Final answer on Jerk and Hesitation!?

[aj1taw]

Hello all, I am a long time reader and first time poster. I have a '90 Cherokee 4.0 Auto and I have what seems to be a common problem or i should say problems.
1. Absolutly no pressure in fuel rail when turned off (it almost immediately falls off)
2. Takes a long time to start anytime (warm or cold)
3. If I am driving on the freeway and step on the gas to speed up the engine jerks, sputters and dies and sometimes backfires a little.

I am almost positive all of these are connected... reading other posts has led me to try out some stuff. I have yet to pressure test the fuel rail to see if it is the pump or the regulator that is leaking. but I have tested the voltage to the pump... it seems to be low when running (around 11.25 volts) I don't want to buy a fuel pump when it is something else...
has anyone fixed these problems?
much thanks for any help on this subject....
-ajita

[JDPascal]

That voltage does sound low.... should be equal to battery voltage when the engine is running.. at least 13.8V.

The regulator leaking down will cause the hard starting for sure.

The sputter when you step on it could be a combination of the two.

JD

[xj31]

the voltage is normal.there is a ballast resistor that slows the pump down at idle so its quieter.its a white ceramic piece inside the fender.it sounds like you need a fuel pump but you might get lucky.there is a rubber hose that connects the fuel pump to the sending unit.its inside the gas tank.i have seen a lot of those hoses split.i think you can figure out what that causes.well anyways,good luck

[JDPascal]

Hey xj31

Is that ballast resistor common equipment on other models too?

JD

[Cam7]

Originally Posted by JDPascal

Hey xj31

Is that ballast resistor common equipment on other models too?

JD

Only on XJ Had it go out on my 93. Jeep used the resistor to reduce the noise level on the Fuel Pump. My first jeep, replaced the fuel pump and fuel pressure regulator still no go. Then Reading the Factory Service Manual the resistor will bypass in WOT sure enough it stared in WOT. Took a jumper wire to the resistor terminals and fired right off. Replaced it and about a year latter went out again on the Freeway and bypassed the resistor never replaced it again.

[aj1taw]

well whaddya know... i took out the fuel pump today and there I find that the hose clamp had tweaked and punched a hole right in the hose.
I am going to try it out and see how it acts on the freeway...

[aj1taw]

okay, btw thanks for everybodys help here... you guys are awesome.
so I fixed the hole in the fuel pump hose and that fixed the long starting problem more or less but I still have the jerk/die/hiccup that I get when traveling at speeds and then stepping on the gas. a peculiar thing I also noticed was that it also happens at very low speeds when i am just barely touching the gas but in between it drives perfect.

1. could the CPS be the culprit here? I tested it and is has about 2.14 ohms resistance when off (disconnected) i heard there is supposed to be none?

2. and is there any way to see if the TPS might be the one doing this.

thanks everyone....
aj

[xj31]

try taking the vaccuum hose off the egr valve and drive it.

[Kevin Wyatt-Scott]

just new to this forum, just bought an 88 cherokee 4.0l. fuel pump makes a whining noise, and seems to miss and sputter at low rpm acceleration, after that lots of power. starts all the time, but after turning over for a bit (5 times?). Previous owner (not very honest about the history of this jeep) said he replaced the fuel pump.....maybe the wrong type or installed wrong?

any ideas before i go and get a new pump?

[lm18]

here is my story:
the only problem that i saw on my 89 cherokee 4.0 was to take a lot of time to start some times, then, sudenly, when i turn to the right at more than 30 mph the motor dies, so i need to put in neutral and start it again, the shop check for codes and nothing, i check the ignition switch and cero, then, i bougth a fuel pressure tester and the fuel pressure was ok,
but, when i turn off the key (see test sequence at the instructions), the pressure was gone (it shall be present at least for half hour with just a little lost of pressure); the problem, a faulty check valve inside the fuel pump ....
i didnt find the check valve alone so i was forced to replace the pump.
the problem was gone and now it takes only a short time to start
i hope this story helps you