4.0 problem when Accelerating

[rolo]

I have a 1988 Cherokee 4.0. with 150 000 miles. The problem that I am having is that when the vehicle is warm and accelerating it will buck and miss with a total loss of power. The problem is only there when the engine is warm and under load. When warm and revving out of gear there is no miss/problem; also when engine is below operating temp there is no problem. The Jeep has normal power when it is cold. Any Ideas on what could be the problem?
The Jeep has new exhaust (new Cat), Plugs, Wires, Rotor, Cap.
I have disconected the vacume like to the EGR, problem still there.
The Jeep starts all right.


Any help would be great, Thanks.

[scuba4321]

are you getting a "check engine light"?

[rolo]

Originally Posted by scuba4321

are you getting a "check engine light"?

No engine Light, and I havn't had a chance to find a scanner yet. Could this be from a Coolant Temp. Sensor?

[scuba4321]

could be, mine a 1993 was having similar problems, I tested every sensor, cleaned everything I could. I too had new "fairly" new plugs wires and cap/rotor. No light either, turned out it was a fouled, more like a cracked plug!! was the onset to your problem slow or fast?


go to www.autozone.com, they have an awsome site and diagnostic procedures for all the sensors, valves ect..

[rolo]

Originally Posted by scuba4321

could be, mine a 1993 was having similar problems, I tested every sensor, cleaned everything I could. I too had new "fairly" new plugs wires and cap/rotor. No light either, turned out it was a fouled, more like a cracked plug!! was the onset to your problem slow or fast?


go to www.autozone.com, they have an awsome site and diagnostic procedures for all the sensors, valves ect..

Thanks... the onset was quick.. Like right after the tune up.. I will put the old plugs back in and see if there is a change.... I could have an new plug that is injured.... I would have thought that the problem would have been constant with a faulty plug..

[scuba4321]

mine with the bad plug, ran fine when warm, terrible on start up until first 5 miles. Check your plugs, let me know. good luck

[rolo]

Originally Posted by scuba4321

mine with the bad plug, ran fine when warm, terrible on start up until first 5 miles. Check your plugs, let me know. good luck

Well so far it isn't the plugs... This weekend I will be putting on the old cap and wires, look over the vacume hoses with a fine tooth comb and start cleaning and testing sensors and fuel presure. I have disconected the EGR and no difference.

More problem explination. Also when the engine is warm, driving at highway speeds it will not acerlerate.. I could put the peddle to the floor, the Jeep won't Accelerate or down shift (most of the time).. 3000 rpm and up seems to be the happy spots, but if I hold the the peddle at a specific spot above 3000 rpm it will learch.. Now when reving in park, coming off the Highway, it will miss/chug for the first couple of revs then clear up.

Possible Ideas,

Coolant Temp Sensor, or somthing with vacume - because the problem has to do with heat

Fuel Pump / regulater - when it learches if feels like it isn't getting gas (but it doesn't starve for fuel when it finaly wants to rev). Is there any reason I cannot use an aftermarket out of the tank fuel pump?

TPS - because when it is hot I can push the peddle down and nothing really happens.

This is my first fuel injected vehicle, and so far... it isn't soo much fun

Once again any Ideas are helpfull...

Thanks.

[Saudade]

Wish I had a "silver bullet" for you Rolo. My '88 had a similar problem. Wouldn't downshift to pass or climb a steep grade unless I dropped it into 3rd myself (4 spd auto).

Due to other problems, I've changed the cap, rotor, ign wires, coil, CPS and TPS, trans fluid and screen. Changing the TPS made the biggest difference on mine for this specific problem. I've also cleaned the throttle body and IAC. Now, it shifts great and I can pass like crazy.

[rolo]

Originally Posted by Saudade

Wish I had a "silver bullet" for you Rolo. My '88 had a similar problem. Wouldn't downshift to pass or climb a steep grade unless I dropped it into 3rd myself (4 spd auto).

Due to other problems, I've changed the cap, rotor, ign wires, coil, CPS and TPS, trans fluid and screen. Changing the TPS made the biggest difference on mine for this specific problem. I've also cleaned the throttle body and IAC. Now, it shifts great and I can pass like crazy.

*****Issue Resolved ****
Well the problem has been found, and the charge was the price for a fuel pressure tester. The problem was low fuel pressure in the rail. The culprit was the fuel line in tank; Both Hose clamps were loose and the fuel line was falling off of the pump. That was it, it cleared up everything. The symptoms were very misleading. Well until the next issue..

[Saudade]

Thanks for the feedback. Glad you got it fixed!