Bucking, skipping, popping Ram...

Vehicle - 2001 Ram 2500, Standard cab 5.9 Magnum, Automatic trans 70K
Problem - Engine starts and runs OK. Take it for a test drive and once it warms up
it will act like the timing goes WAY off and it runs out of fuel. You can hear it backfiring through the exhaust, engines dies down for a couple seconds then it will catch and act like you have the throttle floored for a second, then it does it a couple more times. After about 10-30 seconds (depends on ambient temperature) it will suddenly run fine. It won't do it again until you shut it down and let it set for a few minutes (like filling the tank).
NO current or pending codes. Watching the life data showed nothing while it was bucking EXCEPT the timing looked to be dancing a lot.
Once it settled down the timing followed suit.
It has new plugs, wires and cap&rotor, also a new fuel pump (old one failed).
Will be throwing the scope on it to see what the ignition is doing. I'm leaning toward a faulty coil.
Ideas?
--
Steve W.


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Was it acting this way before the parts were changed out? Does the rotor have a resistor in it - if so, put the old one back in and see if that solves the problem. John

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John Selph wrote:

Yes. It was acting up and the owner changed out the plugs and such. The fuel pump was changed out when he bought it (died on the lot!)
I'll have to see if he has the old parts. The current rotor doesn't have a resistor that I can see.

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The only other things I can think that may cause something like that would be the computer getting faulty input. How is the O2 sensor? Oh, and also, check all ground connections. John

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John Selph wrote:

O2 reads good. So does the post cat sensor. Also did a back pressure test and found nothing wrong there.
I started going through all the connections today. FUN... I figure I'll bench test all the sensors as I come to them.
Since it's a minimal pay job (FIL owns the truck) I just work on it in spare time. It is one of the times I wish I had a full parts room in the back...
--
Steve W.

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Just because you put a fuel pump on it means nothing, especially if it was an after market one. What is the fuel pressure reading???
Glenn Beasley Chrysler Tech
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maxpower wrote:

50 psi. Holds that while running and is delivering almost 1/2 liter in 10 seconds.
I pulled and cleaned the injectors and checked the spray patterns. Also flushed the rail and the tank line.
--
Steve W.

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up
while
was
Cam and crank in sync?

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maxpower wrote:

Yep. I am wondering if it isn't related to the P1606 buss failure code. Except an intermittent failure that isn't setting a code. I would expect that to show up on a data capture but don't see it. Scope showed good spark sync and it didn't drop out.
--
Steve W.

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Did you ever find out what was causing the problems? John

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John Selph wrote:

Went through every connection on it, along with a bunch of cleaning and testing. Flushed the fuel system and cleaned the injectors. I also reflashed the PCM. It seems to be OK now, but I don't trust it yet.
Steve W.
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