CM 870 Engine Brake

[Truckdriven]

I have a cm870 with 2 jake solenoids, howenver only one will come but occasionally after several seconds of engine brake the second one will come on. Watching the commanded output with Insite it only shows one on and if the second one comes one the commanded output goes right with it. Could it be sensor inputs that are doing this? Does the ecm monitor resistance on the solenoids and not turn them on if they are bad? I only have a coolant level sensor fault but don't see any relation with that. Demandate was done by RR

[Nostalgic]

Could be a lot of things. Bad connection in jake harness, poor contacts or bad solenoid, lack of oil pressure due to worn shafts or jake rocker bushing, bad o-ring in solenoid, etc.

You can check with the cover off at idle, look for oil gushing (or lack of oil) and test the solenoid by pushing the button down and see if you have an oil issue at the solenoid itself.

[Truckdriven]

(03-15-2022 )Nostalgic Wrote:  Could be a lot of things. Bad connection in jake harness, poor contacts or bad solenoid, lack of oil pressure due to worn shafts or jake rocker bushing, bad o-ring in solenoid, etc.

You can check with the cover off at idle, look for oil gushing (or lack of oil) and test the solenoid by pushing the button down and see if you have an oil issue at the solenoid itself.

But would those prevent the ecm from commanding it on? When I watch it with insite it goes precisely with the ecm command on or off, I'm trying to figure out why the ecm doesn't command it on.

[Rawze]

If it fails a resistance check, it will throw a fault for it.

What is the boost pressure doing?.. it may be from turbo lag.

[Truckdriven]

(03-15-2022 )Rawze Wrote:  If it fails a resistance check, it will throw a fault for it.

What is the boost pressure doing?.. it may be from turbo lag.

I didn't pay real close attention to boost but i beleive it was around 20, And no there is no fault code for the jake

[Truckdriven]

Here's what the issue turned out to be, this was an engine swap project and we initially didn't have the vehicle speed sensor connected for the engine because it needed rewired, when we connected the speed sensor engine brake worked perfectly. The minimum speed in Insite was set to 0 and with no vehicle speed input this caused the ecm to not command engine braking because the vehicle speed was at the minimum speed for engine braking

[Rawze]

(03-22-2022 )Truckdriven Wrote:  ...
The minimum speed in Insite was set to 0 and with no vehicle speed input this caused the ecm to not command engine braking because the vehicle speed was at the minimum speed for engine braking

Just some words of wisdom ...

- I have seen ISX's destroy themselves when some idiot has it all set to instant engine brake and the engine is not fully warmed up, leading to a piston striking a valve. This especially on a fresh inframe. In fact, for the first 50k miles or so.. a person should not even be using the engine brake on their ISX on its highest setting until the head has had time to settle and a second over-head valve adjustment (the one recommended at 50k miles after an inframe) was performed after an inframe.

- I have also seen ISX's destroyed because of a sudden mass inrush of extreme cold air after the engine is real hot due to labouring up a hard to pull mountain .. and someone suddenly let off of the throttle to shift .. and that engine brake kick in too fast because of zero delay .. causing a piston to strike a valve too.

therefore ...

My own recommendation to protect someone's $40,000 investment (their engine) is to ... Set the minimum speed for the engine brake to be set to above 3 or so mph to protect the engine. It should also be set to a minimum delay of 5 seconds before it comes on for the same reason... and if that truck drives thru high mountains and winter extreme cold areas, then it should actually be set to about a 10-20-seconds delay minimum to protect the engine.

I know people get away with that 0-delay engine brake and that instant on .. but it really is risky (especially so on a new head/fresh inframe) and can be hard on the engine under some conditions ... just saying.

[Truckdriven]

Thanks for the info, I don't have enough experience to know all that!