Parking brake self-activation

[Nicholas Tinling]

I did a search and could not find this problem discussed. On my W-24 (2007 Fleetwood Pace Arrow), I installed some after market spark plug wires that had a problem of disconnecting after driving for awhile. When the wires, usually just one, would disconnect the engine would misfire. On the three occasions that this occurred while I was driving, the parking brake engaged without any action on my part. The first two occasions I didn't connect the engine misfiring with the parking brake coming on. The last time it occurred, I connected the dots. Needless to say I have gone back to the stock wiring, but I am concerned about why the parking brakes would engage because of engine misfiring. I thought about it some and I have a theory that the raw gas that was sucked into the exhaust system may have ignited and caused the hydraulic fluid to boil, and that this may have caused the brake to engage. Anybody else have this happen because of engine misfiring?

[Nicholas Tinling]

I did a search and could not find this problem discussed. On my W-24 (2007 Fleetwood Pace Arrow), I installed some after market spark plug wires that had a problem of disconnecting after driving for awhile. When the wires, usually just one, would disconnect the engine would misfire. On the three occasions that this occurred while I was driving, the parking brake engaged without any action on my part. The first two occasions I didn't connect the engine misfiring with the parking brake coming on. The last time it occurred, I connected the dots. Needless to say I have gone back to the stock wiring, but I am concerned about why the parking brakes would engage because of engine misfiring. I thought about it some and I have a theory that the raw gas that was sucked into the exhaust system may have ignited and caused the hydraulic fluid to boil, and that this may have caused the brake to engage. Anybody else have this happen because of engine misfiring?

[Rocky 2]

I had one of my Taylor wires that would not stay connected to #1 spark plug. Replaced that one wire and have been good to go. I hope you didn't give up on whatever brand of after market plug wires due to one problem wire. What did you do with the wires after you put the oem wires back on?

[tropical36]

Firstly, when brake fluid boils you usually lose your brakes and we're talking wheel brakes here which I don't think has anything to do with your parking brake. I suspect you have one form of the other J71 or J72 auto park that uses Dextron III. No matter, it clamps down on your drive shaft, not your wheels.
Driver could tell you exactly what type of parking brake is in your rig.
Secondly if for any reason, you lose 12v. power to this system, the brake goes into default which is on. Your ignition isn't failing intermittently is it?

[edgray]

ALL W-24 chassis equipped with an AAPB system use the J-72. ED

[oldusedbear]

The J72 is pretty much a totally different beast.

It might help to know if the parking brake stays ON after the engine misses. If so, what are you doing to get the brake to release? What is the AutoPark warning lite on the dash do while all this is going on? How do you know for sure the AutoPark is applying?

On some of the newer engines, things like bad missing of the ignition MIGHT cause the engine to derate. Tell us more about what you are seeing and hearing.

We need more clues - - symptoms - - pieces of the puzzle.

oldusedbear

[Nicholas Tinling]

OK. Here are a few more facts.
1. Driving along engine starts missing. No engine warning lights, no emergency brake lite. All appears normal except for missing engine.
2. After some time, maybe 10 or 15 minutes, red light for emergency brake (upper left corner on my Pace Arrow) comes on and vehicle slows (brake is obviously on)
3. After stopping, smoke appears, smells like spent fuel, not the burning of brakes. Red emergency brake lite goes off. Emergency brake is not engaged and vehicle can be driven. Engine still misses.
Mechanic at work horse facility told me that he is puzzled by the brake activation. Hydraulic line for brake does not go near any exhaust part.

[tropical36]

What exactly does this red warning light (emergency brake light) say? Does it say "auto park" for example?
I'm still thinking that there is a loss of full 12v power somewhere causing the miss and applying the brake. Also thinking that the power loss is due to some high resistance due to heat buildup, rather than a completely open circuit. May even be in a ground return, rather than the hot side.
I know this isn't much to offer and only fuel for thought, so good luck with it, and hopefully, someone else, like oldusedbear will have more to offer.

[Nicholas Tinling]

Yes, the light is exclusively for the auto brake. "....Loss of electrical power due to heat buildup?" interesting. I've never hear of that. Does anybody have an explanation?

[tropical36]

Let me rephrase what I'm trying to say. If you have a loose connection or some other reason for something not making good contact, bad ignition switch...whatever, then the circuit will have some resistance, producing heat and more resistance, until it reaches a point of minimal current draw by the load, also creating a voltage drop across this resister of sorts. At this point, things aren't going to work like they should.
Just trying to find some corelation between an engine that miss fires and an automatic driveshaft brake that falls back into it's default condition at the same time.

[oldusedbear]

I'd be tempted to see if there is anything like an error code available. It does make sense that whatever (lo voltage?) is causing the engine to miss, is affecting the AutoPark.

J72 shares some behavioral characteristics with J71, but there are some differences too. One is that the J71 is pretty much totally applied, or not at all. J72 however, has a proportional solenoid that can partially bleed off the pressure that is keeping the brake released - - so you can have PARTIAL application of the brake.

I suspect the disc brake on J72 is a lot more effective than the drum on J71, and it sounds like this may be a partial application as the OP describes it. Also, the AutoPark lite on J72 starts coming on at less than 900 psi. It can indicate SOME braking, as opposed to FULL braking I think.

On a J71 as an example, if you lose the alternator, the engine will run fine - - for a while. Eventually tho, the voltage will drop to a point where your tach and speedo go nuts, the engine misses etc. IF one at that point applies the brakes, turns on the AC, or introduces some other large load, the voltage will drop to the point where the AutoPark solenoid (held closed by voltage) will open and the AutoPark applies. The OP has not mentioned the battery going dead, but as suggested, there COULD be a lo voltage issue which affects the ignition first, and at some point it affects the AutoPark.

I'd start by looking for the error code. Might be a good excuse to buy a ScanGauge. Otherwise, I'd monitor voltage to the ignition system - - bring out a couple of leads from under the doghouse to a digital voltmeter you can watch going down the road.

We are quick to say we don't have a lot of information on the J72. Just guessing like everyone else in this case. If anyone has information on what's inside the little ECU that controls the J72, we'd sure like to have it fot the AutoPark Library.

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by oldusedbear: </div></BLOCKQUOTE> Thank you for your contribution to this discussion! We appreciate it every time you find the time to help out the AAPB folks.