[John]

Since this is chassis related, I would start with the breakers in the steering bay. I had a 94 Liberty and had problems with wierd things happening to the breakers in the steering bay and found water was getting in during rain or washing. Once I took care of the water leaks, all was well. Just might be something you want to check. If you have power at the breakers, then the dash area and switches need checked for power and ground.

[Harry]

The grounds could be anywhere. The first question I would ask however is how you know all the problems are ground related. It is not uncommon for the thermocouple on a pyro to fail for example (the probe at the manifold). Have you tested for power at the driving lights for example and do you have power to them but no ground?

Fuses and circuit breakers are not on the ground side of the electrical circuit so you are questioning items now on the positive side of the DC circuits.

On your Liberty the driving lights, fog lights and cigarette lighter should be on the house electrical circuits. Liberty marks the wires that terminate at the device with a number. You should look for that number in the electrical bay on the LH wall. That is the source of power, but remember it goes through the switch on the dash before it reaches the lights. I would start at the device and just check working backwards.

The pyro gauges and associated wiring back to the thermocouples are Prevost. as is the Jake. Trouble shooting the pyros from my perspective would start at the probe which fails over time. The Jake problems could be at the switch or the solenoids under the valve covers or any place in between. Not to gloss over it, but diagnosing a Jake problem requires a lot of additional info, such as is one side working and not the other? Is the whole Jake system not working? etc.

You can rule out the switch by jumpering power from the 12V stud in the rear electric box to the studs for each side of the Jake. I can’t tell you the numbers, but the diagram on your engine door should show which numbers they are. With the engine idling, as you supply power to each Jake stud, you are effectively bypassing the switch up fromt and verifying the solenoids work and the wiring to them is not compromised. You will note the engine lug if all is OK. Do that on both terminals and each should produce a notable load on the engine. If not you problem is isolated in the wiring or solenoids in the rear.

If the engine lugs on each terminal, focus your search on the Jake switch pad.

Free advice……..repair problems as they occur. As little problems accumulate repairing each is by themselves not big issues, but when they build up after a while you don’t know if you are on foot or horseback. If your pyros were both working they would have told you enough information to be able to do a pretty good diagnosis of your Jake problem while you sat in the driver’s seat. Now without them you increase the effort required.

[Kevin]

Thank you for the help. I have much to do now before needing more help than you have given me. Today I found one breaker in the bay directly above the steering bay that had popped. I reset it but have not had a chance to see if it fixed the pyro or the jake. I have only one pyro gauge in the instrument bezel, but sounds like you are saying I have two. Are you referring to the gauge(s) or the sensor(s) of which I would have more than one? My intuition, based on the way the gauge began to show lower and lower temps, and finally show no temp, is that it is the sensor or sensors.

I pulled the jake switch out of the dash and began multimeter testing for voltage. Got none, but decided maybe I didn’t have a good ground. So ran a ground wire from the base of the passenger seat to the meter, and put the hot lead into the cigarette lighter socket to test for a good ground. Never got any voltage but I think I may have shorted the probe accross the socket. Found fuse number 16 popped in the electrical bay number 2 left side.

Here is where I hope I’m at:

1)Fuse fixes cigarette lighter

2)Breaker fixes jake

3)New sensor(s) fixes pyro gauge

4) LF fog and both driving lights need to test for voltage at the load and then for a good ground.

Didn’t mean to imply I know all problems are ground related.

Didn’t mean to imply fuses and breakers are on the ground side of the circuit.

Our jake has two positions low and high. Both positions stopped operating abruptly not gradually, so I hope it was that breaker.

Thanks again for the advice, Dan.

[jack]

Correct me if I am wrong but does your pyro have a pair of needles and scales to reflect the temps in the left and right manifolds?

On coaches I have seen equipped with pyrometers the gauge(s) monitor the left and right exhaust manifolds. I am making the assumption if is an 8V92, but if it is a Series 60 then there is a single exhaust manifiold. If that is the case I stand corrected assuming the pyros were for an 8V92.

I should point out that the confusion in part would be because I have not known of a pyrometer gauge on Series 60 engines. I might be about to learn something new and would prove guity of making assumptions.

Your fuses and circuit breakers on both the house and chassis, front electrical compartment (Prevost) and 2nd bay (Liberty) respectively should be numbered such that you can identify their purpose so you can be sure if resetting breakers and replacing fuses is consistent with the circuits giving the problems. If those trip or blow again, before resetting and replacing you need to find the problem with the circuit.

[Archived]

Dan,

Do you know if your bus is DDEC II or DDEC III? With DDEC III the ECM controls the Jakes and DDEC II uses a seperate module that has an input from the throttle and I think RPM to control the Jakes. I would not apply voltage or grounds to the Jake circuit unless I knew exactly what I was doing. You could fry the engine ECM or the Module.

Ken

[Archived]

The pyro is a one scale/one needle gauge. The motor is a detroit 60 series DDEC serial number 06RO138753. But don’t know if it is a II or a III. It is fueled to make 430 hp and 1450 foot pounds at 1100 rpm. It is 774 cu. in. which works out to 12.7 liters. It is mated to a Allison HT-755-CR tranny, a 5 speed.

I am having no luck on the internet finding a probe, any help with this would be appreciated. Planning to just replace it and see what happens.

Our bus is very unmolested and all the number labels seem to be intact, so this should expedite the fog/driving light fix. It is pretty hot out, so might take a while.

Will not introduce voltage to the jake curcuit, but wanted to test with a multimeter if there was voltage at the switch. Since reseting a breaker, will drive it once and see if it works before testing the switch now.

Thanks again. Dan.

[Scott]

On the rear electric compartment cover will be an aluminum label with the engine data. It should tell the DDEC version. I suspect it is DDEC II but it could be III.

Detroit Diesel should have thermocouples.

[John]

The aluminum label in the engine bay on the electrical box shows the following data:

engine family: PDD 12.7 FZA7

model: 60 12.7L

mfg date: August 1993

unit: 06RO138753

model: 6067GU28

spec: 51-0431

From all of this, still couldn’t tell if it is a II or III.

Went to the wiring schematics that came with the bus, and they clearling say II. So I’m going with that for now.

The fuse did fix the cigarette lighter.

You are going to think I was born LAST night! All the light failures were fixed with new bulbs, jeez can it get any simpler!

Tried the jake test while idling at 800 rpm and 1050 rpm. Then it dawned on me that this was an invalid test. When the jake was working, it would shut off below a certain rpm as I coasted to a stop, so it wasn’t going to activate at idle. Still need to drive it.

Waiting for a week day to search for a thermocouple to hopefully fix the pyro gauge.

[Archived]

Dan,

The Jake test I described bypasses everything and applies power to the solenoids that engage the Jake. The reason for the test is to verify that everything associated with the engine on the Jake is OK. So unless something has changed from the way I used to do it on 2 stroke engines you should have noted the engine lugging as you applied power to the Jake at the electrical studs in the box. This test is not sensitive to speed or gear or engine RPM. It tells you if your should look forward in your trouble shooting or toward the engine. Some folks have reported simple issues such as wires or terminals coming loose. Some have had bad solenoids.

Ken is very much up to speed on this stuff and if I am wrong or if any of the Prevost folks know I am not correct on this they should post it and order me some crow to eat.

One of the difficult things on a Prevost conversion is trying to figure out who is responsible for what. Here’s an overview. If it would have been on the chassis as an empty shell delivered to the converter it is a Prevost responsibility. Go to Prevost for parts and information. Except for the engine and transmission and tires. Go to their dealers such as Detroit Diesel or Allison or the tire manufactuer. The engine includes the stuff bolted to it such as sensors, turbo, etc. Even the Jake and the air compressor. However other things like the belts, radiator, alternator(s) etc. are Prevost. Confused?

Everything else, the converter.

[Archived]

Dan,

Here’s a link to the diagnostic manual on the Jacobs web site.

Jake

There are 2 possible control modules you could have, the one with 3
postions or 2 postions. The link is to the 3 position. That’s most
likely I think, both are on the site.

Jon,

Thanks for the complement, but I just know enough to get into
trouble. If I post something that is incorrect please everyone correct
me.

Ken

[Archived]

Thanks Ken, mine is a two position.

Re pyro sensor: Tried three Detroit dealers, non could find the application even with the motor serial number. Called Prevost parts in Elgin, Illinois (20 miles from my house), they had a listing as part number 56-1157, but it was discontinued. They gave me the vendor part number 015-002 Hewitt Industries in L.A.,Ca. Googled that, and bingo, ordered two of them at $33 each. Only needed one, so if anyone else needs one, I will have a spare.

Still need to drive it to see if the breaker fixed the jake.

[Archived]

To bring closure to this thread:

1) All light problems were corrected with new bulbs.

2) Cigarette lighter was fixed with a fuse.

3 Jake was fixed by resetting a popped breaker in the chassis electrical bay just above the steering compartment.

4) Pyrometer gauge on dash was NOT fixed by replacing the sensor. Gauge ground is next try, or whatever you guys think.