Boost surging

[srichard]

First, a little background:

I have capped my rail due to a faulty pressure valve, using the FloorIt! valve. I have been running with my Quad Race box turned off, but present for the past few months, and the truck has been running fine, with the exception of putting out a bit of smoke when i get on the accelerator. It boosts up nicely to 32psi and stays there. If I put the box on setting 1, it goes up to 34psi pretty quick and runs fine, but smokes more.



Now, over the weekend, I removed the Quad box since I need to send it in to get the latest flash (I was still using the version with the throttle position sensor tap)



When I got back in the truck, and I accelerated hard, I noticed that the boost was surging up to 32 then back down, and then back up.

I tried many times, and it is easiest seen in 5th gear (that lets me accelerate for a while before running out of revs) and here is what it does:

boost goes to 32, down to 24, up to 30, down to 26 and then gets to 28psi, where it stays more or less steady.

There is no smoke at all.



This tells me that the Quad box, that does boost fooling even when it is off, was masking a problem with the truck.



Does anybody have any idea what it could be? I would say it's something in my fuel supply, but then, why does it seem to work fine with the Quad box in place?



any help appreciated.



S.

 

[DieselFiend]

Without actually seeing it, I'd say that it's normal. Your wastegate is opening and closing. Mine does the exact same thing at WOT. I'll peak from 30 to 32 then drop down to 26-28 then back up if I stay in it.

 

[YFZBOB]

Mine does the same too! Waste Gate doing it's job, ya Blow up the plastic intercooler if it wasn't.