matt91xj

I bought a 91 xj with a 4.7 stroker (homebrew stroker, not a kit) a few months back. 2 weekends ago it started running VERY bad after I 1) did an oil change and 2) got gas from a sketchy gas station outside of town. It was missing very bad and even cut off while idling a few times.

I put in new plugs, wires, rotor and cap this past sunday, and it ran good... until today. Pulled what I called the number 1 spark plug (closest to the firewall) and it looked nasty - burnt looking / starting to get buildup.

Today is monday, 1 day after replacing plugs and jeep is starting to miss again, and has cut off on me no less than 5 times today (only at low rpms - stopped at stopsign / stoplight)

I pulled the # 1 and 6 plug and swapped them, and the jeep ran resonably better, still missed some, but not as bad. - The number 6 plug (closest to radiator) was in better shape than the #1 plug, (the ceramic was still white except for a little black in one area, and no buildup)

The best way i can describe the look of the pulled plugs would be the ones on a plug chart that are called burnt ash buildup.





Any help on what may be the issue? From reading and looking at spark plug charts i'm thinking bad valve seal maybe? The oil in dipstick is also black already from 1 week in the jeep, and has a hint of gas smell to it.

Please help! My first wheeling trip is in two weeks and I want to be running as good as I can when I go.





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Pics attached are of 2 of the sparkplugs that I pulled sunday, will post pic of the #1 sparkplug in the morning.





Also attached is video of the jeep idling.***

AtomicNL5

i have the same issue with mine i replaced the crank sensor and it stopped for a while but has started back also throws a check engine code saying immediate lose to crank position sensor.

Ianf406

Do you have any codes? What kind of injectors/intake/exhaust do you have?


My Stroker runs rough if 1.) I don't run premium fuel,

2.) If I have the incorrect plugs- I cant run Normal XJ plugs or they foul in about a week. I have to run colder/shorter plugs (I started with RC9YC4 and now run NGK BKRE6) Stock ones are RC12LYC or similar and are about 1/4" longer/ burn hotter.

Being black usually means you are running rich- and no plug change will probably permanently fix that. Mine runs a bit lean (white) with 24lb injectors/62 mm TB/ spectre cowl intake- some guys on jeepstrokers.com run 27lb injectors and have to upgrade their air intake quite a bit to keep up.

If it is really really black, You could be burning oil or the bad gas could have also caused it. Are you loosing any oil/smoke in exhaust? Do you run any additives?

As far as I know, the burnt oil on the dipstick is normal when using conventional motor oil- I never have it happen when using sythetic in the same motor (my stock XJ) I scrape it off-seems to be just oil break down on mine.

Bustedback

The cylinder closest to the radiator is number one and number six is closest to the firewall. Number one will always be at the front of the engine bay on any rear drive vehicle.

Rogue4x4

This. Make sure you're running premium and have the right plugs for your setup...then run it and see what happens. Eliminate one thing at a time. I would start with the fuel (unless you are running premium already), then plugs, then injectors, etc....until you track it down. BTW have you down a compression check?

Ianf406

Also- not related to your problem but remember to run a high-zinc oil in it. If I dont, it voids my warranty. The cam really needs it.

I use Amsoil Zrod but there quite a few others out there. There are also zinc additives you can get for any oil. Most classic cars (everything with a flat-tappet cam) also require high zinc so it is all over.

AtomicNL5

yea, i don't run prem fuel either but i am running stock intake, throttle body, and exhaust i have replaced almost every sensor trying to figure the problem and a left with the MAP sensor left so i am going to try that next i did have a check engine light but it was o2 sensor and the same crank/cam position lost i have replaced the crank sensor about three times and still don't know why its keeps throwing a code.

Ianf406

Mine just recently threw the cam sensor code. The crankshaft position sensor is not always the answer depending on what code you get. I ultimately had to replace the distributer to fix mine (That is where pre 2000 cam sensor is). You can buy the "cam sensor" separately (called a stator at most parts stores) but a whole distributer is not that much more.

AtomicNL5

Yea sir Ian Thank You very much that sensor inside the distributor was my problem the whole time I went ahead and changed the whole distributor also because it had a little corrosion on the rotor under the stator.

Ianf406

No problem! glad you got it fixed!