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Old 02-08-2014, 08:38 AM   #1
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4.0 Timing: Firing on exhaust stroke?

I recently put a new reman 4.0 in my 2000. After some fighting and treating all the issues we came across, she finally fired up and purred beautifully. There was only one problem; my check engine light is one and sometimes she fights me cranking over. It'll turn over just fine, but it won't catch and fire up. However, if i turn the key off and back on she fires up almost immediately.

I took it to a garage just to have them check it over and make sure everything is kosher after the swap. He let me know that the cam position sensor and the crank position sensor are out of sync, and that's the reason for my trouble cranking over. He mentioned that when we set the time, we must of have cylinder 1 on a exhaust stroke instead of a compression stroke.

This is the part that confuses us, as we don't understand how the engine isn't backfiring and how it's even starting at all if cylinder 1 is on an exhaust stroke when it's plug sparks.

Can anyone put sense to this? We're going to re-time it today and see if that fixes it.

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Old 02-09-2014, 12:44 AM   #2
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What is the actual code you are getting?

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Old 02-09-2014, 02:38 AM   #3
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I havent looked up the exact procedure for it but your going to need a scan tool unless you get lucky when you stab the oil pump shaft in, ive been able to do it before. But the scanner makes it alot easier. Your not on the exhast stoke the engine would not run the oil pump shaft just isnt lined up right. Think of it like a distributor and your trying to time it. The computer will take up for it being off a bit a few degrees or so. Search how to sync the cam sensor.
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Old 02-09-2014, 08:07 AM   #4
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The ignition system changed in the 2005 and 2006 model years, and in those years, the camshaft synchronizer does fire the cylinder on compression and exhaust strokes. My understanding is that was a change to the ignition system in 2005, so I don't believe the earleir years fired on both compression and exhaust strokes. The camshaft position sensor looks different in 2005 and 2006 from previous years. This is what it looks like in the 2005 and 2006 model years:
Dorman Products - 689-201

... and this is what they look like from 2000-2004:

Dorman Products - Search Results
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Old 02-09-2014, 08:17 AM   #5
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Quote:
Originally Posted by ieatglue View Post
I havent looked up the exact procedure for it but your going to need a scan tool unless you get lucky when you stab the oil pump shaft in, ive been able to do it before. But the scanner makes it alot easier. Your not on the exhast stoke the engine would not run the oil pump shaft just isnt lined up right. Think of it like a distributor and your trying to time it. The computer will take up for it being off a bit a few degrees or so. Search how to sync the cam sensor.
The oil pump drive gear is not timed at all and you can always rotate it with a screw driver to line it up to where it needs to be in order to sync the cam timing. I can't say what the procedure is for a 2000-2004, but it may be similar to the 2005-2006 procedure that you can find in the link below. If you are not sure if your engine is at top dead center, most instructions have you remove the number 1 plug and cover the hole with your finger to feel for compression as your helper rotates the crankshaft until the alignment marks line up on the crank pulley:

https://docs.google.com/file/d/0B-kG...=sharing&pli=1
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Old 02-09-2014, 08:20 AM   #6
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No guys as soon as they went to a coil PAC in 2000 or so the 4.0 always twin fires the cylinders so it always fires 1 and 4 with one on compression the other on exhaust same with cylinders 2 and 5 and same with cylinders 3 and 4. The spark is timed exclusively by crank angle sensor timed off flywheel with no indication wether it is approaching top dead center on compression or exhaust just the CRANK position

The cam angle sensor which turns 1/2 the rpm of the crank is used to control timing of fuel injector pulses and here exhaust vs compression stroke makes a difference
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Old 02-09-2014, 08:21 AM   #7
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No guys as soon as they went to a coil PAC in 2000 or so the 4.0 always twin fires the cylinders so it always fires 1 and 6 with one on compression the other on exhaust same with cylinders 2 and 5 and same with cylinders 3 and 4. The spark is timed exclusively by crank angle sensor timed off flywheel with no indication wether it is approaching top dead center on compression or exhaust just the CRANK position

The cam angle sensor which turns 1/2 the rpm of the crank is used to control timing of fuel injector pulses and here exhaust vs compression stroke makes a difference
Edit pairs are 1 and 6
2 and 5
3 and4
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Old 02-09-2014, 08:22 AM   #8
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Edit pairs are 1 and 6

2 and 5

3 and 4
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Old 02-09-2014, 08:23 AM   #9
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We fixed it with re-timing it, apparently the mechanic was right. When we were timing it, we took the cam position sensor cap off. We noticed when it was on the exhaust stroke. The little metal half-moon piece was almost at the timing spot. We cranked the engine to the next time cylinder was at TDC, and the sensor was 180 degrees off. We switched it around to the proper timing spot, and she fired up perfectly 3 times in a row and every time since then. Engine light is off. It still baffles us how the engine managed to fire up no problem when the timing was 180 off.
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Old 02-09-2014, 08:47 AM   #10
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The spark tinging remains unchanged what was completely out of sync was the injector timing

Of course it ran the intake valve still controlled when the air fuel entered but the 180 out injector timing decreased efficiency as fuel sat and was less atomized as it was loosing the sequential fire benefits and running like batch fire
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Old 02-09-2014, 08:53 AM   #11
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Thanks Digger. That is very helpful and makes sense. Do you know what changed then in the 2005 model year that caused the redesign of the OPDA? I read that it had something to do with a change to the ignition pairing of the cylinders. I've recently been doing a little reading on forums on this topic as I'm getting ready to change my OPDA out because of the bearing issue in the later model years.
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Old 02-09-2014, 01:23 PM   #12
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Quote:
Originally Posted by Digger84 View Post
The spark tinging remains unchanged what was completely out of sync was the injector timing

Of course it ran the intake valve still controlled when the air fuel entered but the 180 out injector timing decreased efficiency as fuel sat and was less atomized as it was loosing the sequential fire benefits and running like batch fire
Thanks! That's extremely helpful and explains why she still ran like a dream even though timed wrong. I also had an additional problem; I was at the gas station and started the jeep. When I was pulling out, I noticed my jeep had next to no power and was spitting and sputtering. I pulled off the side of the road, turn it off, and back on. It was fine after that. And has been ever since I reset the timing.
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Old 02-10-2014, 06:54 AM   #13
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If you have an engine with a coil pack instead of a distributor, it likely fires on every revolution. I was not aware of multiple systems put in place for timing at the 04/05 break, but i can confirm that my '04 fires on the off-stroke. Being 180° off on ignition timing would still spark when needed.
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Old 02-10-2014, 12:33 PM   #14
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Quote:
Originally Posted by C.L. View Post
If you have an engine with a coil pack instead of a distributor, it likely fires on every revolution. I was not aware of multiple systems put in place for timing at the 04/05 break, but i can confirm that my '04 fires on the off-stroke. Being 180° off on ignition timing would still spark when needed.
Yup, mine has a coil pack. Mine must fire on the off-stroke as well.

For reference, the codes that came back were 1391, lost of cam/crank and code 1281. Codes come back immediately.

That's exactly what it says on my paperwork. Thanks for the info all!

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