I need help really bad completely lost.

Ramoyer1

Member
Joined
Jul 20, 2011
Location
Morehead City
I need help here im stumped. I got a 88xj 4.0 with new dizzy,plugs,wire,rotor and cap less then 4 months old.
It will start up and idle just fine but if you go to give it any gas it misses and shakes and fights to get above 1-2k rpms.
Does the same thing when you try to go down the road BUT after about 2-5mins of fighting to get it to go down the road it clears up and drives normal until I come to a stop and try to take off again.
It is so bad ive had to park it. ANY ideas on what it could be??

It just started doing it this week
 
Crank position sensor on tip of bell housing.
 
I thought if that was bad it wouldn't start at all? and why does it clear up? I unplugged the cps this am and it shuts off the min it comes unplugged
 
Sounds like either a solenoid in trans issue or a TCM issue. From what I read, and have experienced, I think you may be starting off in high gear, and not 1st
 
I put a 4.0 together once, the distributor was not timed correctly, it would start, idle, and run, but was way low on power, and generally ran like crap. Pulled out the FSM, re-read how to install the distributor, put it in RIGHT, and all was good.
 
Bad gas? Have you checked for water in your tank? Ran into this on an 01 XJ similar problems.
 
Work on jeeps every day. To me sounds like low voltage at fuel pump. Check fuel pressure at idle then again giving it gas
 
How do I up the voltage at pump if it isn't pushing enough gas.
 
Check your injectors and see if they are leaking at all. Check the fuel pressure regulator. Both common problems on renix 4.0's. The injector body's will leak and pressure regulators also leak.
 
If pump has low pressure then its a bad pump. I've got one right now that runs great but when it goes to down shift it just about dies out. Pump drops below 6psi
 
Could also be the TPS.
 
I almost guarantee it's the crankshaft position sensor! My last grand Cherokee did the exact same thing! Ran like complete crap first thing in the morning unless I would let it warm up first. I couldn't go above 35mph cause it was spitting, sputtering, backfiring and popping so bad. I put a new crankshaft position sensor on it and never had the problem again. Yes, in some cases a car won't start with a bad CPS but in my case it would.
 
on the renix xj(87-89) you either most likely need to adjust TPS, very very common on those renix jeeps, or as someone said the dis is off a tooth cause it will run and idle but act like that and the jeep dis HAS to be exact at 5 oclock and can easily be off a bit to make it run like crap. make sure voltage on TPS is good and right than proceed with the rest. I've owned 9 renix jeeps and tps is always culprit if not the dis. install. hope you have it going.
 
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