fuel pump relay no work

After doing a crap load of troubleshooting and electrical diagnoses, I've come to one last idea which I would like to check.

First of all, the indivisual wire which runs from the computer to the coil in the relay is not being grounded by the computer which is causing the relay to not switch on and run the pump. After checking the wire at the computer (note its labled orange/black for 87-90 cherokee) I determined the computer was not opening the ground. So i assumed the computer was bad and replaced. After replacing it still no luck and now I had no idea what could be causing it. Now I relized it must be something telling the computer not to switch on the fuel pump relay but I don't know what this would be because from what I've understood the fuel pump stays on the whole running time but after the 1st few seconds the Ballast Resistor drops the voltage and then the EGR (evaporatic canister soilenoid) controls the amount of gas return to the tank from the fuel rail.

I still have to check some more random stuff but as of now I'm stumped still. Theres not much else in the schematic that is helping.
Also whatever is controlling this will reset its self over time so the relay will flicker on and off for a few seconds and then not do it again till turning the key off for a while and then turning it back on. Any help would be nice, i'm trying to provide as much info as possible, If you'd like to see the schematic I might be able to scan it also. thanks

Got some erroneous information there.

1. When you first turn the key to ON, the fuel pump receives 12 volts from the B Latch (later models ASD) relay, bypassing the ballast resistor. If the ECU doesn't sense a signal from the CPS/CKP crank sensor it will cut the ground to the B Latch (ASD) relay after 3 seconds.

2. When the key is in the START position, the fuel pump gets 12 volts from the starter relay, bypassing the ballast resistor.

3. Key in the ON position, engine operating from idle to just short of WOT, the fuel pumps receives its power from the fuel pump relay, through the ballast resistor where it is reduced to about 6 volts.

4. Key in ON, engine at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Have you renewed the grounds at the dipstick tube? The ECU itself grounds there and they are critical for a Renix.

joe_peters said:

Got some erroneous information there.

1. When you first turn the key to ON, the fuel pump receives 12 volts from the B Latch (later models ASD) relay, bypassing the ballast resistor. If the ECU doesn't sense a signal from the CPS/CKP crank sensor it will cut the ground to the B Latch (ASD) relay after 3 seconds.

2. When the key is in the START position, the fuel pump gets 12 volts from the starter relay, bypassing the ballast resistor.

3. Key in the ON position, engine operating from idle to just short of WOT, the fuel pumps receives its power from the fuel pump relay, through the ballast resistor where it is reduced to about 6 volts.

4. Key in ON, engine at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Have you renewed the grounds at the dipstick tube? The ECU itself grounds there and they are critical for a Renix.

Click to expand...

this is all correct.
Don't forget to pull test all of your fusible links. They go bad, and sometimes show no external signs, but will pull apart.
Also, don't forget the ground strap from the back of the block by the temp guage sender. It has the nickname "renix killer" for a reason.

Alright, thanks for the info. I'll have to check all that and the bad ground might be possibilty since I wasn't getting spark at the coil either in the first place.

Also I'm new to this site and got alot more response with better answers than on Pirate4x4 thanks alot.

joe_peters said:

Got some erroneous information there.

1. When you first turn the key to ON, the fuel pump receives 12 volts from the B Latch (later models ASD) relay, bypassing the ballast resistor. If the ECU doesn't sense a signal from the CPS/CKP crank sensor it will cut the ground to the B Latch (ASD) relay after 3 seconds.

Click to expand...

Alright, after I got home from school today i checked for grounds and fused links and found they all tested good. Then I moved onto test what you were talkin about the other relays and became completely confused when in the schematic showed the B Latch relay had no connection with the fuel pump and in a picture diagrahm it was in a different order on the relay mount by the battery(swapped with the o2 heater relay) . I'm not sure if my manual is wrong or not (though now has a reputation for having errors (had wrong info for testing the CPS)) but I pulled up a picutre of it to see what you guys think. I can't make it any bigger though for some stupid reason. I'm gonna check this stuff over tommarow when I have some more sunlight so i can figure out exactly whats what and where.

Life lesson number one: burn your Haynes/Chilton manual--the money you spent for it was WASTED. If you have an outhouse hang it in their for TP.

Get a Factory Service Manual, FSM, for your year XJ, licensed CD versions available at http://www.autobooksbishko.com/index.html for less than $37, and they do charge for shipping. You can copy it to your harddrive, search--its in PDF format, and print.

Following a Haynes/Chilton is like getting in that creepy guy's van to help him find his dog--really, really bad idea.

Is this also true for post-91 models?

joe_peters said:

Got some erroneous information there.

1. When you first turn the key to ON, the fuel pump receives 12 volts from the B Latch (later models ASD) relay, bypassing the ballast resistor. If the ECU doesn't sense a signal from the CPS/CKP crank sensor it will cut the ground to the B Latch (ASD) relay after 3 seconds.

2. When the key is in the START position, the fuel pump gets 12 volts from the starter relay, bypassing the ballast resistor.

3. Key in the ON position, engine operating from idle to just short of WOT, the fuel pumps receives its power from the fuel pump relay, through the ballast resistor where it is reduced to about 6 volts.

4. Key in ON, engine at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Have you renewed the grounds at the dipstick tube? The ECU itself grounds there and they are critical for a Renix.

Click to expand...

I'd like to thank Joe Peters for sending me copies of that manual but the Relay problem is still pretty foggy.
From quite a few manuals I've looked at so far they've all said the B Latch relay only functions for after the ignition is off to set it up for the next start (ex. the air stepper motor) and in the schematics it seems to have no connection to the pump.
All the other relay information seems to be correct though.
So far the only problem I've found is that on what I beleive to be the Oxygen Sensor Heater relay (from having an 87 and 87a ground but is in place of where the Latch relay is said to be) is that it has no power coming to it. Im guessing its a direct source so Ill check that
I also found that the Fuel Pump relay(when bypassed) is sending power 10-11volts at the pump (I would expect less through the Ballast Resistor) This is also the relay that flickers on and off for a few seconds when the key is first ON.
It's hard to diagnose anything now that I don't have a schematic i can trust so its been hard to test anything with any idea.
Thanks again

What year rig?
My fuel pump relay has a loose cover.
1991 4-door, 4.0L auto-trans, Laredo
I can take the cover off the relay, push the little armature, and run the fuel pump without a key in the ignition.
The resistor on mine is ALWAYS in the circuit and not bypassed at any time.

Now this post doesn't say what your problem is.
What are you trying to do?

dennis461 said:

What year rig?
My fuel pump relay has a loose cover.
1991 4-door, 4.0L auto-trans, Laredo
I can take the cover off the relay, push the little armature, and run the fuel pump without a key in the ignition.
The resistor on mine is ALWAYS in the circuit and not bypassed at any time.

Now this post doesn't say what your problem is.
What are you trying to do?

Click to expand...

Basically whatever runs the fuel pump when the key is in the "on" posistion before startup, is not working properly. So now I'm trying to find what exactly controls what to diagnose the problem since I have now been given mixed information.
Also its an 87 4.0 and I can also run the pump with out the ignition by taking the relay out and bypassing it, which susposibly runs through the resistor. The weird thing is my jeep dosn't have the Ballast resistor located in front of the EGR soilenoid like it should and it hasnt been relocated by anyone and I have yet to see it. (note I have just received this jeep)

Now this post doesn't say what your problem is.
What are you trying to do?

Does you jeep start up?
Does it start up when spraying starting fluid into the air filter box?

dennis461 said:

Now this post doesn't say what your problem is.
What are you trying to do?

Does you jeep start up?
Does it start up when spraying starting fluid into the air filter box?

Click to expand...

I just told you what my problem is, did you even read what I just explained??
And the engine does not start right now which is why i'm trying to fix this electrical problem(obviously) so why are you asking?

Super mud said:

Basically whatever runs the fuel pump when the key is in the "on" posistion before startup, is not working properly. So now I'm trying to find what exactly controls what to diagnose the problem since I have now been given mixed information.
Also its an 87 4.0 and I can also run the pump with out the ignition by taking the relay out and bypassing it, which susposibly runs through the resistor. The weird thing is my jeep dosn't have the Ballast resistor located in front of the EGR soilenoid like it should and it hasnt been relocated by anyone and I have yet to see it. (note I have just received this jeep)

Click to expand...

1. If the resistor isn't there, don't worry about it. Its purpose is to reduce fuel pump noise and has been eliminated on quite a few XJs as they tend to be problematic, and because it was problematic Chryco eliminated it in 94+ XJs during production.

2. If you are NOT getting the 3-second prime of the fuel pump, that means that the B Latch relay is not working OR not being activated by the ECU. That also USUALLY means that you won't have spark, as the 12 volt supply to the ICM/coil comes from the B Latch relay. When the key is turned to ON, the ECU provides the ground to the B Latch relay, the fuel pump runs, and IF the ECU has NOT detected a signal from the CPS/CKP it will remove the ground to the B Latch relay and the fuel pump will shut off.

3. Yes, if you jumper the fuel pump relay then the pump will run until the jumper is removed or the battery dies or the pump burns out.

4. Get a spare relay and put it in the B Latch relay's socket. You can use the o2 heater relay, the fuel pump relay, or the a/c relay if so equipped. Note that if you use the fuel pump relay then the engine might start but will die as soon as it runs out of fuel.

5. So, do you have spark?

Subscribed. When my '90 did this I pulled the fuel pump relay and added a toggle switch putting power to the pump. Looking forward to a real solution.

Tommy

joe_peters said:

1. If the resistor isn't there, don't worry about it. Its purpose is to reduce fuel pump noise and has been eliminated on quite a few XJs as they tend to be problematic, and because it was problematic Chryco eliminated it in 94+ XJs during production.

2. If you are NOT getting the 3-second prime of the fuel pump, that means that the B Latch relay is not working OR not being activated by the ECU. That also USUALLY means that you won't have spark, as the 12 volt supply to the ICM/coil comes from the B Latch relay. When the key is turned to ON, the ECU provides the ground to the B Latch relay, the fuel pump runs, and IF the ECU has NOT detected a signal from the CPS/CKP it will remove the ground to the B Latch relay and the fuel pump will shut off.

3. Yes, if you jumper the fuel pump relay then the pump will run until the jumper is removed or the battery dies or the pump burns out.

4. Get a spare relay and put it in the B Latch relay's socket. You can use the o2 heater relay, the fuel pump relay, or the a/c relay if so equipped. Note that if you use the fuel pump relay then the engine might start but will die as soon as it runs out of fuel.

5. So, do you have spark?

Click to expand...

You just opened a door for me, that would make sense. yes I am not getting spark, and before that I had been testing the CPS for resistance.

What happened is I was testing the CPS and misc. other things in the first place.
I then found I wasn't getting spark so started diagnosing that.
After that was when the fuel pump stopped coming on. So it was one big chain. At first I logically thought I must have done something to cause each of these problems in order but everything was reasssembled correctly.

I said this earlier
"So far the only problem I've found is that on what I beleive to be the Oxygen Sensor Heater relay (from having an 87 and 87a ground but is in place of where the Latch relay is said to be) is that it has no power coming to it."

It dosn't make sense to be the Latch relay but apparently from a picture diagrahm pointing to the location, it is. I still have yet to check this more but its power source also dosn't come directly from the battery fro what it looks like. This why I was trying to get diffinitive schematic/etc to know exactly what is what too.

I don't kno if I was high when i tested that but scratch that. I went and took a look at it again and found that what I beleive to be the Latch relay is working properly and switching on and sending voltage (still dont know what I was looking at before)
I also checked the ignition module/coil when I wasn't getting spark and found that it was getting incoming power around 11 or so volts along with also being grounded.
I'm now going by this picture here.

that's the correct picture.
Don't wory about the ballast resistor, it wasn't installed in 87 unless the customer complained about the pump noise, then they were retrofitted.

joe peters has you on the right track.
it's been a long time since I had to fool with mine.

here's my thread from 5 years ago, there's a lot of raw information about the fuel system in there.
http://naxja.org/forum/showthread.php?t=68504&highlight=fuel+pump

I didn't really make it clear in my last reply but with the Latch relay working properly(full voltage on the 87 and 30 pin) which hasn't made sense why its still not priming the fuel pump and the I'm not getting spark.
So is power to the pump coming directly from the Latch relay just like the coil should too? If so it would make sense that something farther down the line has been disconnected.

Alright I got some more clarification. Apparently the relay I've been testing which I though was the latch relay, is the O2 relay since i traced it back all the way to o2 sensor. So it looks like they are out of order like i suspected even though the grouping of wires looks from the factory (not messed with) So now i got the one on the far right (pink wires) and the one on the far left (org/blk86, org30, green87, and black87a) for my possible suspect. Also it looks like my Haynes manual has been correct on the fuel pump and o2 relay so far. Though what I noticed is the far left relay is not receiving a power supply on the org30 terminal (this might have been what I was accidenly testing before) So I'm thinking this might possibly be a problem, though in the picture its labled as the AC relay, and in the schematic the far right one is labled the Latch relay.
I forgot to try jumping the relay from a power source so I'll try that tommarow.

Also one more thing: This dosn't make sense but the ignition coil is receiving 12 volts all the time no matter if any relays are connecting power or not. The only thing that would make sense would be the coil gone bad but I tested it all to spec a while ago and it tested good. Also its grounded too.

Well heres what I got now.
Magically started getting spark and the fuel pump started working with the key in the on posistion to prime the fuel rail. But....I didnt do anything recently to cause any of this (which bothers me cause this kind of randomness isnt a good thing) Though now the fuel pump only comes on half the time before startup and more recently it comes on rarely now.
Also the fuel pump relay still switches on and off before start up.
One more thing, I narrowed it down some more and the Latch relay ends up being in place of the oxygen sensor with the pink and black wires like my manual says correctly.
Any way I went ahead to try to get the motor running and now I'm having a fuel problem. from what observed the injectors arnt spraying like they should (only noticed each spray about twice out of a couple sessions of cranking over) I'm not sure if the rail was primed enough or not but the starter relay I know is sending power to the pump on start up. I'd like to check regulary with a fuel pressure gauge. Also injectors are clean. And I got it running for 5-7sec a couple times before cutting out again. Also fuel is deffinetley coming to the rail.
Could some one confirm that the Latch relay has pink/blk wires running to it? Also could it possibly be causing the injector problem since they receive power from the latch realay?