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07 Granite Jake brake issue


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I'm looking for information on a problem I'm having with the engine brake in my 07 Mack CV713 with AMI 335 engine. The Jake brake doesn't seem to work under 1800-2000 RPMs then will kick in and be very strong but will kick in and out every 2 seconds, like someone is turning the switch off and on. It does this very consistently. I'm thinking it's got to be an electrical issue, clutch switch is good, not sure how to check the fuel switch on this one. Is it hooked into the crank sensor and could that cause this issue? Any ideas as to where to look would be great appreciated!

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I think you have what some call a "Gray Motor"?  If so? do you have a code for it? if so, good chance its a wire issue. This system will be "power leash".. If the engine is "red", then it's a volvo MP-7. Anyway ... try to post more info when you can. 

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It's 728 cubic inch mack engine, 335hp. Basically and E7 with EGR from what I understand, it is painted Grey.

There is no check engine lights, I haven't tried to pull any error codes but can check that.

Not sure on the model engine brake, definitely a factory installed brake, I assumed it was a Jacob's 

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If it has a spacer between the cylinder head and the top cover then it will be a jake brake. Most of those engines had the power leash. Try removing the electrical connector to the valve cover and stick a test light in each of the electrical connectors (front and rear head) Turn on the engine brake and snap the throttle at varying rpms and see if the light stays on. If it flickers then you have a electrical problem on the outside. I believe the engine has to be up to temp before you can turn on the brake. Simple check, let us know what you find.

V

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around 125- 150 degrees for engine brake operation. "V's" test is a good reliable test procedure... ...... I hope you are having a great summer in Maine. I lived there for 23 years. I miss the taste and smell of the fresh air... Joey

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Took another look at the brake, it's definitely electrical as anytime there is power to the head they work, took it for another test drive, engine is only heating up to 175*. Once the engine is over 150* they, work but only over 2000 rpms as soon as you slow down under 2k it will cut out the will come back on over 2k again causing them to pulse off and on.

Is it tied into the crank sensor? Could that be causing this? Tachometer seems accurate. 

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Powerleash rocker shafts have a nut on the ends of the rocker shafts instead of at welch plug... Jacobs set-up could pop a plug and drop pressure, however, the Engine brakes wont work at all, and oil pressure gauge will reflect the issue...  Are the valve's and E-brake adjusted correctly... Powerleash adjustment requires you to leave the .045" feeler in the engine brake position , then set the exh. lash to .024"... Jojo

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If it has circuit breakers maybe a short in the cabling is causing the breaker to pop then reset. I have known breakers to do that every couple of seconds. Try running a direct power supply from a remote switch inside the truck and go for a drive. 

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Everything is in adjustment, Brakes work perfectly when direct wired to 12v, even at idle. 

Still consistently only works over 2k rpms when on factory switch and wiring, cuts out as soon as drops below 2k and comes right back as soon as the engine accelerates over 2k.

 

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19 minutes ago, Dalton1 said:

Everything is in adjustment, Brakes work perfectly when direct wired to 12v, even at idle. 

Still consistently only works over 2k rpms when on factory switch and wiring, cuts out as soon as drops below 2k and comes right back as soon as the engine accelerates over 2k.

 

When you road test the truck and activate the engine brake with an external switched 12V power source, you say it works as it should?

V

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I dont remember which relay is for the engine brake, but I think its the same as the headlight relay, swap them and run the truck normally, without the jumper, and re-test. if its good during the test, the relay is bad...

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I'm not seeing any relays that appear associated with the engine brake? Any ideas where it might be? Looked in the glove box panel and panel on drivers side firewall. 

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there is 4 or 5 relays to the left side under  the right fuse cover. I think one of them is the engine brake relay... I am not near a truck right now, so I cant pop the cover and look, sorry... jojo

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Still haven't been able to locate a engine brake relay, there was 5 relays next the the block on the passenger side dash but 4 were labeled "Power Relay" 1-4 and the other was for the power steering fluid low light.

I put a new engine speed sensor in, truck seems to start quicker but no change with the engine brake.

Is it possible the brake cut out is programed at a higher than normal RPM? It's a former N.Y. dot truck and I know the order some stuff special. 

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Anyone have any ideas as to where to look next?  I've swapped all the relays I wasn't sure about,  as well as inspected and reset ecu connectors and checked as much of the harness as I could for chafing. 

Took a video of what it's doing but not sure how to get it on here.

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okay....  just because..... did you remove the engine brake celenoids and see if the orings are bad?  you will need to remove the ground wire from the head bolt to unlock the celenoid, no biggie, 13mm wrench... when they are out, look in the hole for debris...  rear, but it happens, the orings are crucial. 

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