ok, working on my friends 92 cherokee sport 4.0

he was claiming when it got up to operating temp it would shut off and wouldnt start. it also would act like it would fall on its face when you gave it gas. im thinking cool replace the CPS and all should be ok. replaced the CPS and still wont start, i got it to start once after WOT and it sputtered for a min before smoothing out. turned it off and tried to start it agian and itll crank but it wont start.

so i start tooling around with it and it has good fuel pressure at the rail and it has spark....the plugs are a little fouled up and i had to regap them, but still no start.

he said the distributer plug wires IAC O2 MAP and TPS have been replaced. The TPS was used so i tested the TPS and it doesnt seem to be working correctly.

also he took out the temp sensor on the therm housing and replaced it with an aftermarket sensor and ran it to the dash for a gauge.
is that sensor the ECU needs for air fuel mix?

any thoughts?

 

im having the same exact problem ....would love to know the solution....if you find out tell me 2 please thanx

 

Did you pull the injectors? There's fuel in the rail, but it it making it into the engine?

Also is it throwing any codes? If the TPS is bad and comes up on a diagnostic, it should probably be replaced. I'm not entirely sure, perhaps someone else can chime in.

 

I didn't pull the injectors. But the spark plugs smelled like fuel. Besides i got it to run once and before i replaced the CPS it would run from time to time No CEL on

 

1. Never overlook basic tuneup hardware. Plugs, wires, cap, rotor, fuel filter. The importance of this stuff cannot be overstated and is involved with a high percentage of issues.

2. Two other suspects when you experience "thermal" (heat related) failure are the ignition coil and the camshaft position sensor. In that order.
If the engine runs fine when cold, these two guys are possibilities.

3. Be sure that fuel pressure is 31 psi at idle. You MUST verify this with a fuel pressure gauge; no shortcuts! Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be darn sure that the vacuum line is pulling good vacuum and check it for raw fuel. If that line has fuel in it, you have a ruptured fuel pressure regulator which can lead to excess fuel going to the cylinders.

4. The coolant temp sensors can be tested, but because it is kind of a pain to do it properly, most guys just replace them. Map sensor is also involved with fuel/air ratio.

 

X2
plus the temp sender in the housing is used by the computer I would put the old one back or better still replace it.
the dash temp gauge sender is in the back, top of the head, drivers side, single wire.
just spent the last 3 days fighting the same symptoms, it was the 18 month old MSD "performance" coil.
Good luck with it.

 

ballast resistor

 

was getting spark from plug wires, i think it looked like good spark. i might pick up an inline plug tester to make sure.

i hooked up a fuel pressure gauge and i was able to check it in "on" position and during cranking, looked good but wasnt able to get it started again to check idle. no fuel in vac line off the regulator.

 

can you bypass that real quick to see if thats the issue

 

yeah, but i wouldn't for very long.

 

But if the ballast was out wouldn't it not be getting fuel?

 

nope, it would still get fuel.
the ballast just reduces the voltage to the coil. so if the ballast goes, it won't run when the key is in the run position.

will your jeep start if you hold the key in the start position?

again, you can bypass the ballast with a jumper wire, but you don't want to run it for long.

 

Jumpering the ballast resistor is not dangerous. That resistor is only in circuit to reduce noise on the fuel pump. Later models don't even have this resistor. Many guys have run jumpered indefinitely.

 

It'll crank. But it'll only start at dead cold like if I let it sit over night. But I noticed its flooding when I try to start it. I think the fuel trims are too high. I'm leaning towards the coolant sensor

 

Get a new coolant sensor in there. Not expensive and easy to replace.