Rough running 350

[krigermoose]

'86 C1500 350

Hey all, I've been fighting my truck for a while now and am coming on here to get some opinions. The thing doesn't run smooth, always sounds like it's missing on a cylinder or two. The first thing I did was replace the old quadrajet (which was warped) with a reman, which didn't really fix the problem. I've probably reset the air/fuel mixture screws 20 times now, along with the timing. It seems to run the best (still terribly though) at something ridiculous like 16 btdc. So I don't think my fuel system is the issue.

Just for the heck of it I threw on the old ignition coil to see if it would do anything because I had replaced it originally thinking it was bad and it wasn't. For a few minutes it actually ran smoother, but when I shut it off and started it again it was back to how it was before, misfiring nonstop and struggling to idle.

So I think my next steps are going to be replacing the cap and rotor and getting a voltage reading from the coil to see if anything is out of place.

Any thoughts or other ideas? Could also be some vacuum leak but I've looked pretty hard for one.

[JohnnyPopper]

Have you pulled any plugs?

#6 usually gets fouled up from something to do with the EGR, (see bd for the gory details)

You can also pull plug wires off the cap one at a time to see which cylinder is acting up. Don't do it while running unless you have thick rubber gloves.

[VileZambonie]

Check the firing order is correct. After that, mist the ignition wires with water and see if it gets worse.

[bd]

In addition, snap the throttle full open for roughly one second.  Does the engine pop-pop-pop-pop- back through the carburetor?

[krigermoose]

I forgot to mention that pulled a few plugs earlier and yes, they were pretty dirty, looked like fuel. I'll try the things you guys suggested when I get home from work, thanks. I forgot about the plugs, I should replace them.

[JohnnyPopper]

I replaced mine with NGK IRIDIUMix plugs.

Problem solved.

I like VZ's point about misting the cap, never heard that one before!

I did look at the cap while running in the dark, looking for St. Elmo's fire.

[TexasRed]

1) check grounds
2) if you can, get the ignition module checked at auto parts store. If it's bad, the ignition coil is likely bad too. The ignition coil may have over loaded the module.
3) also check the resistance of the plug wires

[krigermoose]

Alright, so while replacing the cap and rotor I noticed the little black ground wire on the ignition coil was loose... the one that screws in the cap. I mention this because after putting it back together and starting it up it runs noticeably smoother now.

I snapped open the throttle for a second and yes it responded with a loud pop.

When I misted the wires it MIGHT have gotten a tiny bit worse but I might have been imagining things. I don't think it affected it.

I'm going to throw in some new plugs now too to see what changes.

[krigermoose]

update: plugs didnt help in the slightest

[JohnnyPopper]

How did #6 look?

How old are your cables?

Did you check the firing order?

[krigermoose]

johnny popper #6 actually looked similar to the rest, but #8 was actually significantly worse than the rest, there was some gunk buildup on it. the cables are probably around 8 months old, and i did double check the firing order when i put on the new cap.

unfortunately though i did notice that there was oil on all of the spark plugs, so there may be a further problem.

[JohnnyPopper]

Oil on the plugs as in on the tang, tip, and insulator? Better known as fouling?

[TexasRed]

I'm with JohnnyPopper, are you sure it's oil and not gas that's mixed with carbon that looks like oil?

[krigermoose]

should have clarified: the tips were dry but the threads were wet with oil the entire way up. smelled like oil too. could oil make it in that far if it leaked in from the outside like a valve cover leak? no oil on the electrode or anything.

[TexasRed]

Doubtful an external oil leak leaked past every spark plug into the combustion chamber.

Did you replace the distributor at any time? Possibly a tooth off?

Why did you have an old ignition coil? What type is both the old and the new?