my step dad is having some problems with his 94

[XCastleXJ]

94 sport, 4.0 HO, 201k miles, manual

i tried searching, but didnt really know what to search for.

untill about a month ago, his xj would start right up every time - no problems. but lately he's been having a hard time getting it started.

on a cold start, there is no problem. but once its warm/running temp. and he tries to start it again it wont start without pulling off the air intake hose (far end of the air filter cover hose) and spraying starting fluid in there.

he is getting fuel, he is getting spark, the coil is about 8 months old and he recently replaced the spark plugs and put in a fuel injector cleaner additive but has since run a full tank through the jeep.

lol, im doing my best to be the middle man/messenger boy between you guys and him.

any idea on what could be going on?

 

[Skully]

CPS (crankshaft position sensor) NSS (neutral safety switch)? .....both of those will cause the Jeep not too start.

Sounds like an intermittent problem specifically when it gets warm, thinking temp plays a part in the problem.

 

[90xj4x4]

Some type of a vapor lock issue? Otherwise maybe the CPS is on the fritz. I think that they can start acting up when they get old/hot.

 

[Hypoid]

CPS (crankshaft position sensor) NSS (neutral safety switch)? .....both of those will cause the Jeep not too start.

Sounds like an intermittent problem specifically when it gets warm, thinking temp plays a part in the problem.

A bad NSS won't allow the engine to crank at all.

Some type of a vapor lock issue? Otherwise maybe the CPS is on the fritz. I think that they can start acting up when they get old/hot.

I'm leaning toward a weak fuel pump. You need to have a pressure gauge on the rail when it acts up to verify the problem.

Fuel pumps are not cheap, and invariably go out immediately after filling the tank. LOL That is why I like to confirm the problem before throwing parts at it.

 

[YELLAHEEP]

Ask him to put the gas pedal flat to the floor when it won't start normally. If it'll start that way, It's likely a Throttle Position Sensor.

 

[XCastleXJ]

where is the CPS? is there a way to test it before replacing it? how much do they run?

if it was the fuel pump would it cut in and out before going out completly? like i said, he's getting fuel. without the jeep running and with the key in "on" position he's getting pressure. we tested this by pressing in the valve in the rail and seeing gass spray out. could it just be that there isnt enough pressure?

 

[XCastleXJ]

Ask him to put the gas pedal flat to the floor when it won't start normally. If it'll start that way, It's likely a Throttle Position Sensor.

he's tried both putting it flat on the floor and pumping, neither of which work.

 

[Hypoid]

where is the CPS? is there a way to test it before replacing it? how much do they run?

if it was the fuel pump would it cut in and out before going out completly? like i said, he's getting fuel. without the jeep running and with the key in "on" position he's getting pressure. we tested this by pressing in the valve in the rail and seeing gass spray out. could it just be that there isnt enough pressure?

Could be! I don't remember the majic number, but if you don't have enough pressure on the fuel rail, the ECU will not fire the injectors. Lower than normal pressure will also allow the fuel to boil in the line when it gets hot.

The symptoms are classic, but for $100 I'd like to know I'm headed in the right direction.

 

[Frank Z]

The PCM doesn't care what the duel pressure is, there's no fuel pressure sensor either.

Pressure at the rail should be 39psi. Have him moniter the pressure with the engine cold and at normal operating temp (190Deg. F).