Engine losing throttle response

rschim · 05-21-2021, 09:08 PM

I have a 2001 Ford E350 w/V10 4X4 with 150,000 miles and an electrical issue. Here's what is going on: I'll be driving down the road when suddenly the speedometer will start jumping and then go to zero. At the same time the Engine Service light comes on and flickers. The engine continues to run, but there is no throttle response and it generally misfires and no power. I'll pull off the road, shut the engine off, let it sit a minute or 2. If the Service Engine light still flickers, I don't bother trying to start the engine. Instead, I'll disconnect the battery with a quick disconnect switch, let it sit a while longer(5 to 15 minutes) then try again.
If the engine service light stays on, I start the engine and the light remains off, down the road I go till the next time, which can be 5 miles or 500. So far, it has always started up and run fine for a while.
I've taken the van into Ford and 2 other automotive shops. Ford found nothing.
The second shop replaced the speed sensor in the rear Diff. I have now changed that out 4 times. Always works for a while, then not. We changed out the pigtail just prior to the sensor. Not it. We then found 4 sparkplugs loose and then changed all plugs and new coils. Not it! No codes were found after it happens. No one can figure it out. Temps don't matter nor speeds, otherwise the engine runs fine. Does anyone have a clue? I put this in the Engine thread also

REF · 05-22-2021, 07:07 AM

Have you checked your ground cables? Either that or your alternator might be on its way out, fire it up and meter your output

boywonder · 05-22-2021, 09:43 AM

^^^^^^

what REF said.....

Check the grounds..make sure they are clean and tight. I had a similar issue after playing around in spare tire area under the van. It was the ground back there for the fuel pump.

carringb · 05-22-2021, 12:21 PM

Also check both battery leads for corrosion at the terminals. Or even just loose terminals. Either basically cause the alternator to come in and out and lose the battery's buffer ability, which means the power spikes and drops from the alternator can cause the PCM to cut out.

highandwildjs@gmail.com · 05-23-2021, 09:35 PM

Battery is new and without any corrosion. Charging system seems fine, but I will test the alternator output just to see where its at. I will also check every ground I can get to.
We are now thinking that the PCM may have a loose connection somewhere inside. Do you know if the PCM has its own ground? I will look up the wiring diagram when I get back home in a few days.
Thanks for your reply.

carringb · 05-23-2021, 11:31 PM

Your symptoms are consistent with the PCM losing power. It’s grounded through the firewall, so corrosion can affect it. So can corrosion at the windshield cowling to block ground.

That said… because it sometimes takes a while to restore PCM function, I actually suspect the PCM itself is failing. Probably just some blown capacitors.

FWIW - I once had the exact same thing happen, except mine would always restart immediacy. I could even do a rolling restart in neutral. Im my case, I had a Banks chip installed into the PCM programming slot. But I later had my local dealer reflash the PCM for a gear ratio change. For whatever reason, the new flash would cause the PCM to freeze up under very specific circumstances. A new chip from Banks fixed it in my case.

highandwildjs@gmail.com · 05-24-2021, 08:27 AM

Hello Carringb, yep, I agree with your reasoning. At one time I had my windshield replaced and after that it leaked into the interior a bit, so it is possible that water traveled to that ground. If the ground is clean then I suspect there is an internal issue with the PCM. If that was the case, how would you proceed? Replace the PCM? Are they available? Is there a way to test the PCM without driving the vehicle? Also, because the problem is intermittent, I would think that testing would be problematic, but I have no idea.
When I first purchased the van in 2000 (December), the first thing I did was to drive it to Banks in LA and had them instal a shift module. That was a huge improvement. Do you think I could ship the PCM to them for testing?
Because you had a very similar problem, I really think your on to my issue. Thanks so much for your reply. Good on ya! Jay