Engine/Transmission (1998.5 - 2002) 1998.5 Cummins reads 30+ psi on Scanner?

[Waydin Stewart]

I have a Truck 911 thread about new injectors and exhaust noise now but I have another question that isn't as serious. Okay so I installed an Airdog II and a new VP44. Ended up needing to get the computer rebuilt as well as my throttle sensor circuit was friend somehow. So I had it sent off to be rebuilt. Got the computer back and the throttle worked. The truck doesn't have a prime cycle anymore and I cant access system function on a scanner among other things I haven't figured out yet. Well on my way into to town this morning I decided to hook a scanner to it and read the sensors while I was driving. Well everything seemed to be reading fine so I got on it a little bit going up a small incline in 5th and I looked at my boost and it was at 24.33(?)psi and began to rise to 35.97 at full throttle before I let out of it cause it confused/worried me. I have a code for throttle position sensor circuit low but O'reileys wont give me another sensor as they say I cant prove it is bad...But! I have no overboost code. I have no boost fooler. No aftermarket/adjustable wastegate elbow or aftermarket wastegate. So it should be opening at around 23psi anyways shouldn't it? I want to know why my map sensor reads that without throwing a code. I also want to know if its accurate or not. I was gunna buy an adjustable turbo elbow but now I'm kinda scared too.

 

[AH64ID]

MAP sensors read in psia, so that reading includes the standard 14.7 psi (at sea level) of atmosphere pressure. Subtract 14.7 to get your boost pressure in psig.

 

[Waydin Stewart]

It reads like 14.35 at idle so that would make sense. I cant recall clearly but I think before the computer had ot be rebuilt it wouldnt read 14 at idle it read like .5 or something like that and then ready up to 26 and would throw the boost code. Thanks for the help! Okay so that solves that question. When I had stock injectors and a failing vp44 the truck would make enough boost to "overboost" the truck. So why cant I do that with 100hp injectors now. I'm assuming the company that repaired my computer put a different tune in the truck as it seems to be different in a lot of other ways too. Like it doesn't prime for 3 seconds like it used too and it sounds slightly quieter than it used too and it used to smoke with the stock injectors and old computer internals. But now after the new computer and before the bigger injectors it wouldn't smoke. And even now with 100hp injectors it almost seems like the stock injectors smoked more if I lay into it lol

 

[klcammie]

Maybe new computer has boost fooler in it.

 

[JR]

You'll need a boost elbow to take advantage of the extra fuel you've got. With only +40 hp injectors and a Smarty I can easily peg 32 psig @ wot. You'll definitely want an EGT gauge if you work your truck. 100 horse sticks will push the limits of a stock turbo under a load.

 

[Waydin Stewart]

I've got a adjustable boost elbow and a boost fooler on the way. After I install those and replace the 2 banjo washers at the back of the head cause they are starting to suck air, I will adjust my valves as they are long overdue anyways and see if my super weird exhaust sound goes away and I'm getting higher boost.