Occasional power loss and backfire on acceleration - JeepForum.com
 
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post #1 of 10 Old 08-25-2017, 08:58 AM Thread Starter
JonMopar
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Well, new problem. I had a choppy idle which i was about to chalk up to a dirty IAC value . Before i even found the time to do that, NOW a new problem thats really becoming an issue..

In the past, if i was lower on fuel and took a hard corner during acceleration, i would have a power loss and hear backfire, almost sounds like through the intake. Now it's doing iton straight stretchs with anymore than mild throttle. When it does it, it wont rev to 3k. The jeep will bog down. But then moments later it'll pull fine...with the power of a freight train. New plugs, wires, cap, CPS (non mopar, 4mths old). 98 4.0 rwd 189k


98 Laredo ZJ 4L -3.73, 5.9 "ultrastar" rims, slotted brakes, Dynomax turbo, CAI.
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post #2 of 10 Old 08-25-2017, 11:05 AM
GOLDWING
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I would start by testing fuel pressure. Are you getting a CEL?

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post #3 of 10 Old 08-25-2017, 11:20 AM Thread Starter
JonMopar
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No Check engine....?

98 Laredo ZJ 4L -3.73, 5.9 "ultrastar" rims, slotted brakes, Dynomax turbo, CAI.
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post #4 of 10 Old 08-25-2017, 11:40 AM
MrRoundel
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I know that you know, that using non-Mopar CPS, CKP, fuel-pumps (Bosch OK here, of course.) is risky. From what I've read over the years, 3-4 months is about the life expectancy of such things. That's where I'd be looking. But perhaps a quick fuel-pressure check would be advisable first, as suggested.

As usual, there's a problem with using non-Mopar electronics even if there's not problem with the electronics themselves. It's the nagging suspicion that it could always be attributable to those parts. Good luck.

After writing/posting this, I searched for the Mopar CKP and didn't have a lot of luck. Maybe they have morphed into automotive hens' teeth? Hmm...not good.

1998 Laredo 4.0L 4x4, 242 TC. Turned over 200K miles in 06/18. Original owner.
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post #5 of 10 Old 08-25-2017, 04:05 PM
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How many miles? V8 o 6? When did you change the spark plug wires? Could they have gotten hot or melted on the engine?

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post #6 of 10 Old 08-26-2017, 01:46 AM Thread Starter
JonMopar
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4.0 6cyl with 189k. wires are newer and plugs are 4mths old if it matters

98 Laredo ZJ 4L -3.73, 5.9 "ultrastar" rims, slotted brakes, Dynomax turbo, CAI.
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post #7 of 10 Old 08-26-2017, 09:26 AM
Malachi73
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I've experienced the same thing. 1998 ZJ 4.0, Auto Trans, about 175K miles.

Mine was doing that very sporatically. Then a week or so ago I had to replace the Trans cause mine went out. While in there I replaced the CPS and have not noticed it since. But, like I said, that was just over a week ago so haven't had time to really verify if it's totally gone or not. And, I don't even know for sure if the CPS will cause that kind of problem. I just figured I'd replace it while I was in there.

PS: when it first happened I replaced the Fuel Pump, thinking that was the culprit, and cause I knew the check valve on the pump was bad anyways. But, that didn't fix it for me.
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post #8 of 10 Old 08-26-2017, 01:22 PM
Uniblurb
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I'd have to agree with what MrR said earlier. You best be using a Mopar crank sensor along with a Mopar (same one made by Bosch) or Bosch fuel pump module in replacing either of these parts.

In replacing 4-5 crank sensors on my 96 4.0 I found out just how bad aftermarket ones were. Installed 2 brand new BWD crank sensors from Advance and they acted just as bad as my bad Mopar one which drove me nuts! (see crank sensor resistance test in my signature)

It should also be noted you best have a real clean/good PCM ground on one of the coil bracket studs on the 4.0. Corroded/oily PCM ground on mine took out 2 PCM's and 2 Mopar crank sensors to boot.

As far as the aftermarket fuel pump modules we've seen real problems with Airtex, AC Delco, etc, and about any other non-Mopar one which uses an Asian made regulator/filter in the 'can' on top of the module on the 97-98. Know one member on here who installed 4 AC Delco pump modules in 1 year on his 97-98 and everyone of them failed.

I would try the fuel pressure test JonMopar and it's best to get an extension hose and tape the gauge face to the windshield. Then you can look at your fuel pressure when driving to see what it reads when you start losing power.

It's not good to have such low fuel when you're turning corners your 98 starts cutting out. The pump can also pickup dirt/water that may be in the bottom of the tank when doing this.

My 96 had a strange quirk as the fuel pump was failing. Engine would start cutting out on only left turns and this was even with almost a full tank of fuel. Same thing happened to member Polka on here. Go figure...

2004 4.7L WJ Limited, 96 4.0 ZJ


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post #9 of 10 Old 08-26-2017, 08:01 PM Thread Starter
JonMopar
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Thanks for the advice so far guys. I too noticed it on left turns when it does happen. Maybe thats because you tend to turn faster left (because you're crossing over a lane), so the fuel sloshes over more..??

Im going to try to track down a mopar CPS, or equivalent.

98 Laredo ZJ 4L -3.73, 5.9 "ultrastar" rims, slotted brakes, Dynomax turbo, CAI.
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post #10 of 10 Old 08-26-2017, 08:44 PM
Uniblurb
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I'm not quite sure why my pump wanted to fail on left hand turns and with 3/4 tank the pump would surely stay submerged in fuel.

I searched around last night for a Mopar crank sensor for a 98 4.0 and there is no equivalent to Mopar. Unfortunately these Mopar crank sensors are 2x the price they were 5 years ago. Cheapest I could find one was on ebay for $88.

http://www.ebay.com/itm/97-04-Jeep-G...25.m3641.l6368

Kind of surprised this fits the 4.0 from 97-2004.

I still think I'd try some testing and try that crank sensor resistance test in my signature on your aftermarket one. Plus a fuel pressure test wouldn't hurt and some parts stores have loaner testers to fit Chrysler/Jeep so if you don't have your own you wouldn't have to buy one.

2004 4.7L WJ Limited, 96 4.0 ZJ


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