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do I need a new fuel pump.

A

austinaubinoe

NAXJA Forum User
Location
Montgomery County, MD
Hey so I picked up a cheap OBD1 1994 Jeep W/ a 4.0. Been trying to figure out the issues as it cranks but does not run. I bought it from my buddy after it randomly left him stranded.

Today I was cranking it then thought about how I never considered fuel to be the problem. So I left the key in the ON position and went to depress the schrader valve on the fuel rail.... no fuel squirts out. Had my sister sit in the jeep and turn it on.... fuel pump does not prime. pulled the fuel pump relay....not burnt or melted.


However, when I put fuel in the throttle body it did not fire. I just replaced the cap/ rotor and spark plugs. How can I tell if my ignition system is not working at all? It has 186,xxx miles, so could the coil be bad?


Thanks.
 
ANYTHING can be bad.

Step one: determine the missing element.

Check for spark--use a spare plug or pull one out of the engine, put the spark plug wire back on it and ground the plug body to the engine. Have a spare pair of hands crank the engine over for you--got spark? Hot, blue, snappy spark?

Check for fuel pump operation--I think 94 was the last year for the ballast resistor on the driver's side fenderwell--white ceramic thingy--if it is there, jumper the two wires together using a piece of wire of equal gauge--14 ga I think. Got pump?

Also, two relays are of concern--the ASD relay and the fuel pump relay. The ignition switch sends 12 volts to both, the PCM controls the energizing ground signal, pin/cavity 51 of the 60-wire connector. So, check for 12 volts to the relays with the key ON.
 
SPARK + FUEL+ COMPRESSION+ AIR = START

For a new-to-you vehicle that didn't run when you bought it, DO NOT ASSUME ANYTHING!

As Joe mentioned, I ALWAYS start by verifying spark. It must be a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.

If good spark is verified, move onto fuel delivery.

If that is verified, be sure injectors are "pulsing" (noid light is a good tool here)

If all of that is okay, get out the compression gauge and run a compression test on ALL cylinders. You are looking for 120-150 psi, with no more than a 30 psi variation between cylinders.

Good luck and let us know what you find!
 
sweet thinks for the advice. I knew there was a way to get the spark plug to spark! Ill try grounding the plug tomorrow.

I gotta say, it ran pretty well 3 months ago, then it just died. So right away I did the basic tune up. It appeared that the cap and wires were replaced, but not the rotor or plugs. All of the plugs looked very bad, but 3 of them actual had large chunks of ceramic missing!

The fuel pump is not making any noise. Where and what is the ASD relay? In the distribution box?

Its not my DD, so its not urgent to fix it ASAP. I actual kinda bought it to get better at fixing electrical issues. :cheers:
 
look up the specs for your resistance on the primary and secondary side of the coil and check it with a digital multimeter. if its in spec your good. if that checks out i would see if there is a testing procedure for the cps. if there is, check it if not, see if someone can loan you one as a means of testing yours. replace as you see necessary.
 
In the PDC--power distribution center--look for the ASD relay--auto shut down--and the fuel pump relay. If you have the PDC cover it should be indicated on that which is which. The ASD relay controls power to the coil, along with other functions.
 
oh ok AUTO SHUT DOWN, ill check it out. I do have the PDC cover. However, one of the first things I did was pull every relay and check for burnt or melted plastic..... all looked fine. Also, I thought relays rarely fail.

When I bought the jeep I originally thought it was just the CPS, but I don think that a failed CPS would cause it not to start... just not to stay running.

Ok im gonna fool around with a MM tomorrow. thanks.
 
Just to make sure we are all on the same page, terminology has changed over the years. CPS can refer to the crank sensor (aka engine speed sensor or CKP) or to the synch sensor (aka CMP) in the distributor or oil pump drive. The crank sensor can prevent the engine from firing. So can the synch sensor on 91+ XJs.

Relays fail. Those in your 94 have been going for 16 going on 17 years. Not bad service from a part supplied by the lowest bidder.

You should test the ASD and fuel pump relays, or at least swap around the o2 heater relay and the a/c relay with them to see if that makes a difference.
 
joe_peters said:
Just to make sure we are all on the same page, terminology has changed over the years. CPS can refer to the crank sensor (aka engine speed sensor or CKP) or to the synch sensor (aka CMP) in the distributor or oil pump drive. The crank sensor can prevent the engine from firing. So can the synch sensor on 91+ XJs.

Relays fail. Those in your 94 have been going for 16 going on 17 years. Not bad service from a part supplied by the lowest bidder.

You should test the ASD and fuel pump relays, or at least swap around the o2 heater relay and the a/c relay with them to see if that makes a difference.
Click to expand...
:worship:

This is a really good tip! I took the Fuel pump relay out of my 2000 TJ and was like this aint gonna fit haha. I thought when relays failed you could tell by looking at them?

And I was talking about the thing on the trans bell housing. Awsome to know that there could be another sensor possible broken :rolleyes:. Is that the one with the 3 wire running into the dizzy?

So your saying that if im not getting any spark, and the coil checks out, its probably the Crank Position Sensor?

As always :cheers:

EDIT: regarding your comment on everything being 17 years old, once I can get the thing to fire I plan to replace a bunch of stuff that is very worn out ( steering joints, belt, u joints, etc,etc.) Looking to turn this mechanics special into a reliable jeep for my sister we she turns 16!
 
Last edited:
austinaubinoe said:
:worship:

This is a really good tip! I took the Fuel pump relay out of my 2000 TJ and was like this aint gonna fit haha. I thought when relays failed you could tell by looking at them?

No, there are moving mechanical contacts inside that could be damaged or corroded. So even if it clicks it might still be bad inside. Or the coil could have shorted/burned out, not moving the contacts.
And I was talking about the thing on the trans bell housing. Awsome to know that there could be another sensor possible broken :rolleyes:. Is that the one with the 3 wire running into the dizzy?
Yes, the cam sync sensor is the three wires running into the dizzy, I've never seen one failed, but apparently if the bearings in the dizzy are going bad it can eat the sensor when it wobbles. It's been discussed here.
So your saying that if im not getting any spark, and the coil checks out, its probably the Crank Position Sensor?

Most likely, the CPS is probably the #1 cause of no starts in the 4.0, or any newer MPFI vehicle for that matter, followed closely by the fuel pump.
As always :cheers:

EDIT: regarding your comment on everything being 17 years old, once I can get the thing to fire I plan to replace a bunch of stuff that is very worn out ( steering joints, belt, u joints, etc,etc.) Looking to turn this mechanics special into a reliable jeep for my sister we she turns 16!
Click to expand...

When you turn the key to RUN you should hear the pump prime, if it does not then you should get out a multimeter and check for voltage at the pump. There's a plug., and unless chryco changed the wire color it's the orange wire for 12V. If you've got voltage and the pump still doesn't run then it's likely the pump. If no voltage then you'll have to double check all the relays an fuses, and then start looking at the harness for damage. Pay particular attention to all of the connectors, and the spade terminals in the PDC for the relays. Double check the ground from that harness as well, I'm not particularly sure about the XJ but in MJ's it runs back to the ground used oin the taillight harness on the drivers side, and when that ground gets nasty your fuel pump doesn't work.

The pump should prime for about 3 seconds in Run, and then when the PCM see no crank signal it will turn off the pump. It should always run in "start"
 
Check resistance at your CKP also.
 
ok so there is 3 prongs on the end of the CPS wire. I put the multimeter on every possible combination of prongs and still got nothing. I set it to ohms. This was my first time using a MM.

This is the one I have (in the picture):http://www.kk.org/cooltools/archives/002894.php


87manche said:
When you turn the key to RUN you should hear the pump prime, if it does not then you should get out a multimeter and check for voltage at the pump. There's a plug., and unless chryco changed the wire color it's the orange wire for 12V. If you've got voltage and the pump still doesn't run then it's likely the pump. If no voltage then you'll have to double check all the relays an fuses, and then start looking at the harness for damage. Pay particular attention to all of the connectors, and the spade terminals in the PDC for the relays. Double check the ground from that harness as well, I'm not particularly sure about the XJ but in MJ's it runs back to the ground used oin the taillight harness on the drivers side, and when that ground gets nasty your fuel pump doesn't work.

The pump should prime for about 3 seconds in Run, and then when the PCM see no crank signal it will turn off the pump. It should always run in "start"
Click to expand...

The pump does NOT prime. But would a pump just randomly fail? Why would all of these things leave my friend stranded all at once? I think there is one central issue.

Im a little confused on where to check the grounds however. I pulled the Distribution thing under the hood and pretty much dismantled it. I closly inspected all the wires and everything looks good. gave a little tug on the wires to make sure they were all still in snug. Where would be the place to fins an issue once you get past the transmission, like how many wires go past that point on a 94? Maybe a wire came loose in the tank?

THANKS
 
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A failing cam sensor (inside the distributor) should not inhibit the fuel pump from energizing and running for 2 seconds with the key turned to the ON position. I'd look elsewhere for your problem.

Unless I missed, it I don't see any evidence of you verifying spark. That is really important in determining where to look.

Pull a spark plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark; not good.

You really need to test for spark. The reason being if you are missing JUST the fuel pump or if you are missing BOTH the fuel pump and spark really dictates a different strategy.

Test for spark. It will take you all of 10 minutes and it is an important data point here.
 
birchlakeXJ said:
A failing cam sensor (inside the distributor) should not inhibit the fuel pump from energizing and running for 2 seconds with the key turned to the ON position. I'd look elsewhere for your problem.
Click to expand...

Agree.

Key to ON, 12 volts is provided to the ASD and fuel pump relays from the ignition switch. The PCM provides the energizing ground to those relays, then cuts the ground if it hasn't received a signal from the crank sensor.

If you are not getting the "prime" of the fuel pump you need to determine what is the source of that issue first.
 
austinaubinoe said:
ok so there is 3 prongs on the end of the CPS wire. I put the multimeter on every possible combination of prongs and still got nothing. I set it to ohms. This was my first time using a MM.

This is the one I have (in the picture):http://www.kk.org/cooltools/archives/002894.php




The pump does NOT prime. But would a pump just randomly fail? Why would all of these things leave my friend stranded all at once? I think there is one central issue.

Im a little confused on where to check the grounds however. I pulled the Distribution thing under the hood and pretty much dismantled it. I closly inspected all the wires and everything looks good. gave a little tug on the wires to make sure they were all still in snug. Where would be the place to fins an issue once you get past the transmission, like how many wires go past that point on a 94? Maybe a wire came loose in the tank?

THANKS
Click to expand...

Did you check for voltage at the pump connector by the tank?

Yes a fuel pump can just fail. I drove my DD 2 hours to a junkyard and back, stopped or gas, stopped at the junkyard, no problems. Parked it at work, came out 4 hours later and the pump was dead. Replaced the pump and it fired right back up.

You need to check for voltage at the pump. If it has 12 volts when the key is turned to run then the fuel pump circuit is good, simple as that.
like I said, unless Chryco changed the color wires it's the orange wire for positive and the black wire is ground. Set your meter to volts, probe those two wires and have someone turn the key to run while you watch the meter. There's no sense inspecting the harness if you don't know that the pump isn't getting voltage.
 
See here for a similar set of circumstances that got fixed.

http://naxja.org/forum/showthread.php?t=1049788

you need to verify that you have spark and then troubleshoot the fuel pump.
It is possible that a shorted CPS could be keeping your PCM from operating properly. Verify spark, if you have spark the CPS is not bad.
 
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