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Old 12-03-2019, 04:23 PM
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Fuel or spark?

I have a 98 TJ manual with 120K mi. I fill up with regular gas as I learned with my XJ these 4.0l don't like premium.



I have an issue that has worsened, initially showing itself intermittent in second gear at about 1500 RPM when cold. Now it is in 1st and 3rd and easier to replicate.


Now when cold, pull out of drive way and step on gas and the motor stutters at 1200 rpm or so, shift up and the same a little higher in the RPM band and again in third (I used to be able to shift from second to third and this would make the stumble go away). I watch the tack drop in and out with the stumble, but I think the engine just goes down to idle RPM and isn't necessarily in risk of cutting off.





Any suggestions?

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Old 12-03-2019, 10:20 PM
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I was hoping someone else had experienced this. Maybe a computer issue?
Does the 4 liter have separate fuel and spark computers?

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Old 12-04-2019, 11:47 AM   #3
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Quote:
Originally Posted by jmc0369 View Post
I was hoping someone else had experienced this. Maybe a computer issue?
Does the 4 liter have separate fuel and spark computers?
Same computer. Do you have some form of a scan tool that can see live data? Something like torque pro?

If you do you can look at o2 sensor data and fuel trims. This will tell you if you are not getting enough fuel when there is load on the engine.

That's where I'd start. Checking for spark is a little harder when you trying to do it under load. It very well may be a crank/cam sensor cutting out which is affecting spark but that is harder to check.

When you first mentioned the issue, I thought transmission problem but with a manual it's much less likely. Does your clutch feel like it's in good working order?
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Old 12-04-2019, 11:49 AM   #4
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Another idea is throttle position sensor. Best way is to hook up a DVOM to it and sweep the throttle. Look for cut outs. Best to do on a graphing meter but I suppose you can do it on a regular DVOM. Harder to see quick cut outs but worth a try.
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Old 12-11-2019, 06:58 PM
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Had it scanned. Came back with bad fuel pump and O2 sensor.
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Old 12-14-2019, 04:28 AM   #6
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See if any of the injector harness wires are mixed op

On the 2.5 people tend to cross three and four which tends to make a stumble at around 1500 rpm

Fuel timing is really controlled by intake valve opening but screwing up injector sequence can lead to a stumble


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