4.0 High RPM Miss and Sputter

[XJ20]

I ran my ’91 jeep through a running wash of about 6” of water and now I have no high rpm engine power. It starts great and idles perfectly but if I try and rev it up fast it will try and backfire. Anything other than 1st gear or 5th gear with over 1000/1500 rpm and its not going anywhere. It seems I can drive it all day long in 5th gear as that keeps the motor rpm’s down.

I have a good tune up and just checked everything again. Removed the cap and checked the wires. I use silicone and have run this jeep through rivers many times. I replaced the O2 sensor just now but no change. Should I just start replacing other sensors starting next with the TPS and maybe a new fuel pump or is there a procedure I can perform tonight to narrow it down so I can get parts tomorrow. The O2 sensor and TPS is the only advise I got out of some searches but the search engine doesn’t know what a TPS is and I am not too familiar with it myself. Thanks.

 

[anony91xj]

Interesting, 6 inches of water is barely enough to come up to the wheel, I don't know how that could have caused any real damage like this...did it happen immediately after the water, or could it have just been a coincidence. No matter at this point really though...

Hard to say without doing some diagnostic work. Definitely do not just go throwing parts at it. The easiest way to diagnose this would be to use a scanner such as the Snap-On one with a Chrysler OBD adapter.

Since most people don't have access to that kind of equipment (those scanners cost thousands), start by checking your timing...it's easy enough with basic tools. Make sure that when #1 is at TDC the distributor rotor is pointed at the #1 position...if it's directly opposite rotate the crank one more time to TDC and make sure it lines up.

If that checks out, get your hands on an FSM and DVOM and start testing sensors, start with the TPS and ECTS.

 

[buffalomatt350]

Food for thought: When's the last time you changed the fuel filter? I'm not sure if that particular year has one on the outside or only in the tank, but perhaps it was either a coincidence or water or something else hit it and knocked crap inside of it loose? It's kinda a stretch, but I think it would be wise at any rate to consider all aspects of fuel delivery, the easiest of those being the filter. Good luck.

 

[buffalomatt350]

Another thought to check for loose wiring and connectors.

 

[XJ20]

The loss of power is directly related to going through the small amount of water. Since it happened very close to home it wasn’t until the next morning that I noticed how bad it really was. I was thinking that it had to be the O2 sensor just because of the location, but it’s not running any better after replacing it. I checked every electrical connection and of course the ignition. I stopped and got a TPS, fuel filter and a fuel pump module last night but haven’t installed them yet.

If no sensor is commonly known for going out after going through water then I am expecting it to be a fuel delivery related problem and possibly coincidental. The ignition components and fuel filter were all replaced in January and the jeep has never run any other way than great. However I used the jeep to tow a trailer with an AMC 360 engine for my J20 last weekend. The trip to Phoenix and back to Tucson was during an extreme heat advisory. It was 114°f in Phx and one stretch of I-10 near Casa Grande was over 116°f for twenty miles. The jeep ran great the whole trip and barely went above normal running temps. When I got back to Tucson it was only 105°f but as I pulled in after the long haul my fuel pump was screaming over 80 decibels. If a fuel pump can cause my systems then the water may have done something more to it. I just thought for sure this was going to be a common sensor problem that has happened to many people. I’ll know by tomorrow if it is a fuel delivery problem.

 

[Dr. Dyno]

If no sensor is commonly known for going out after going through water then I am expecting it to be a fuel delivery related problem and possibly coincidental. ...
When I got back to Tucson it was only 105°f but as I pulled in after the long haul my fuel pump was screaming over 80 decibels.

I'm almost certain that your fuel pump has just got its gold watch and gone into retirement. Replacing it should cure the problem.

 

[XJ20]

The jeep is back to normal with a new fuel pump module. It may even run a little better! Problem solved. Thanks.