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Timburrr

Exhaust Brake Intermittant - Suspect APPS

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Posted (edited)

A little while ago my exhaust brake (BD remote mount) started to work intermittently.  It seems that when I first turn my truck on, if I flip the switch at idle it works normally, but after driving around for half hour or so, at an idle the exhaust brake will only engage sometimes.  It also seems like if I'm driving and coming to a stop the exhaust brake will engage, then as the RPMs get close to an idle, it will cut out.  If I down shift and the RPS go up again, it will engage again, then cut out as I get close to an idle.  It didn't do this before.  I can hear the switch under the dash click as it tells the brake to go off or on, so I know its not the physical workings of the brake (spool valve or anything like that).  Sometimes even after driving for a half hour or an hour it still works normally and sometimes at an idle it will go off and on.  My hunch is the APPS, but I'm not sure what would suddenly make it go out of whack.  There's always a chance some hard bumps put the brake switch out of calibration because I had it set to disengage the brake with very little APPS signal.  I found this article
LINK

here on the forums which is super informative (Thanks Michael!), but I don't understand what causes the APPS to need calibration.

 

Should I go straight to calibrating the APPS or does it sound like it could be something else or something simpler?  I admit I haven't checked for AC noise from the alternator which I plan on doing as soon as I have time (not sure when that will be!).  I should also mention ever since I got the truck (3 or so years ago) the cruise control is wonky and it will slowly accelerate to higher and higher speeds until I have to shut it off which I assume could be related.  When I'm looking at my Edge Insight CTS2 I notice as I'm decelerating in gear it shows the APPS as being a steady 0% but when I'm at an idle it spends most of the time at 0 but blips up to 5-8% momentarily.  The refresh rate on the Edge isn't great, but that's what I'm seeing.

 

Thanks for reading and thanks in advance for any help!

Edited by Timburrr
to make it make more sense

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APPS reset on programs the ECM the span of voltage from idle to WOT. The Exhaust brake is typically based off the IVS (Idle Validation Switch). If the switch is triggered for idle then the exhaust brake should be active. Depends on the type of APPS. Timbo APPS is fully mechanical so there is no voltage value to flip-flop the IVS it all based on angle. Now the Stock APPS and Wells APPS both rely on voltage to flip-flop the IVS.

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Thanks for the replies. It does have the controller under the dash that engages the break via the idle verification (thanks Michael I was mistaken and thought it was the APPS ).  I did have it set pretty sensitive so my plan is to turn it up a hair (it is a very fine adjuster so I'm guessing a good bump could possibly back it off enough). I'm just worried it could be another problem like funny signals from AC noise (maybe an early warning sign). I have read AC noise can cause all sorts of funny behaviour.

 

My understanding is when the truck senses the APPS has been engaged it bumps the truck out of idle mode and starts to control the motor via sensor inputs? So there is a chance I might need to recalibrate the voltage of the APPS

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Here is the installation manual to mull through. Might be helpful.

 

BD Remote Brake Installation Manual

 

My old turbo mount brake had a main arming switch on the shifter and then there is a micro switch on the throttle that activates when in neutral position. 

 

You could hear the switch click on and off when letting off accelerator and pressing down. 

 

I really don't see why the remote brake would be any different than turbo mount.

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So a little update. Truck was labouring to start so took it in to the auto electrical shop to test the batteries and the drivers side was bad and the other was fairly bad. Put in new batteries and the exhaust brake has functioned 100% normal without any other interventions. I'm not an electrimagician but my only guess is a dead cell was causing some issues? Voltage always showed as fine so I don't know. Anyhow it seems good now. 

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I would test the alternator for excessive AC noise. When the batteries are weak like that it puts more stress on the alternator and diodes are known to get damaged from overheating. Now that the electrical load is reduced because the batteries are fresh the alternator AC noise will be less but the problem still remains. I would test it just for safety sake. 

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That's a great idea, I'm planning on doing it as soon as I have time. If there is excessive ac noise, are there brands that are good replacements or do you guys like to find a good rebuilder? The shop said a rebuilder might be better but it will still be Chinese components going in.

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Basically its not the alternator but more like the grid heater. High current load for an excessive amount of time overheat the diodes. If you want to upgrade to 180 to 250 amp alternator to overcome the problem but comes at very high price tag. Upwards of 500 for alternator. So in my case I'm using a Autozone alternator now but left my grid heaters unhooked since December no issues to report. 

 

@W-T has a great ground wire mod that some report reducing the AC ripple noise. 

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Interesting.  Thanks for the information. Hopefully it tests fine but I would consider an upgraded alternator if I can find the funds. If I remember right the key is to disconnect any added on electronics to get a true reading. I'll find the write up and check it out. Thanks again Michael.

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