Need help big time!!!

OK heres the skinny to what is going on....searched and searched and searched and still no clue!

Everything replaced in the last 2 months:
CPS
O2 sensor
Plugs Plug Wires
Dist. Cap
Rotor
Coil
Fuel Filter

88 Cherokee 4.0 A/T

Starting is normal and the idle is fine even taking off is fine but when it switches from 2nd to 3rd and the RPM's drop it starts bucking, spitting and sputtering and if i step on the gas it drops to passing gear and takes off like theres nothing wrong with it but as soon as it goes back into 3rd or 4th gear it starts the problem again. I've checked the TPS with key on/engine off and the supply voltage is 4.98 volts and the return voltage is at .815 volts. I've checked the EGR valve by pulling the little pin out with a screw driver and the motor runs like crap and when i let it back in it smoothes back out like it's supposed to do. I've checked the Map sensor with key on/engine off and and terminal B has 3.96 volts and with engine at running temp terminal B while idling terminal B has 1.236 volts and the supply has 4.96 volts. I pulled the Vacuum hose off the fuel regulator and plugged it then drove it and the performance was exactly the same so the fuel regulator is working i suppose.

What could it be causing this. Its almost like it is either starving for fuel or getting to much while RPM's are low (while driving) sitting still at idle the thing runs perfect....

I will be back in just a little while I'm going to buy a new TPS just to see if it changes it.

You say it runs the same with the vacuum line disco'd from the fuel pressure regulator? It shouldn't.

If you can get it up here, I'm sure we can straighten it out.

Tom thanks for replying! I think I might have to take you up on that but it won't be untill this weekend. I have slaved over this thing all day to no avail and had to arrange a ride to work tomorrow so i can get a company vehicle. I think I could get it to Loveland tho because I can still drive it I just have to keep the RPM's high enough. There is a sweet spot in third gear with my 4:56's that I can somewhat cruise along but barely i just have to keep putting the pedal to the floor. I definitley will hit you up towards the end of the week to see what your schedule looks like. Thanks a bunch Tom!

Oh ya it ran exactly the same with the vacuum hose off the fuel reg. as it did with it connected. There definitley is vacuum there too. The diaphram in the regulator is good because there is no fuel in the vacuum hose.

I had this same issue. I replaced fuel filter, fuel pump, checked fuel lines and I finally figured out that the CPS wire was grounding out. It's an easy check for a complicated problem.

Cody

codysown said:

I had this same issue. I replaced fuel filter, fuel pump, checked fuel lines and I finally figured out that the CPS wire was grounding out. It's an easy check for a complicated problem.

Cody

Click to expand...

Thanks Cody! I just put the CPS on about a month ago but I will definitley get under and check the wiring again. I always thought that the CPS was either good or bad but just recently learned that it can be troublsome as well and make the engine run like sh!t. Nothing garauntee's a new part won't have problems either!

codysown said:

I had this same issue. I replaced fuel filter, fuel pump, checked fuel lines and I finally figured out that the CPS wire was grounding out. It's an easy check for a complicated problem.

Cody

Click to expand...

Thanks Cody! I just put the CPS on about a month ago but I will definitley get under and check the wiring again. I always thought that the CPS was either good or bad but just recently learned that it can be troublsome as well and make the engine run like sh!t. Nothing garauntee's a new part won't have problems either!

Sorry for the repost!