Help with an odd misfire problem

M

motorcycleman

New Member
Joined
May 5, 2023
Messages
4
Location
TN
Hello all, new to the forum and need some help with an odd misfire problem (have searched site and read most misfire related posts but don't seem to find my issue). 2002 Jeep wrangler sport, 4.0, auto, 175,000 miles, all stock.
Problem ——— Intermittent flashing CEL, sometimes goes out and engine keeps running ok, sometimes stays on with codes P0300 thru P306 (not always all of them) and engine runs terrible.
Solution —— Turn off engine, reset ECM (jumper disconnected hot at battery to ground on battery for 30 seconds), reconnect and good to go(3 minutes total time to back on the road). Can go from hours to months between episodes. Runs great until it happens, good mileage (17-18 avg)
Tried ——— full tune-up - new plugs (ones recommended here) gap 35, new coil (OEM), new CPS (Crown), new injectors, new fuel pump, new alternator, fuel pressure test(good) , smoke test (good- tiny smoke at throttle body where rod goes in), noid test (good), compression good

Seems to happen more when driving over 55 mph sustained (highway driving). Seems to happen more when lowering/releasing throttle on down hills at highway speed.

The odd thing to me is it runs great, good idle, good power, etc then misfire but a quick reset of the ECM roadside and it is fine again.

Any ideas or insight would be greatly appreciated, Thanks, Jack
 
Similar issues with my 97 4.0.

Random misfire codes through all six...usually all six codes.

Napa Eichlin CPS solved my problem.

Never gotten more that 14 mpg.

-Mac
 
@motorcycleman exactly what brand and exactly what model # spark plugs are you running? Newer model TJs like yours will experience misfires with single tipped platinum spark plugs like the Champion 3034 or Autolite AP-985.
 
If the above suggestions don resolve it and since you’re getting random misfires across all cylinders, I’d check vacuum. Especially since it occurrs more often when closing the throttle. Basically I’m spitballing a vacuum leak.
 
Check this thread here. I have a very similar issue that seemed to only occur over 3000 RPMs.

https://wranglertjforum.com/threads/check-engine-light-flashed-while-driving.67087/#post-1239998

However more recently I got the flashing light going downhill at around 70mph with RPMs under 3k similar to you so not sure. The issue first started when installed an NGK crank sensor as Mopar replacements were nowhere to be found. Replaced that with Napa echelon as suggested and still have the exact same problem. Finally managed to track down a new mopar unit and installed it a few weeks ago but haven’t gotten a chance to test it yet. Will update as soon as I do but all sensors seemed to work fine.

I mostly expect to just live with it as it’s a strictly a weekend fun vehicle for me.
 
Jerry Bransford said:
@motorcycleman exactly what brand and exactly what model # spark plugs are you running? Newer model TJs like yours will experience misfires with single tipped platinum spark plugs like the Champion 3034 or Autolite AP-985.
Click to expand...

Hi Jerry,

I believe it was the Autolite APP985 or Autolite XP985 (based on reading previous sparl plug posts, I didn't use the ap985).

Thx
 
  • Like
Reactions: Jerry Bransford
Top Bottom
Back