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Old 04-12-2010, 05:29 PM   #1
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Help! I keep stalling!

My 1999 TJ jeeps stalling out for no apparent reason. I have taken it to the shop twice and they can't figure it out. Here are the details: I have a 1999 TJ Sahara, 4.0L, Auto Trans around 120K mi. I just put new plugs/wires in, air filter is clean. It will stall out in reverse or forward, at slow speeds or highway. I notice it a lot at slow speeds going over bumps (speed bumps, pot holes, etc.). The shop says everything is working correctly (all sensors, fuel pump, etc.). Has anyone else had this experience? if so, any suggestions on what it might be?! Thanks for your help!

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Old 04-12-2010, 05:35 PM   #2
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Does it start right back up? You mentioned bumps and potholes, is that the only time that it stalls?

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Old 04-12-2010, 06:20 PM   #3
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Originally Posted by Big_B View Post
I notice it a lot at slow speeds going over bumps (speed bumps, pot holes, etc.)
Sounds like something is loose.

Check your plug wires where they connect at the distributor (or coil, unfamiliar with 6cyl) and ensure they're fully seated/connected.

I once owned an '86 Pontiac Fiero that did the same thing....trouble-shot the problem for months, turned out to be the main distributor wire had separated from the metal connector that holds the spark plug, and made contact most of the time. Darndest things sometimes......
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Old 04-12-2010, 06:26 PM   #4
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When the engine suddenly stalls on its own, it is usually electrical. The top two reasons for this are, in no particular order, the crankshaft position sensor and the ignition coil.

The CPS is what provides the engine's master timing signal and when it goes bad, the engine stalls suddenly. Mounted on the tranny bell housing on the driver's side near the top, it generates the timing pulses from notches cut in the flywheel.

The ignition coil can suddenly go bad too and cause the same symptom. Mine went bad in the middle of a difficult trail ride last year. Reseating its connector a few times got me home until I could replace it.

If you have fuel pressure at the fuel rail but no spark, I'd guess the ignition coil. If you have no fuel pressure at the fuel rail and no spark, I'd guess the CPS. You can check for fuel pressure via the valve on the fuel rail that the fuel injectors connect to. It has a big black screw-off cover with what looks like an oversized tire valve stem that you push the little center pin on to check for fuel pressure. Only do that after you've tried to start it so it is pressurized if the CPS and fuel pump is working. The fuel pump won't work if the CPS isn't working.
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Old 05-19-2010, 03:22 PM   #5
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I'm having the same problem...99 TJ stalls intermittently, mechanic can't diagnose because it doesn't do it when he drives it. Fuel pressure is normal. I replaced plugs,wires,cap,rotor and the CPS pickup in the distributor. Sounds like I need to go to the coil and the CPS on the bell housing?????
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Old 05-22-2010, 10:36 AM   #6
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I have also experienced sudden engine stalling, 3 times in 4000 miles, twice after moderate offroading 20 miles, once while highway driving after 100 smooth miles. Engine jerks, bucks, nearly quits, then catches and is fine for 6 months. Fuel pressure is good, new plugs & ignition wires after first event. If it's the CPS, is that reasonably easy to replace? Thanks,
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Old 07-21-2010, 03:08 AM   #7
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Try beating the hell out of your rear tank skid. I kept my ZJ rolling for 9 months this way. If your fuel pump may be going out and sand particals may be stalling out your pump. Find the largest rock around and give it a few bumps.if it starts you know whats wrong.

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