I posted this here because I have a lot of high perf stuff even though I don't know if it has contributed to this issue... So here goes.

I was driving on a hunting trip. About 60 miles in, I pulled into a rest stop. When I restarted my truck I had the check engine light on. Pulling onto the highway, I knew something was wrong as it took me about 20 seconds to hit 60mph. Very low on power. I'd floor the pedal and nothing would happen. Couldn't get over 65mph. My egt's weren't excessive at all as I didn't have any fuel it seemed. Radioed up to my bro-in law and told him we had to pull over. Thankfully I had my Diablo with me to read codes and clear them.
Underboost condition was the code. I checked underhood as I thought maybe I had popped a boot or something. Everything from the turbo, intercooler, to the manifold checkout out fine. The turbo sounded fine... same whistle as always. So I cleared the code, started the truck and she ran fine for the next 300 or so miles. To clarify, I was running stock programming, no boxes, 100% stock except mechanicals obviously. Oil level is perfect, no diesel smell. No drips anywhere of any liquids. Ran over 350 miles on half a tank of fuel so I'm not dumping anywhere.
And it just happened again and I cleared it and now it's fine. I wasn't hard driving at all when this happened. Low boost, 4-6lbs, and occasional 10lbs. After first time, I did go up to 30lbs to see if something was causing a loss of boost but nothing popped and she lasted up until an hour ago when it happened again and was driving very conservatively again.

Sorry for the length... any replies appreciated...
List of what I have still connected...
XZT box but bypass installed.
Recon rail pressure guage
VA 3.2 but running on stock switch position.
No programmers as stated...

Maybe something with the XZT or Recon connection or the bypass plugged into the turbo connection???

 

Or it could very well be MAP sensor FUBAR. Pull all electronics and eliminate the variables. Put back to stock... if it still occurs then MAP sensor is likely. If not, put one device back on until it occurs again, then that is the likely culprit.

 

Good idea... and the MAP sensor is the one plugged into the manifold? correct?? just behind the intake horn...

 

Correct and it is the most likely source of the fault. Could just be a loose connection on the MAP but it may be dieing.

 

Recon and XZT are disconnected. Stock plugs are back in their respective locations. Will see what happens and post back in a few hundred miles...

Thanks

I've never really read any threads about MAP sensors going south... maybe I just missed them?

 

I've replaced one on mine. But I've also seen dirty connections causing problems. I'd clean the plug real well with ether (starting fluid) or an electrical cleaner; and coat it with dielectric grease before replugging.

 

Are you sure it's not due to stock fuel spooling a II 64 turbo?

 

If you are getting an underboost code I am guessing it is caused by the low psi at cruising speeds with the larger turbo. In my experience the bigger turbos make considerably less boost at cruise with stock electronics than a stock turbo does. If you are city driving, stop and go the MIL will never get set because it has to be in an "underboost" condition for a period of time, not just for a second. If you have cruise set or are cruising without throttle play for a period of time is when this will show up.

It could be any of the other stuff but, odds are that it is not a real issue other than what I stated or you would get different codes. If it was a bad/loose/dirty connection you would likely also get a 0069 or something related to IAT.

 

bigwheels, I was wondering about stock fuel with the larger turbo.... but I have been running like that, on and off, for a few thousand miles now. This was the first time traveling long distance with cruise control on as you mentioned Qzilla. Now it makes sense to me... darn stock fueling...

I'm surprised others haven't run into this situation in the past. Even if you're running more that stock fueling, at lower highway speeds (55-60mph) I don't think there is much more that 2-3psi boost.