hesitation and stumbling problems

I recently put a crank postion sensor in my jeep because i thought it was giving me the stumbling and hesitation problems and also because the check engine lite code indicated that there was no signal to the pcm. but much to my suprise it didn't fix it. my main quandry is would the fuel pump be causing this situation because i have replaced most of the major sensors on the truck and i'm running out of money. there is also no external fuel filter and i have replaced the cts, tps, cps, and cleaned the throttle plate and i ran seafoam through the intake system. i appriciate everyones input and help.:us::cheers:

I'm thinkin I'm goin through the same thing...

http://www.naxja.org/forum/showthread.php?t=942900

I haven't replace my CPS yet but it does sound promising... but I guess you thought the same thing lol. I thought of fuel though too. I need to check my fuel pressure. But it doesn't seem likely that it would do the exact same thing all the time if it was a faulty fuel pump.

yes, a bad pump will cause those symptoms. Get a gauge and check the pressure at the rail.

What year is your rig? I see 87 in your name....if it is an 87 you do have an exturnal filter (97+ has the filter in the tank)

Definitely suspect the fuel pump. A faulty crankshaft position sensor will not normally result in stumbling, hesitation. You most often see a NO-START when the CPS fails.

If I were you, I would get fuel pressure data and compare to spec as Jess mentions. Simple things first and fuel pressure is often overlooked. Get a gauge on that puppy.....
It goes on the schrader valve on the fuel rail near the valve cover.

Oh shit I just remembered, the other day, I got in my Jeep and I had to crank for several seconds before it started right up. That never happens. My Jeep has always been really quick to start. And during the cranking it never even TRIED to run untill it started up like normal. And it hasn't done that before or since... so maybe it is the CPS... I'd check my fuel pressure but I don't have a working gauge atm...

what year, your name has 1987? the 87 has an external fuel filter but you said you read the codes and the 87 does not have codes.

i just looked at your profile and i assume 1987 is your birth year.

I have a 95 4.0 and occasionally, if I shut it down sit for a minute and then restart It will hesitate & sputter like it's starving for gas or flooding with it. I havent changed any sensors my check engine light doesnt come on (which makes me think a previous owner disconnected the panel) But as I read this I noticed my jeep also sometimes takes a little longer to start some mornings, and I just had a complete tune-up. so you guys think this is normally a fuel pump problem?

read this post...it may explain your hot restart problem....

http://www.naxja.org/forum/showthread.php?t=62409&highlight=heat+soak

the link above states this.....but this happens in the winter also not just hot conditions...but you would think that most engine compartments will be above 90 degrees. right??

Fuel System - Hot Start Misfire/MIL ON/DTC's/Rough Idle
NUMBER: 18-031-03

SYMPTOM/CONDITION:

Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32°C (90°F) or higher. This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder # 3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector # 3 and causes fuel vapor to form within the injector. This in turn may cause a momentary misfire of cylinder # 3 until the fuel vapor is cleared of injector # 3. The insulator sleeve lowers the injector # 3 temperature to a point below which the fuel will not normally vaporize.

REPAIR PROCEDURE:
1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves about 25-30 mm (1 in.) in length.

2. Install one sleeve around injector # 3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.

3. Confirm sleeve is flush to intake manifold surface around injector.

4. Check injector # 3 wire and ensure that the injector is rotated to a 2 o'clock position (from driver's side of vehicle).

If your 99 or newer XJ has a rough idle for 20-30 seconds or so on a HOT restart, then definitely refer to the technical bulletin that Jeepman 121 so kindly provided. This is a very common fail; my 99 had it. And very easily fixed.

If however you Jeep sputters and hesitates pretty much all the time, then the problem is something else. Checking your fuel pressure is a reasonable thing to do if you have tried some other common things like cleaning/replacing the IAC, cleaning throttle body, etc.

Long cranking periods in and by themselves can often be traced to a drainback of fuel into the tank, therefore it takes a while to get the proper fuel pressure at the rail which is accomplished by cranking the engine.

One thing you can do if your vehicle takes a lot of cranking to start is this: Turn the key to the on position (do not crank engine) which will run your fuel pump for a couple of seconds. Turn key off. Repeat two more times for a total of three cycles of the fuel pump. NOW try to start it. If it starts right up, then the problem is possibly the regulator/check valve in the fuel pump. I know it sounds weird but low battery voltage, in some instances, has been found to be responsible for a long crank before starting too.

PurpleCherokee...if yours cranks a long time, then starts cleanly, the problem is NOT your crankshaft position sensor. If your crank sensor is dead, you're not going anywhere. You will have no spark of fuel. Concentrate on the fuel pump circuit. :wave:

birchlakeXJ said:

If your 99 or newer XJ has a rough idle for 20-30 seconds or so on a HOT restart, then definitely refer to the technical bulletin that Jeepman 121 so kindly provided. This is a very common fail; my 99 had it. And very easily fixed.

If however you Jeep sputters and hesitates pretty much all the time, then the problem is something else. Checking your fuel pressure is a reasonable thing to do if you have tried some other common things like cleaning/replacing the IAC, cleaning throttle body, etc.

Long cranking periods in and by themselves can often be traced to a drainback of fuel into the tank, therefore it takes a while to get the proper fuel pressure at the rail which is accomplished by cranking the engine.

One thing you can do if your vehicle takes a lot of cranking to start is this: Turn the key to the on position (do not crank engine) which will run your fuel pump for a couple of seconds. Turn key off. Repeat two more times for a total of three cycles of the fuel pump. NOW try to start it. If it starts right up, then the problem is possibly the regulator/check valve in the fuel pump. I know it sounds weird but low battery voltage, in some instances, has been found to be responsible for a long crank before starting too.

PurpleCherokee...if yours cranks a long time, then starts cleanly, the problem is NOT your crankshaft position sensor. If your crank sensor is dead, you're not going anywhere. You will have no spark of fuel. Concentrate on the fuel pump circuit. :wave:

Click to expand...

What gets me though is that if were a lazy fuel pump, why would the pressure kick back up AFTER 4 grand? I mean, it seems that if it can produce at a higher RPM then it shouldn't be shortin me between 3 and 4. Unless the pump's just sporatic and in that case, then why is it so consistently sporatic (oxymoron?). Meaning, why does it screw up in the exact same manner every time?

jeepman121 said:

I have a 95 4.0 and occasionally, if I shut it down sit for a minute and then restart It will hesitate & sputter like it's starving for gas or flooding with it. I havent changed any sensors my check engine light doesnt come on (which makes me think a previous owner disconnected the panel) But as I read this I noticed my jeep also sometimes takes a little longer to start some mornings, and I just had a complete tune-up. so you guys think this is normally a fuel pump problem?

Click to expand...

A bad TPS will also cause some of these problems. The original poster had already replaced his, but for others with with hesitation and stumbling a bad TPS or bad TPS wiring, connections will casue this problem.

Jeepman, another possibility for your problem is a leaking injector that does not seal completely. Durring shutdown it can flood the engine making restart difficult. Does not sound like a fuel pump problem.

birchlakeXJ said:

I know it sounds weird but low battery voltage, in some instances, has been found to be responsible for a long crank before starting too.

:wave:

Click to expand...

That gives me a hint because I've been running on a low battery for about 5 months now. maybe the ignition, and all the other electronics kicking on reduce the fuel pumps output.