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Author Topic: Grand Cherokee 4.0 litre - fails to start  (Read 9122 times)

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Badger

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Grand Cherokee 4.0 litre - fails to start
« on: May 05, 2008, 09:50:23 AM »

'ello 'oomans !

I'm experiencing a problem with a 1996 Jeep Grand Cherokee Ltd. It's a 4 litre, 6 cylinder petrol model which has performed superbly for 3 years but which now refuses to start. The engine will crank over very readily and petrol vapour can quickly be detected hence the fuel supply seems okay. The vehicle is dual fuel - petrol and LPG. It starts on petrol and switches over to gas automatically after a minute or so. As it normally starts on petrol I don't see that the LPG side of things can be responsible for this failure. There was no spark at the plugs so I have replaced both the distributer cap and coil but to no avail. Any other suggestions would be much appreciated...
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Tragic

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« Reply #1 on: May 05, 2008, 10:26:51 AM »

Crank sensor would be my guess, a common reason for a non-starting 4.0 Jeep :-( .
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Bubba

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« Reply #2 on: May 05, 2008, 10:38:44 AM »

yup tis very posible
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trucks


shedric
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mr whippy

I spent most of my money on alcohol, women and old  iron........ the rest of it I just wasted.

Badger

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« Reply #3 on: May 05, 2008, 10:49:17 AM »

Is there any way I can check that, or is it something only a dealer can do ?
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Bishops Finger

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« Reply #4 on: May 05, 2008, 10:49:36 AM »

Possibly O2 sensor?
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Tragic

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« Reply #5 on: May 05, 2008, 11:18:18 AM »

Quote from: "Badger"
Is there any way I can check that, or is it something only a dealer can do ?


Probably, but don't ask me how :roll: First off, check the wiring, one of mine burned through on the exhaust manifold.

They're only 2 bolts and a multiplug to change, and they're not that expensive.
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Badger

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« Reply #6 on: May 05, 2008, 11:26:04 AM »

Quote from: "Tragic"
Quote from: "Badger"
Is there any way I can check that, or is it something only a dealer can do ?

Probably, but don't ask me how :roll: First off, check the wiring, one of mine burned through on the exhaust manifold.

They're only 2 bolts and a multiplug to change, and they're not that expensive.



er, would that be the O2 sensor, or the crankcase sensor ?
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Tragic

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« Reply #7 on: May 05, 2008, 11:35:25 AM »

Quote from: "Badger"

er, would that be the O2 sensor, or the crankcase sensor ?


Crankshaft position sensor. You'll find it on the top of the bellhousing, passenger side.
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Badger

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« Reply #8 on: May 05, 2008, 12:08:13 PM »

I'll look into that. In case it turns out not to be the problem, are there any other things that could be to blame?
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Jonny Jeep

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« Reply #9 on: May 05, 2008, 10:04:37 PM »

There are two sensors that can cause no spark condition. The power to the coil is supplied via fuse 20 (20A) and the ASD (auto shut down) relay - both are in the underhood PDC. You could also have a faulty coil. Coil resistances should be 0.95-1.2 Ω for the primary and 11,300-15,300 Ω for the secondary.

One sensor, as already suggested is the crank shaft position sensor which is at the ten o'clock position on the bell housing. Check the wiring as suggested. The sensors themselves fail as well. With the sensor disconnected you could probe the wires with a multimeter to look for a change in resistance when the engine is cranked. Not sure what values you would look for for that sensor.

The other sensor is the camshaft position sensor which is within the distributer. There are three wires on that. White/black is the 5V supply, Black/light blue is the ground, Grey/black is the signal wire. Here's how to test the cam position sensor...

CAMSHAFT POSITION SENSOR
The camshaft position sensor is located in the distributor
 on all engines.
To perform a complete test of this sensor and its
circuitry, refer to the appropriate Powertrain Diagnostics
Procedures service manual. To test the sensor
only, refer to the following:
For this test, an analog (non-digital) voltmeter
is needed. Do not remove the distributor connector
from the distributor. Using small paper clips,
insert them into the backside of the distributor wire
harness connector to make contact with the terminals.
Be sure that the connector is not damaged
when inserting the paper clips. Attach voltmeter
leads to these paper clips.
(1) Connect the positive (+) voltmeter lead into the
sensor output wire. This is at done the distributor
wire harness connector. For wire identification, refer
to Group 8W, Wiring Diagrams.
(2) Connect the negative (-) voltmeter lead into the
ground wire. For wire identification, refer to Group
8W, Wiring Diagrams.
(3) Set the voltmeter to the 15 Volt DC scale.
(4) 5.2L/5.9L Engines: Remove distributor cap
from distributor (two screws). Rotate (crank) the
engine until the distributor rotor is pointed towards
the rear of vehicle. The movable pulse ring should
now be within the sensor pickup.
(5) 4.0L Engine: Remove distributor cap from
distributor (two screws). Rotate (crank) the engine
until the distributor rotor is pointed to approximately
the 11 o’clock position. The movable pulse ring
should now be within the sensor pickup.
(6) Turn ignition key to ON position. Voltmeter
should read approximately 5.0 volts.
(7) If voltage is not present, check the voltmeter
leads for a good connection.
(8) If voltage is still not present, check for voltage
at the supply wire. For wire identification, refer to
Group 8W, Wiring Diagrams.
(9) If 5 volts is not present at supply wire, check
for voltage at PCM 32-way connector (cavity A-17).
Refer to Group 8W, Wiring for location of connector/
terminal. Leave the PCM connector connected for
this test.
(10) If voltage is still not present, perform vehicle
test using the DRB scan tool.
(11) If voltage is present at cavity A-17, but not at
the supply wire:
(a) Check continuity between the supply wire.
This is checked between the distributor connector
and cavity A-17 at the PCM. If continuity is not
present, repair the harness as necessary.
(b) Check for continuity between the camshaft
position sensor output wire and cavity A-18 at the
PCM. If continuity is not present, repair the harness
as necessary.
(c) Check for continuity between the ground circuit
wire at the distributor connector and ground.
If continuity is not present, repair the harness as
necessary.
(12) While observing the voltmeter, crank the
engine with ignition switch. The voltmeter needle
should fluctuate between 0 and 5 volts while the
engine is cranking. This verifies that the camshaft
position sensor in the distributor is operating properly
and a sync pulse signal is being generated.
If sync pulse signal is not present, replacement of
the camshaft position sensor is necessary
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Badger

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« Reply #10 on: May 07, 2008, 08:51:17 PM »

Thanks for that, I'll check it out
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Badger

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« Reply #11 on: May 30, 2008, 08:38:23 PM »

Hmmm, that didn't seem to work. Oddly enough, the car started and then ran perfectly well for 16 days before failing aagin this morning. The garage is baffled: they don't know what caused it to fail / start last time, and can't find anything wrong with it this time. It passes all diagnostics checks...
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demonicwillow

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« Reply #12 on: June 01, 2008, 05:52:30 PM »

Hmmm, If you have a coil fitted not plug coil packs, wot I do on the marine v8's etc is pull the king lead off the dizzy, put it somewhere safe it can spark without igniting fuel vapour and crank the engine, see if its sparking, then I use a neon spark tester to see if there is a very weak non spark to see if the crank/cam sensors are working If all thats ok then have you checked the fuel pump and or relay, if they are sticking then that will be a pain.

Hope this helps a bit  8-)
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Badger

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« Reply #13 on: June 11, 2008, 08:36:19 PM »

I've checked the fuel system and that is fine - fuel, at high pressure, is reaching the cylinders. The garage (main dealer)  is clueless as the diagnostics utilities all check out okay,  as was the mobile auto-electrician that they recommended. "It might be the distributor mate" was his best suggestion.  I agree. It might be. I just don't fancy spending £300 to replace it and find out that it isn't. (Main dealer quote)
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Bishops Finger

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« Reply #14 on: June 11, 2008, 10:29:55 PM »

Dizzy £300?????? :shock:
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Mike Pavelin

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« Reply #15 on: June 11, 2008, 11:09:15 PM »

What is the fuel gauge reading? They used to have a habit of failing at 1/4 full and running out of petrol. A favourite for baffling AA men.
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Badger

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« Reply #16 on: June 14, 2008, 01:34:29 PM »

Quote from: "Mike Pavelin"
What is the fuel gauge reading? They used to have a habit of failing at 1/4 full and running out of petrol. A favourite for baffling AA men.


There's fuel in the tank, plenty of it.... and fuel is reaching the cylinders in vast quantities and under high pressure, as can be shown by unscrewing the pressure test point on the fuel rail. The problem is that it won't ignite...
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demonicwillow

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« Reply #17 on: June 14, 2008, 07:09:24 PM »

Have you done a spark test yet??? compression test yet??? Dump some juice straight down the throttle body and crank it!! see wot happens.
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Badger

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yes...
« Reply #18 on: June 19, 2008, 06:49:43 PM »

...a spark test was the first thing I did, and as there were none, I checked and replaced the distributor cap and coil. I still harbour a suspicion that it is one of the electronic modules or sensors but the dealer insists those check out okay on the computer diagnostic system.

As the engine is a fuel injected unit, 'dumping' fuel down the throttle isn't really an option.
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Mike Pavelin

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« Reply #19 on: June 20, 2008, 08:06:46 AM »

Are the plugs getting wet with fuel? if not it probably is a sensor problem. You will have no spark or injection without a good cam and crank signal to the PCM.
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Badger

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« Reply #20 on: June 21, 2008, 05:50:08 PM »

There's plenty of petrol at the plugs - I can smell it coming out of the exhaust as the engine cranks over.

I've got a new crank position sensor  but it's proving almost impossible to fit - there's a complete lack of access to the bell housing. Am I right in thinking that the engine needs to come out to get access ?
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Mike Pavelin

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« Reply #21 on: June 21, 2008, 06:05:53 PM »

It takes long arms and about 15 minutes.
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demonicwillow

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Re: yes...
« Reply #22 on: June 21, 2008, 06:52:48 PM »

Quote from: "Badger"
...a spark test was the first thing I did, and as there were none, I checked and replaced the distributor cap and coil. I still harbour a suspicion that it is one of the electronic modules or sensors but the dealer insists those check out okay on the computer diagnostic system.

As the engine is a fuel injected unit, 'dumping' fuel down the throttle isn't really an option.


What about the rotor arm, pull the king lead off and see if that sparks.

As I mentioned before when it happenes to me If there is no spark I use a neon spark tester as it will more than likely flash even if you couldnt get a proper spark, it will show the relavent crank/cam sensors are working.

If you got fuel the sensors are probably ok, but they can be cantankerous little mofo's :lol:
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Badger

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It's fixed...
« Reply #23 on: July 06, 2008, 11:17:28 PM »

It was acombination of two faults.

A crankcase position sensor that was sending out a weak signal - strong enough to pass diagnostics but not strong enough for the distributor, which was worn, to do anything with. Both the sensor and distributor would pass as okay on the diagnostics check, but in combination they failed to fire the engine.
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Badger

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It's fixed...
« Reply #24 on: July 06, 2008, 11:17:51 PM »

It was a combination of two faults.

A crankcase position sensor that was sending out a weak signal - strong enough to pass diagnostics but not strong enough for the distributor, which was worn, to do anything with. Both the sensor and distributor would pass as okay on the diagnostics check, but in combination they failed to fire the engine.
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