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Old 09-16-2021, 04:31 PM   #1
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I need to tap the diagnostic hive here

OK... for all interested in helping a brother figure out the next step here grab a beverage – this may take a minute.

I bought a 2000 Chevy Express 3500 454 V8 SMB High Top from a good friend who had had enough of trying to resolve an intermittent running issue. The van has 100,000 miles on it. She bought it from a rancher (2nd owner) who had used it then stored it in a barn and not driven it for a couple years. We drove our van out to Montana to pick it up... in case we had to end up renting a trailer and towing it some of the 700 miles home. I had arranged for it to be taken to a well regarded GM shop in Great Falls (Fritz's Automotive) before hand. They put 100 miles on it and never experienced the issue so we caravaned back to the Gorge with our fingers crossed. 90% of the trip the van ran flawlessly - quiet, smooth and powerful. I started noticing that the engine would occasionally miss (actually felt like the key had been turned off for a micro second rather than a cylinder missing) when I hit a bump – road bridge transition, pothole, rough patch. It might just do it once or it might run rough for a bit before smoothing out again. Stopped for food in Spokane and drove over a couple speed bumps in a parking lot and it ran terrible for the next 15 miles before finally smoothing out. Finally threw a code indicating MAF sensor on the way up the driveway to our house. It never blew any smoke that I noticed. The fuel gauge would intermittently go haywire and bounce around but I was not able to connect the original problem to when that happened.

Here is its service history for this problem:

4/16 – MAP and MAF sensors replaced
5/12 – Fuel Pressure Regulator and Crankshaft sensors replaced
5/28 - 2 Oxygen sensors replaced
6/7 – all new plugs, wires, cap and rotor
6/10 – ECU replaced – after this repair it ran great for 200 miles
8/24 – Fuel filter replaced and top of ECM harness shake tested
9/14 – repair hinky fuel pump harness (had been crushed between tank and
frame), replace fuel pump and clean MAF sensor

Only the last repair tech actually witnessed the symptom... everyone else was just throwing parts at it to clear codes.

Picked rig up yesterday after fuel pump install. Ran great the 7 miles home but started acting up when I took it out later in the day. This time I could not connect the problem to any specific bumps... just did it periodically seeming like after it warmed up some. I just drove it again around town with no problem then got out on the hiway and the symptoms returned. I guess at least if it gets worse it will be easier to diagnose. I've budgeted for repairing this, knowing it could take a bit, but it would be great to have it resolved as it's an amazing, powerful, well kept rig in excellent shape (when it's running right) that someone should be out enjoying.

Any input appreciated. Also any recommendations for a shop that might have expertise in something like this out near Portland/Vancouver.

Thanks
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Old 09-16-2021, 04:50 PM   #2
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These intermittent problems…. Sounds like primarily chasing fuel problems. Maybe electric. Few thoughts, but nothing specific.

Wonder if a wonky ground could be involved.

Intermittent injector issue?

Voltage regulator problem?
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Old 09-16-2021, 05:15 PM   #3
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I solicited help here for almost the exact same symptoms (but for a 6.0 diesel). Although my engine actually cut off occasionally while all the electrical components still functioned. Very frustrating. Lot of great advise, but in the end the gremlin turned out to be a engine harness wire which was barely making contact with the exhaust manifold (heat burned a small wedge off the sleeve of the wire and suspect the exposed wire either barely touched the manifold or when it got real close it arched just enough to cause the disruption).
The fact that it had been stored in a barn for years brings up the possibility of rodent damage to a wire...somewhere.
Hope its something that rears its ugly head sooner than later - can be very frustrating!
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Old 09-16-2021, 10:53 PM   #4
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Sounds like an electrical rabbit trail chase....bummer but you’re right if you can find the problem and get it fixed the 454 is a great motor.
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Old 09-17-2021, 10:13 AM   #5
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I can't be of any specific help but your odyssey definitely smacks of a wiring issue, the biggest possibility that comes immediately to mind is one of the wiring harnesses has contacted a ground source it was meant to be isolated from.

I would painstakingly inspect every inch of every wiring harness looking for an area that's typically already close to metal and/or a hot surface. One of my friends with a 2003 Chevy van recently had an issue with his transmission not allowing the van to start---it turned out to be a single wire inside a harness leading back to the PCM had contacted an exhaust pipe. Once it was temporarily moved away all was back to normal.

These things are frustrating and test the patience of mechanics and diagnosticians. I don't know that there are any diagnostic computers capable of detecting an errant voltage due a short circuit.

In the end I'm sure this will be a quick and relatively cheap repair---the key being finding or identifying it first.

Be persistent and hang in there---hoping for a good outcome!
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Old 09-17-2021, 10:18 AM   #6
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Check all of your grounds. Battery ground cable, all the chassis to body grounds, engine to chassis. Funny things happen on vehicles when there are insufficient grounds.
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Old 09-17-2021, 11:09 AM   #7
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"I started noticing that the engine would occasionally miss (actually felt like the key had been turned off for a micro second rather than a cylinder missing) when I hit a bump – road bridge transition, pothole, rough patch."

Definitely sounds like a bad ground or sporadic loose connection.
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Old 09-17-2021, 01:17 PM   #8
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If that rig sat in a barn for a while maybe a rodent took a bite of a wire.
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Old 09-17-2021, 06:23 PM   #9
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Sounds to me there is some large debris in the fuel tank. When the van gets banged around a bit it creates some stuff which starts floating in the tank and blocks your pickup tube. I had the same issue with a 74 Bronco I use to own.
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Old 09-17-2021, 08:22 PM   #10
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"Sounds to me there is some large debris in the fuel tank. When the van gets banged around a bit it creates some stuff which starts floating in the tank and blocks your pickup tube. I had the same issue with a 74 Bronco I use to own."

I presume the 454 is a Fuel injection system motor and they don't pass stones like a carb motor. Once it gets in there it's rarely clear after that. For it to happen repeatedly and keep cleaning out seems unlikely. If it was a Ford van of that era it could much more possible, as they had a fuel tank liner coating de-laminating problem. Most had that problem said their vans ran like crap all the time, never cleaned out.
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