Mysterious V10 limp mode

[urbanhermit]

1999 V-10, F53 chassis.  Sporadically goes into limp mode -- once after about 10 miles, stayed in limp mode the last two miles to storage, ran fine/no code after being towed to a shop the next day.  Ran fine with no code recorded when started by the shop the next day.  Into limp mode at 19.5 miles being driven to cause limp mode, returned to shop, left running, found a code that covers everything from acne to terminal cancer.  "Wires wiggled" on all sensors; could not replicate code.  Drove again to get limp mode and pick up mechanic and drive farther .  A few miles into that, limp mode; turned around, started back to shop, came out of limp mode a half-mile later. Another 50 miles no limp mode, gave up, returned to shop. 

When in limp mode runs smoothly -- no coughing, sputtering, surging, just very low power and sounds like "can't get breath."  Fuel delivery problems have been ruled out (new tank, new rubber lines from tank, new fuel pump, clean filter, shop confirmed proper fuel delivery).  Engine coolant problems also ruled out.  Shop says could be any one of ten or so sensors.  They can't isolate a faulty one by the covers-almost-everything code. Shop went on line to professional mechanics' web sources, no help.  Choices seem to be replacing one sensor after another until the phenomenon stops or replace all of them at over $100 each plus labor.  Replacing one then another impractical because there's no immediate way to tell if a bad sensor has been replaced as the limp mode phenomena is sporadic and codes are not present when not in limp mode.  There is some slight evidence that it might be connected with weather temperature but not at all conclusive, though both the shop and I believe heat is the cause of intermittent malfunction of the problem sensor.  A possible clue pointing a different way is that the first time recorded here was during acceleration from a red light and I think I remember that the second was during light acceleration driving at near-constant 40-50 mph.

I want to put the coach (Itasca Sunflyer 34) on the market but will not do so until I'm convinced the problem has been solved or without disclosing it exists, which will kill any potential sale.  But I am loath to spend over $1,000 plus labor to get rid of one bad sensor.

QUESTION:  Does anyone know if this engine's sensors can be bench tested?  All I get from other shops, including the rare Ford dealership that will work on vehicles more than ten years old, is "bring it in and let us charge you a bunch of money with no assurance of success."

 

Edited October 25, 2020 by urbanhermit

[rockylarson]

Do you have an Allison Transmission?  The several times I went into limp mode is was all transmission related. Not engine.  Workhorse V8 not Ford V10,

 

Good Luck

[dickandlois]

urbanhermit, 

    Kind of sounds like the PVC check valve is sticking open. Might check it out and the big vacuum line connected to it for age brake down issues..

Rich.

[rayin]

You might consider either buying or borrowing a high-quality code reader and leaving it hooked up while driving in hopes of capturing any generated codes when this event happens. When you buy from Amazon you generally have at least one month to return the item.

[jleamont]

Urban, when this happens was the O/D light blinking on the shifter? The last Ford that I worked on with this issue it was a problem within the transmission harness, not the engine. When the PCM cannot detect the transmission it cuts the power back on the engine so as not to cause any damage to the transmission. 

[urbanhermit]

Rocky and J:  Months before this started it would go into limp mode and shifting would hit like a bone-jarring sledgehammer.  That was a (Ford F43 chassis) transmission sensor.  There is no transmission function anomaly I can detect now, though I don't rule out that sensor, which I understand is mounted close to the exhaust pipe.

J, I don't notice a blinking OD light.  In fact I fail to notice if the Service Engine Soon light comes on consistently, though I did notice it on once. 

****, thank you for the suggestion about a sticking PVC valve.  I'll pass that along to the Ford dealership which still has the coach and has declared themselves stumped. 

If anyone wants to chime in on this, I'll be grateful. 

[dickandlois]

20 hours ago, urbanhermit said:

Rocky and J:  Months before this started it would go into limp mode and shifting would hit like a bone-jarring sledgehammer.  That was a (Ford F43 chassis) transmission sensor.  There is no transmission function anomaly I can detect now, though I don't rule out that sensor, which I understand is mounted close to the exhaust pipe.

J, I don't notice a blinking OD light.  In fact I fail to notice if the Service Engine Soon light comes on consistently, though I did notice it on once. 

****, thank you for the suggestion about a sticking PVC valve.  I'll pass that along to the Ford dealership which still has the coach and has declared themselves stumped. 

If anyone wants to chime in on this, I'll be grateful. 

****, thank you for the suggestion about a sticking PVC valve. There is a Vacuum line involved also. It supplies vacuum to the PVC valve. One can use a vacuum gauge on the intake manifold to check the negative pressure level. Low vacuum level equals poor performance  when engine is under heavy loads. 

Rich.

[rikadoo]

When working for ford, its all about the diagnosis not part replacing. When you encounter someone who wants to just replace parts... RUN AWAY!!! There are so many  things that can cause that, like a torque converter one way clutch not holding, Also when you have a coil become biased and starts making RF it can shut down a PCM. I have had MAF sensors go bad and lean the fuel system Nooooooo power, even a bad alternator can cause a no power condition. You need someone Monitoring the pids while someone drives it, on those old dogs there are very little surprises. Find someone who knows how to diagnose. Those old 2 valve V-10s were awesome with there power and performance.