Weird issue with engine - Not running on all cylinders

[Buckeye]

Last week I was backing out my 500 and it ran very very rough. It felt like it was running on not many cylinders. I looked at the tail pipe and it was wet and very black. I had I towed to my mechanic. They started it up and it did the same thing, but then it cleared up and ran great.

They have driven it 5 times and it has run great every time. It has new plugs, new spark plug wires, new upper and lower wire harnesses and new fuel filter.

Any ideas ? Thanks for the help and have a great Thanksgiving !

 

[gsxr]

Sounds like classic symptoms of secondary ignition problems, extremely likely to be caused by moisture in the distributor caps. After running to operating temp this usually clears up, and if driven frequently (daily, or close to it) the engine may ran perfectly every time. The issue will recur after being parked longer than a week or three.

Step 1: If the caps are new, skip to step 2 below. If the caps are old, the first step is to remove both for visual inspection. If in bad condition, replace the caps and/or rotors with OE/OEM only. Also remove the insulators and inspect the back side for liquid... new insulators are a good idea with new caps/rotors.

Step 2 is to cut additional ventilation slots in the new caps or good existing caps, as shown in the thread below. This makes a big difference in preventing the moisture problem from recurring, but will be of limited help if there's oil leaks (see step 3) or if the caps/rotors are in bad condition.

Step 3 is to eliminate oil leaks from the camshaft seal, and the cam advance solenoids. If there's any oil, even just a trace, at the bottom edge of the cap... this needs to be fixed.


Thread with all the info:

FYI - Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot] | M119 Engine

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire...

www.500eboard.co

 

[Buckeye]

Thanks, I just put additional slots in my caps a month ago. I will check for oil. Thanks

 

[Efraim]

@Buckeye Which spark plugs there in your engine with or without resistors? Original ones are without.

 

[nocfn]

And just for giggles, has you car been on ramps lately?

 

[Buckeye]

I changed plugs at 75k it now has 81k. That was 10 years ago. I guess they aren’t brand new but they should be good. I put the plugs in that this web site recommends.

Interesting question about ramps. Until 2 weeks ago it was part on a flat surface. It is now parked on a garage ramp in my condo. The drivers door is higher than the passenger door. Could that cause this issue

 

[gsxr]

Plugs should be fine for 25-30kmi or beyond. 6kmi, it's unlikely plugs are at fault, but you could pull one or two for grins and see if they look normal. Since the problem went away and it was running normally, I expect the plugs are fine.

Have you removed the insulators to check for liquid on the back side?

 

[Buckeye]

I will on Monday

 

[nocfn]

Well not necessarily. But if you pull the plugs, back to front maybe one will be oil soaked..usually one of the back two near firewall... If so there is a remedy, and that may be contributor to the problem but not the only issue. If you get around to it, not bad to see how that plug looks. But the insulator moisture caps oil out the cam shaft seals are most likely the issue.