Engine brake troubles need some input

[Nater1977]

OK, engine brake has drastically improved. So now what’s Happening Once it gets past 220° and you hit 30 psi it will Fall off like it’s one cylinder anything less than 220. It feels ok. I do have a 215 thermostat in it. The engine reached 235 today. (These are oil temps ) It was 90° out and I was pulling 80,000 up some pretty long Hills It’ll come down about two 220 when the fan comes on. Maybe I have a bad injector causing this issue. I’ll rerun the test again once I have a moment to see if any that are failing again. And once I’m able to hook up to the truck, I will send out the ECU mapping. I was also thinking. Is it possible it could be timing causing this? Because the engine does have that helicopter/freight train noise the TSP does not pertain to this truck with the fuel pump gear, but if the timing is out, I could possibly get that noise I would think from the injector pump And maybe causing this brake issue?

Also, when I was Running the engine brake I would notice once the engine brake was falling off. It would never come back unless I restarted the engine brake meaning hit the fuel pedal or clutch pedal and I will come back on and be strong again. And like I said before, it only feels like half of the engine brake is working when this happens like you’re in setting one

[trucklogger2]

(07-14-2025 )Nater1977 Wrote:  OK, engine brake has drastically improved. So now what’s Happening Once it gets past 220° and you hit 30 psi it will Fall off like it’s one cylinder anything less than 220. It feels ok. I do have a 215 thermostat in it. The engine reached 235 today. (These are oil temps ) It was 90° out and I was pulling 80,000 up some pretty long Hills It’ll come down about two 220 when the fan comes on. Maybe I have a bad injector causing this issue. I’ll rerun the test again once I have a moment to see if any that are failing again. And once I’m able to hook up to the truck, I will send out the ECU mapping. I was also thinking. Is it possible it could be timing causing this? Because the engine does have that helicopter/freight train noise the TSP does not pertain to this truck with the fuel pump gear, but if the timing is out, I could possibly get that noise I would think from the injector pump And maybe causing this brake issue?

Also, when I was Running the engine brake I would notice once the engine brake was falling off. It would never come back unless I restarted the engine brake meaning hit the fuel pedal or clutch pedal and I will come back on and be strong again. And like I said before, it only feels like half of the engine brake is working when this happens like you’re in setting one

Your oil temps are perfectly normal just carry on you’re good.
As for your Jake mr hagg kindly tested my turbo with c”L term and figured it was weak and not holding pressure- it wasn’t within spec.
Got a reman turbo works good and haven’t looked back. Was doing what yours is doing - maybe a coincidence but worth looking into.

[Nater1977]

I am still at a loss. I have been through quick serve Multiple times. I cannot find any good pinpoint test on the diagnosis of this engine brake issue. The engine break starts feeling well about 220° and the oil temp and it gets about 30 psi on the boost. It seems like one of the cylinders is loosing compression, like one of the rockers is a letting oil by. If I could add a lot of pressure to the exhaust and then manually activate the solenoid, I could probably find the problem. But there’s no test I can see on how to do that. Any more help would be very appreciated.

[Rawze]

what is the boost getting to during jake operations?.

How many miles ago since the jake solenoids were replaced?.

Have you run the engine with the valve cover off it and pressed down the jake solenoid plungers, see if they are hemorrhaging oil?.