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Old 05-26-2010, 08:22 AM
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4.7 HO wan't run urgent advise needed

Hi all, A new member form Australia. My 4.7 HO has developed a bad miss. Whole story> On a recent trip I stopped for a coffee, about 30 minutes later tryed to start and it coughed and did not start, tryed again and it started but was missfiring. Took it to the dealer on the back of a truck where it has been for 6 weeks. First diagnosed as a faulty injector which was also what the codes said. replaced and no difference. Then suspected a faulty wire checked nothing found. Then decided it was a PCM, orded a new one from Germany and you guesed it did not work. Apparently the same part number as the original. What I was told is they can not get the new PCM to take the Chassis number of my vehicle. Removed the new one put in the old one and it accepted the number tryed again with the new one and no go. Does anyone have any ideas on what the problem may be or how to enter the chassis number. Dealer is stumped and is receiving no assistance from Jeep Australia. Thanks for your assistance
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Old 05-26-2010, 08:44 AM
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Re: 4.7 HO wan't run urgent advise needed

Welcome!

So is your old PCM ok? If so I'd just put it back in.
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Old 05-26-2010, 11:33 AM
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Re: 4.7 HO wan't run urgent advise needed

maybe a bad valve?? something mechanicall instead of a elecronic problem check every sensor out there isnt that many. sorry im lost on this one
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Old 05-26-2010, 12:04 PM
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Re: 4.7 HO wan't run urgent advise needed

What was the actual code, i know you said it was for an injector.

Chances are the PCM is fine.
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Old 05-26-2010, 04:24 PM
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Re: 4.7 HO wan't run urgent advise needed

It will not run with the old PCM it just has a massive miss. This happened with no warning and the it apears to be all over the engine, very erratic. I do not know what the code was the dealer read it. I was told that the injector was faulty and the pulse to it was affecting the other injectors. If the new PCM could be accepted then it would indicate if the old PCM is ok or not. Being able to put the chassis number into the PCM would eliminate it as the problem.
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Old 05-26-2010, 09:51 PM
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Re: 4.7 HO wan't run urgent advise needed

the new PCM could be no good
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Old 05-26-2010, 10:10 PM
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Re: 4.7 HO wan't run urgent advise needed

This sounds like a bad cam or crank sensor. Did they check them?
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Old 05-27-2010, 03:31 AM
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Re: 4.7 HO wan't run urgent advise needed

The dealer managed to get the new PCM to accept my chassis number and it runs, however, he says there is still a miss there somewhere. I will go over tomorrow and have a listen to see first hand whats going on. The new injector fitted was a superceded model. The original had 2 jets the new 4, so I am told, but have been assusred that it would not make any difference.
Is there a history of these engines having PCM or any other engine problems???
Thanks for the feedback and keep it coming
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Old 05-27-2010, 05:46 AM
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Re: 4.7 HO wan't run urgent advise needed

A couple of possibilities:

1. Remove the serpentine belt from the AC compressor, and try and duplicate the misfire. If the misfire is eliminated replace the AC compressor. Typical codes are P0301-P308.

2. For cylinders that are missing, check rocker arm / lash adjuster to make sure it's not out of position. If any are, replace them.
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Old 05-27-2010, 08:34 AM
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Re: 4.7 HO wan't run urgent advise needed

I will check the lifters if the head does need to come off. But I do not follow the AC belt could you explain the potential problem there.
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Old 05-27-2010, 10:23 AM
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Re: 4.7 HO wan't run urgent advise needed

Checking for a popped off cam follower could definatley cause you miss fire issues. Also run a compression test and see what you come up with. You will also be able to check you timing chain with the valve cover removed so put it on TDC of cylinder #1 and the cam sprockets should have the V8 at the top and a letter "L" and "R" on either side. That will tell you if you jumped a tooth or anything like that.
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Old 05-28-2010, 02:01 AM
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Re: 4.7 HO wan't run urgent advise needed

Quote:
Originally Posted by scout View Post
But I do not follow the AC belt could you explain the potential problem there.
This is probably unlikely in your situation, but still an issue with 4.7 HO and other engines so I thought I would list it.

The discharge reed valves in the A/C compressors are failing and causing the high side pressure to fluctuate rapidly. The compressor drive belt then has uneven loading on it and the idler pulley jumps up and down. This in turn is transmitted to the crankshaft and the crankshaft speed sensor sees an uneven crankshaft speed. The engine controller interprets this as an engine misfire. The check engine light is then turned on and a P-0300 Multiple Cylinder Misfire code is set. This condition only occurs when the A/C compressor clutch is engaged. The compressor must be replaced to repair the condition.

Here's one more scenerio:

Engine Idling, intermittent misfire, no trouble codes, spark plugs and injectors replaced.

Do a cylinder leakage test.
Listen to the throttle body, exhaust tail pipe and engine oil fill hole for air leaking from the cylinder being tested.
If air is heard at the tail pipe inspect the exhaust valves.
If are is heard at the throttle body inspect the intake valves.
If air is heard at the engine oil fill hole inspect the piston rings.

The valves must be closed in the cylinder being tested. Before charging the cylinder with compressed air, place the cylinder being tested at compression TDC or remove the rocker arms for the cylinder being tested.
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