My Mechanic has given up

[Flentz56]

I don’t want to geek out on this but let me explain, your engine has a few devices on it that connect to the ECU (engine control unit), these devices determine how the engine responds to conditions like driver input, vehicle speed and such. These inputs operate on a very critical voltages, usually 5 volts input from the ECU and it reads the ECU reads the output from that device. Some of these devices read a square wave ( on or off) and some read a sine wave like O2 sensors or MAF (mass air flow sensor).

Now with that out of the way, if the voltage that is supplied to the ECU fluctuates (like a bad ground or a momentary short) the fluctuation can cause the ECU to go into limp mode (reduced power). Someone stated earlier if you get a proper scanner that reads live data you may be able to see codes in the ECU where these occurred and also see the captured live data. If I were you I’d take it to a good mechanic who can properly diagnose what is happening.

[F4Gary]

Originally Posted by pasdad1

Attachment 380403

That is a sensor, not a gage (or gauge?)...

[pasdad1]

Originally Posted by F4Gary

That is a sensor, not a gage (or gauge?)...

Yep, I guess I just expect bad terminology and bad spelling as normal these days…. [emoji26]

[SergioP]

Originally Posted by thomashill1

Update. Went back to shacking cable harnesses. Found that a thick 12v supply line that feeds the main fuse box in the engine compartment was cutting into metal frame and actually sparked when I wiggled it hard . It did not throw the wrench light when it sparked, but I have to think it has something to do with it. I have covered the broken insulation in electrical tape. And pulled the cable up in a different direction so it no longer comes in contact with that piece of metal. Have not had a chance to drive it on a bumpy road, but here's hoping this takes care of it.

Post 13 looks like he found the problem. We will have to wait til he has time to drive it to know if its fixed.

[cb727200]

Originally Posted by thomashill1

I have a 2012 Winnebago Class C (ford f450 w/6.8L gas. I bought it used about 8 months ago and have had an ongoing issue with it. When driving at highway speeds while pressing the accelerator if you go over a really rough patch of road the wrench light will come on and the the coach will go into limp mode. (no power, just enough to pull to the side of the road). I can than turn the engine off, wait 5 seconds and turn it back on and all works again.

If I see a rough patch coming up, (big potholes, or bridge expansion joints will normally cause this) than I can pull my foot off the gas pedal and glide over the rough road and then reapply gas and all works fine.

this issue has happened to me at least 20 times. During that time, there are never any codes to read, (once you restart the rig the wrench light goes away and so do the codes). However, there were two times the the engine light also came on and both times it indicated that there was a issue with the throttle body.

I have replaced the throttle body twice- the first time was an aftermarket, it did it again, and they put an original ford part on it the second time. but the issue still happens.

Just for other information, we have already done a complete tune up, Plugs and coil packs and the transmission was replaced with a Jasper rebuilt transmission. In addition, we have already wiggled every ground wire we can find looking for a bad ground.

I am at a loss at this point, any other ideas what can be done?

When you do not get codes the ecm is the problem

[cb727200]

When you do not get codes the ecm is the problem[/QUOTE]

[Unplanned Tourist]

Originally Posted by cb727200

When you do not get codes the ecm is the problem

Most ECMs require the fault to be logging for up to 30 seconds or more to log and be stored as a fault. That's the problem with trying to troubleshoot CEL flashing on for only a short time. That's when finding the problem can be hard.

The rubbing, bared wire is one of those instances. Glad the OP found it.

I would be replacing that section of wire if possible, in case the size is reduced from the arcing.

[GypsyR]

Originally Posted by cb727200

When you do not get codes the ecm is the problem

Wow. 40 years of mechanic work and I've never heard that one before. I would say more like "when you do not get codes, the ECM is not capable of sensing or assessing the problem." And you won't catch me calling that a hard rule either. I'd like to have dollar for every time someone misdiagnosed an engine issue as needing a new computer. I'd be long retired instead of typing this with black under my fingernails.