Todd71106 Posted March 12, 2022 Share Posted March 12, 2022 Greetings 2013 Mack Granite MP8 13 Speed 300k miles My engine brake seems to not be fully disengaging. The deceleration function shuts off, but the part that makes it hard to shift does not. Are used to be able to turn the switch on and off a couple times and it would fully disengage. Now, when accelerating, at about 1500 RPM the engine makes a swooshing over rev sound. If anybody out there could point me in the right direction, as to where to start looking, it would be greatly appreciated. 95B3056A-19D4-4D57-BED6-96739D9B80F5.MOV Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/ Share on other sites More sharing options...
Onyx610 Posted March 12, 2022 Share Posted March 12, 2022 Powerloss? Sounds like an air leak. Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-491883 Share on other sites More sharing options...
Joey Mack Posted March 12, 2022 Share Posted March 12, 2022 you reckon the V.E.B.C. is failing or maybe a bad oring in it?? jojo 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-491893 Share on other sites More sharing options...
Onyx610 Posted March 12, 2022 Share Posted March 12, 2022 12 minutes ago, Joey Mack said: you reckon the V.E.B.C. is failing or maybe a bad oring in it?? jojo That is very possible. I haven’t seen one go bad yet, but you have seen a lot more of this then I have. Sounds like a communication issue Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-491899 Share on other sites More sharing options...
Onyx610 Posted March 12, 2022 Share Posted March 12, 2022 Does it do it with the switch in either position? Take the valve cover off and inspect. Anyway to get the engine brakes to work while running it stationary Joey? Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-491901 Share on other sites More sharing options...
Todd71106 Posted March 14, 2022 Author Share Posted March 14, 2022 (edited) On 3/12/2022 at 4:11 PM, Joey Mack said: you reckon the V.E.B.C. is failing or maybe a bad oring in it?? jojo What is the V.E.B.C.? Variable engine brake control? That’s just a guess. Lol. There is no power loss. Yesterday for the first time the engine brake shut itself off even though the switch was turned on. It came back on about 10 seconds later. I am pulling 130 barrel tanker, so that engine brake really makes a big difference. I don’t know if it matters, but the truck was deleted about six months ago. This is my first big truck. I chose this model because of the camelback suspension and the rough lease Roads that I am running. Edited March 14, 2022 by Todd71106 Spelling error Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-492123 Share on other sites More sharing options...
fjh Posted March 14, 2022 Share Posted March 14, 2022 (edited) 2 hours ago, Todd71106 said: What is the V.E.B.C.? Variable engine brake control? That’s just a guess. Lol. There is no power loss. Yesterday for the first time the engine brake shut itself off even though the switch was turned on. It came back on about 10 seconds later. I am pulling 130 barrel tanker, so that engine brake really makes a big difference. I don’t know if it matters, but the truck was deleted about six months ago. This is my first big truck. I chose this model because of the camelback suspension and the rough lease Roads that I am running. Does the dash show any malfunction lights? Is the truck auto or manual trans? NO ? then The V.E.B.C is the engine brake valve under the valve cover these have been known to have issues at times! We have had them failed right out of the box! could also be the switch on the dash or the clutch switch if equipped ! Edited March 14, 2022 by fjh 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-492145 Share on other sites More sharing options...
Todd71106 Posted March 14, 2022 Author Share Posted March 14, 2022 5 hours ago, fjh said: Does the dash show any malfunction lights? Is the truck auto or manual trans? NO ? then The V.E.B.C is the engine l No engine lights on. Truck is a 13 speed manual. It’s really not a big deal other than making look like I don’t know how to drive a manual and wearing out my brake linings faster. It sure is nice though when it works. I guess I’ll pull that valve cover off or get permission to swap engine brake switches with another Mac truck on the lot to see if that is the problem. Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-492164 Share on other sites More sharing options...
Popular Post Todd71106 Posted November 15, 2022 Author Popular Post Share Posted November 15, 2022 Just following up on this topic. It turned out to be bad programming. I had the truck deleted and the guy did not put the right program in. This is an oil field truck and I stay within 50 miles of my home base. I purchased a trailer up in Oklahoma and wanted to be able to go over 65 mph. I took the truck to have it reprogrammed so I could drive a little faster. Upon completion of the service not only was I able to do more than 65 mph, the symptoms of the problem went away. Another benefit of the reprogramming is my fuel economy jumped up from 4.2 mpg to 5.1 mpg. I suffered with this problem for six months. Now the truck has more power and better fuel economy and I am much happier. Lol 2 2 Quote Link to comment https://www.bigmacktrucks.com/topic/69367-mp8-engine-brake-not-fully-disengaging/#findComment-515206 Share on other sites More sharing options...
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