Ok here is a little background.  I bought the truck with about 100k miles on it 16 years ago.  I thought it still had the original Injection pomp but going through old paperwork from the original owner the Injection pump was replaced at 70K miles.  Shortly after purchasing the truck I installed a mechanical fuel gauge.  I have replaced the lift pum 3x over the years yeah yeah I know why did I not put in a FASS or something so shoot me.  The fuel Pressure is always at or around 17psi at idle and I never get below 10 at WOT.  Truck is stock so no big injectors or anything.  

Now onto my issue.  About 2 years ago I got the 122 Code which I troubleshot to the APPS which needed to be replaced.  I got a TIMBO installed it and it ran great until about 4 months ago.  I would get an engine miss at Idle every once in awhile when fully warm but no Engine code.  I figured it was due to injectors being tired they are the original ones I know that for sure.  So about a month ago I started getting engine misses when the truck started up.  At this point I decided to check the Alternator AC Noise and it was high.  I had the Alternator Rebuilt locally and now the AC Noise looks good.  Yesterday I fired up the truck and it stumbled after 15 seconds of idling but this time it died on me.  Very sick feeling btw. I cranked it and it started right back up.  The codes thrown at this time are 122, 366, 1688 and 1690.  I reset the codes but they came back the next time I fired it up except 366 and 1690 with another stumble.  I have read through the troubleshooting on all the codes.  Basically 122 which I am familiar with points to the APPS with its wiring.  I have gone through this no problems.  366 and 1690 point to the Crank Sensor with its wiring.  I can check that no issue but I don’t think that it is a problem due to no repeat.  So that leaves me at 1688 which from what I have heard is a death code for the VP44 IP.  Problem I am seeing is that most of them are dead dead...like no start.  Mine seems random as far as the stumble.  It is driveable but I don’t trust it right now.  

My theory is the VP44 IP has 200k on it right now and I feel it is going south with a slight miss/no communication here and there causing all of the other codes at random especially when it died.

Anyone else have experience with 1688/122 combo?  As you all know it is an expensive repair I would like to be more positive it is the VP44 IP before moving forward.  Feedback is appreciated.  Thanks guys 

Basically if you clear the codes and the P1688 returns the VP44 is done. 

 

 

Mike thanks for the words.  I need to clarify something 1688 has yet to come back on a second time at this point it just happened once.  122 is the hard code at this time that will not go away if it does it comes back again.  I just tested again for AC Noise and I saw something a little odd.  Truck was cold I started it up and had it hooked up to test Alternator for AC Noise. It was reading high like .075 V.  Once about every 10 seconds or so it would even spike above .1 V almost like the Alternator was engaged and charging.  After about 4 min or so it leveled off at .030 V which is what is was when I checked it a couple of months ago after a long drive home.  Could this high AC noise at the beginning cause issues?  Or is this normal charging after starting the truck? New batteries??  They are pretty old.  I am going to find some time to pull the ECM connector to finish the troubleshooting for 122 yet again but I don’t think I will find anything wrong like last time.   

4 minutes ago, deehammer said:

 Once about every 10 seconds or so it would even spike above .1 V almost like the Alternator was engaged and charging.

 

Sure is every time the grid heaters drop there massive load of 95 Amp load on the alternator the PCM is ramping up the field voltage to keep the batteries up so you see the alternator charging against the massive load of the grid heaters. 

 

5 minutes ago, deehammer said:

After about 4 min or so it leveled off at .030 V which is what is was when I checked it a couple of months ago after a long drive home

 

Again now the grid heater cycle has ended and this is normal AC noise level. This is one of the few reasons we are disconnecting the grid heaters.

 

6 minutes ago, deehammer said:

I am going to find some time to pull the ECM connector to finish the troubleshooting for 122 yet again but I don’t think I will find anything wrong like last time.

 

Go through the process and double check the wiring.

 

6 minutes ago, deehammer said:

I need to clarify something 1688 has yet to come back on a second time at this point it just happened once. 

 

Lucky... So I would keep that in mind. Weakness? Maybe...

Maybe not so lucky....

I was sifting through my Code Reader Logs during my lunch break today on my phone and I not only had the 1688 Code pop two days ago also again on 21 Feb so a couple of weeks ago.  Must have been an oversight on my part.  1688 Code is currently not showing but I am afraid it is a matter of time.  I will double check the wiring again for the current 122 Code.

I feel like my original theory that the IP is missing/no commination (electronically) at Idle is causing Sensors/APPS to disagree with the status of the Engine. 

Two separate issues. The APPS sensor is going below the minimum voltage level and tripping the code. The P1688 is a PSG electronics failure of the VP44. VP44 has zero to do with the APPS sensor and visa versa.

Edited March 6, 20187 yr by Mopar1973Man