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Unread 11-03-2005, 05:26 PM   #1
-Joe-
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1995 ZJ 
 
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Starting problem

Ok, first the fuel pump went. Replaced that and now having a start up problem.

Turn the key and it just cranks and cranks, turn it back off then on and it starts. Sometimes it will crank a bit then start fine on the first try. It used to not even hesitate to start.

What should I look into? (I6 4.0)

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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
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Unread 11-03-2005, 05:33 PM   #2
Woody
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Just for verification purposes, you have swapped the fuel pump relay with another one and the same with the ASD relay, right?

I almost sent you the test for the fuel pressure regulator, but that's part of the Fuel Pump assembly in the 95's. If you replaced the pump in the cannister, you aren't going to like this, but you may need a new cannister. I don't know if you can get the regulator seperate to install in your cannister. The Swampy bypass would've eliminated this problem.

Sorry Joe.
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Unread 11-03-2005, 05:36 PM   #3
Woody
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I just looked and there is no part # referance for the regulator on the 95-96's. The 97-98's used one that mounts on top of the cannister that is able to be changed seperately, and the 93-94's have one on the fuel rail.

You can kick me in frustration if it will help.
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Unread 11-03-2005, 05:54 PM   #4
-Joe-
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Yes new relay actually, didnt help. I didnt swap it with the shut down relay i may try that.

Its part of the evap cannister behind the bumper on the drivers side. I already considered this, but didnt really think too much into it.

When it does start its as smooth as ever, just hesitates on starting
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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
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Unread 11-03-2005, 06:08 PM   #5
CajunWon
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Do I recall correctly that you purchased a fuel pressure guage?
Slap it on there to see if you're losing pressure after shut-down. I hear a new Mopar gasket is needed and sold separately when installing a new fuel pump assembly.

& catch us up of what you replaced, was it the whole fuel pump assembly, just the pump module within the assembly, or the external MSD pump?
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Unread 11-03-2005, 06:14 PM   #6
-Joe-
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I replaced just the pump motor, and re-used the old gasket.


When running the pressure is steady at around 40 psi.

If i just turn the key 2 clicks it goes up to about 10 psi then drops back off.
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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
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Unread 11-03-2005, 08:25 PM   #7
-Joe-
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Well unless someone pops up with a possible fix, im going to see about replacing the fuel pump gasket and change out the fuel vapor canister (Canister is only $31 at advance)
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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
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Unread 11-03-2005, 08:56 PM   #8
Woody
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Where did the fuel vapor cannister come in? I said fuel pressure regulator which is part of the fuel pump cannister, per the Haynes manual.
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Unread 11-03-2005, 10:46 PM   #9
-Joe-
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Sorry loosing it in my old age. For some reason I was thinking the canister might be a problem have so many miles on it.

I dont recall seeing anything in the fuel pump module that could be a regulator.

That would suck even doing the swampy bypass if the regulator goes bad, guess i could bypass it and make it external as well.
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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
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Unread 11-03-2005, 11:05 PM   #10
Woody
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If you had done the swampy bypass, the pump then provides pressure without the assistance of the factory regulator. The regulator will only regulate what's being pushed through it, if it's pulled through (Swampy's) then it will not be able to affect the pressure, as there is none going into it.

Do you have a Haynes? It'll tell you more about it in there.
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Unread 11-04-2005, 06:25 AM   #11
greasefingers
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Quote:
Originally Posted by joe.ls
I replaced just the pump motor, and re-used the old gasket.


When running the pressure is steady at around 40 psi.

If i just turn the key 2 clicks it goes up to about 10 psi then drops back off.
This is now I think the system functions:
When you turn the key to the On position, the fuel pump is fully energized and running and you should see 40 psi at the rail. The engine does not have to be started to see this pressure. Now if you do not start the engine soon, I believe the ADS relay gets timed-out by the PCM and then you will see a drop-off in pressure, but it should not drop off to 10 psi for several minutes.

The condition of the fuel pump gasket does not matter. It is more for sealing the tank so that vapors do not escape to the atmosphere and to allow the charcoal canister to absorb any of these gases in the head-space.
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94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 11-04-2005, 08:48 AM   #12
CajunWon
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NOt the mechanic here, but following the logic:

Sounds like it runs fine after starting?

So starting is the only issue?
"it should not drop off to 10 psi for several minutes. " Tells me the check-valve is not functioning, AFAIK it is located within the fuel pump canister. BMW has a $5 in-line check-valve others (Jeeps) have used to retain pressure after shut-down.

I have a '95 I6 motor and the fuel pressure regulator is located on the fuel rail near #1 cylinder, yours may be different. I don't know how it works but it's suppose to maintain pressure by returning excess fuel back to the tank. I'd say it's working fine if the motor runs well after it's started.

Which in-tank fuel pump module did you buy? $$? As I know mine will need replacing soon. thx
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Unread 11-04-2005, 10:10 AM   #13
Woody
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Just wanted to show you guys that I'm not smoking crack. Won, if your pressure regulator is on the rail like this picture, then the Haynes is wrong. (Won't be the first time)

Here's where I got the part about where the 95-96's regulator is at.


I did a SEARCH for lengthy starts and when I searched back awhile I ran into this.
Searched Text

This guy had similar issues and it was his ECM. I started thinking about what was going on Joe and it makes sense. The regulator would make a difference if you were not getting enough pressure, but it would be a fairly constant problem. If it's just hard to start the ECM might not be sending the signals it needs to right away.

Grease, before you say the ECM has no effect on the fuel pump, you posted in the above link I put up. The ECM still directs a lot of things on our GC's and is probably something to look into.

The next most common item that people posted was the gasket around the fuel pump cannister.

I knew there was more info, just needed to do some more searching.
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Unread 11-04-2005, 12:53 PM   #14
-Joe-
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I also found this on what all happens on startup


Ignition Switch On:

This is an OPEN LOOP mode. When the SFI system is ACTIVATED by the ignition switch, the following actions occur:

* The PCM prepositions the idle air control (IAC) motor.
* The PCM reads atmospheric air pressure from the manifold absolute pressure (MAP) sensor and calculates the basic fuel strategy.
* The PCM monitors the throttle position sensor (TPS) and engine coolant temperature (ECT) sensor input. The PCM uses these inputs to modify fuel strategy.
* Intake air temperature (IAT) sensor is monitored.
* ASD relay is energized for 3 seconds.
* Fuel pump is energized for 1 second, unless engine is running or cranking.
* Oxygen sensor heating element is energized.

Engine Start-Up:

This is an OPEN LOOP mode. When the starter motor is engaged, the PCM receives input from:

* Battery voltage
* Crankshaft position (CKP) sensor
* Engine coolant temperature (ECT) sensor
* Intake air temperature (IAT) sensor
* Throttle position sensor (TPS)
* Camshaft position (CMP) sensor
* Starter relay

Based on these inputs the PCM will:

* Monitor crankshaft position sensor. If no signal is received within 3 seconds, the PCM will shut down the fuel injection system.
* Supply the injectors with a ground path, firing all injectors until the PCM determines crankshaft position.
* Determine proper ignition timing.
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- Joe -

'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
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Unread 11-04-2005, 12:57 PM   #15
greasefingers
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When your key is in the run position, juice is supplied to the ASD & fuel pump relay. The PCM grounds the circuit at pin51. If there is no feedback, battery, to the PCM on pin 57, then the PCM provides an Open instead of a ground. This kicks out the power to the ASD relay, fuel pump relay, injectors, and the ignition coil.

Also if there is no Distributor, Crank or Camshaft signals being sensed at the PCM, it will also shut the ASD relay down, however this is NOT evident by looking at the electrical schematic of the fuel injection system. (chapter 4 page 5 of my Haynes Manual)

The PCM does not ever know if the fuel pump is working. It only supplies the juice to the ASD relay which then in turn supplies battery to the fuel pump relay. There is no feedback signal from the fuel pump motor to the PCM.
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94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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