Anatomy of an APPS - the SEQUEL!

[Gary - K7GLD]

Sorry for the length of these opening posts - this is a condensation of a MUCH larger original thread on the same subject.

4 years ago, due to their high and premature failure rate, I started a TDR thread on the 2nd generation APPS, entitled "Anatomy of an APPS". That thread ran MANY pages, with hundreds of viewers and posts. After lots of intense discussion and a few dead-ends looking for solutions towards improving on the "Fly-by-wire" engine throttle DC gave us, we finally arrived at some excellent, working and CHEAPER alternatives to what formerly was available to us.

Why be concerned about the APPS, and the apparently high rate of premature failures? Well, they aren't cheap - nearly $500 plus installation, and at about half the cost of a VP-44 injection pump, are certainly WORTH a bit of concern and attention!

This thread discusses and describes what was developed, and eliminates the need for readers to wade thru over 12 web pages and 400+ posts of the original thread.

LEGAL DISCLAIMER:

EVERYTHING pictured and described below is PURELY for information, and IS NOT a recommendation that ANYONE do as is shown here - and if some DO choose to copy any part of what is seen here, they do so at their own risk!

OK, now down to business!

The APPS on our trucks is mounted on THIS bracket, on the driver's side of the engine:



Here's the back side, where the actual APPS module is mounted:



Once removed, and opened up, the inside of the APPS module looks like THIS:



The above is the electronics side, showing the Idle Validation Switch (IVS) section - here's the other side, showing the rotary potentiometer that actually signals the ECM when the accelerator pedal is depressed - you will note the resistance traces in the printed circuit backing, and on the removed part to the left, the rotary contact fingers that actually make contact with the traces:



That potentiometer is NO DIFFERENT in construction than a common volume control as used on many radios and stereo amplifiers! In fact, what you are seeing on BOTH sides of the APPS circuitry is NOT a solid plated board, but rather, a thin Mylar membrane - like a sheet of photo film - that is plated with printed circuitry, to which the individual electronics components are surface mounted - the potentiometer traces are similarly an applied thin resistance track, then both sides are simply GLUED to a support backing. In my opinion, a POOR and flimsy method of construction, especially for the purpose it's used for, and PRICE this one demands! Far more like a dime-store kid's toy than a several hundred dollar automotive part!

(MORE BELOW!)