my truck and I had cylinder 3 and 6 that were mifiring/backfiring on low rpms.

I looked at the distributor gear on the bottom of the distributor and the teeth were worn down to as thin as a razor, so I replaced it and it runs great now... My truck has about 191k...

 

 

Hope this helps let me know how it comes with getting the problem fixed.

 

Hrm, I'll have to check that out. The thing is that it didn't misfire at all before I did the tune up. I double checked my wireing to make sure I didn't plug one in the wrong spot. But if I had, it wouldnt idle properly anyway.

 

What are the chances of a bad wire causing the spark to be weak?

[Kyle1911]

I've just heard that non AC Delco parts run like s**t in small block GM's. Is there any truth to this?

[dietz4ibanez]

You can check the gaps on the plugs but they shold be fine and even if they were off its usually not bad enough to cause a misfire. Those NGK's you got should be fine I usually dont use ac delco probab;y for that reason.

[Kyle1911]

The gaps were fine, the plugs looked whitish and ashy when I took them out. I decided to switch to ac delco plugs cause I thought they may be in the wrong heat range as the truck would run worse as it warmed up.

 

 

But the AC delco plugs didnt help. So I'm planning on swapping in the old distributor after I clean it up.

 

What a PITA

[Kyle1911]

After some further inspection on the 31st. I found the problem. The rotor from the cheapy set was garbage with way less precise holes where it attaches to the mechanical part of the distributor. Allowing for a lopsided spin.... But I fixed that the other day... so I decided to check the plugs again.

 

Turns out two of the all mighty AC Delco Plugs (that came from the same package) had cracked insulators so I swapped the NGK's back in and threw on some Die-electric grease and its running really good now.

 

I got some seafoam that I put in my fuel for good measure.

[dietz4ibanez]

glad you got her fixed! My plugs turned white at the tips too. I think that the truck is running lean when it shows up that way. huh, those ac delco's sure seem notorious for cracking like that!

[Kyle1911]

glad you got her fixed! My plugs turned white at the tips too. I think that the truck is running lean when it shows up that way. huh, those ac delco's sure seem notorious for cracking like that!

 

Yeah, the misfires causes the truck to run lean as f**k and misfire more. Compounding the problem till WOT where it runs full ritch instead of stoic so it actually moves haha

 

 

Are they? Wow, what a pain the ass.