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Help!!!! 4.7L HO problem!

 
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cmoodie
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Joined: 01 May 2011
Posts: 1

188.56 points



PostPosted: Sun May 01, 2011 2:21 pm    Post subject: Help!!!! 4.7L HO problem! Reply with quote

I had a 2002 4.7L HO rebuilt and cant get it to run due to a problem that nobody seems to know how to fix or where to start. Here's what happens. Start the truck and it runs good for about a minute or so. As soon as the ECU looks at the o2 sensor it begins to run rough and backfires like its lean. The codes say it's and intermittent crank/cam sensor. both sensors have been replaced. The wheel on the the cam has been replaced. The tone wheel on the crank has been checked. The complete wire harness has been replaced. ECU has been traded for a used known working ECU. The crank was turned and straightened. It's almost like the crank is twisted or something although nobody has ever seen that happen. I have $4000 plus in building the motor and don't even know what to try at this point. Can anybody help???
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clay
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Joined: 24 Nov 2002
Posts: 3209
Location: South Carolina
318129.23 points


1972 Chevrolet Nova

PostPosted: Sun May 01, 2011 6:53 pm    Post subject: Reply with quote

There are several people on here better at this than I am and I'm sure they'll be along in a while, but I'll share my train of thought. To me the engine has to have the crank sensor period or it won't run - open or closed loop. It is one of the few sensors that can keep an engine from running at all. When it goes closed loop your problem starts so has the oxygen sensor been replaced? I had a very intermittent problem on a 95 Dodge truck similar to what you are describing. It would run fine and while you were cruising down the road, it would lose power, start missing and you would have to pull over. It would surge along barely running for a minute or so then it would all of a sudden smooth out and be perfectly fine for a month - maybe 2 or three - drive me crazy. When it starts to run badly in closed loop, if you have a scan tool or access to one, look at the rest of the engine data and make sure it makes sense - coolant temp, inlet air temp, make sure rpm isn't jumping around, etc. I have also seen a sensor that would short out at temp and cause havoc. Clay
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I have done so much with so little for so long, I can now do anything with nothing.
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af2
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Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Sun May 01, 2011 7:54 pm    Post subject: Reply with quote

Sure is a lot of closed loop problems lately.

I had my Dodge van with a shorted pre cat O2 that gave me fits.
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10sec.et
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Joined: 29 Mar 2006
Posts: 3473
Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Sun May 01, 2011 10:50 pm    Post subject: Reply with quote

you will need a scan tool to watch live data if you hope to get anywhere with your diagnostics. could be as simple as leaking intake manifold gaskets. they will cause the exact same symptom you describe. problem with diagnosing them is that the ECM is faster than the human ear. you can spray carb cleaner to check for vac leaks but you will never hear a difference like you could on an old carbed Chevy. you have to be watching short term fuel trim. do you know what short term and long term fuel trims actually are when the engine is running ?
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It seems we can look at our magical Balls and come up with a fix?

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