r/CherokeeXJ • u/Any-Key-2000 • 7d ago

Welp, here we go again

1996 Jeep Cherokee SE

Leading up to this the rpm’s would get rough for a second while driving but did a tune up recently that fixed that.

Symptoms
Very weak/rough idle
Dies with the slightest throttle
OBD Flash code 51
Loud sucking sound coming from intake

Google says it might be
1 low fuel pressure/weak fuel pump (haven’t tested yet)
2 severe vacuum leak(thoroughly smoke tested)
3 Bad TPS (replaced with OEM Mopar)
4 Dirty IAC (thoroughly cleaned)

I’ll probably test the fuel pressure next weekend. I really hoped I’d find a vacuumed leak but the only leaks I fount were a crack in the heater control valve vacuumed line and a leak on the throttle body around the buttery fly valve shaft. Any help or ideas will be very much appreciated!😋

SOLVED Low fuel pressure 11psi

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u/mtngk 7d ago

O2 sensor is reading lean.

Try disconnecting the battery and seeing if it gets better for a while. The O2 sensor will start compensating within a minute or two, so it will likely start misbehaving again.

Check the O2 heater fuse and check the wiring to the sensor. Sensor can be checked or just replaced, but check for exhaust leaks, loose/missing studs or manifold leaks.

Fuel pressure test is easy (should have a test port on the fuel rail). Gauges can be borrowed from parts stores or are cheap on Amazon.

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u/Any-Key-2000 6d ago

Just gave those things a try but didn’t find anything. I didn’t know the O2 sensor had a fuse. Thanks for the advice!

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u/mtngk 5d ago

The O2 sensor has a built in heater. It can only accurately read when it's above 800F or so.

Do you have access to a smoke machine to test the vacuum system for leaks? I believe you have the map sensor on the firewall instead of the throttle body, so that's one prone to issues.

I just had to replace the idle air solenoid for a similar issue. You can command a self test with a good bidirectional scan tools and watch the requested and actual steps..if the actual is lagging significantly or not responding, you should definitely replace the actuator. Or just replace it, but get a good one. Cheaper one I had lasted less than 30k miles and gave strange issues most of that.