XJ random power loss and pop

[alexgalexg]

BTW, from your description it would likely be the fuel pressure regulator.

Good fuel pressure but it drops fast once I shut the jeep off. I smell fuel while I'm driving but can't seem to find any leak. It has done this over the course of 2 new fuel pumps, both with new check valves, I have poor mph and then of course the occasional stumble pop. 98 the regulator is part of the pump assembly so it's been replaced twice. So my thought is an injector for that reason.

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[alexgalexg]

*poor mpg

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[alexgalexg]

Update:
Last night the jeep got worse. It now has a range of 5ft-30ft then it dies. Lucky I have a short commute do I made it home. I have some genuine oem injectors from another xj that I will be able to go pull on Sunday morning.

Plan from here is to verify the fuse for the o2 sensors is good, install the injectors and start with that. What I plan on doing after that fact highly depends on results.

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[CJR]

Diagnosing from afar is always a WAG! So my Wild A__ Guesses are:
1. Injectors dribbling gas when momentarily OFFf during the running Duty Cycle, hence the "enrichment".
2. Check valve in fuel-pump module not sealing to prevent gas flow-back to tank. If your 98 XJ is like my 00XJ, i.e. w/ Fuel Filter/Fuel Pressure Regulator/Module mounted on fuel tank, I suspect some o-rings in that Module are cut or leaking and not holding pressure after engine shutdown. Normally the fuel line should hold pressure after engine shutdown. If not, some o-rings, there at the fuel tank module, may be leaking to quickly drop the fuel pressure. Check your FSM.
3. Faulty TPS, with good injectors, causing computer to randomly change the fuel injector duty cycle to cause enrichment, or
4. Good TPS, with random enrichment from bad dribbling injectors. The O2 sensor detects the random enrichment and the computer responds by trying to correct the enrichment either with the good TPS , which changes the bad injector duty cycle).

Best regards,

CJR

 

[SleeperXJ]

I've had good results with the seller fuel-injectors on ebay. I bought a set of re-man Bosch 4 hole injectors. They were a matched set and they've performed well. I did have to clean the injectors after replacing the fuel pump, some junk broke loose and clogged #5 injector.
Cleaned the set and it's been running great since.
If your handy with a soldering iron, you might want to consider changing out the injector connectors too.

 

[jhenke]

Pull the fuel rail with the injectors still attached, key on to prime the fuel system, check to see if one or more of the injectors are leaking.

But I have a feeling the fuel pump needs to be switched out for a Bosch Pump / Regulator.

 

[fahadwizz]

Check for dying ignition coil. Easiest would be to replace it with a known good coil once it starts popping.

A single failing injector or a spark plug should not cause a 6cyl engine to die.

 

[RCP Phx]

It's to bad your on the other side of the world, my son has a Maximus 4.0 that can read individual signals to fuel injectors/coil fire , etc..

 

[alexgalexg]

Okay you guys brought up some good points. Let me update you on where I'm at.


So the o2 heater fuse was blown and now replaced. No surprise, the downstream o2 wire had a short caused by it becoming damaged. I replaced that o2 with my new exhaust.

I got ahold of some factory injectors out of another jeep.

I replaced the spark plugs which were very fouled.

I took it on a short test drive, no codes. It still does not like to start but once it does I haven't had it bog down yet. I have a feeling it's going to have problems again though.

Stumped. Aside from spark I'm not sure where to go with this at this point. It's going to be an interesting ride to work tomorrow.

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[alexgalexg]

Last night after some more tinkering and trying to get it to throw codes I ended up trying a coil. No change. Left me on the side of the road on my way to work today. Same issue with bogging and then stalling out. No codes thrown.

I think someone mentioned it here but could this be the cps? In my experience with them going bad they typically cause the vehicle to run, or not run. Not bog down and die. But I'm running out of hypotheses to explore.

Limped it home (I made it maybe 1 mile from home) same as the other day. I figured out that the longer I wait to start it after it dies, the better my odds are of it running for a little longer then if I immediately restarted it.

I badly want to blame the new fuel pump for this but to remind you that I had this issue before I replaced it, it has just gotten worse.

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[alexgalexg]

It's to bad your on the other side of the world, my son has a Maximus 4.0 that can read individual signals to fuel injectors/coil fire , etc..

I wish! I moved during the pandemic to a new place in Massachusetts and know NOBODY. Although, aside from when I used to work in a couple auto restoration shops I never really knew many other car people.

 

[maxbraketorque]

There are reports of the CPS slowly crapping out.

 

[alexgalexg]

There are reports of the CPS slowly crapping out.

I really need to test that. The thing that gets me is I could idle this thing in the driveway all day it's not going to die. Only when driving and operating temp doesn't seem to be a factor. I wish this would happen at idle because I can't actually be under the hood at the times the issue happens.

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[maxbraketorque]

Yeah, kind of a tricky situation when you have to drive it to assess the situation. No many people have a flatbed available to follow them around. Besides a possible failed CPS, having to drive it does also suggest a missed wiring issue. A few comments on CPS - 1) My CPS failed catastrophically overnight in my garage. It just stopped working overnight. No CEL.
2) Non-OEM CPS's have a spotty record for quality. A number of people have reported parts store CPS's not working out-of-the-box. My NAPA Premium has been working fine for about six months, but I carry a Mopar spare.

 

[alexgalexg]

Yeah, kind of a tricky situation when you have to drive it to assess the situation. No many people have a flatbed available to follow them around. Besides a possible failed CPS, having to drive it does also suggest a missed wiring issue. A few comments on CPS - 1) My CPS failed catastrophically overnight in my garage. It just stopped working overnight. No CEL.
2) Non-OEM CPS's have a spotty record for quality. A number of people have reported parts store CPS's not working out-of-the-box. My NAPA Premium has been working fine for about six months, but I carry a Mopar spare.

I have a 99 xj as well, when it's cps failed it faild like yours. Just one day it wasn't working but the day before it was perfect. Like you I have a store one in that jeep and it's been fine for 2 years thus far. I went over the wires a few times, when I restored this jeep and put the engine in I was a lot younger and a lot less experienced so I looked for mistakes. I also just checked the rest of my fuse box as well as tapped on the ecu + connectors to see if it would change the idle (checking for poor computer connection). Still nothing.

I moved and no longer have room for all 4 vehicles at home, my fiance drives the second we have here. In the neighboring town there is a mech shop that constantly has AMC products. Seems to be a popular spot for them. Lots of cherokees, Comanches, hornets and ambassadors. I can't miss another day of work. So if I can't sort this out today I may aaa it to them and have them finish the puzzle, then drive the 2 hours to where my other vehicles are in storage and drive one of them. I've tested so much I can't imagine they would need much for labor hours to root it out. Regardless of if I, or they are the ones to fix this problem I will keep this thread updated. This could save somebody else the countless hours of troubleshooting, if they're willing to read.

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[alexgalexg]

Little update. So, this issue was the fuel pump... again. I couldn't drive down the road with it connected without the risk of damaging the gauge. But if left on the vehicle at idle for a prolonged period of time (like 20 mins) it would start to show the signs. Dropping to like 15 psi and lower if the throttle was touched.

This is news to me, may not be to some of you. But rock auto is selling knock off parts as genuine. The 2 pumps that have been in this jeep over the past 6 years have been Delphi pumps from rock auto which I'm learning were knock off garbage I paid genuine part prices for. For years I have battled fuel and detonation issues and always ruled out the pump since it would have good pressure and good power going to the pump. With the knock off garbage out it runs like it never has before and all these issues are gone!

I now have a Carter fuel pump in the Jeep. When I was working in auto restoration I worked on/rebuilt lots of Carter carbs. They have always seemed about as reliable as a carb is going to be. So hopefully they make their pumps as well as they made their carbs. But what I can say for sure, stay away from rock auto. Hope this thread helps somebody out there someday.

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[maxbraketorque]

Glad you found the issue. Did you ever try monitoring this XJ with and OBD-II logger? With a bad fuel pump, you should have seen short term and long term fuel trims going to very high positive values.

Interesting to hear about Rock Auto. I wonder if they are knowingly selling knock-offs, or perhaps their sources are selling knock-offs without Rock Auto knowing.

 

[alexgalexg]

Glad you found the issue. Did you ever try monitoring this XJ with and OBD-II logger? With a bad fuel pump, you should have seen short term and long term fuel trims going to very high positive values.

Interesting to hear about Rock Auto. I wonder if they are knowingly selling knock-offs, or perhaps their sources are selling knock-offs without Rock Auto knowing.

With the old pump, all I was dealing with was a slightly crappy start and some ping at low end 4th unless I ran premium. Fuel trims were okay. With the second pump, I couldn't drive it long enough to even get that far because it kept stalling and the mixture was all over the place. I filled it with regular yesterday and it ran fine. I'll be verifying the ping is completely gone today. As for Rock Auto I can't say, all I know is I don't trust them anymore. Going to be interesting getting a refund for my fake pump.

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[jhenke]

As Max has stated, you should monitor fuel trims. Hope the Carter holds out for you, I always use Bosch Fuel Pumps on Cherokees, they seems to last the longest and have a good regulator. A/C Delco and Delphi have been loosing quality for some time now.

 

[alexgalexg]

I cannot tell you how wonderful it is to be able to run regular fuel again! No ping, no shake, it sings up hills instead of a miserable racket... it's like meeting for the first time, again. I also like Bosch equipment. I have heard good things about them. Only time will tell with the Carter pump but I can say it's working wonderfully for now.

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