• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

fuel problem

M

Mike Mike

NAXJA Forum User
Location
Tucson Arizona
OK, Wifes 89 4.0 dies and acts like it ran out of gas. Has gas in the tank and the fuel pump runs for the 2 sec. like it's suppose to when you turn the key on. But real loud. No fuel at the fuel rail. So I install a new Mopar fuel pump and filter and it acts the same. When i spray stater fluid in the air breather the motor fires and tries to run, so getting signal from cps.
So what the experienced out there have to say.
 
Your 89 has a ballast resistor, a small cream colored unit probably on the firewall somewhere. If that resistor is bad, it inhibits fuel from getting to the injectors (although it is bypassed while you turn the key so sometimes vehicles start, then die when key is released)

You can try bypassing that resistor with a small piece of wire. It is safe to do this for troubleshooting. The resistor is there to reduce noise on the fuel pump circuit and is not even found on 91 and newer.

It might be something else, but you can bypass in about 5 minutes, so worth a try.
 
Mike Mike said:
There's no fuel at the fuel rail
Click to expand...
Seems then that you might not be getting power to the fuel pump somehow, after the initial 2-3 second prime.
I'm not sure how it works, but reapers pump would run 2-3 seconds when key was turned to the on position.
I'm sure someone will chime in here in a bit to give more info.
 
Last edited:
The Renix fuel pump operates in a number of strange and mysterious ways.

Key turned to ON power goes from ignition switch to fuel pump relay, ECU provides a ground to the fuel pump relay to energize the relay, then the ECU cuts the ground after a couple seconds if no crank sensor signal has been detected.

Key turned to START, power is provided to the fuel pump by the starter relay, bypassing the ballast resistor so a full 12 volts gets to the pump.

Key turned to ON, engine running from idle to just short of WOT, power to the fuel pump is through the fuel pump relay and the ballast resistor.

Key ON, engine at WOT, power to the fuel pump is through the oxygen heater relay bypassing the ballast resistor so a full 12 volts reaches the pump.

So what to do? I would consider replacing the fuel filter and inspect the lines from the tank all the way to the fuel rail checking for damage.

When you replaced the pump, did you replace the piece of rubber hose from the top of the pump to the tank flange? Did you make sure those clamps were tight?
 
birchlakeXJ said:
Your 89 has a ballast resistor, a small cream colored unit probably on the firewall somewhere. If that resistor is bad, it inhibits fuel from getting to the injectors (although it is bypassed while you turn the key so sometimes vehicles start, then die when key is released)

You can try bypassing that resistor with a small piece of wire. It is safe to do this for troubleshooting. The resistor is there to reduce noise on the fuel pump circuit and is not even found on 91 and newer.

It might be something else, but you can bypass in about 5 minutes, so worth a try.
Click to expand...

Think that was 95+.
 
Thanks Joe Peters. Replaced the filter when we put the new pump in. Removed fuel line on engine side of filter and cranked enigne no fuel to filter. Tonight I'll check to see if power to pump in start poistion. Is the ground to the pump always thru the ECU??
 
Mike Mike said:
Thanks Joe Peters. Replaced the filter when we put the new pump in. Removed fuel line on engine side of filter and cranked enigne no fuel to filter. Tonight I'll check to see if power to pump in start poistion. Is the ground to the pump always thru the ECU??
Click to expand...

no, which is another source of frustration, it is a chassis ground. I'm about to go troubelshoot the same thing in an 87 . On the Mj it goes to the tail light harness, drivers side, and if that ground fails the pump will not run. I'm unsure of the ground location for the XJ, but suspect it's in the same general area.
 
joe_peters said:
Think that was 95+.
Click to expand...
I believe 93 or 94 removed it. I am not certain, if I had my FSMs next to me right now I could figure it out. I know 91s had it because my MJ had it (before I removed it, because it was in lousy shape and I don't care about the extra noise.)
 
kastein said:
I believe 93 or 94 removed it. I am not certain, if I had my FSMs next to me right now I could figure it out. I know 91s had it because my MJ had it (before I removed it, because it was in lousy shape and I don't care about the extra noise.)
Click to expand...

For the longest time I thought the last year of the ballast resistor was 93, but then I found in the 95 FSM a statement that it was eliminated for 95. Might be one of those "date of production" changes.
 
Any thoughts on how to check this stage if the enigne is'nt runinng

Key turned to ON, engine running from idle to just short of WOT, power to the fuel pump is through the fuel pump relay and the ballast resistor.
 
You must log in or register to reply here.

Similar threads

WGxj
1997 XJ 4.0L AW4 Long Crank Problem
Replies
5
Views
90
Tim_MN
Tim_MN
P
Fuel pump will not prime
2
Replies
35
Views
226
Patrick dimel
P
Ecomike
87 Renix XJ No fuel, No brake lights, cranks fine
2
Replies
27
Views
865
Anak
Anak
S
1998 XJ no start - No fuel pressure
Replies
11
Views
2K
sjx40250
S
J
2001 4.0L issues
Replies
15
Views
266
Saudade
Saudade
Back
Top