J.Barsugli

Hello forum, I have a question regarding my 94 Jeep XJ that has a rev problem. Jeep also has an extended cranking time that I've now mastered the art of getting her to start, because continually cranking the engine for no longer than six seconds at a time will not get her to start. I have to turn the engine over three times, let it sit for about 5-10 seconds then it'll start up after another 2-3 cranks. I've tried the fuel pump priming trick but doesn't help. Anyways back to what my main concern with the Jeep is. When driving, in park, or neutral I can't get the engine to get above 3000 RPM. I don't gun my engine around but when I get on the freeway and there's a slight incline I need it to get to around 32-3500 for it to accelerate and shift adequately, so I'm not getting on the freeway at 40mph.. Also climbing up a slight incline the engine gets bogged down to wear it goes 40mph in drive, so I have to shift into third to go at least 50 at 2500 rpm. It sounds like a transmission problem but it's limited to 3000 when I'm parked or in neutral.. The engine shakes real bad around this rpm but it has all new engine mounts and trans mount. Let me know what you guys think. There are a lot of forum topics on this issue but it's 2016 and most other threads are from five or so years ago so hopefully I can get a couple of you to chime in on what the problem could be from your experience. Also I've replaced the air filter, fuel filter, crankshaft position sensor, ignition coil, spark plugs and wires, and distributor due to a broken cam shaft sensor, which all of this started after the day I found the broken cam shaft sensor due to a no start issue. I'm pretty darn positive the distributor was replaced at proper timing alignment so look past this for now, because it runs smoothly even all the way up to 75mph on the freeway but once you gun it to hard or fast and hit 3000 it just starts shaking and gets bogged down.

dac612

My first thought is fuel pump.

1 clarification.

Will it NOT rev over 3k both in neutral and while driving?

fuel pumps can give really weird symptoms when failing. So you'll want to do some extensive testing or think about when the last time it was changed and just consider changing it knowing it isn't going to hurt anything.

to best check for this even though it is hard to check while driving. And naturally other problems can come into play such as the fuel pump may build less pressure when hot ie been running a while etc.

check record, and post each of these.

1. fuel pressure at rail after 1st prime attempt.
2. fuel pressure while cranking and * amount of time it takes to get to 30psi.
3. fuel pressure at rail after 3 prime attempts (poor man's prime)
4. get full pressure to the rail i want to say it is 39 psi. shut key off and check psi after 5 mins. (checking for psi drop)

Other thing to check, record and post up.

1. if you have an analog meter make sure it isn't jumping around as you - slowly open the throttle plate.
- TPS readings at closed
- TPS reading at WOT (full open).

2. MAP sensor readings.
- key on engine off map reading. voltage.
- engine on and idling map reading. voltage

I have some other ideas too but post up your findings.... chances are there will be something amiss here.

J.Barsugli

Thanks for your reply. Did some running around and tested the pressures as you described

1. After first prime attempt 16psi
2. Fuel pressure while cranking goes from 16 to 26 then stays at 38 psi until it eventually starts after several attempts.
3. Fuel pressure after poor mans prime 38 psi but noticeable drop in psi about 2 psi every 5 seconds
4.After 5minutes pressure is below 10psi

So after these tests it's clear that fuel pressure is being lost at a quick rate at rest. Which would lead me to believe that the check valve for the fuel pump is no good. I'm going to get the pumpbseapped out and see how that changes things as the regulator did not help. Also while revving the engine up slowly the psi goes from 38 down to 30 at around 3000 rpm so there's a drop in psi when accelerating but immediately jumps back to 38 psi but falls to 36 psi when idling. Thanks again for your feedback.

Turbo X_J

Not only pressure there is probably a flow issue as well check for restrictions. (sock in the tank packed full of wonderful, kinked fuel line, etc)

J.Barsugli

I'll be pulling the pump this weekend to check the whole enchilada.

Also to clarify dac612 it won't rev past 3000 in park, neutral, or while driving...

dac612

Sweet. Good work man. Definitely pull that pump and check it out.

In my experience the 94 does not have a check valve unless I've just never seen it which is possible haha. The drop in pressure at rest is more than likely the regulator or injector (s) but I guess could be that intermediate line from the pump to the sending unit hardline being deteoriated or something. I agree you have a flow problem causing your stumbling at higher rpms.

So you could have 2 separate problems but you'll know more when you get to that pump.

Keep the post alive so we know what worked for you when you fix it.

J.Barsugli

So here is some pics of old vs. new. Ill upload some pressure test videos in a few minutes.


New fuel Pump assembled.



Old fuel pump.



Old fuel pump

J.Barsugli

Please check out this vid to see my problem. Looking at it again makes me think its a tranny issue???

dac612

hmm, maybe try a longer video and type out an explanation of what you're doing. Or dialogue it in vid is fine.

Hard to tell exactly what's going on in that short vid for me. I obviously see the tach but it's hard to tell At least from my phone anyway. Kind of thought I heard a bang? I also can't tell when you let off the pedal.

Cane

TPS issues can often be mistaken for transmission problems. not necessarily saying it's the case here, but might want to test that before contemplating work on the tranny

also if the issue is also happening when in park or neutral, doesn't that rule out the tranmission? i could be mistaken but you said it also happens when not in drive, so since you're not moving i don't see how the tranmission could cause a drop in RPMs.

x2 on the longer video, to make the "online diagnostic" easier