Bad Fuel Pump or Fuel Injectors?

YonderNorthwest

TJ Enthusiast
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Portland Oregon
Hello, all. About a week ago I was climbing on the freeway in my 1999 4.0 5-speed manual and it started skipping. By skip, I mean I would very briefly (like .1 seconds) lose power and then regain it. It did this 10-15 times in rapid succession as I was overtaking a semi. My first though was the fuel pump. I just hit 213,000 miles and am on the original.

Then on the ride home, my passenger and I both noticed that our sandaled feet were cooking down in the foot wells. I've been driving this jeep with the whole inside of the tub bed-lined and carpetless for about 10 years, and never experienced this kind of heat.

In the last week of daily driving, the heat coming from beneath the dash has not subsided. Based on the digging I've done on the forum, it sounds like the heat is coming from my catalytic converter. The other tidbit I found is that faulty fuel injectors can cause an overly rich mixture which causes the cat. to overheat. On occasion I've noticed a fuel smell in the air while driving, but I am kind of a hypochondriac with my car, so who knows if that's legit or not.

Could a bad/failing fuel pump cause a fuel injector(s) to fail and create these symptoms? I would be thrilled if this is just a bad injector I can replace, but since the pump is right in front of the injectors in the system, I'm worried the failure is happening upstream.

Going to do some more office chair research on testing and replacing fuel injectors.

Thanks in advance for any guidance you can provide.
 
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i would seriously doubt the fuel pump to cause your floor to heat up, however i could see the injectors causing the cats to heat up. personally i would change the injectors, i put some 4 holes in my last 2.5 and i think it was $80, so it's not crazy expensive...
 
i would seriously doubt the fuel pump to cause your floor to heat up, however i could see the injectors causing the cats to heat up. personally i would change the injectors, i put some 4 holes in my last 2.5 and i think it was $80, so it's not crazy expensive...
Ya that would be a seriously jacked up fuel pump to do that. But I thought maybe the fuel pump misbehaving was causing the fuel injectors to fail. Glad to hear replacing the fuel injectors isn't too expensive.
 
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To add...a little more info would be useful.
Is the CEL illuminated?
Is it missing at idle?
High rpm?all rpm?

IMO without fancy million dollar scan tools like we have at the shop...
From your brief description of symptom I'd focus on your coil and spark plugs.
A weak coil will break up under a heavy load (passing, hills, etc)
 
No codes. Miss firing has stopped. I've tried to recreate (stomping on it up hill). The only constant the last week has been the furnace under my feet when I travel on the highway.

I've done sparkplugs myself in the past. Is the coil an easy self-performed job as well?
 
No codes. Miss firing has stopped. I've tried to recreate (stomping on it up hill). The only constant the last week has been the furnace under my feet when I travel on the highway.

I've done sparkplugs myself in the past. Is the coil an easy self-performed job as well?
you had to pull the coils of each plug when you changed the plugs so yes, it is an easy job.
 
Probably ~80,000 miles ago or so. Maybe less.
Ok..

Grab 6 NGK (ZFR5N)
That's exactly the plug the MFG recommends and considering you've got a problem it's always best to start at ground zero. Ground zero being as close to original equipment as possible.

Those plugs are inexpensive and pretty much always gapped properly out of the box.

When have you changed your coil?

If not for a while I'd also replace that.

Then retest.
 
Thanks for all of the input guys. I think I'm going to go ahead and replace the plugs, plug wires, coil, and injectors. Engine is getting old and needs some love I think. Found some remanufactured mopar fuel injectors for sale on ebay for $125. I'd like to go with the mopar, but if y'all think I should buy something aftermarket instead, please educate me.

Thanks
 
Ok..

Grab 6 NGK (ZFR5N)
That's exactly the plug the MFG recommends and considering you've got a problem it's always best to start at ground zero. Ground zero being as close to original equipment as possible.

Those plugs are inexpensive and pretty much always gapped properly out of the box.

When have you changed your coil?

If not for a while I'd also replace that.

Then retest.
Part# recommendation for the coil? I know I've changed the cap, but I don't remember if I did the coil.
 
Pull your plugs and visually inspect. That can provide you some insight into what's going on as well.
If not sure..take some pics and post them.

Don't lose track which one is in which cylinder in case you've got a localized issue in one or a pair of cylinders and not all 6.
 
i ordered mine from K suspension. we've used their 4 hole bosch injectors on 2 jeeps and had no problems with them. take a look at them, i'm pretty sure jeep used bosch anyway . their $114.99