wiggles

Could you possibly let me in on witch relay it is?

Jaredk

I have the same issue with it jerking after I hit bumps in the road and my tach drops and when I give it more gas it will try take off but the rpms bounce for a bit then comeback and I'm fine for a while until the next big bump anyway lol..and it gets worse if I drive down a rough road..and it will die sometimes but start right back up..so does anyone know what it could be?it's 96 4x4 4.0 I recently changed plugs wires cap and rotor bug I'm thinking cps but dk for sure

CoffeeCommando

Fuel pump or a wire that has been cut/frayed a little is grounding. If it's any wires it would be the the crankshaft (CKS) position sensor, the camshaft (CPS) position sensor, the manifold absolute pressure (MAP) sensor or the throttle position sensor (TPS).


MAP, CKS and TPS all connect from the same spot on the wiring harness at the top of your manifold. The crank is physically mounted to the top/driver side of your transmission and runs up to the manifold.


The CPS is in the distributor, and has a little harness that runs out of it.


The TPS is what everyone usually refers to being the "culprit" but 80% of those times it's not. It's something else. All of these things I mentioned can have an effect that COULD cause your outcome.


I was going to say hope to god it isn't the pump because it's the hardest to do and most expensive, but you have a 96 so it's a lot easier and a 4th of the price the rest of us 97 and later XJ's have to pay for it.

...it's still the hardest and most expensive for you though. Whatever you do, DON'T buy an airtex. Just type Airtex into the search function and you'll see what I'm talking about. They don't do well in jeeps, I don't care what the idiot at the parts counter says.

The only place to get a fuel pump that works is NAPA, and you're looking for a Bosch fuel pump. ONLY Bosch.

Even if your airtex does work it won't maintain full fuel pressure, and at top end you'll run abnormally lean... until it finally fails. I bought one two months ago. I just bought a bosch to replace that POS. I've been running at lean above 2500 RPMS for at least the past few weeks.

Running as lean as mine was can cause engine damage via burning up the pistons. Eventually resulting in recycled pistons in your engine which can eat up your cam lobes and/or your crankshaft main/rod bearings. Staythe the hell away from Airtex. Don't think about Airtex. Don't even look behind the parts counter at one if you go to Advance or Autozone. You know what, just don't even go to advance or A-zone because that's ALL they sell.

Get an account with Amazon.com and you can find one on there for cheaper than you can in the store.

Also, before you replace any parts... check all of your engine grounds. If there's rust on there... clean it off with PB blaster and a steel wire brush. Then see if you still have the problem.

If you know someone with a fuel pressure gauge.. that's an EASY way to diagnose the fuel pump. But before you do that I would run some good fuel system cleaner in there FIRST. you could have crud in there affecting the fuel pressure and your fuel pump might be just fine. The chances of that are rare though since crude has to go through the pump anyways. But if you just bought it... you don't know how new or old that pump is to begin with.

I'm not familiar with good fuel system cleaners though. I had sears do fuel system/manifold cleaning about a year ago. Holy crap did it clean the **** out of my manifold. There wasn't any gunk in there after that, and I saw what my manifold looked like before I went there.

Well worth the 80 bucks since I personally cleaned the manifold myself and couldn't reach in there (with a knife) and clean out all of the black gum that had been growing in there. The walls are smooth alluminum now.

Jaredk

Thanks man I'll be doin some lookin and hopefully I can figured it out..and to save u some money I would quit usin amazon..I've been shopping here at www.rockauto.com and they are just about the cheapest on everything! But u still get the same part as u would anywhere else..and thanks again for all your help and info!

ooteedee

@wiggles:

Under the hood on the passenger side... is a fuse box.
In it are several fuses of different sizes.... plus 4 to 8 plug-in relays.

The relays look like black cubes.
They are often interchangeable. Same part number.
About 8-12 dollars depending.

- Engine start
- Fuel Pump
- Cooling Fan
- Automatic Shutdown
- A/C Compressor
- Fog lamp2
- Fog lamp2
- Anti Lock brake controller

I replaced Fuel Pump relay, Auto Shut Down relay and Cooling Fan relay.
All three were the same part number.

I still get a stall at low RPM's every once in awhile.... but the momentary hesitations at speed and the failure to start hasn't happened since.

CoffeeCommando

Relays either work or they don't. They're like fuses in that aspect. Replacing one will not "reduce" problems.

Some of the problem reductions that are in incurred when people are tinkering around in the engine trying to fix problems can be from accidentally moving a round a loose wire/ground/vacuum hose that was actually the problem.

A simple way to test whether or not a relay is working (they don't come in degrees of working "better" and reducing problems.. unless they're covered in some sort rust/acid/mud etc etc) is to just swap one with the other. Before I replaced the fuel pump I swapped the starter relay with the fuel pump. Started just as strong as before. And I knew the starter relay worked.

Then I went to test the fuel pressure the cheap way, just cover the pressure relief valve with a napkin and push it in with a screw driver. I got a little fuel then dribble. THe last time I did it I went through 6-8 shop towels filled with fuel, so I knew I had a problem with the fuel pressure. I knew my injectors were new and not suspect since I tested them not even a week ago..

... More importantly a week after I had the airtex installed I found out how crappy they were and knew that down the road I would inevitably have to replace it. I've also had a fuel pump die on me in mid drive 3 years back. That seems to be when they like to die the most. So by that point I was positive the Failtex had lived up to its name.

wiggles

Thanks, is the order that you put them in the order that they are under the hood? Like the top of your list is windshield and the bottom is the grill?

ooteedee

@Wiggles: On the inside/underneath of the fuse box lid (in the engine compartment) .... there is a printed list of each relay and fuse.

Here is a handy diagram.
http://www.justanswer.com/car/1dacg-...ar-turned.html

wiggles

I didn't think to look under the lid, but that diagram shows a different configuration than in my 93

robscherokee

Ok, so I replaced the fuel pump with a new Bosch Fuel pump and it cured the random stuttering of power problem! I drove my jeep about 100 miles already and no problems at all! Thanks a lot for your help!

robscherokee

Holy crap! What year is your XJ? I just replaced my fuel pump in my 95' XJ and it was $89.00 for Bosch from Advance auto parts.

wiggles

Wow.. I wonder if its the same price for a 93, I checked at mine and they said it was something that they would have to special order in and that it would be $150! I should have you send me one

CoffeeCommando

97 and later have a newer far unimproved fuel pump system that's a lot less easier than yours. Especially if your tank has anymore than a few gallons in it.

ooteedee

Update: my problems were caused by a disconnected wiring harness back near the trans. Ground wire, too. Previous owner who had replaced the engine somehow missed it. Computer was partial operation or none. Runs fine now. Not sure how it ran between then and now.

CoffeeCommando

What was unplugged?