92' Cherokee with a hangover? No fuel pump unless its sunny....

This damn thing is driving me totally nuts... It's been going on for close to month now. It acts like it has a hangover or a major attitude about 'waking up early'........
You can only hear the fuel pump kick >after< the sun has been hitting it for about 20 minutes. Anytime earlier than that, before the sun comes up over the mountain or if its crappy weather out, fat chance & not happening.
When the fuel pump is not engaging, the check engine light also does not blink on and off as it usually does.
When the sun has warmed it up it seems, then I turn the key, fuel pump immediately does it's thing and we are good to go. I can drive it all day, leave it sit for hours and it's fine. Until the next morning when we start the same stupid **** all over again.
Before the sun hits it: turn key, can't hear fuel pump/ no cel dummy light. After it's gotten warm from the sun, turn key, fuel pump kicks on, cel light blinks along with the antilock, brake etc. cranks right up and 'off we go!'

Does anyone have any clue, I am really not going to keep sinking money into it...might as well drag my Ford back out of the weeds.....

_It's a '92 Cherokee Laredo, straight 6HO, auto/4 wheel drive. 188K. Everything works on it, except the cig lighter.

Poor electrical contacts.

Clean your main cables, both ends. Just for grins have the battery load tested WHEN IT IS COLD.

Renew you grounds--clean to bare metal, treat with an anti-corrosion agent, make the connections TIGHT.

Turn the PDC over and check for corrosion. Clean the contacts, use a little dielectric grease.

For grinz and giggles swap another relay into the fuel pump position.

Good luck.

I have swapped out the battery(which is a new one), using 2 good ones from the other trucks we have. New cables for it as well. Bought extra relays and switched them all around, no difference. I talked to alot of people who said it's this or that....

Thus far, at the suggestion of others, the Cherokee has gotten new fuel filter, new ballast resistor, new relays, new fuel pressure regulator, and as of last night, a new crankshaft position sensor..... not a bit of difference, but eh... the sun is starting to creep up over the mountain and as soon as the jeep is out of the shadows and the sun has been hitting it for a bit, it will start up, it does everytime.

And...also i should mention when it has it's attitude going, there is also no pressure at the schrader valve on the rail, it will make bubbling noises, but nothing comes out.

No clue as to where the grounds are except the battery which is clean. The chiltons & haynes book don't show where the grounds are that I have found.... The box where all the relays live is clean and dielectric greased all the connections that I could see.
I have read countless posts here, and on other jeep forums where people have similar symptoms. Nothing I have done so far has fixed this.
When it does start to 'wake up' you can hear a series of little clicks like it's purring then the fuel pump kicks up, prime it a few times and it cranks/starts right up.
As I said before, when the fuel pump doesn't feel like it the check engine light doesn't blink on at all with the other dummy lights. I don't know where to look for 'grounds', so if someone could please point me in the right places that would be great....
It's a daily driver and I really need to go to work when they want me there, not when this xj decides I should go.....

i know it's kind of dumb but did all this start when you changed the fuel filter... maybe it was put in backwards...

have you pulled the whole pump assembly out to check it... could be something corroded or disconnected...

another long shot i just thought of would be the coolant temp sensor... mine had similar symptoms and that helped out... it won't through a code if that sensor is bad because it is normal to be in hot mode or whatever when the engine is warm...

they are cheap enough... i think like 15 at autozone and easy to change...

No, it started randomly around the first week of august. The fuel filter got replaced afterwards. I've had it for a year or so, and never had this problem before. All the parts that have been replaced came from Autozone, I don't do Advance.... I really don't think it's the fuel pump, when the jeep does finally wake up, as I said I can go all day till late evening with it. No problems whatsoever, never gags or stalls and starts right back up even if I leave it sitting for hours. This is something that seems to happen overnight.... On a few occasions I have thrown a light under the hood and wrapped an old hunting blanket over it, tucked it in like a child and put it to bed literally, that has worked sometimes..... but see it is not really cold up here at night so I don't get it at all.

It sounds as if it is getting condensation buildup somewhere that is shorting things, rather than a temp thing necessarily. Once the sun dries it out it works ok. Is the fuel pump the only thing not running when this happens? Or do other systems not come on either (like warning lights, blower motor, etc)? Can you garage it or keep it indoors somehow?

Greg

Pin 51 of the PCM should be providing the ground for activation of the fuel pump and ASD relays. Start at the PCM and clean the connector and pins and treat with dielectric grease, then work your way around the engine bay towards the PDC cleaning the connectors and treating them with dielectric grease.

There is a POS braided strap from the rear of the head, driver's side, to the firewall. Replace the strap with a 4 or 2 gauge cable. Clean the surfaces down to bare metal, treat with an anti-corrosion agent, and make the connections TIGHT.

No fuel pump prime, no pressure at the Schrader valve, good indications that the fuel pump relay is not operating. Test for power to the relay when the key is ON, that comes from the ignition switch, same to the ASD relay. Grounds for both are from the PCM, test for an open in that circuit.

I would go out in the morning when it's acting up and remove the relay, jumper the socket to eliminate ALL the computer controlled stuff. Pin 87 to pin 30. Then does it have fuel pressure?

I wonder if the rubber hose from pump to hardline, down in the tank is coming apart..

To answer 'ShowMeCherokee' the only things that don't work are the fuel pump and the check engine light. Everything else, power wise works, windows, ac/blower, all the lights etc......when it does kick on the check engine light will blink on & off normally like the others do. After the sun warmed it up for about 20 minutes this morning it started right up. I went to work and it sat in a parking lot in the sun all day till evening and I had no problems starting it to come home.
>Joe Peters I don't know what pin 51 is or where to look, if you mean the box with all the relays I have already cleaned it and dielectric grease in every single plug hole. While it has it's attitude going I can swap relays with new ones/extras that I have and it makes no difference. Another thing I also noticed is there is no fuel pressure at the valve BUT when I know it's warm enough to start I check and then out of the blue there is fuel coming out of it, even though the fuel pump has not woken up yet.
I have read countless forum posts on similar symptoms, and have seen the reference to jumping 87 to 30...if someone could please kindly explain?
Replacing the ground strap may help in this? I have thought all along that it's something getting damp from the dew or something and then when the sun comes up and warms up the truck it burns off.... whatever it is, is directly affecting the fuel pump & the cel, as those are the only things that do not work in the morning.
Thanx guys for any input you are giving me!

If you pull the relay out there's a little diagram on the side showing 85, 86, 87 and 30. Figure out which pins those are on the bottom of the relay. Then transfer that down into the socket and jump directly across the two pin holes. This eliminates everything that fires the relay and runs 12v directly to the pump. If the problem is gone then you know it's electrical, on the control side of the relay. If the problem remains then there is either an issue with the wiring to the pump, or its ground.. or an internal issue within the tank such as the feed line or pump itself. Process of elimination.

Capiche?

Yep, got it Thank You!

Longshots but easy, fast, and no cost!---

Next time it 'don't'.
-Go loosen gas cap and retest. thinking of a vent sys failure and causing a vacuum in tank. (Retighten cap after test!)

-Could it be under dash? run a hair drier to warm that area to test?

-Neutral safety switch on trans? Try start in neutral and wiggle shifter.

Jumped 87 and 30 fuel pump kicked right up, won't start but not sure if it's supposed to like that. So I guess I need to undo the relay box?

So it had pressure with the pump powered up. That rules out the pump and pump wiring and internal pickup hose as the culprit. I'll have to look at a manual and see if the fuel pump relay is powered off the ASD relay. ASD feeds the PCM at least so that is consistent with your problem.

It's been in the shade for a couple of hours, and of course, it's doing the same crap again...no fuel pump buzzing.

:tearCM...clean/greased, no change. Ground strap at the back of the motor squeaky clean and tight, no change. the PDC same thing...next? really starting to get aggravated...........

Ok, now you have fuel at the rail.

Do you have 12 volts to the primary side of the coil? If not, the ASD relay isn't passing the voltage. It would be that pesky pin 51 of the PCM that provides that ground to the ASD relay, the power comes from the ignition switch, same as the fuel pump relay.

Do this--with 30/87 jumped so you have power to the pump, do the same for the ASD relay so the coil is powered and then crank it over.

Post up what happens.

--->Joe Peters:
I jumped both relays holes for the ASD and fuel pump (30 to 87) and then tried to crank it, it cranks but doesn't start. I don't know how to check if the coil has 12v going to it. It's still doing the same thing although the sun just started to hit the front end.

Also, not that I know if it has anything to do with this, but there was a plug disconnected from the coil, that seems to connect to something on the edge of the ac thing. I connected the two together and tried to start it, no fuel pump and made no difference. I don't know if there is a reason related or not to this, why the two ends aren't plugged together or what it even is. It's double wire one leg connected to the edge of the ac by a screw(ground?) and the other part seems to go behind the pulley.

Fuel pump relay feeds off ASD which gets signal from PCM. Since you are not getting fuel pump or pressure I would suspect PCM is not signaling the relays to switch on. PCM must get signals from Crank and Cam Sensors (I believe) to provide that signal. All signs point to a signal problem to or from PCM. I am currios if this is moisture or temperature related. Moisture can provide a short, temperature can affect current flow. Have you verified connections at the PCM? Try a used PCM or a friends PCM to see if this does anything.