Hybrid with "stuck" revs

[abcinv]

I searched to see if anyone has experienced this but I couldn't find anything.

We were coming down Lookout Mountain (Ga side), coasting mainly and three different times the mpg showed 999.9 (not electric) and the rpm's seem to be stuck around 2500 (guessing as there is no gauge). I would give it a good bit of gas and it would settle back down and flip over to electric. No other problems and once down the mountain we had no more issues.

Anyone have any idea what caused this? I have a little over 2k miles on the truck with no complaints or problems.

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[SuperDave71]

I’ve heard there could be an instance in which the battery is fully charged and the truck does something to waste extra electrical energy, maybe drive the traction motor and use the gas engine in engine brake mode (no fuel) to keep speed down. That would explain the 999 mpg, the engine was spinning while using no fuel.

 

[jsus]

Sounds more like engine braking as the HVB doesn't need the charge from regenerative braking. Not burning gas, just letting the engine spin to help slow you down.

Otherwise, when coasting with regenerative braking unavailable, the vehicle would hardly slow down at all, compared to the ICE vehicles you may be used to. Coasting downhill would lead to speeding up significantly, even if unintended, etc.

When you got on the gas, no more braking force was needed, so the engine was stopped.

 

[Chicora]

I live in Asheville NC and going down mountain grades of 6+% the engine sounds like it is seriously over revving. Is that what you are experiencing?

I've found I can replicate the scenario quite dependable on different descents. I believe the hill descent control is the source for the high rpms.

One "trick" (if you will) to reduce the over revving is to put the hybrid truck in slippery drive mode. Apparently this reduces the effect of engine breaking of the automatic hill descent control to (mo) half.

 

[abcinv]

All of these makes perfect sense, I just didn’t put it together. It was a little freaky but now I get what was going on.

Thanks all for taking the time to respond!

 

[Bushpilot]

Yeah, it will automatically "downshift" going down a long steep grade.

 

[MakinDoForNow]

I live in Asheville NC and going down mountain grades of 6+% the engine sounds like it is seriously over revving. Is that what you are experiencing?

I've found I can replicate the scenario quite dependable on different descents. I believe the hill descent control is the source for the high rpms.

One "trick" (if you will) to reduce the over revving is to put the hybrid truck in slippery drive mode. Apparently this reduces the effect of engine breaking of the automatic hill descent control to (mo) half.

And probably increase hydraulic braking.

 

[MakinDoForNow]

I’ve heard there could be an instance in which the battery is fully charged and the truck does something to waste extra electrical energy, maybe drive the traction motor and use the gas engine in engine brake mode (no fuel) to keep speed down. That would explain the 999 mpg, the engine was spinning while using no fuel.

The HV battery accepts Regen braking up to 70% SOC and rapidly drops to prevent overheating of battery. I suspect that the capacity of the battery from 70-80%may be reserved to accept Regen braking in emergency stops if needed to aid the hydraulic brakes.

 

[TedTX]

Lol don’t give it gas during engine breaking like this. May sound/feel better but that is just the gas getting squeezed and shot out the tailpipe. Likely unburned and damaging the cat.

 

[Chicora]

And probably increase hydraulic braking.

Fwiw Not in an automatic way that I can tell.

 

[Chicora]

Lol don’t give it gas during engine breaking like this. May sound/feel better but that is just the gas getting squeezed and shot out the tailpipe. Likely unburned and damaging the cat.

Giving it gas is the only way to stop the over revving (except for my "trick" above). When you experience it, you gladly give up some gas to get it to stop revving. Remember this occurs on significant mountainous downgrades - areas where losing your engine could be very, very bad.

 

[MakinDoForNow]

Lol don’t give it gas during engine breaking like this. May sound/feel better but that is just the gas getting squeezed and shot out the tailpipe. Likely unburned and damaging the cat.

No gas if injectors are shut off. See manual = in the event that ice overheats maybe due to low coolant or ?? Possibly other conditions, the 2.5 hybrid will run on TWO cylinders to help reduce heat. Also during engine braking the instant mpg will read 999.9!= No fuel used. Cannot find it again but I read that within the muffler their is a bypass valve (butterfly type?) Which I ASSUME is to open and let the compressed air exit the muffler easier and quicker. This may not have been on maverick as I haven't been able to find it?

 

[TedTX]

Go ahead and disregard the Truck trying to save itself. Giving it gas will cut the revs, make you happy and put more energy into a system that is trying to shed the excess.
If you got that way to monitor the hybrid battery I would be curious if it forces the battery over its safety limits.
I was reading up on ways to regain capacity on a old battery pack, maxing out then drain past normal limits once or twice a year late in its life works.

 

[Rivers90]

Using the engine to slow down so the brakes don't over heat. Losing your brakes from over heating could be very bad.

 

[jsus]

Go ahead and disregard the Truck trying to save itself. Giving it gas will cut the revs, make you happy and put more energy into a system that is trying to shed the excess.
If you got that way to monitor the hybrid battery I would be curious if it forces the battery over its safety limits.
I was reading up on ways to regain capacity on a old battery pack, maxing out then drain past normal limits once or twice a year late in its life works.

Accelerate down a mountain, you say...? This very important feature is designed to prevent exactly that, without command from the right pedal. To prevent a runaway truck.

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