Real poor performance

JEEPDOWN

MEMBER
1998 JEEP WRANGLER
4.0L
6 CYL
4WD
MANUAL
150,000 MILES

Recently my vehicle started to perform poorly. The vehicle starts fine. Idles fine. When I drive, the vehicle will shut off when I let off the gas and push in the clutch. There are times I can bump the throttle and the vehicle will remain running at idle. It also has no power above 3,000 rpm's in any gear. It acts like there's a rev limiter (but there isn't).

I changed the throttle position sensor and the MAP sensor. No change.

Also, within the last year I changed the fuel pump, crank position sensor, fuel injectors, and basic tune up. I am loosing my imagination. Any thoughts?

7 Replies

KASEKENNY

MECHANIC
18,907 POSTS

This sounds like a possible ignition or fuel issue that could be caused by a sensor or a mechanical issue. As you can imagine, this is pretty broad and so we need to start limiting it down to see where we have some issues.

First and foremost we need to look at a fuel issue. Let's start checking fuel pressure and make sure it is correct. Let's hook up a gauge and tell me what the pressure is or just get a video of it when this is happening.

Once we check fuel pressure off we can move on but this sounds like a fuel issue so I would like to start there.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

let me know if you have questions. Thanks

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Monday, August 17th, 2020 AT 8:24 AM

JEEPDOWN

MEMBER
4 POSTS

Finally checked the fuel pressure. Steady at 52psi. Barely drops 1-2psi during hard acceleration. Still stalls out when clutch depressed and no power above 3,000 rpm's.

I am ready for the next step.

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Friday, September 18th, 2020 AT 12:58 PM

KASEKENNY

MECHANIC
18,907 POSTS

The next likely cause would be lack of air. I understand that you put the MAP sensor and and throttle sensor but it acts like it is just not getting enough air. Can you remove the intake and drive the vehicle and see if that makes a difference?

Next, do you have a scan tool that can monitor live data? If so, can you drive it and monitor the MAP, temperature sensors, and o2 data? Let's see if this is running lean and go from there. Thanks

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Friday, September 18th, 2020 AT 6:46 PM

JEEPDOWN

MEMBER
4 POSTS

I removed the intake tube. No difference. I made a few runs up the street from standing start, full acceleration through first and second gear and then clutch in to stop and idle. Here is the graphed data:
MAP during run
TPS during run
O2S B1S1(V) during idle
O2S B1S1(%) during run
O2S B1S2(V) during idle
O2S B1S2(V) during run
O2S B1S2(%) during run
Any thoughts?

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Sunday, September 20th, 2020 AT 12:36 PM

KASEKENNY

MECHANIC
18,907 POSTS

Unless I am seeing that wrong, it looks like sensor 1 was lean (.360 v) on run up and sensor 2 was rich(.800 v)?

If that is the case, have you swapped out the o2 sensors?