rgs80074

hello Everyone,


I have a
1996 jeep grand cherokee
4.0l engine


the other day i was getting ready to do some errans and was waiting on family to come out and go and the jeep stalled and would not restart.

it cranks over so its not the starter or battery. what i could not hear was the fuel pump pressureising. you know if you turn your key but not all the way you get the fuel pump sound as it pressurized the line for about 3 or so seconds, i stopped hearing that.

now its been setting for a day and a half and i've not looked at it have not had the time.

but how likely is it the fuel pump?

i mean after all the vehicle is 20 years old and i am not sure how well maintained it was kept before i got it a year ago since then i've done oil changes on time etc.

I did buy a relay yesterday and fuel filter but i am afraid if it starts i'll just think those solved it and could still be driving a vehillce ready to die at any moment.

someone suggested turning the key to build up pressure or so it should build up pressure and taking a **** on the engine off and pressing it in and see if gas comes out, is that wise or safe to do.

what would be everyone's suggestions?

from videos it appears the 1996 fuel pump can actually be accessed without having to drop the gas tank that was goign to determine if i did it or had someone else but with money the way it is i might have to try it either day and only pay someone if i can't get it done right.

thanks and I look forward to everyones thoughts.

ryan from orlando

dave1123

Try swapping the fuel pump relay with another from the box. A headlight relay is good because you can at least drive it without a headlight if you need to. You can check the plug connection at the pump to make sure you're getting power to it and a good ground. You may have lost the ground because of rust. If the ground is good, try hotwiring the pump to see if it runs. All this stuff you can do without spending a penny.

See if you have spark. Pour a tablespoon or so of fuel down the throttle body and see if it fires. If it does, you know for sure it's fuel. If not, then it's probably the ASD relay. Again, try swapping.

The ASD relay controls the ignition and fuel injector circuits. It's energized by the PCM once it gets a signal from the CPS that the crankshaft is turning. No signal, no fuel or spark. The fuel pump relay is also controlled by the PCM.

One more obvious question. Is there fuel in the tank? I only asked this question because it WAS running and then quit.

rgs80074

hello dave1123


thanks for the tips. I'll try them. I already have a brand new relay to use.

I can do limited stuff and video's help me but how would I test for power at the pump? Also the pump is in the tank and not sure how to hotwire it without dropping the tank and then still not sure how to hotwire it.

electrical stuff always confuses me.

well more like scares me i am going to blow something up(rip my 1976 duster).

ryan

rgs80074

also yes there is gas in it. just under a quarter of a tank. so if i can access the pump without dropping the tank i dont have too much gas that it'll spill out pper videos ive watched with the same year jeep

dave1123

You take apart the wiring plug connector at the pump. IDK which pins do what so I can't help you there, but you should be able to check for power and ground without taking the pump out. My point was to test the pump before removing it. I looked at my wiring diagrams for my 2000 and can't find the pin-outs for it either. The transmission section shows you what each pin does on the connector, but not the fuel pump section.

Wait one! I found it in Haynes of all places. I'll get right back to you.

dave1123

Okay, looking at the harness connector with the lock tab up, there are 6 spade pins. The upper right one is 12v power to the pump. the lower left one is the ground. Connect a voltmeter to the power pin and a ground and have someone turn on the ignition. The voltmeter should show 12v for a couple of seconds. Use the ohm setting of the meter to see if the ground terminal is grounded to the body. If you don't see the 12v power, the problem is between the relay and the connector.

On the pump side of the connector, the upper left one is the power to the pump and the lower right one is ground. Put 12v into the pump supply pin and ground the other one. The pump should run. If not, it's the pump.

This is a bit complicated, but will keep you from removing the pump if it's okay. Of course, there is a good chance the pump quit because of age.

rgs80074

Hello Dave1123

A few updates and a question or two maybe you can answer.


Updates: Well being in orlando florida it gets hot as hell this time of the year and I don't do very well in the heat and when working the only time I can get out to do anything is more or less the hottest part of the day (too early to do anything when I get off work and when I wake up its hot).

So today I wanted to move my jeep (figured i'd have to push it) so it was in a better spot to work on (not on the hill) and so the yard could be mowed where it was at.

Just for ****s and giggles (yes sometimes I do giggle on the throne) I got in and turned the key and I heard the pump (not as loud as normal but i heard it) turned the key and the vehicle after a second started up. I was able to move it doing a 3 pointish type turn going forward and backwards and let it sit for about a min or two. Even revved up the engine a couple of times and it acted just like normal.

I'm afraid there is still something wrong to trust it completely at this point.

So Since I already purchased the relay I might install it and keep the old one as a backup for it or the my van (since most of the parts are the same on them) and install the new fuel filter(can't go wrong there).

I will get out my voltmeter(is it sad I had to look it up to see what it was, I have a few that I got for free from harbor freight) see if I can follow your instructions to make sure its getting the proper power and ground. I believe I'll be down there anyways replacing the fuel filter.

Now on the meter and forgive me as I've never used one before you said to use the ohm setting and if its grounded right I should see the 12v for just a second or two (I assume as the pump pressurizes the system) and if I see that and it stops its grounded properly?

Other than that at this point is there anything else you'd suggest I do or if those tests turn out ok I should move onto other projects on the jeep and van such as the oil leak (valve cover gasket and oil adapter o-rings, dash light switch and master door switch, and third brake light if I ever get around to figuring out how to install it. Then I have priority issues on my Van such as trying to determine if my wheel bearings are going bad, think they are and when I check them if the rotors and/or pads need replacing too I might just purchase new rotor/with hub assembly and replace it all at once and see if that problem goes away.

I have a list of things for each vehicle that needs done and in a priority order for what I consider most needed to replace/fix first.

My last question is and I don't know if you recall when I first joined two people constantly responded to tech and help issues. There was you and metalbreakdown(who actually offered to work on my jeep(old one)). I've gone through my pm's from him and can't find his phone number and he's been MIA for almost a year now, have you heard anything from him did he send a goodbye message I didn't see or just vanish.

Anyways thanks again and I'll update again probably tuesday or wed when I get a chance to do more.

ryan

97grand4.0

You're in deep here now, Dave.

Ryan, have you put a pressure gauge on to verify no pressure? That said, if you say you can't hear it run for 2 or 3 seconds when you turn the key on, and you know you should be, then t is 99% sure the pump is the problem, most likely the pump itself but maybe the wiring ground, relay etc. I understand the 96 is a stand alone year meaning it's different than any other and so for that reason I will step back. Rather than spend alot of time diagnosing it I would plan on a pump esp if has high miles. Have it done in half the time.

dave1123

DO NOT use the ohms setting on power! You'll blow the fuse inside the meter. The fact that it ran proves there is power and ground at the pump.

The HOT part just hit me. You may have experienced "vapor lock" where the fuel boils in the rail causing air bubbles to form in the fuel. In that case, it wouldn't start back up until it cooled. HOWEVER, the pump may be weak and not delivering enough pressure. That will make vapor lock easier to happen. Try borrowing or renting a fuel pressure tester from some place like Autozone and test the fuel pressure. The gauge has a hose on it that screws into the shrader fitting on the fuel rail. That's like a tire valve under a black cap on the rail. Your 96 should show 37 to 41 psi running at idle. Anything less than that may be a weak pump or a restricted filter or bad pressure regulator. On many jeeps, the pressure regulator is on the pump unit outside the tank or is part of the filter. If your new filter has 3 fittings on it, the regulator is in it.

Vapor lock is common in hot climates when engine heat isn't dissipated by forward motion, as in sitting in traffic. The exhaust manifold heat rises up and heats up the injectors and fuel rail. My WJ was recalled for a heat shield to help stop that because the cast iron manifolds get REALLY hot and don't lose the heat quickly. It's just an aluminum wafer blanket that just lays on the intake manifold under the injectors. I'm sure one would fit your ZJ. It's got tabs that slip over some bolts to hold it in place.

Test your fuel pressure and we'll go from there.

About metalbreakdown, There are many posters that just disappear, probably because of other concerns. I had a friend from a small town nearby that just vanished, but he had termites in his back porch, was working long shifts, and his wife was having a baby. No time to post. He may come back, but I'm not expecting it. I have another in Hungary, but they are being flooded with refugees, so who knows what's happening.

rgs80074

Hello Dave1123

from what I was reading online and your other post the fuel pressure should be 49 plus/minus 5.

We've had a tropical storm rolling through so I've not done much but I did move the vehicle a couple of days to be able to work on it and picked up a pressure gauge from harbor freight.

picture #1 of the gauge after turning the key but not starting the vehicle.

picture #2 of the gauge with the engine running.

what picture two really don't show you is the movement of the gauge, not sure if its the vibration of the vehicle or something abnormal here is a link to the video if you want to see it, its like 55megs.
https://www.dropbox.com/s/smqei0nez6...84414.mp4?dl=0

picture #3 is the gauge after the engine is shut off

picture #4 is the gauge after about 6 mins












picture #1



picture #2





picture #3




picture #4

97grand4.0

Honestly, that looks dead on. I would discount a fuel pump or regulator issue based on those photos, period. Just what they should be.

What it doesn't rule out however, is the errant, intermittent operation that would come from a bad connection, broken ground wire, etc. On my 97 every wire to the pump is in a single cable and connectors which is fastened above the driver side back wheel to the frame. If the 96 is different, and I hear it is, you may want to poke around and look for a loose ground in the area of the fuel tank and tail lights.

From there I think you have ruled out fuel pressure as an issue and need to look elsewhere. jmo

rgs80074

I also did a couple of other tests out of curiosity while doing these.

Hooked up a multi meter to the battery:

the meter read 12.55 volts

turned on the engine but didn't start it, the pump kicked on etc
volts dropped to 11.3 ish

turned the engine on
volts went up to 13.53
with engine under load with everyone on i could think of, headlights on bright, fog lights on, radio on, heat on hi, windshield wipers on
volts was right around 13.03
revved the engine got up to 13.65

i am thinking this is normal for the jeep. the dash gauge reads just under 14volts and thats what my old jeep (bless her destroyed soul, freakin texters) always said as well and I had her for almost 10 years.

but just throwing it out.

I hope the weather has cleared up enough tomorrow I plan on replacing both the relay and the filter figured already have them why not do it.

then i'll run these tests again and see if there is any change.

but if not these tests seem to indicate stuff is good i think what would be the next suggestion? I'm thinking if there's nothing else to indicate an issue i might just try driving it again and see what happens.

also the day it died and would not restart was at like 9am so it wasn't that hot outside yet. the engine just got up to its normal operating temp (jeeps seem to get up there quick) and then just died. My impala (1981) has an electric fuel pump that i think was installed aftermarket and it got vapor locked all the time. I thought of that at first but had never had that issue on this jeep nor the old one.

ryan

97grand4.0

If it's a 96 and you haven't done the crank position sensor, you're overdue anyhow. GEt a MOPAR do NOT do what I did, and disregard what everyone says about not putting in the aftermarket stuff. I proved positive that the magnet in the Mopar one is 4 times stronger on the OLD sensor than the new one from AZ. Oh, and for the cam sensor, 2 bad out of the box from AZ, they would cause a no start. Put the old one back in, it's running like a champ with it.
That being said, I wouldn't swear this is your problem yet , either.

dave1123

Sorry! I even though about the CPS, but ignored the thought because I've never heard of one dying while sitting idling.

On the fuel pressure. I was going by the Haynes manual that calls for 37-41 for a 96 and 44-54 for 97 up. Who cares, you have fuel pressure that's constant and within a normal range. On some jeeps there is a compensator on the fuel rail to eliminate that needle bounce.

This guy's right, though. after 23 years, the CPS is tired. It's a good place to start. pun intended. Everything else seems to check out. The new Mopar CPS comes with a paper wafer on it that sets the proper distance from the flywheel when you mount it. This wafer gets ripped off in initial start. If it doesn't have this spacer on it when you buy it, ask for one. They're supposed to have them in stock in case they have to remove a CPS in the shop for some reason. If you buy Mopar on-line, it should have one on it. Hopefully.

97grand4.0

Point of order, the CPS is the cam sensor, the CKPS is the crank sensor. We recommend a CKPS. The piece of paper is for the sensor that uses only 1 bolt, not the 2 bolt, depends on which one you have, likely the 1 bolt.

As far as the fuel pressure, Dave has a point, the actual pressure expected depends on the year, yours being a 96 is different. However the pressure does look high enough and steady enough, and upon shutoff does not bleed off which would indicate regulator problems.
Only thing I can think of after that would be the cam sensor, and then the PCM.
Your voltages look spot on for the charging system. That would have little to do with your instant problem, anyway. hope this helps.