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It did it again! &^$#)(*&&%^&(*


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Drove a load of grass clippings to the transfer station, about two miles. Fine. Drove another two miles to the post office. Fine Drove around the block on the way to Mickey D's for lunch, and it died in the middle of the street just as I got to a light. And would not restart.

 

This time I was (somewhat) prepared, with a jumper wire. I jumpered the fuel pump ballast resistor ... and it still wouldn't start. The middle of a busy intersection is not the place to be trouble-shooting, so I called AAA and had it hauled home. This is becoming a nuisance. I have to get this truck reliable again. Who has any suggestions? If it isn't the fuel pump resistor, could it be the fuel pump itself?

 

1988 4.0L, 5-speed.

 

The CPS is brand new, and has the bypass harness installed. Amd the truck runs perfectly when it runs -- right up to a brief stumble, and then it dies.

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How long does it have to sit before it'll start on it's own? does it have to totally cool down or just a little while?

 

Have you checked the fuel rail pressure? Could thier be a momentary blockage in the fuel filter or tank?

 

Mine did the same thing..the PO indicated it happened when the engine got hot, and he felt it was a resistor or electrical problem. Naturally he had bunged up the wiring under the hood so it's really hard to tell if that is the case. Given evidence of fuel, I wonder if it could be the camshaft position sensor in the distributor. See this link...

 

http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm

 

Then again, it might be the ECM itself puking out bad info when it gets hot. I have a couple of spares if you need one.

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If it re-starts after a while, after it cools down, and you mentioned the stumble before it quit, I would think the fuel pump.

 

If your doing alot of driving (not from your story) I would guest the ignition module. Getting hot and shutting down.

 

on the way to Mickey D's for lunch, and it died in the middle of the street

 

Or.........Your MJ don't like Micky D's :teehee:

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This has happened three times, each time after driving on local roads for about 4 miles (maybe 10 minutes). The first time it restarted after about 45 minutes and drove home. The second time it restarted after 30 minutes and drive home. I didn't have time to waste today, so I had it towed. Funny thing is, I've made the same run twice with no problem between episide #2 and today.

 

CPS and harness are brand new. Possibly defective, but highly unlikely.

 

I was thinking fuel pump relay, too. Anybody remember which one of the four is fuel pump? Or have a link to that picture that shows them and IDs them?

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Auto shutoff relay? I can't remember if the Renix ones have it. I know with this frikin XJ sitting here, after I swapped yet another pump into it, it wouldn't prime, wouldn't prime, then on a whim swapped the autoshutoff relay an it would prime again.

 

Just an idea.

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Eagle - according to the FSM, the relays are (in order from firewall to front of vehicle);

 

Fuel Pump Relay

Oxygen Sensor Heater Relay

B+ Latch Relay

A/C Clutch Relay

 

Page/Section 14-34

 

EDIT: (and I quote from the FSM 14-71)

 

"...During engine start and wide open throttle conditions the fuel pump relay and the fuel pump ballast resistor are bypassed. During startup, battery voltage is supplied to the fuel pump through the starter relay, and during wide open throttle conditions battery voltage is supplied to the fuel pump through the oxygen sensor heater relay."

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Ahhh.. you almost have to read all this crapin the FSM. I love RENIX! :redX:

 

Section 14-71

 

Evidently the O2 sensor relay is normally closed upon start-up, which supplies voltage to the O2 sensor during warm up and initial idle conditions. The MAP sensor and the speed sensor tell the ECU that a pre-determined output has been reached (what pre-determinied output they don't say :hmm: ) the ECU opens the relay (through interruption of its grounding path) and stops the voltage.

 

It doesn't say what causes the ECU to determine an wide open throttle condition is occurring and what triggers the ECU to close the O2 sensor relay again to provide the fuel pump voltage.

 

What I'm getting at here is you might want to consider replacing both the relays, and/or look at the O2 sensor heater (which is the O2 sensor), and/or the MAP sensor, and/or the speed sensor.

 

You say it died when you were approaching the light. Were you accellerating to go through the (green) light when it died?

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I was having the same problem with my mj a couple years back. It turned out to be the fuel pressure regulator on the fuel rail. It would start fine and run great for like 10-20 minutes then studder a little bit lose power and die. I would let it sit for like an hour or two and it would start back up again. Good luck :wrench:

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If it were one of my GM's, I'd guess ignition module. That's where I'd start.

 

Where did you get the CPS bypass harness, Eagle??

 

I think you get them thru the dealer.

 

Originally posted by TAZ:

 

The Patch Kit (part #4443965) shows to be used through 1990. There are still plenty available with a retail price at $65 - $70 depending on dealership used.

 

I would contact TAZ if you want one.

 

here's the TSB with how to instructions:

 

http://www.greatlakesxj.com/tech/cps.pdf

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The fuel pressure regulator is mounted to the output end of the fuel rail, and is a vacuum assisted non-adjustable type. The vacuum source comes from the intake manifold, and the regulator is calibrated to maintain fuel system pressure at about 214 kPa (31 psi) with vacuum applied and the engine at idle. With vacuum disconnected the fuel pressure will be about 55-69 kPa (8-10 psi) higher. The regulator contains a calibrated spring, a diaphragm, and a fuel return valve. Fuel system pressure provided by the fuel pump exists on one side of the regulator, while spring pressure and manifold vacuum are present on the other side. Spring pressure on one side of the diaphragm forces the fuel return valve closed, and fuel pressure, with vacuum assistance forces the return valve open. Fuel system pressure is the amount of fuel pressure with vacuum assistance required to open the fuel return valve, against spring pressure. By using vacuum assistance it is possible to vary the fuel system pressure based upon varying engine conditions, such as wide open throttle, low vacuum, which will cause an increase in fuel pressure at the time it is most needed. At high vacuum conditions, such as idle and deceleration, fuel system pressure will decrease, when there is no need for extra fuel.

 

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If it were one of my GM's, I'd guess ignition module. That's where I'd start.

 

Where did you get the CPS bypass harness, Eagle??

 

I think you get them thru the dealer.

 

Originally posted by TAZ:

 

The Patch Kit (part #4443965) shows to be used through 1990. There are still plenty available with a retail price at $65 - $70 depending on dealership used.

 

I would contact TAZ if you want one.

 

here's the TSB with how to instructions:

 

http://www.greatlakesxj.com/tech/cps.pdf

 

Not trying to hijack this thread, but the TSB is for 4.0L trucks. Is there the same problem with the 2.5?

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If it were one of my GM's, I'd guess ignition module. That's where I'd start.

 

Where did you get the CPS bypass harness, Eagle??

 

I think you get them thru the dealer.

 

Originally posted by TAZ:

 

The Patch Kit (part #4443965) shows to be used through 1990. There are still plenty available with a retail price at $65 - $70 depending on dealership used.

 

I would contact TAZ if you want one.

 

here's the TSB with how to instructions:

 

http://www.greatlakesxj.com/tech/cps.pdf

 

Not trying to hijack this thread, but the TSB is for 4.0L trucks. Is there the same problem with the 2.5?

 

Good question. I'm not sure.

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Not trying to hijack this thread, but the TSB is for 4.0L trucks. Is there the same problem with the 2.5?

Probably. I have an '88 MJ 4-banger and it also has the C101 connector, so I would expect that the CPS (being the exact same part as used in the 4.0L) suffers the same signal loss and would benefit equally from being wired directly to the ECU.

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relays for 4.0

 

Went out when I got home from work and tried starting the MJ. As always -- started right up. But ... get this -

 

ALL those diagrams of which relay is which are either wrong, or my MJ is wrong. Having found two conflicting diagrams and descriptions, I took the cowards way out and pulled all four relays, then stuck them back one-by-one until I heard the fuel pump run when I first turned the key. The one that got the fuel pump running was the one all the way to the front.

 

I'll have to do the same thing on the '88 XJ in the morning, after it has had time to bleed off the pressure.

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relays for 4.0

 

Went out when I got home from work and tried starting the MJ. As always -- started right up. But ... get this -

 

ALL those diagrams of which relay is which are either wrong, or my MJ is wrong. Having found two conflicting diagrams and descriptions, I took the cowards way out and pulled all four relays, then stuck them back one-by-one until I heard the fuel pump run when I first turned the key. The one that got the fuel pump running was the one all the way to the front.

 

I'll have to do the same thing on the '88 XJ in the morning, after it has had time to bleed off the pressure.

 

That's strange. Mine was where the diagram shows. The only differnce is mine is an auto.

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relays for 4.0

 

Went out when I got home from work and tried starting the MJ. As always -- started right up. But ... get this -

 

ALL those diagrams of which relay is which are either wrong, or my MJ is wrong. Having found two conflicting diagrams and descriptions, I took the cowards way out and pulled all four relays, then stuck them back one-by-one until I heard the fuel pump run when I first turned the key. The one that got the fuel pump running was the one all the way to the front.

 

I'll have to do the same thing on the '88 XJ in the morning, after it has had time to bleed off the pressure.

 

That's strange. Mine was where the diagram shows. The only differnce is mine is an auto.

 

Chico - funny, mine are in the order I described, which are different then yours and Eagles...

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