TJ 4.0 cuts out around 3k RPM...Fuel Pump???

[Boludo]

My engine started cutting out at around 3000 RPM when I'm on the gas pretty hard. It also feels like it has less power under normal driving circumstances. For example, I've had to down shift in places on the free way where I didn't have to before.
Today I left it in 3rd gear on a pretty hard acceleration...it cut out, then went, cut out, then went, as if I was quickly stomping on the gas then letting off over and over.
Normal driving it runs mostly normal....just less power.
I'm thinking my fuel pump is going out, but don't want to replace it if that's not the problem.
Any thoughts on this one?
Thanks.

 

[mbryson]

I had a CPS act like that once.

 

[ProStreetZ28]

first thing I'd check would be the fuel pressure, then turn it off and see how long it holds fuel pressure. You dind't mention it, so I'm assuming that it isn't throwing any codes (turning on the check egine light).

If fuel pressure isn't the issue and no codes I'd look intot he cat after that. if you suspect a cat they sell a fitting that you screw into where the O2 sensor is and you connect a fuel pump pressure gauge to see if it's building back-pressure.

 

[Boludo]

Thanks for the tips..I will check into those.

 

[RockMonkey]

I've had two bad catalytic converters that exhibited nearly identical symptoms.

 

[74highboy]

we used to just drill a small hole in front of the cat if its plugged it will have alot of presure their if not it will be the same at the tail pipe

 

[Boludo]

No check engine light. I haven't checked for codes since this started, but I will check that.

Thanks

first thing I'd check would be the fuel pressure, then turn it off and see how long it holds fuel pressure. You dind't mention it, so I'm assuming that it isn't throwing any codes (turning on the check egine light).

If fuel pressure isn't the issue and no codes I'd look intot he cat after that. if you suspect a cat they sell a fitting that you screw into where the O2 sensor is and you connect a fuel pump pressure gauge to see if it's building back-pressure.

 

[Boludo]

I hadn't thought about the CAT causing this but it sounds like it very well could be that too. It wouldn't surprise me....I have about 205,000 miles on the Jeep.

 

[mbryson]

No check engine light. I haven't checked for codes since this started, but I will check that.

Thanks

I've lost two Jeep CPS and 4 (?) F*rd Powerjoke ones. I haven't had a check engine light yet.

 

[Boludo]

I had to replace one on my wife's car too. Her engine would die completely instead of just cutting out. They can cause grief. I wish there was a way to test those out first...they are $85 bucks for those little things...but that could very well be the issue too. Looks like I have more troubleshooting to do.

I've lost two Jeep CPS and 4 (?) F*rd Powerjoke ones. I haven't had a check engine light yet.

 

[Boludo]

Just went and checked for codes. I got a 12 and a 42. I always get a 12 whenever I check, although I have not disconnected anything to the PCM.

Here are the code descriptions:

12 Direct battery input to PCM was disconnected within the last 50 Key-on cycles.

42 An open or shorted condition detected in the auto shutdown relay circuit. An open condition detected in the ASD relay output circuit. An open or shorted condition detected in the fuel pump relay control circuit. An open circuit between PCM and fuel gauge sending unit. Circuit shorted to voltage between PCM and fuel gauge sending unit. No movement of fuel level sender detected.

My fuel gauge has been acting up...just not accurate, but I don't think these codes are what's causing the engine to cut out only when I'm on the gas hard. Someone correct me if I'm wrong.

 

[Bart]

I had mufflers do that also. Twice.

 

[ProStreetZ28]

Just went and checked for codes. I got a 12 and a 42. I always get a 12 whenever I check, although I have not disconnected anything to the PCM.

Here are the code descriptions:

12 Direct battery input to PCM was disconnected within the last 50 Key-on cycles.

42 An open or shorted condition detected in the auto shutdown relay circuit. An open condition detected in the ASD relay output circuit. An open or shorted condition detected in the fuel pump relay control circuit. An open circuit between PCM and fuel gauge sending unit. Circuit shorted to voltage between PCM and fuel gauge sending unit. No movement of fuel level sender detected.

My fuel gauge has been acting up...just not accurate, but I don't think these codes are what's causing the engine to cut out only when I'm on the gas hard. Someone correct me if I'm wrong.

Is the fuel gauge reading higher or lower then it should? How much isit off by?

 

[Boludo]

It's reading lower. If I fill up when the low fuel light comes on, it will only take 8 or 10 gallons. I can fill up and the gauge will say full, then drop to 3/4 after a few minutes.

It's reading low by about 1/4 tank.

Is the fuel gauge reading higher or lower then it should? How much isit off by?

 

[Boludo]

It seems to be worse on the freeway or up a hill. This morning I accelerated from a stop after a red light. It went to about 4000 RPM then I shifted and it felt pretty normal. Then I got on the freeway going up east side I-215. I had to down shift to 4th gear at about 6200 south and leave it there for the climb up toward 4500 south. A one point I had it almost floored just to go 60 MPH in 4th gear. This seemed worse than previous days. I pushed it the clutch, reved it a little and tried to accelerate. It cut out. After I got off the freeway, I accelerated hard in 2nd and it cut out then went and cut out and went like the other day. This was at about 3200 RPM.
So...it's worse when I'm on gas for a longer period of time, like going up hill on the freeway.

 

[ProStreetZ28]

I'd check the fuel pressure first. Auto Zone rents the fuel pressure gauge for free, you give them a deposit and they refund it when you return the tool. Does it have a schrader valve to check the fuel pressure?

 

[DOSS]

Im putting my $$ on your Cat.. go to Autozone and get some pipe peices and some clamps.. cut your Cat out and put the pipe in its place if you don't want to drill in front of the Cat to test it.

 

[mbryson]

That's really starting to sound a lot like my 4.0L in my XJ with the bad CPS. I chased fuel and ignition issues forever. Bought a new DEALER CPS and the problems all went away. I'm just saying....

 

[turbovee]

I have this same issue with my jeep. It is a 95 zj with the 4.0. Mine wont rev over 3000 rpm either. When i bought the jeep 2 years ago it would run fine till it warmed up and then it would not rev over idle speed. I changed the fuel pump, cam sensor, map sensor, PCM and CPS. Now it runs great up to 3000 then it cuts out and backfires. sounds almost like its loosing fuel. Sometimes it will rev over 3000 once it gets really warm. I was told that it could be the coolant temp sensor? What do you guys think of this?

 

[PolarXJ]

How long as it been since your spark plug wires have been changed. I had a Saturn that would cut in and out like that. Almost always when I was accelerating. I ended up getting it checked while some warranty thing was getting fixed at the stealership. It didn't make them happy when I told them I'd change the wires.