Boost gauge flutter

[Schwind]

I installed my boost gauge and pyro a couple of weeks ago so that I could monitor and gain knowledge of the factory setting on my truck prior to any more mods I may do. My boost with the factory vacuum system was WOT no more than 8 psi. then it would cut back. At cruise it would run between 2 and 4 psi depending on the road conditions (from flat to slight up hill runs). Tow or not. I installed a boost fooler at the beginning of this week and set it at 10 psi WOT with trailer in tow (had no real heavy loads this week). At cruise the reading is between 4 and 6 psi same road under same conditions. Today I ran my truck without the trailer and at WOT once the boost got to 10 psi or just a little above the gauge started to flutter. Not really losing boost just fluttering at around the 10 psi mark. Other than at WOT the needle is steady at what ever point on the gauge it is at. It also doesn’t flutter when I am pulling. Was just wondering if this is a sign that the PCM is trying to defuel or what? My EGT’s are not any higher than they were without the boost fooler. About 950 at the highest with trailer in tow.

I am running factory vacuum system for the wastegate and my exhaust is totally factory with cat and muffler. The boost fooler sure has awoken the beast and my throttle response has greatly improved. My top end acceleration is about twice what it was before. I like it!!! I even gave a Dmax a run for awhile today he was smiling when he finally passed me but he had a hard time doing it.

Any ideas of why it flutters and/or what I can do to get more out of it without harm would be greatly appreciated. I know this is probably old school for alot of you but its my start.

 

[qwomack]

The fluttering is the typical factory short comings on these engines. A turbo-master is the only way to get consistent steady boost and it makes a world of difference.

 

[Deere Freek]

Well i have a tm on my truck and i notice it too, only in high rpm though, i immagine its just a shortcoming of the GM turbos.

 

[iamdave0887]

exhaust pressure overcoming the vac in the canister or T/M spring pressure perhaps? mine does it as well but only when the boost gets towards the point that the T/M is set at.

 

[Acesneights1]

I am running TM. No flutter. I would imagine guage quality and placement of tap would have an effect. I run Autometer full sweep and am tapped into the side of the upper intake. Always consistent and nuts on with GMTDScan which is what the engine sensor sees.

 

[Schwind]

exhaust pressure overcoming the vac in the canister or T/M spring pressure perhaps? mine does it as well but only when the boost gets towards the point that the T/M is set at.

That’s what I am beginning to believe too. That the exhaust is trying to over come the actuator at the higher boost level. Just don’t know why it is doing it when I am not towing and not doing it while towing.

 

[iamdave0887]

That’s what I am beginning to believe too. That the exhaust is trying to over come the actuator at the higher boost level. Just don’t know why it is doing it when I am not towing and not doing it while towing.

more load on the engine affecting it somehow?

 

[Turbine Doc]

What is range of the gauge 0-30 or 0-15, lower scale will be more sensitive to pulsations,
where did you tap for the reading,

what kind of muffler on it, my Banks muffler was reverse flow, and caused rapid boost pulsation on acceleration, when I changed to a Heath straight thru flow muffler it stopped,

What brand boost gauge, I have a Faze boost gauge (cheap) on my exhaust backpressure and it pulses a lot, very sensitive to pulsed exhaust gas, you may need to incorporate a pulsation chamber or go with larger dia. tube

For test onlt wire it shut and see if it makes much difference that way you will know if it due to wg opening or something wrong with way you are sensing the boost

 

[Schwind]

It is a 0-30 gauge from glow shift. It is what I could afford. As far as the muffler it is the factory one and I also have the cat as well. The factory down pipe too. The exhaust is the next mod on my list but it has been put on hold till after christmas, so says the other half. The pulsation is only at the higher boost reading the needle is steady at other readings. Here is were I installed the NPT fitting

 

[DennisG01]

For test onlt wire it shut and see if it makes much difference that way you will know if it due to wg opening or something wrong with way you are sensing the boost

That's a good idea - it should at least narrow down the possible problems, if there are any. As stated above (with higher load on engine when towing) maybe it's exaggerating a small leak somewhere (vac line, etc)? I mean, with a load on it, you're probably staying at that level of boost for a longer time.