96 Grand Cherokee Stalling

fuel pressure I'm starting to think the regulator might

OK, I timed it. After 4 minutes, the pressure had dropped from around

49 psi to about 35 psi. After 12 minutes, it had dropped to 20 psi. To add to my fun, the 96 GC does not have the fuel pressure regulator attached to the fuel rail: it's built into the fuel pump. @#$% There's just a direct connect fuel line going to the fuel rail.

Will a regulator fail in this intermittent way? If that's the case, then I have to pony up the $300 plus for a new fuel pump. Sure wish I could be sure before I make the financial plunge.

By the way, the coil I used was regular old AutoZone Duralast.

Doug B.

fuel pressure I'm starting to think the regulator might

Hard to tell, the 96 made a lot of changes and my books are only good up to the 95. 49 psi might be normal. Still though I thought pressure was supposed to be maintained longer than that. I'd suggest calling a dealership and asking if a mechanic could look that up for you. It's worth a shot.

I don't think it is your fuel pump. Pumps and pressure regulators usually fail to the low pressure side and what you get is a lack of power at wide-open-trottle or even pinging.

You have a second regulator on the engine for the return line I think.

How good is the body to engine or frame to engine or battery to the body ground strap? One of those with a bad connection can cause your symptoms.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

fuel pressure I'm starting to think the regulator might

I replaced the cap today. It didn't help. I have not replaced the rotor.

Doug B.

From the '96 FSM

DIAGNOSIS AND TESTING

FUEL PUMP PRESSURE TEST-4.0L ENGINE

NOTE: The fuel pressure test port is used on certain

engines only. If equipped, the test port will be

located on the fuel rail (Fig. 8). A sealing cap is

screwed onto the test port.

All fuel systems are equipped with a fuel tank module

mounted, fuel pressure regulator. The fuel pressure regulator

is not controlled by engine vacuum.

With engine at idle speed, system fuel pressure

should be 338 kPa 6 14 kPa (49.0 psi 6 2 psi).

WARNING: DO NOT ALLOW FUEL TO SPILL ONTO

THE ENGINE INTAKE OR EXHAUST MANIFOLDS.

PLACE SHOP TOWELS UNDER AND AROUND THE

PRESSURE PORT TO ABSORB FUEL.

WARNING: WEAR PROPER EYE PROTECTION

WHEN TESTING FUEL SYSTEM PRESSURE.

(1) Remove the protective cap at the fuel rail test

port. Connect the 0-414 kPa (0-60 psi) fuel pressure

gauge (from gauge set 5069) to the test port pressure

fitting on the fuel rail.

(2) Start the engine and note pressure gauge reading.

Fuel pressure should be 338 kPa 6 14 kPa (49.0

psi +/- 2 psi) at idle.

(3) If pressure is at O psi, connect DRB scan tool

and refer to operating instructions in the appropriate

Powertrain Diagnostics Procedures service manual.

(4) If operating pressure is above 51.0 psi, fuel

pump is OK but pressure regulator is defective. Regulator

is not serviced separately. Replace fuel pump

module assembly.

FUEL PRESSURE LEAK DOWN TEST

Abnormally long periods of cranking to restart a

hot engine that has been shut down for a short

period of time may be caused by:

² Fuel pressure bleeding past a fuel injector(s). ² Fuel pressure bleeding past the check valve in

the fuel pump module.

(1) Disconnect the fuel inlet line at fuel rail. Refer

to Fuel Tubes/Lines/Hoses and Clamps in this section

of the group for procedures. On some engines, air

cleaner housing removal may be necessary before

fuel line disconnection.

(2) Connect the appropriate Fuel Line Pressure

Test Adapter Tool (number 6539, 6631, 6541 or 6923)

between the disconnected fuel line and fuel rail (Fig.

11) or (Fig. 12).

(3) Connect the 0-414 kPa (0-60 psi) fuel pressure

test gauge (from Gauge Set 5069) to the test port on

the appropriate Adaptor Tool. The fittings on both

tools must be in good condition and free from

any small leaks before performing the proceeding

test.

(4) Start engine and bring to normal operating

temperature.

(5) Observe test gauge. Normal operating pressure

should be 338 kPa 6 14 kPa (49 psi 6 2 psi).

(6) Shut engine off.

(7) Pressure should not fall below 24 psi for five

minutes.

(8) If pressure falls below 24 psi, it must determined

if a fuel injector, the fuel pressure regulator or

a fuel tube/line is leaking.

(9) Again, start engine and bring to normal operating

temperature.

(10) Shut engine off.

(11) Checking for fuel injector leakage: Clamp

off the rubber hose portion of Adaptor Tool between

the fuel rail and the test port "T" on Adapter Tool. If

pressure now holds at or above 24 psi, a fuel injector

or the fuel rail is leaking.

(12) Checking for fuel pump module or fuel

tube/line leakage: Clamp off the rubber hose portion

of Adaptor Tool between the vehicle fuel line and

test port "T" on Adapter Tool. If pressure now holds

at or above 24 psi, a leak can be found at a fuel tube/

line. If no leaks are found at fuel tubes or lines,

replace the fuel pump module.

Wow, thanks. At least I now know that 49 psi fuel pressure is correct for my vehicle. I'll double check it, but I'm pretty sure the pressure stayed above 24 psi for at least five minutes after shutting off the engine.

Doug B.

needed. This was the same coil Jeep installed to

you might swap that relay with the AC or Fog relay

Doug, What is the "harness" you're referring to with the coil? The wiring harness? I'll try swapping out the ASD relay with something harmless, too.

Thanks again, Doug B.

The two connector plug that goes to the coil. About 95-97 Jeep had a TSB for coil problems, the fix included a new coil body and a short harness wire that adapted the old connector to the new coil. That wire had a built-in resistor. I'm not sure what year they incorporated that into the existing build. I got it in from Napa as part# IC409

Hmmm. I'd start with all coil-related connections, including any resister packs it may have. I don't have the schematic in front of me or I could be of more help to you. I've used an ohmeter with safety-pin probes in the past to detect internal wiring problems, but I have a feeling this is just a connector-related problem.

I switched out the ASD relay with the wiper relay, but alas, no luck. The vehicle ran fine on the way into work this morning, but coming home, I was doing about 60 mph on the local freeway, when all of a sudden it loses power and starts to cut out. I shifted into neutral and gave it some gas. It then started to run awful, shaking and vibrating, like it was running on one or two cylinders. Then it somehow righted itself as I was about to pull over, running OK again, and I made it the rest of the way home.

It didn't add any new codes. It still just has the five separate code

43's on the odometer.

I'm almost at the point of throwing in the towel and taking it to a shop for diagnosis, but I hate to start paying someone else to guess at the problem. I guess I can try wiggling the wires tonight and see if I can make anything happen. I'm running out of ideas.

DougW, question: You said if the distributor rotor moves from side to side, it's shot. By side-to-side, I assume you mean motion from the center of the rotor towards the outer diameter of the distributor (i.e., along the length of the rotor). Mine has maybe a little over a

1/16" of play in that direction. Is that a concern? Could that cause my symptoms?

Thanks for all the help.

Doug B.

Yep, radial movement. ( o )

There is another movement, axial. where you hold the rotor down and slowly rotate it clockwise/counterclockwise. It shouldn't move up and down.

Make sure your grabbing the metal shaft and not the plastic rotor.

1/16 is quite a bit. That definitly could be causing your problems as it has a great effect on timing. Is there a lot of oil in the bottom of the distributor?

It might also explain the problem when hot because the bushing is worn and oil will work its way up in there and cause arcing. The inside of a distributor should be bone dry.

might want to read here.

I wasn't having stalling but the motor did feel like it wanted to jump out of the mounts at certain RPMs. Replacing the distributor didn't fix all the problems but it did run a lot better.

Hate to say "throw more parts at it" but sometimes that's the only way. There is no real diagnostics for the spark side under load unless the shop has a rolling road. I'm still in the process of throwing parts at my 93. :) But then again if I wanted it to run like new I'd be buying new.

More times than not, decent mechanics will have seen the problem before and have a pretty good idea what is causing it. Often, if they do pin it down to couple of things, they will change something out and if the problem is something else, they will reinstall the original part and not charge you for it. Many use databases that collect information from others with the same problem, and look up the solutions in those cases for clues to your mystery. I don't have a problem paying someone to research this stuff: there's no point in reinventing the wheel.

If it makes you feel any better, think of all the money you've saved on DIY maintainance and such already; at some point, you have to give a little back when a real head-scratcher comes along. Better: think of how NICE it will be when the big-guys solve the problem and it runs like it should for a change!

Well, I thought I had the problem nailed. Last night, I started it up and decided to try the wire wiggling that someone had suggested. I wiggled the wire leading to the coil, the plug wires, the sensors on or around the distributor. Nothing happened.

Then I said "Hmm, what's this big ol' wiring harness back here?" I jiggled it around. *stumble cough sputter* The engine started to hiccup! I pushed on it again, and the engine stalled. Aha! I've found it. It turned out to be one of three wire harnesses that hook directly to the ECM. So I took out the coolant bottle and removed the little plastic cover over the ECM connectors.

The ECM itself is held to the firewall by three screws. One of mine was (and currently still is) totally missing. A second one was just kind of hanging in there not really holding it securely. When I pushed on any of the three wire harnesses, though, the engine would sputter and even die if I kept pushing on it. I could jiggle them around some more and then I'd be able to restart the engine.

So I removed the three connectors, and sprayed everything down with my handy dandy contact cleaner, replaced the connectors, and securely tightened my two remaining bolts to hold the ECM on the firewall. I started it up, and jiggled the wires, but now the engine just kept purring away. Sweet!!! I put everything back in place, did some more jiggling of the wire harnesses, but the engine kept running fine. Took her for a test drive of about five miles, and everything was great.

I took the kids to school in it this morning, then headed on in to work (about 20 miles). Ran great, no problems. Leaving work this evening, though, less than a mile down the road, bam, it stalled out again! Talk about the agony and the ecstasy!

I got out (in the rain of course) and jiggled my wires around. It didn't want to restart. Kept pushing the wires in various ways, and trying to restart, and finally got it going. I went 40 feet and stalled again. Repeat the push-jiggle-start routine a few times and it finally started up. I was then able to drive it the rest of the way home without incident.

So now what? I guess something else is either loose, shorted or otherwise electrically hosed. I guess I'll continue to try to push and jiggle more wires to try to get it to stall and locate the problem.

Should I look into replacing the wire harnesses? That looks like a nightmare as a DIY job. I couldn't even find any online sources of places to buy wire harnesses. It's probably some little short or something somewhere, but how to find it? Could it be that the ECM itself is hosed?

This GC certainly has its share of weird little electrical issues. For example, you know how the instrument lights and odometer and all will dim slightly when you turn on the headlights? Well, for as long as I've owned it (8 years) that dimming effect will sometimes happen despite the headlights not being on. About 5 or 6 months ago, the little trip computer in the overhead console just stopped responding to either the Step or US/M buttons. It's perpetually stuck on the Distance To Empty reading, which works, but I can't change it to show temperature, trip miles or anything else.

Such fun.

Doug B.

soooo close. At lest you have a better idea of what is wrong.

Might try wiggling again, but this time hold the harness still and wiggle the wires that come out of it one at a time.

Inside that massive thing are several ground spices that can corrode. I've had mine apart once already and it's a real pain in the ass even with the wiring book.

Dealership is the only place for that harness. :(

You need the service manual and the wiring diagrams for your Jeep. Then with a ohm meter and ..several days.. you can go through each wire and check.

Get some replacement wrap and tape because the stuff that's there tends to break due to age.

Yeah, I was the guy who suggested moving to the 'wiggle test' phase. Sometimes (!) you can pin it down this way.

When you mention in your message that dim lights and intermittant but persistant electrical issues are present, I can't help but think BAD GROUND. And yes, some of the wires you wiggled are ground wires.

It sounds to me like you're closing in on your gremlin. Before you go any further, double-check all ground straps, from battery to engine, battery to firewall, etc. Even if they look good, unbolt every one and clean with sandpaper, and smear some vasoline or dilectric grease on them before reassembling.

If it helps any, every mechanic I know has said that electrical gremlins are the most difficult thing they ever deal with.

Uh, stupid question:

When you say it won't 'restart', do you mean that the starter will not crank the engine over, or that it cranks, but will not fire?

Big difference!