Misfire at Startup, Otherwise Running Fine

[jckrieger]

I've been taking some time to tie up all the loose ends on my 91 R/T. It now has a T1 radiator and is holding coolant pressure without issue. Now for the next issue:

For the last year or so, when the engine is cold, it will run on 3 cylinders for up to about 15 seconds, then will clear up and run perfectly until the car is shut off an allowed to cool. The plugs look ok, I've swapped injectors and cleaned the injector harness, and inspected the plug wires. So far I don't see anything concerning.

Has anyone else had an issue like this? Could it be the coil pack or a cam/crank sensor? It's very repeatable, and does nearly the same thing every time. Hot restarts are without issue. Let me know what you guys think.

[Ondonti]

Turn off the engine after you first notice the misfire, then pull the plugs. See if one of them is damp and smells like gas. Then concentrate on that cylinder.
If its truly misfiring just one cylinder, it could be ignition or oil fouling. I would figure a bad injector would not get better after 15 seconds.

[Force Fed Mopar]

Weak lifter or 2 maybe. Is it just one cyl? Do you know which one?

[jckrieger]

Weak lifter or 2 maybe. Is it just one cyl? Do you know which one?

I'm going to install fresh plugs and fire it up to see if one of them gets wet. Sometimes the car has a lifter tick on startup, sometimes it doesn't. It always goes away after a little while. I installed FWD-P upgraded lifters about 50K miles ago and now they're no better than the originals were at 50K miles. I'm not looking forward to mixing and matching lifters, but that's probably what it'll come down to. I'll let you guys know what I find out. I thought maybe a flaky cam or crank sensor could do something like this and it was a common problem.

[jckrieger]

I changed the plugs, as they had about 40-50K miles. The car starts fine every time now. The gap was perfect on all of the plugs, so I don't know what happened. Either way, it was a $6 fix.