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tree98 · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

870 in a kenworth t800 with 422,000 mi. Demandated(Unilever) gets a cel when loaded and going through the gears. Been doing it for a while. It doesn't happen at any certain rpm but I did notice that when the light comes on the boost gauge is at 40 and sometimes a hair over. Isn't that to much boost? I know a turbo overspeed code could be caused by a boost leak but could it even make that much boost if it had a leak?

Brock · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

When you have a boost leak with a vgt/vnt turbo, the ecm corrects and compensates for the low boost condition and "adds more boost" which causes it to overspeed.

Please trust me here as it cost me a turbo, this is no joke man...... Fix that boost leak now because it won't be long till your pushing oil.

marek4792 · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

40 is maximum. about the code on mine it only happens above 6500 feet. And my boost is around 37-40 but if you are less than 550hp your boost should be around 35 substained. You could have a small boost or exhaust leak as well. I actually watched on insite how the turbo rpm increase 2k rpm a second and then it jumped from 120k exact to over 150k rpm in a 2 second window. I was reassured by Uni that a 30k jump that quickly would destroy a turbo so I question the valadility of the data, and according to the troubleshooting tree it points to a sensor/harness issue or even electrical interference.

tree98 · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

I'm at 650 hp. I'll have to try to find this leak.

Rawze · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

(07-21-2018 )tree98 Wrote: I'm at 650 hp. I'll have to try to find this leak.

Leak or not, and even at 650hp, you should not be hitting 40+ lbs boost if you care about your engine longevity. Have it backed off to about 37 - 38 or so max instead. engine only needs 38 lbs boost even at 900+ hp.

Starlight · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

Have seen bad turbo speed sensor cause overspeed codes and derates more times than i can remember. Some of them had heat damage from being in the vicinity of the turbo and others had nothing obviously wrong. Maybe swap that out if you dont have any boost leaks. But like others said, boost leaks is the first thing i would check for.

tree98 · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

The sensor was changed a few months back. Didn't fix the problem.

tree98 · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

(07-21-2018 )Rawze Wrote:
(07-21-2018 )tree98 Wrote: I'm at 650 hp. I'll have to try to find this leak.

Leak or not, and even at 650hp, you should not be hitting 40+ lbs boost if you care about your engine longevity. Have it backed off to about 37 - 38 or so max instead. engine only needs 38 lbs boost even at 900+ hp.

I'll be looking into that quickly.

Chamberpains · 07-21-2018, **(Subject: 870 turbo overspeed cel )**

Also check the air piping and actuator on the turbo for leaks. I just recently had my actuator leak at certain positions but not under full extension (like it is when using Insite actuator test mode) It was also causing the ECM to over correct intermittently with really erratic boost pressures and pretty violent spikes. I never got overspeed codes though. Then it finally gave up the ghost and completely blew the actuator seal and I was able to find the leak using Insite actuator test mode.