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KoopaTroopa
Need a Spot


Reged: 05/10/10
Posts: 21
Loc: canada
2000 jeep grand cherokee wont start
      #1220304 - 08/15/10 02:53 AM

I have a 2000 jeep grand cherokee laredo
it is inline 6 4.0L
it cranks and turns, sounds like alot of misfiring going on, wont start.

here is all the info I have pulled for now:
battery is good (have it charged up to 250 amp big battery charger, and more)

fuel pressure is 39psi with ignition ON, and 49psi-80psi when cranking. I also hear the fuel pump go with ignition ON, so probably good. also there is half tank of gas...when turned off, the pressure sometimes drops a psi or 2 but stays fairly steady afterwards

compression test shows 120-150psi on cylinders (I think I checked first 4)

all the fuses work (some need to be cranking, like the fuel injector fuse)

the ignition coil rail (no spark plug wires/distrib cap) works. Checked power to the rail (get 12-14v when cranking, so supposedly rail and crankshaft position sensor should be good) and also bought a new one just to be sure as I wasn't sure if it was sparking

spark plug wires are dry and black, really black (and week old)

fuel injectors get 10-13 ohms of resistance, seems to be good by what I hear

swapped around asd and tcm relay (asd for fuel injectors according to book, same thing happening)

crankcase vent valve (front one) is busted, but I wouldn't think it has any effect on starting, probably would run rougher

took off air intake/filters/air hoses, still nothing

poured a bit of gas into the throttle body, when cranks you can see a bit of fire there, but nothing

when I crank for a longer time (5 seconds) the throttle body area explodes, big poof, and one hose usually gets popped off from pressure

had 2 codes earlier when scaned, P0340 and P1391, but after deleting them 3 days ago, they havent appeared

wednesday, the car would start after 4 or 5 longer cranks (we assumed it was to get fuel pressure, were guessing fuel pump gone) and would start but would die within 10 seconds, then again after 4 or 5, and then never again (heard something blow, and it was the throttle body area mentioned). Didn't touch the car until saturday morning afterwards.

what is there left to check? could it be timing? does it use belt or chain, and would that have any impact on starting and could it be that bad off if it started earlier.
could the spark plugs be sparing too early? and dry/black, too rich, maybe there is no air? But we opened up whole throttle body and everything, took off air intakes and all, and still nothing. Could fuel filter affect even if the fuel pump seems to work and get enough pressure (hasn't been changed since bought, now has 220KM, about 135k miles). The valve, not sure whats it called but is totally broken, its like a pcv valve but its not and theres 2 of them, shouldnt affect starting I believe.

any ideas? i am really starting to be lost, I have a few ideas left, like neutral safety switch, map sensor, pcm, but there is less and less ideas as I am slowly testing everything one and twice over

edit: when cranking , or turning ignition to start, i dont hear any click of swirl sound from the injectors (should I?) as I hear them on some of my other cars

Edited by KoopaTroopa (08/15/10 03:02 AM)


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MartySoCal
Mudrunner


Reged: 05/31/09
Posts: 304
Loc: SoCal
Re: 2000 jeep grand cherokee wont start [Re: KoopaTroopa]
      #1220312 - 08/15/10 11:44 AM

Code P0340 is no cam sensor signal.

Code p1391 is intermittant loss of cam or crank sensor signal.

The cam sensor is usually OK, what fails is the oil pump drive seizes and rotates in the block, and/or the drive gear breaks. The oil pump drive/Cam sensor is where the distributor would be on the older version of the 4.0l. If the sensor drive gear is broken, the cam should be inspected, as sometimes it breaks the distributor drive gear cut in the camshaft. If you install a new oil pump drive, it has to be "synced" to align it to top dead cylinder #1.

Another very common failure is the Crankshaft position sensor. It's mounted on top of the transmission bellhousing, on the driver's side, near the engine block. It's held in with one bolt and reads a tone wheel on the transmission flexplate. If you have access to a scan tool, check for RPM while cranking.

Without both sensor signals, you will get no spark or injector pulse.

Hope this helps!


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KoopaTroopa
Need a Spot


Reged: 05/10/10
Posts: 21
Loc: canada
Re: 2000 jeep grand cherokee wont start [Re: MartySoCal]
      #1220325 - 08/15/10 01:55 PM

Hiya, thanks for the response.

I was going to reply with an update on what I have planned next, and camshaft position sensor is on the list, along with the crankshaft one, testing MAP sensor, and also neutral safety switch on the starter.

I will test all that out today, I am fairly certain it is the camshaft sensor (just a hunch).

Thanks and I will update later on in the day (hopefully).


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sunder
Wheeler


Reged: 07/23/09
Posts: 111
Loc: Saratoga Spring, NY
Re: 2000 jeep grand cherokee wont start [Re: KoopaTroopa]
      #1220332 - 08/15/10 03:32 PM

The neutral safety start would disable the starter motor, not the ignition/injection. It is there so that you don't start the jeep in gear...

I think you are on the right track with the cam position sensor. You are getting a NO/Intermittent code from the computer. Combined with the backfiring through the TB, the timing/sensor is messed up.

If Marty is right about the oil pump gear having problems you should probably pull of the distributor cap and watch the rotor turn while the engine is cranking. It would probably also help if you just try and rotate the shaft with a little force by hand (engine NOT cranking) to see if you can feel anything weird going on.

If the Cam position sensor is cheap, and you have the money, replace it.
You may also want to check to make sure that the distributor is in the correct orientation, but I'd check the simple stuff first.

--------------------
91 YJ
2 Seater Sand Rail
Handfull of other fun toys...
And a brand new, spit shined, B.S.
Oh, and a job to boot.


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KoopaTroopa
Need a Spot


Reged: 05/10/10
Posts: 21
Loc: canada
Re: 2000 jeep grand cherokee wont start [Re: sunder]
      #1220342 - 08/15/10 07:30 PM

camshaft position sensor checks out to being ok (5v from PCM with ignition ON) and oscillates 0-5v when cranking

same with crankshaft position sensor, seems to be working too (5v from PCM ignition ON, 0-5v if you rotate engine extremely slowly)

when i reconnected the TPS (throttle position sensor) it finally gave me the sound you hear when you turn on the car, so going to try giving it a start in a bit when I put everything together, just out of curiosity.

side note: there is no distributor cap, in the inline 6 i have this "bar" which has all its coils and sparkplug wires into one. closest thing here to distrib cap is the camshaft sensor


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KoopaTroopa
Need a Spot


Reged: 05/10/10
Posts: 21
Loc: canada
Re: 2000 jeep grand cherokee wont start [Re: KoopaTroopa]
      #1220364 - 08/15/10 11:30 PM

Alright, another update time.

the MAP sensor is also shot.

I tried getting a spark, connecting a sparkplug to the ignition bar to a ground and starting, no spark, so must be ignition problem.

starter, crankshaft position sensor, camshaft position sensor, battery, all work. so ASD (auto shutdown) relay or pcm?
is this a good test on the relay?
http://www.cherokeeforum.com/f2/fuel-pump-wont-turn-no-start-no-spark-27690/#post316107

i guess it is down to those 2 because i believe oil pump drive and drive gear have nothing to do with spark...

Edited by KoopaTroopa (08/15/10 11:58 PM)


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sunder
Wheeler


Reged: 07/23/09
Posts: 111
Loc: Saratoga Spring, NY
Re: 2000 jeep grand cherokee wont start [Re: KoopaTroopa]
      #1220414 - 08/16/10 08:27 PM

I'm sorry, I didn't realize that model year was running coil pack ignition (distributorless).
So there are four good reasons I can think of that will cause a no spark condition.
1. The sensors giving your computer enough input to calculate and time an ignition curve are not there or sporadic.
2. The actuator (coil packs) that makes the spark is malfunctioning.
3. The wires leading to the actuator are messed up.
4. The computer is broken, and unable to generate or process a signal.

There are a few sensors your jeep needs to get enough info to fire a spark plug.
1. Crank position sensor. This tells the computer how fast the engine is spinning.
2. Cam shaft position sensor. This tells the computer what cylinder is where so that it can time the spark/fuel.
3. MAP sensor. This tells the computer how much vacuum is in the manifold so it can calculate what load is on the engine, and ultimately how much fuel to give it.

Considering you have test the cam and crank position sensor, I wouldn’t mess with them too much more. If you think the MAP sensor is bad, test and replace as necessary...

Have you checked the coil pack? If I remember right (not too likely) there is something like 0.8 ohms from the middle right/left to the other. It should be like middle is right/left is power to the coils, then the remaining 3 are grounds the computer pulses. On the coil pack you should measure all 3 coils and get less than 1 ohm resistance on each one....


If the coil pack checks out, I’d start suspecting and internal fault in the coil pack that lets the spark jump out before it hits the plugwire/post...

Looks like a good way to test the relay, how much does a new relay cost?

--------------------
91 YJ
2 Seater Sand Rail
Handfull of other fun toys...
And a brand new, spit shined, B.S.
Oh, and a job to boot.


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KoopaTroopa
Need a Spot


Reged: 05/10/10
Posts: 21
Loc: canada
Re: 2000 jeep grand cherokee wont start [Re: sunder]
      #1220439 - 08/17/10 12:08 AM

Alright

my friend said before it happened the RPM went crazy and then just died.
I did test the crankshaft position sensor, but for 40 bucks i will buy it to replace and test out, if none then I will return it. I just have this gut feeling it is not the ecu because the gauges work and everything seems to work other than spark.

the coil packs (the bar with the 3 coil packs and sparkplug 'sockets') I bought a new one to check, and like the old one, both don't create sparks.

MAP sensor is good, and plus it affects fuel, not spark

so I have to check the wires up to the coil packs, and I will have to check the ASD relay, but I had one other relay identical to it, swapped them, and still nothing.

if nothing goes, then we are ordering a new ecu


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KoopaTroopa
Need a Spot


Reged: 05/10/10
Posts: 21
Loc: canada
Re: 2000 jeep grand cherokee wont start [Re: KoopaTroopa]
      #1220473 - 08/17/10 12:10 PM

did a little further investigation

With the key in ignition on ON
I get no voltage to the ignition coil rail from the auto shut-down relay and power distribution center.

I checked the auto shutdown relay and it checks out good.

I guess its time to check the relay to the PCM? any tips on how to do it, doesnt say in haynes.


edit: the relay shows up at 66.4 ohms, not sure if that is good enough/close enough to the 75 ohms

Edited by KoopaTroopa (08/17/10 12:14 PM)


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sunder
Wheeler


Reged: 07/23/09
Posts: 111
Loc: Saratoga Spring, NY
Re: 2000 jeep grand cherokee wont start [Re: KoopaTroopa]
      #1220512 - 08/17/10 07:34 PM

On your jeep, the tachometer is controlled by the PCM. To me, a freaking out tach indicates a bad sensor/bad connection to the computer.
This is how I am thinking.
1. The computer runs the tach and spark plugs.
2. The tach signal in the computer is generated based on the coil output.
3. The tach and coil are working intermittently, and linked.

Based on those three things, the PCM is trying to generate a signal intermittently.

This in combination of the p0340- loss of cam position sensor signal, and p1391 intermittent loss of cam or crank.

I decided to look up what would set those codes really quick and this is what I found...


P0340- Set condition- at least 5 seconds have elapsed with Crank position sensor signals present, but no Cam position sensor signal

AND

P1319 – set condition – crank or cam position sensor was intermittently lost 20 times for 2 “trips”

I think you really need to look into the Cam Position Sensor because...

1. Both of those 2 codes talk about the Cam Position Sensor. (one code is saying that that it is being lost, and the other saying its been lost for a while)
2. The Tach and ignition system is not functioning right.

A relay would cause the Coil’s to not fire, but wouldn’t really effect the tach. I don’t know the intimate details on how that particular computer is setup, but I bet that an intermittent flow of juice through a mosfett would not cause an internal sensor to register crazy RPM. I do bet that an intermittent signal from a cam sensor could be breaking and getting signal super quick causing a really weird sensor reading which would cause a really weird output (freaking out tach).

I forget, Have you check out the connector on the Cam Position Sensor?

The connector coming from the computer should have 3 wires... I don’t remember the order, but...
1 wire should have 5V reference voltage.
1 wire should have a good ground.
1 wire is feeding the computer with the signal from the cam position sensor.
To test for 5 volt reference from the computer...
1. Disconnect the connector
2. Turn the key to run
3. put my volt meter on DC volts
4. put my ground probe on the bat ground
5. test all 3 pins for DC
6. a pin should have 4.5-5V DC
To test for ground....
1. Disconnect the connector
2. Turn the key to run
3. put my volt meter on Ohms
4. put my ground probe on the bat ground
5. test all 3 pins for continuity
6. a pin should have practically no ohms << 1 ohm

If you have a good ground and good clean 5 volts reference, I think it is time to check the cam position sensor.
Unfortunately... You need a digital storage oscilloscope to check it right.

BUT as Marty pointed out they sometimes like to die at the oil pump. I know on some of the cars I worked on the if you remove the bolts holding the sensor you could actually see the chunk of metal that spun around and generated the signal. I’d try pulling the bolts that hold the sensor to the little stand off and see what is underneath. If you can see something that might rotate, crank the engine see if it spins, put your hand on it (not cranking) see if there is play...

Good Luck


--------------------
91 YJ
2 Seater Sand Rail
Handfull of other fun toys...
And a brand new, spit shined, B.S.
Oh, and a job to boot.


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