1997 4.0L engine problem - miss or stumble - JeepForum.com
 
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post #1 of 5 Old 07-17-2019, 06:45 AM Thread Starter
srlbotanical
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1997 4.0L engine problem - miss or stumble

Recently, I put my TJ up for sale and it just started acting funny. I don't think it wants to be sold.... :'(

New plugs, wires, full distributor assembly, ignition coil were all put on this winter.

Scan tool (snap-on) shows timing is good, distributor is clocked correctly.

Fuel pressure is 51 psi.

Here's my problem:

- At idol, the engine purrs just as it should, except every 20-30 seconds or so it will very briefly drop out, like it looses fuel for just a fraction of a second, the engine recovers and continues to idol just fine.

- While driving, it runs like a champ under any load, and will accelerate great when I'm on the gas. However, When I'm cruising at speed, on a flat road with the RPM in the 1,500 - 2,000 range it will consistently stutter and miss. I can give it some gas and the jeep will have no missing or stuttering on acceleration.

I'm stumped guys.

The only other part of this system that hasn't been replaced is the CPS, but that's been a run/no-run issue when they've gone bad on my other jeeps.

I've come close to selling this thing 3 times and the buyer was scared away by this issue. I'm not sure what else to check.

Any ideas?

Thanks in advance.

Steve


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post #2 of 5 Old 07-17-2019, 08:42 PM
Kaptainkid1
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How many miles on the car now? Have you consider cleaning your throttle body with carb cleaner? Run seafoam in the Gas tank for a couple full tanks of gas? Also the single hole fuel injectors tend to have problems once over 100k. People have changed their injectors because they wear out and upgrade them to 4 hole and 12 hole injectors from bosch. Dont buy Chinese knock off. They are a huge problem and unreliable.

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post #3 of 5 Old 07-19-2019, 07:23 AM
JeffBowser
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How old is your cat and upstream O2 sensor?
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post #4 of 5 Old 07-19-2019, 02:00 PM
fastblack
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My Jeep did this exact same thing. I replaced the fuel pump (for the fuel pressure regulator) and while doing that noticed the return line was rusted. Replaced the rotten section of line as well. Runs like a top since then.
Out of curiosity, does it start fine or do you have to try a couple times before it fires? Mine was doing this as well and is what led me to do the repairs. Fuel system wasnít holding pressure.
In hindsight, I bet my fuel pressure regulator was fine and it was the rotten return line causing my problems.


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post #5 of 5 Old 07-21-2019, 10:33 AM Thread Starter
srlbotanical
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I cleaned the throttle body, it was pretty dirty. I installed it with a new felpro gasket and had no change.

I double checked my fuel pressure at the rail and I'm actually running lower than I thought. Its 41 psi and drops to 35 when I punch it.

I'm thinking it's the fuel pump.

The 97 4.0L shoudl be 49 psi +/- is that correct?

Thanks everyone.

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