1996 Cherokee driving me nuts.

[grizzlybear310]

First a little background on my Jeep.
It's a 1996 Cherokee with 130000 miles on it.
I use it ever day on a 90 mile stop and go run.
I deliver the local daily newspaper in my area.

I have had it since October and after I first got
it, it had a problem with wanting to miss and act
like it was running out of gas.
It would only do this after about 80 miles or so.

I took it back to the dealer and he had his mechanic
drive it till it started doing this and then he hooked
it up to the computer and found nothing, no codes
were on there.
No check engine light ever came on.
He then took it to another place to put it on their computer
with the same results. No codes.

So, he put a fuel pump on but not the pressure regulator.
New cap, plugs, wires, rotor, even a distributor.
No good. Same thing. After about an hour and a half into the run, start acting the same way.
I talked to some people and after that, I put an 02 sensor on and it ran great up till 2 days ago.
Now, it is doing it when you go up a grade.

It is like you have the gas pedal pushed down and then let it up and then back down again.
A surge if you will. No missing, no acting like it's running out of gas, just the surging.
Not on flat ground, just when you are going up a grade.
I am at my wits end with this thing.
Has anyone got any ideas?
Could the fuel pressure regulator be doing this and if so, why wait so long before it starts?
Thanks in advance.
Going nuts in Kentucky.(Lester)

[grizzlybear310]

Update.
Have tried a couple things and no good.
I think I may have found it, but will know more tomorrow for sure.
Am trying one more thing tonight and will take it on my run in the am to see if it fixed it and will let you know.

[grizzlybear310]

Update;
Well found out a couple things.
1) My Jeep is a change over Jeep as in a late '96.
Found this out when went to buy a CPS for it.
All the parts houses had one for a '96, but was different than mine
and they did not have it so, had to go to dealer and after giving him
my last 6 digits of my VIN, they told me that it was a change over
model and it took a different CPS.
Well after $122 and change, no different.
Now here is some more ammo for you fellows to see if you can figure
it out.
It was warm here this am and I was riding around with my windows down.
I noticed a faint smell of gas and right after that, it would start
running bad again.
This time I mashed the gas a little more and it would backfire
through the intake it sounded like.

Now another clue, I could stop, turn engine off, count to 5, start
back up and run like a champ for about 20 minutes or so and it would
do it again.
Again, I would shut it off and start it back and it would run fine
for a little while and right back to the problem.
Each time it would do this, I could smell some gas fumes right before
it acted up.
Please help, I am out of options on this thing.
Lester

[XJnick]

Hi,

1996 Model year Cherokees are known for having fuel system problems.

It sounds to me like you either have:
1) A leaky vacuum or fuel vapor line somewhere
2) Leaking injectors (you smell excess fuel being burned upon start-up)
3) Bad gas cap or slight leak in filler hose allowing the system to loose vapor pressure.
4) Exhaust system or EGR system leak

Other than those possibilities, it would probably be a computer related problem.

-Nick

[grizzlybear310]

Originally Posted by XJnick

Hi,

1996 Model year Cherokees are known for having fuel system problems.

It sounds to me like you either have:
1) A leaky vacuum or fuel vapor line somewhere
2) Leaking injectors (you smell excess fuel being burned upon start-up)
3) Bad gas cap or slight leak in filler hose allowing the system to loose vapor pressure.
4) Exhaust system or EGR system leak

Other than those possibilities, it would probably be a computer related problem.

-Nick

Thanks Nick.
First it does not have EGR valve.
I do not smell gas on start up and the injectors are not leaking.
Repaced gas cap with new one and it will build pressure up after running.
Did a pressure test and system holds 49PSI even after engine is shut off for 20 minutes.
I am now getting ready to replace the MAP sensor and see if that helps.

This is a late '96 with a lot of '97 parts on it I am finding out.

[grizzlybear310]

Another question.
Could it be possible that the coil is heating up and breaking down?
The reason I ask is that this morning while out on my run, it started it's stuff and the check engine light came on this time and after I got back home, check the code and it is a #43 which is;
"Peak primary coil current not achieved with max dwell time or
Cylinder misfire", which could be caused by the coil if I am correct.

Anyway, I am going to put one on and see.
Will let you know the outcome.
I will solve this mystery yet if I don't run out of money first.
Lester

[XJnick]

Hi,

I'm really not sure if it is possible for a coil to act up only when hot. I've heard that the coil either works or it doesn't, though. Maybe you could let the Jeep heat up and then check for spark from the coil.

You may just be getting #43 due to mis-fire. I've gotten that code before on my wrangler with just the very slightest misfire. It seems to be a very sensitave code.

-Nick

[grizzlybear310]

Thanks again Nick.
This misfire was enough to make it quit this time so I am going to put a coil on and see what happens.
Won't hurt.

[XJnick]

Good Luck.

Don't give up on it yet...

-Nick

[grizzlybear310]

Update:
I did the coil swap and went out and drove it for about an hour with no problems.
On the way back I stopped and took off and crowded it quit a bit and it wanted to stumble again, but as soon as I let up on the gas and drove it normal, no problem. Just when I get on it heavy.
Now what?
Thanks again.
Lester

[96Classic]

Does it blow any smoke from the exhaust?

[richpinkham]

Have you ever check to see if the fuel filter has been replaced? If its like the older cherokees it has a fuel filter on the inside of the frame above the rear axle on the drivers side. It maybe getting fuel at a low speed but not under demand. Something to check and its cheap to replace it it hasnt been done.

[grizzlybear310]

First let me say that I have been checking things out quite a bit on this thing.
I took it to the Jeep dealer and had them run their tests on it and they found nothing but a slight little bit of rust in the fuel rail and they said that it could cause it if it got into one of the injectors.

They(head tech) told me this was a 4.0HO from 1997 in this Jeep and it should have been titled a 1997 instead of a 1996.

Anyway, he took it out and drove it for 25 miles and said it was one of the best running 4.0's he had drove except for the problem after it got warmed up.
It would only do it after it was warm, not cold.
He also advised getting a new muffler cause mine was swelling some and it may cause some back pressure.

I went straight and put a new one on it.
I am still waiting on the cleaner to take care of the rust before I have to take it to get the system flushed out.

P.S. To answer your questions, no it does not blow smoke other than regular exhaust and yes, it has a new filter on it also.

[j.leo]

I HAVE SIM PROBLEM SO FAR PEP BOYS REPLACED COIL, 3DAYS LATER PROB. BACK THEN DEALER REPLACED FUELPUMP ASSEMBLY, AND RADIATOR, 3DAYS LATER PROBLEM BACK, THEN DEALER REPLACES FAULTY COIL, 3 DAYS PROB, BACK, PEP BOYS HONOR PARTS AND LABOR THEN DEALER INSTALLS CRANK SENSOR NO CHARGE! (THANKS ) BUT YOU TOOK $1400 FOR FUELPUMP AND RADIATOR AND LABOR, 3DAYS LATER PROBLEM BACK , NOW DEALER SAYS CAT CONVERTOR IS BAD WANTS $600, BUT SETTLES FOR 200, BUT NOW WAITING 3 DAYS TO HEAR, gUESS ITS NOT FIXED OR HOPING MIRACLE HAPPENS IN SHOP OVER NIGHT, I FEEL YOUR PAIN AND HOPE YOU AND OR THIS FORUM CAN FIND THE CURES!WAITING DAY AND NIGHT FOR FORUM HELP!!!!!!!!!!

[grizzlybear310]

I am down to the fuel pump regulator which is on my fuel pump and not on the fuel rail.