Stalling and loss of power - JeepForum.com

 
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post #1 of 10 Old 09-21-2012, 02:34 AM Thread Starter
RBourguignon
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Stalling and loss of power

For the past month or so, my 1998 4.0 I6 ZJ has been stalling randomly, usually within a couple minutes of starting the engine and also losing power at anytime whatsoever. I can press the gas as much as I want but I get nothing. I've been told by some that it can be caused by the catalytic converter and by others that its the fuel pump. Any information you could offer would be greatly appreciated

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post #2 of 10 Old 09-21-2012, 05:10 AM
jsadler
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It could be either one or a number of other things. You'll have to figure out the common factor in the randomness to solve it, or just get lucky. I wouldn't suspect the cat, cause its random. When I've seen cats go bad, it starts, then progresses to wont run at all over a few days. There's no come and go with it. It could be the fuel pump, or a wiring issue ledading to the fuel pump. Could be moisture trapped under the distributor cap, or a bad coil. Could be an EGR problem.

94 zj i6 bone stock for now. Purchased broke down :(
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post #3 of 10 Old 09-21-2012, 06:00 PM Thread Starter
RBourguignon
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How can I determine which one it is?
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post #4 of 10 Old 09-22-2012, 12:53 AM
Uniblurb
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It could be a number of things and going through the below list on your stalling problems is a real good place to start.

http://www.jeepforum.com/forum/f13/1...talls-1407423/

You may want to get a fuel pressure tester and connect it to the schroeder valve on the rail to see what your pressure reads. Spec for your 98 4.0 is 49psi at idle when the engines at operating temps and shouldn't drop below 24psi after 5 mins from when shut off.

You can get a loaner fuel pressure test kit at Autozone, pay full price of $100, keep for 90 days, and return for a full refund. I kept the one I borrowed for a full 2 months until I put a new fuel pump assembly in but my problems were a little different than yours.

Not a bad idea to rule out a bad crank sensor too for stalling problems. You can unplug the connector at the back passenger side of the head. Then hold the plug to the sensor itself with the locking tab up and put the probes of a multimeter, set to the lowest ohm setting, on the middle and right pins (B&C). Any resistance = bad CKP.

BTW, ZeeJay who wrote the excellent thread in the link had a 97 4.0 with a clogged cat so you may want to look at that section closely on loosing power. Believe it's in there. Good luck.
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post #5 of 10 Old 09-22-2012, 02:27 AM Thread Starter
RBourguignon
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Well I found out the cat is bad, so that's a definite problem. Could that be a cause of both problems?
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post #6 of 10 Old 09-22-2012, 02:31 AM
misfit77
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I have no cat. Seems ok to me.

My 96 XJ had no cat either.
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post #7 of 10 Old 09-22-2012, 02:42 AM Thread Starter
RBourguignon
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No cat I've heard works fine, but I've heard that a bad cat can cause problems
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post #8 of 10 Old 09-22-2012, 09:16 AM
Uniblurb
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Just curious how it was diagnosed you have a bad cat? Replace it and then you can troubleshoot for other problems. You may want to check your exhaust manifold for leaks since I heard this can cause them to clog. This is best to do when you 1st start up since hairline cracks in the manifold will seal up some as it becomes hot. Also with your exhaust system backing up it can make your o2 sensors malfunction causing engine running problems. So yes, a bad cat can cause multiple problems.
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post #9 of 10 Old 09-22-2012, 11:42 AM Thread Starter
RBourguignon
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It's been making a pretty bad rattling noise when i first start the engine and we never knew exactly what it was. We had the gearbox replaced and when we got it back, the mechanic we brought it to told us that the noise was caused by a bad cat
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post #10 of 10 Old 09-22-2012, 02:12 PM
Oldfrog
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One VERY common issue for 96-08 models is the PCM ( computer) located on the passenger side firewall. Here's an easy test:
Start if, let it idle. Pop the hood and located the three large connectors on the PCM. ( behind the coolant bottle). Wiggle them up and down. Not the wires, but the connectors themselves. If it hesitates or stalls, that's your issue. You either need to re-solder the PCM's bad joints or buy another one. Period. There is no other way, except to send it to one of the guys here on Jeepforum who repairs them. ( I apologize for forgetting his name...dang it !).

IF you decide to replace it, get a the "Cardone" brand from O'reilly's or NAPA, etc. Do NOT buy one from either of the outfits located in Florida. They only half-azzed repair them. Good luck.
BTW, if it isnt bad now....it WILL be, sooner or later. They all go bad.

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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