boost fluttering


Mine since '92
May 25, 2001
boost fluttering **SOLVED**

Just installed my freshly rebuilt engine and now I have a strange boost flutter. It starts at around 10-12 psi and just shutters real hard and doesn't really climb up on boost. The shuttering is pretty violent, enough to shake the car. I thought maybe it was wastegate related, so I unhooked the gate and ran it with just the spring change. O2's read in the 850 range when it happens. Wondering if it could be electrical, like coil pack?? Or maybe fuel pressure regulator??? All hoses look good too.
Steve, I leaned it down a little which decreased the fluttering some. This is happening at 1/4 - 1/2 throttle. The car really acts stupid if I try to go WOT. T63E with an ATR FMIC, GN1s, dual 307s, 50# injs
Part throttle and ten psi is compressor surge territory, but it should clear up completely when you go to WOT and not get "stupid". That's is a weird one. When does the second pump come on? What about your cam and converter? Did it work fine before or is this a new combination?
Could be the orifice in the Y fitting. Check the size, some were too small causing flutter and over boost problems.

I have that happen on mine with the wastegate rod excessively shortened. Try to lengthen it and see what happens.
Running a PTE billet 214 cam and 9" 3400 converter. Car wasn't doing this 3 weeks ago during break-in. Seems it just reared it's ugly head from nowhere. The second pump is not even coming on yet when the flutter starts. I don't think it's wastegate related either. I'm running the same vac. hose setup I've had for years with no problems. I completely removed the wastegate hose from the compressor side of turbo and plugged it off, now running on spring pressure alone. Like I said, it's happening at 10psi(very low) and absolutely will not "drive through" the fluttering. The car almost shuts off! I took all the turbo/intercooler hoses off last night(what a PITA!) and checked for splits and holes, all is good. I'm going to try a friends FPR and if that's not it, I'm going to try his coil pack/ign. module. FWIW I have an ATR BOV on the car. The hose is in the correct place and the spring is set at it's strongest position(set screw all the way in). If all else fails, I may try installing the blockoff plate in place of the BOV. Thanks for the replys, keep 'em coming. PS - anyone experienced a failing FPR? It seems like it would try to run lean, but ya' never know...these things can get really goofy sometimes. Other than the boost problem, the car idles/drives/runs great. Stupid demons!:confused:
Check your clamps on your IC hoses...make sure they're tight...

Also, run a compression test...
Kevin said you were going to come up with an excuse why not to run him.....:p

On a serious note, mine acted kind of like that when the MAF was going out. I know you have the trans/LS1 set-up, maybe swap that out with a good stock unit for giggles.....or you can get my LS1 MAF and try it....
How old is the turbo?? Too much play in the shaft will cause boost flutter. I had the same problem with my old te44. It fluttered at part throttle and went away at WOT, but as it got worse, it stuttered all the time. When I put on my new turbo, the flutter was gone.
brand new turbo...swapped MAF meter for a known good change, still fluttering
Warp6: Your problem is rich mixture.Try leaning it by chip or drop
your fuel pressure down and it should go away.It worked for me.
I have Cas FM ic,Te51,50# inj.;)
too rich and too lean???

Steve and tcgn, I think you guys are right. I dropped the fuel pressure down to 35psi (vac line off)It would still try to flutter just a little, not much but then it would come on STRONG!! The only thing is, now it's too lean on the top end (wants to detonate) I got a reading of .745 with 4.5deg of knock retard. If I try to richen it up, it goes back to the fluttering. I can't find a happy medium:confused:
Do you have BMC tuner 6?If not,go buy one and program your own chip to correct that problem and other problems as well if any.:cool:
The part throttle is very common with the larger turbos and front mounts...I have the LE45 and it can be heck right around zero vacuum to 10# at light throttle. No problem at top end.

Todd K will be along shortly to tell us we need to learn to drive with a big turbo! :)

You will have to tune for the top end first. The light throttle is a problem. I did not have much luck with a bov valve. It seemed to help the problem when lifting off the gas a little but made it worse down around zero-1# of boost when easing up an entry route and holding light throttle...sometimes it just goes into never-never land and starts coughing and refusing to take gas until I lift and then give it substantial pedal.

Too rich will add to the flutter at part throttle, I have noticed.

When backing out of the throttle, it helps to lift completely rather than easing back and catching it part way.

These larger turbos want to make boost easily and when the tb butterfly is only cracked a can't go anywhere and kicks back against the compressor...the twilight zone is more pleasant than the surge zone....LOL
so, I guess I need a chip fix? I tried leaning it with the T+ on the base fuel then adding fuel to the wot. Base switch position 3, WOT switch set to position 7). Seemed to help a little, but it's still not enough. If I try to add to the whole fuel curve with the regulator it goes back into MAJOR flutter-zone.
**UPDATE** problem solved!!

The fuel pressure gauge was WRONG!!! It read 20 psi low!! When I had it set at 45psi it was ACTUALLY 65psi. Put a new gauge on, lowered the fuel pressure and proceded to run 19 psi boost on pump gas. Blows the tires (BFG drag radials - 275/50/15) instantaniously and pulls like a freight train through all gears. Running 50# injectors with a 7th 43#(equivalent to a set of 57 pounders when activated). Also, the car would not start hot with the fuel pressure so longer a problem.
I don't see any thanks to me posted :rolleyes:

I guess I'll have to derail your "little engine that could" now:D