DDEC II Jake Brake questions

[Iceni John]

My Jake works intermittently  -  it used to work consistently, but gradually has become sporadic.   When it works it has the same braking power as before, but now it doesn't always work.   I've checked the wiring into the heads (four white wires into each head) and it looks OK, but I can't remove the driver's-side valve cover to check the solenoids there because the exhaust is in the way.   The Engine Brake light illuminates on the dash when the Jake should be working, so I know the switch is OK.   I have good ground connection between the engine block and battery negative.   There's a cube relay near the switch that (I guess?) takes the place of the Jake 017179 Control Module, and I replaced it thinking it could have had bad contacts, but still the same symptoms occur.   Some Googling has suggested that there may be an engine oil pressure switch for Detroit Jakes  - is this true?

The Troubleshooting Guide (DDEC II Controls) wiring diagram for models 71/92A doesn't show an engine oil pressure switch, only a pressure switch for non-ATEC transmissions like my HT740.   Is this the same thing or not?   If there is an engine oil pressure switch for the Jake, is it the same as the DDEC's or a separate one, and if so where is it?

I really think my Jake problem is electrical, maybe something very simple.   I know the DDEC ECM has one wire (508?) for engine brake, so how does that connect to the relay?   Unfortunately DDEC complicates what should be simple troubleshooting.

Am I barking up the wrong tree with my nooby attempts at this?   Has anyone here had the same problem?

Thanks, John   

[Hard Headed Ken]

Here's a trouble shooting guide from Jacobs for DDEC II, maybe it will help.

https://drive.google.com/folderview?id=0B9Xv0QOH_HT4fkJxU3kwd25zNUhXMk1CS2ZiaVo3b0dVd3V6Rzl5aGdCbW9qZkJVWEdqN1E&usp=sharing


Ken

[Jon]

I don't know how your coach is set up, but if the tail lights come on when the Jake is supposed to engage my guess is the issue is in the head, maybe a solenoid, maybe just a loose connection.

On my 87 Prevost I found two terminals that fed power to the Jakes in the head. With the engine at idle if I jumpered 12V to each one I could hear the engine lug down. If the engine did not lug down I knew the issue was within the wires to the head, the internal connections or the solenoids were bad. But when everything was working at the engine as it should the engine would definitely lug down. If I jumpered 12V to both terminals at once I could stall the engine.

[bevans6]

You probably need to start with adjusting the clearance to the exhaust valve bridge, replacing the rubber O-ring in the oil jumper tube (or at least adjusting them) and seeing if all four solenoids are working.  Which means getting inside that pesky valve cover.

Brian

[luvrbus]

I would check the toggle switch 1st,does the cruise control work ? those can be fun   chasing down how the OEM interfaced the Jake's

[Iceni John]

I would check the toggle switch 1st,does the cruise control work ? those can be fun 

The 2-position switch works OK, as indicated by the Engine Brake light coming on every time the Jake is engaged and supposedly working.   This light doesn't flicker or flash erratically when the Jake is working intermittently, so I assume that part of the equation is OK   I have no cruise control  -  one less thing to deal with!

Thanks, John

[luvrbus]

As you well know it has to have pressure signal from some where to work,where on a Crown other than the transmission I have no idea,you can hook it direct and take control away from the DDEC to help with your troubleshooting makes it easier 

[Iceni John]

If I can operate the Jakes without running through the DDEC, that's probably what I'll do then.   That will definitely make it easier!   I was wondering why the DDEC was in the loop at all, unless it was to provide an oil pressure signal instead of directly from a pressure switch.

I'll read my Jake troubleshooting manual again tonight to better understand this.

Thanks, John

[Iceni John]

I don't know how your coach is set up, but if the tail lights come on when the Jake is supposed to engage my guess is the issue is in the head, maybe a solenoid, maybe just a loose connection.

On my 87 Prevost I found two terminals that fed power to the Jakes in the head. With the engine at idle if I jumpered 12V to each one I could hear the engine lug down. If the engine did not lug down I knew the issue was within the wires to the head, the internal connections or the solenoids were bad. But when everything was working at the engine as it should the engine would definitely lug down. If I jumpered 12V to both terminals at once I could stall the engine.

No, my Jakes don't turn on the brake lights.   I still need to trace back the wiring out the heads and see where it goes.   Unfortunately there's a big spaghetti-mess of wiring in that area for the DDEC box, so I have to be careful to avoid damaging any DDEC connections.   If I can find each head's power input wire (there are four white wires going into each head through the oil-tight gland), I could then do what you did and check each head's Jake while the engine's idling.   That will tell me if there's a mechanical problem, or just an electrical actuation problem.

Thanks, John

[luvrbus]

The four wires to each head are for the injectors on most I never saw a white wire for a Jake.There should be 1 wire(blue) feeding the Jakes for the low side then a brown wire for the high side you just have 2 solenoids on each side   

[Iceni John]

Aha, that makes sense!   I couldn't work out why there were four wires needed for the Jakes in each head.   OK, time to dig further and find the Jake wires going there.   Where do they normally enter the heads?   This all makes sense why those four wires seemed to go straight back into the DDEC!

By the time I'm done with this project I'll know A LOT about Jakes!   These projects, though sometimes frustrating, always result in me understanding more about how everything works, so it's worth me puzzling over it instead of just taking the bus to someone else to fix it.   What's the fun in that?   As always, everyone's help here is priceless and gratefully received.   Thank you so much.

John

[luvrbus]

John,if yours is original under the valve covers DD used a 3 bladed type terminal block bolted to fuel jumper tubes they were nothing but problems pull the covers and you will probably find those with broken wires or blades.

They feed from the front of the head up top behind the T stat housing a real PITA.

If you have the 3 blade terminal set up you can buy the rubber mount harness from a Packbrake dealer for about a 1/3 of DD price, if you have the blade set up replace it sooner or later it will break or rub a hole in a fuel tube.

I can post you a photo of the blade setup on F/B if you go there,I have no luck posting photos here so I quit trying   

[Iceni John]

OK, I'll check them when I next have the valve covers off.   The passenger side comes off easily, but the driver side is under the exhaust making it impossible to remove!   I can try soaking that exhaust's joints with penetrant to get it apart, but I'm not hopeful it will help much after being together for 25 years.

Last night I did eventually find the Jake wires out of each head, next to the blower and behind the thermostats, covered in 25 years of black grime.   Talk about inaccessible!   I traced the wires back to the dash switch, thoroughly cleaned the terminals (they could well have been the reason for intermittent operation), and briefly put 12V to each head's wire while the engine was idling.   As Prevost Jon said, the engine lugged down when I did that with each wire, so I know each head's Jakes are working.   The switch however is a simple On-Off-On SPDT, with one head's Jakes on each throw, so I can have either the driver-side or the passenger-side working, but not both!   I don't know why it was set up that way.   I want either half or both or off, but operated through one switch.   There's no way I can think of to have this happen from a simple SPDT switch  -  how does Jake do this with their 3-position Off-Low-High toggle switch (part 3586)?   It seems I have a simple cube relay instead of the Jake control module  -  maybe the Jake module is needed to be able to use just one switch like I want to do.   Or maybe I'll just have them both on or both off, i.e. everything or nothing, but there may be times I don't want so much engine braking.   Decisions, decisions.

Why isn't anything simple?!
John

[sledhead]

I bit the bullet last spring a replaced my org. jake brake switch that stopped working with a new one from MCI for $ 80.00 it hurt but it works . off 1/2 on or both on

dave