YJ: Need some YJ mechanicl advise....

[dr.dirty]

Ok guys Im having an issue with a buddies YJ. Its a 94 4.0 5 spd.


I think I have the issue narrowed down to the CPS or the Fuel Pressure regulator.

Short back story. Took the Jeep to get smogged and it passed emissions but failed EVAP. So we took it to get the smoke test to find the EVAP leak. The rollover vents in the tank needed new seals. So driving it back to the shop it started spitting and sputtering. I replaced the TPS and IAC and the Jeep will run for about 45 seconds untill the fuel rail runs dry. This is why im thinking the Crank sensor and its shutting off the fuel pump. The Jeep ran and drove fine 2 days ago and now nothing. What are the experts thoughts?

[6spdYJ]

CPS only triggers the spark. (by the way, you can advance this on pre-'99 manual 4.0's) The injectors trigger from the distributor position. It is possible that a return line got pinched when the tank was put back in. Try the MAP sensor on the firewall directly behind the motor. That works with the TPS and sends the signal to establish the duration of the injection. Have you tried reading any codes? The YJ's can be read by switching the ignition on-off-on-off-on. It will flash the check engine light to indicate the codes. Let's say it flashes three times with a short pause followed by six more flashes, then a long pause and four flashes with a short pause and six more flashes. This would be a code 36 and 46.

[dr.dirty]

I pulled the codes and only have two. One that the battery was disconnected and one AC code. I tested the MAP and it test out good on all the voltages. I rechecked all the fuel lines as well but it started acting up before the tank was pulled. I just ordered a new CPS so we shall see.

[aw12345]

Well here is your simpleton test pull a sparkplug wire stick a sparkplug in it. Hook up a fuelpressure gauge and then run the engine.
Find out what you loose first spark or fuel it will narrow down your search for the answer

[dr.dirty]

Im loosing fuel pressure first. I think that the pump is getting shut off with the shutdown relay. If i prime it it will run for 45 seconds to a minute before the fuel rail is bone dry. Im dropping form 36psi to 0psi

[aw12345]

If you have spark the shutdown relay should not shutdown, add a test light to the fuelpump hot wire and repeat test if the relay looses power it's ecm time otherwise start looking at a pinched fuelpump line since this riggamarole started after the tank removal. Probably a fueltankstrap with a hose underneath it

[dr.dirty]

Ill double check the lines again. and test the pump.

[inVERt'D]

The first thing you need to do is replace the grill and the square headlights with round ones. Then it will be worth fixing.

[dr.dirty]

The first thing you need to do is replace the grill and the square headlights with round ones. Then it will be worth fixing.

HAHAHA lol this one isnt mine any longer.

[6spdYJ]

Dumb question... Did you check the connector to the fuel pump?

[dr.dirty]

Yes i checked that. The pump runs like it should but its getting shut down thats what makes me lean toward the CPS. it first started sputtering before i dropped the tank and had no power and was backfiring. I limped it back to the shop and then dropped the the tank.

[6spdYJ]

When you dropped the tank, did you clean out the sock on the pickup? How about changing the fuel filter? The filter position kinda lends itself to the inlet line getting kinked. As for the pump dropping out, it is powered by the asd and the fuel pump relay.

Have you pulled the power distribution center and looked for loose or broken connections under the asd and fuel pump relays? The crimp connections can break from vibration and/or corrosion. The other thing to try is swapping these relays with others. If the contacts are pitted from age, corrosion or contamination it can cause problems.

[dr.dirty]

Fuel pump pick up is all clean, fuel filter is new. all the fuel lines are new because the old ones were dry rot.

[RAT]

Fuel pump pick up is all clean, fuel filter is new. all the fuel lines are new because the old ones were dry rot.

A total long shot here but...If the hoses were dry rot a piece of the inner lining could have dislodged and gone to the fuel rail and is acting like a flapper valve. You might want to pull the fuel rail if you haven't already.

[vwtipeii]

swap the CPS... mine did the same thing... ran fine... the sputtered... hickuped... bucked... then just plain wouldn't start... swapped the fuel pump first... same problem... swapped the CPS... ran like a top!!!