Surging constantly
 

I own a 96 XJ Country 4WD with 330k miles on 4.0L and 4AT and bought it as a learning car of mechanics for only 500 dollars, and so far it's done a decent job of teaching me lol. I've had this XJ for 3 years now and I have only put roughly 150 miles on it, its slowly getting driven more. Recently I've been having this bad surge of about 200 rpms constantly while at idle and while holding the gas pedal in neutral. If I give it alot of gas while driving in 1/2 it will hiccup, loss of power type thing, when I am coming to a stop and coast the rpm will drop into the 500 range and start to almost stall and if I do not give it any gas it will stall out, starts up instantly after, when it's cold it doesn't do this but the warmer the engine gets the more frequent. . I cannot open the throttle open fast in the bay or it'll do the same thing, but if I bring the rev up slowly it will only surge. I have attempted to take a flat head to the fuel valve and it only leaked out, did not spray like I've been told it should. Several people have looked and none of them have given the same faulty part. In June I had to replace my fuel filter because it was leaking gas. I've put a seafoam in my gas and half a can in my manifold and I did notice difference in my acceleration but I still have the issues.

I'm listing knowledge I have so far incase it can help with diagnosing.

Cylinder 4 has a knocking noise from the top, will be doing research on how to do valve adjustments and doing that this weekend and I appear to have smoke coming out of the air intake hose, the part that connects to the throttle body, but my knowledge of smells isn't there yet so I can't tell if it's oil or whatnot. At a dead stop with in gear D it will very slowly take off, no matter how much I push the pedal in, but in 1/2 I can take off and break the dirt and then shift into D and drive just fine, only on take offs. Not sure where it is messed up at but my thermostat just jumps around and when I bought it, it had a thermostat in the center console, but when funds are available I want to do a inline radiator hose mechanical gauge so I know it's accurate.


I have replaced the exhaust manifold, had to remove some major components but had a master mechanic helping me. The exhaust system is broken, bad 02 sensor somewhere, haven't done research on this yet, but it is very loud, a straight cylinder part in the center about under back door is removed because the PO had it held on with a arizona can and the back tail pipe just dangles there for cosmetic reasons. Replaced tie rod, alternator, new ignition switch PO had it broken it and put a toggle switch. Changed rear diff oil but it was clear so am not checking front.

Thank you for taking the time for reading this and I apologize in advance if I confuse with all this information, I can help clarify things.

I had similar symptoms when my throttle position sensor (TPS) was bad, although not quite as severe. IIRC I diagnosed it to be the sensor by back probing the pins for resistance through the sensor and compared the values to the factory service manual specs.

Also would be a good idea to throw a fuel pressure gauge on there to check that.

Thanks for the quick reply, I’ll check some YouTube videos and reference my book while checking the harness, if the values are different am I replacing the TPS?

If the TPS isn't giving the spec output (and you've checked that the connector and wiring going to it are in good shape (they are not far from the exhaust manifold...)) then you should replace the TPS - preferably with a Mopar.

the connector looks fine and so does the wiring. I played around with the tps connector and managed to get my multimeter proves inside it for stable testing and came up with .55 V for closed and 3.2V for wide open and the build up seemed to be steady.
I broke the end of the clip for the harness, is there a possible fix? Its still in the tps solid.

I'm not sure what the proper TPS values are, but if it's steady, that seems like it's not likely to be the cause.

I would bet that the bad O2 sensors are a big part of, if not the cause of your surging issue. You know it's bad, a new upstream one (the one that affects engine behavior) is $30 at Rockauto, so I'd replace that before anything else.
Use only NTK brand O2 sensors, the XJ is pretty picky about them and even normally high quality brands like Bosch are problematic. NTK 23121 is the important one. Rockauto lists NTK 23014 for the downstream one which if it were me, I'd replace, but it wouldn't be likely to impact your particular issue.

The fuel pressure check that was mentioned is an important thing as well.

Have you cleaned the throttle body and IAC motor yet? If not, that's always recommended.

You might have to hit the junkyard for a new connector clip. So long as the actual contacts are in good shape and connected, whatever you do to ensure it doesn't come apart is probably fine - maybe some tape around it or you might try gluing the plastic back together.

Looking at your original post again - you need to definitely check the fuel pressure. The spec for the 96 is 49psi I believe and if it only trickled out the schrader valve.. I doubt it's nearly high enough.

If you do need a new pump, the downside is the pump is a one-off for the year, though folks seem to be able to find replacements and the upside is that you don't need to drop the whole tank to access it.

I cleaned the IAC the first month I got it and it brought the idle almost steady, until recently. I still haven't looked at the exhaust system or what parts are missing, what would be the worst case that I am missing the part the O2 sensor mounts to?

I do not have the jeep at my apartment due to not allowed to have a second vehicle so it's at my parent's house across town.

When I get funds available for parts I'll start with purchasing a fuel pressure gauge and checking the pressure. If my pressure is below 49psi do I need to just replace the pump?

You don't need to buy a pressure tester - check with your local parts stores and see if they have a loaner tool. Put a (hefty) deposit down, but you get the money back when you return the tool.

If the pump isn't producing sufficient pressure, yes, you need to replace it. However, you need to make sure the pump is getting power, the filter isn't clogged, etc. etc.

The "upstream" sensor is located somewhere between the engine and the catalytic converter. On my 95 (with one sensor) it's in the "front pipe".. the pipe connecting the manifold to the converter. There will be a "bung" for the sensor and an electrical connector.. if not, you'll have to find the wires and figure that out..

Most exhaust rot occurs behind the catalytic converter - it's very very hot up to that point, so most moisture burns off and it takes a lot longer to rust out. If you have most of the exhaust piping, you should have the O2 sensor parts at least present.

Found my haynes manual in the truck and read that the tps needs to be replaced if wide open reads anything under 4.8V, so I will be replacing this first. Found out for my year the pressure regulator and the fuel pump is in the same assembly and cannot be serviced so that crosses off one thing I need to check after I check my fuel pressure at the valve, if it is low I will be replacing the fuel pump.