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Pete, Technician
Category: Jeep
Satisfied Customers: 28788
Experience:  Over 17 years diagnosing and repairing automobiles various makes and models with some training and certifications.
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My 2001 jeep wrangler tj sport start running rough with a

Customer Question

My 2001 jeep wrangler tj sport start running rough with a light backfire through the tail pipe. Gradually got worse and soon much worse and stalled. When trying to restart it began backfiring through the intake. I was able to get it moving and idled it out of the highway and towed it home.
JA: How many miles are on the car? What size is the engine?
Customer: 4.0 inline 6 bored and stroked to 4.7 liter. Has run great for approximately 12000 miles
JA: Are you hoping to fix this yourself?
Customer: yes
JA: Great! What have you tried so far?
Customer: Checked plugs, 2 of which showed proper color and 4 were dry black and sooty. Compression on cold engine was 150 psi on all but one cylinder which was 180 psi. Installed new coil rail, replaced crank position sensor and cam position sensor with Mopar part. Had battery and alternator tested. Pull some fuel from fuel rail to check for water, good fuel and pump was working. have not checked fuel pressure. Catalytic converter was changed with new engine build but removed to check for blockage and it's not clogged.
JA: Is there anything else important you think the Jeep Mechanic should know about your Jeep?
Customer: There's a heavy gauge wire attached to the engine block where the neg batter cable is attached that has been hot enough to wrinkle the casing a couple inches up from the stud. I'd estimate the to be an 8 to 10 gauge wire. I'm wondering if this is the pcm ground wire showing signs of a short. Also when I crank the engine an get it to run for a few seconds all the lights on the instrument panel are blinking like a christmas tree, even my tach and speedo are moving which leads me to believe this to be an electrical issue. It seems like a timing issue but don't believe it's mechanical. Wondering if the computer is bad or shorted. There have been no engine codes. I can access the computer with my scanner and programmer. I've returned the computer to stock, reflashed my tune file and set it to open loop. All these processes seem to have worked fine
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Jeep Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Jeep
Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

What needs to be done is to have the fuel pressure tested to see if the pressure is low.This sounds like a loss of fuel pressure causing this fault here.This will cause a lean back fire out of the exhaust and/or intake like this here as well as a stall out.I would start with having this done to see if the pump itself needs replaced.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
Pete, sorry for delay. I have good static fuel pressure 40 lbs min. No leak down. Can't run engine to test further. I have fire on all cylinders. All injectors ohm within 0.2 of each other with 12.5 average. I don't have voltage at either injector plug terminal post with meter grounded to negative battery and probing with positive lead with switch on. Injector fuse is good.
Expert:  Pete replied 1 year ago.

Can you check the injector harness and follow it to see if any broken wires are found needing repaired and let me know?

Thanks Pete