Stoker begins misfiring

[wuvillan]

Talk about bewilderment?!? I had a machinist/mechanic bore and rebuild my blown 4.0 with an AMC 258 crank and rods. The man used aftermarket pistons and a Comp cam. After reinstalling it personally, the engine wouldn't start. I discovered that if I installed the cam positioning sensor 90 degrees perpendicular to the block it would run. I remember it being parallel to the block and facing rear. At 90 degrees, the wiring is terribly strained. Regardless, the Jeep ran very well after that. I'ver put 700 miles on the new motor and followed all break-in procedures religiously. Over the duration of a week the motor began idling rough. It is now misfiring past the point of being suitable to drive. I became reluctant to drive it after the first symptom and haven't put more than 20 miles on it since becoming severe. The morning of my "last straw" I stopped at O'reily's because the check engine light came on. Their scanner read "misfire cylinder 6". I drove it immediately to the original mechanic. He dicked with it for a week. He believes its something computerized. This conclusion was made after a compression test, new coil pack and spark plugs, injector test. He swapped number 6 and 4 injectors. That made cylinder 4 have issues and 6 operate better. He did mention that the plugs he pulled were gummed up, that the engine is running lean. Sooo...I drove it down the road to the Jeep dealer. That effectively removed $60 from my possession and into theirs with no reward other confirming multiple misfires now. Presently, the Jeep is sitting in drive way. Please give your knowledge!!!!

I AM concerned about running stock injectors. The mechanic thought it would be fine.

[sly-jeeper]

ought oh!!! i would pull the valve cover and measure cam lift

[SilverXJ]

I discovered that if I installed the cam positioning sensor 90 degrees perpendicular to the block it would run. I remember it being parallel to the block and facing rear. At 90 degrees, the wiring is terribly strained.

Re index it correctly and check the sensor itself: http://jeep.blackonyx.net/pdfs/jcss.pdf If that doesn't work the cam could be installed wrong. Maybe a bad CPS.

followed all break-in procedures religiously.

This includes a proper cam break-in with proper oil?

That made cylinder 4 have issues and 6 operate better.

Faulty injector

He did mention that the plugs he pulled were gummed up, that the engine is running lean.

Its hard to tell from the state of plugs in an EFI engine how its running. Sounds like he doesn't know what the hell is is doing. Gummed up?

I AM concerned about running stock injectors. The mechanic thought it would be fine.

Under most use they will be okay. Under WOT it will be very lean. You need larger injectors.

I'm guessing you have a 99+ Jeep, but what is the exact model and year?

[wuvillan]

Correct. My Jeep is a 2001 Jeep Grand Cherokee. I followed the break-in procedure as follows...15 minutes of sustained 2500 rpms at initial startup, strictly city driving, avoiding highway miles at a long period of time and constant rpm. I was on the verge of doing the first oil change before these events occurred. I will do as you suggested and Re index CPS. I'm not ready to accuse the mechanic of any wrongdoings. I hope I've quoted him correctly. He has been around for many years and services many of the areas dirt track racers and performance hobbyist. I should mention why he was skeptical of the fuel injection. He had used a nod light on the supposed faulty injector. It showed inconsistencies that lead him to believe that something electronically was wrong. He did replace the #6 injector. Do you have any fuel injectors in mind? I spoke to a man at Golen and he tried sell me injectors specifically made to fit the newer electrical plugs on later model Jeeps. They cost $375. Thanks for your reply, you've already been helpful. Keep it coming

[SilverXJ]

He swapped number 6 and 4 injectors. That made cylinder 4 have issues and 6 operate better.

He had used a nod light on the supposed faulty injector. It showed inconsistencies that lead him to believe that something electronically was wrong. He did replace the #6 injector.

Those two statements don't jive.

Have you checked your fuel pressure?

Do you have any fuel injectors in mind?

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