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Troubleshooting intermittent dead pedal issue

Old 05-16-2019, 10:17 AM
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Exclamation Troubleshooting intermittent dead pedal issue

Looking to get some expert second opinions on this one to see what I might be missing....

This is on the '01 in my sig. 326K total mileage. VP44 was replaced 6.5 years ago and now has ~82K mile on it. APPS was replaced with a Timbo unit probably 12 or so years ago (don't have my records back that far).

The issue is that I'm getting a dead pedal that only seems to occur on the highway running 72mph or more. I haven't been able to isolate a specific set of criteria that will cause it, but that's the range that it happens most frequently. The issue first popped up on Easter Sunday when I was on the highway. At a normal cruise, you just feel it lose power like you lifted off the pedal. Sometimes it's just a quick drop out then it comes right back, other times it may last a couple of seconds. When it happens, no major change in fuel pressure is shown on my mechanical gauge. If anything, it might pick up 0.5psi as it drops out. After that Sunday, I changed my fuel filter just as a precaution and the problem didn't reoccur in the past few weeks while driving around town. Last night I was on another highway trip and the problem came back again. I'd hit stretches where it cut in and out so often I'd have to drop my speed back down to 65, then it would do fine for another long stretch. No codes are ever present when scanning with my Smarty. On Easter, I had a P0602 during the middle of that trip, but it never came back after clearing it.

I'm looking at these as my causes:

APPS - I know this can cause the dead pedal if it gets some bad spots in the range. I'm thinking this may not be my issue since I had instances last night where I could move the pedal up and down while the power was dropped out and it made no difference. At one point, I pushed the pedal down further and held it with no change, then it came back in. So this seems like it's more than just a bad reading coming from APPS.

VP44 - Before dropping the cash on a new one, I would like to verify this. Since I'm not getting any codes at all, I'm hesitant to just throw a new one on.

Fuel supply - This doesn't seem to be my issue. The pressure holds steady when the problem occurs. Last night, I had 17-18psi on the gauge at all times while running down the road. I do think I have a sticking check ball on the regulator for my Raptor as sometimes the cruising pressure will drop down to 15 while the idle pressure always stays consistent at 20psi. But each time this problem has happened, I've had a consistent 16-19 reading on my gauge. And it's backed up by a low pressure light as well just in case the gauge goes bad.

Alternator AC voltage - In my reading last night, I saw some mention of AC output from the alternator causing some interference. I've heard for this before for auto trans issues, but wasn't aware it had an impact on VP44 as well. I'll have to test this one. The alternator was replaced last year with an Ultima unit from O'Reilly. I've found two methods online for testing the AC output. Is it better to check between the output lug and the alternator case? Or check at the battery?

What else am I missing? It's a bit frustrating since I can't reliably replicate it, so letting a shop diagnose the problem might not yield much if they can recreate it. And I don't have the time right now to just start swapping parts hoping to find the magic one.

Thanks in advance for any insight you can provide!
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Old 05-16-2019, 03:00 PM
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I had a similar issue a few months ago. When traveling at highway speeds the truck seemed to "stall" but would not kill the engine entirely. The truck didn't react to the accelerator pedal when this happen. After a few seconds of coasting i would use the pedal again and truck would run like it should. I ended up checking my air filter and it was pretty clean, but upon further inspection, rats had actually climbed in the fender and crawled into the air filter. I hadn't checked the filter in months, but it was enough time for the rats to block the air passage with trash. You may try inspecting the air filter and making sure there is nothing underneath, if you still have factory air intake. Hopefully its that simple, I haven't had any intermittent issues since.
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Old 05-16-2019, 11:55 PM
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No restriction on the air side. It will still build boost like normal.

i checked the alternator this morning. I was getting reading of 0.03-0.04 at idle, with an occasional jump to 0.1. At 1700rpm, it was reading 0.04 at the lowest. So Iím going to get it checked out to see if it can be swapped before my next highway run.
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Old 05-20-2019, 09:50 AM
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UPDATE

O'Reilly tested the alternator on the truck and the handheld tester said it was all normal. Since I wasn't looking forward to the idea of another 4 hour trip with the dead pedal, I went ahead and picked up a new alternator and swapped it in. When I tested at idle, the numbers were still about the same. No issues on the trip home yesterday. So now the question is whether it was because of the new alternator, or the APPS re-calibration once I hooked the batteries back up. Going to take the old alternator back to my local O'Reilly and see if it bench tests out differently.
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