Overboost, boost creep, or ???

[ALBERTAN]

I searched the archives and couldn't find a condition exactly like what I experienced last night. Took the GN out on a back road with the Thrasher 100, 114 octane fuel, and set at what I thought was 18 psi. Ran it and got rock solid 20 psi boost in 1st and 2nd. When it hit 3rd the boost gauge just danced back and forth between 16 and 20 psi. The dial was making a steady back and forth sweeping motion throughout third gear. No knock, car ran strong, but you could feel it surging at the top end. I'm trying to get it dialed in for the first trip to the track on Friday. I figured its the wastegate opening needing to be hogged out until the THDP arrives based on readings in the archives. But it doesn't match 100% with that description so I thought I'd check and see if it may be a faulty wastegate solenoid or something else before I start flailing away with a limited time frame. If anyone can confirm my diagnosis or suggest an alternative it would be much appreciated.

Other mods are here. Thanks as always.

 

[ALBERTAN]

ttt

 

[ALBERTAN]

No one has an answer? Please help me out or at least point me in the right direction. I cannot be the first person this has happened to. Thanks.

 

[Weazel]

Hmmm, just thought I'd throw in my 2¢, dunno if it's worth that though
When I first adjusted my wastegate I was getting inconsistent boost. It would be at 17 solid, then start to fluctuate between 14-17 psi or so. I did the only thing I knew how to do...nothing. I figured I had hosed the wastegate up, and this was before I got my directscan, so I just ran it again. Next day it was fine. Boosted to 17 and held on.
Of course now that I have DirectScan it won't do it again *knock on wood* I thought it could've been knock, but if you're getting none on your DScan (and I wouldn't imagine you would with that kinda octane) than I don't know what could be causing any timing retard. Are you HP ratings similar at a given RPM in 1st, 2nd, and 3rd? Geeze, I'm new to the program and can't really help you out with the other readings. I'm assuming you had DS up and running for the "boost creep" run? Damn, I can't help you, but I bet some people here can, so here's a big, long "TTT".
Sorry I can't be of more assistance.

 

[Nick Micale]

Dean, you do not give a lot of info to go on? From the web site it looks like a rather stock GN. You are seeing boost flutter, but it may be the engine laying down.

Need some data out of the computer like O2 readings, MAF numbers, be nice to know if the fuel pressure is adaquate and steady, RPM at 2-3 shift as there may be valve float?

 

[ALBERTAN]

Hey Nick. I was going to contact you directly on this matter if I didn't get any help. I'll go pull DS after I eat and run through the file. I was thinking maybe valve float too, but wasn't sure of how that usually presents. I definitely plan on replacing the valve springs but was trying to put it off as another Winter project. That's only a couple of months away up here. And you're right Nick...pretty much a stock car although the go fast parts are starting to pile up already. I love this car!

BTW, thanks for posting Weazel. I appeciate it.

 

[ALBERTAN]

Originally posted by Nick Micale
Dean, you do not give a lot of info to go on? From the web site it looks like a rather stock GN. You are seeing boost flutter, but it may be the engine laying down.

Need some data out of the computer like O2 readings, MAF numbers, be nice to know if the fuel pressure is adaquate and steady, RPM at 2-3 shift as there may be valve float?

OK here we go. Pretty stock car as I mentioned. Engine seems to pull hard right through the quarter...doesn't lay down like a stock SyTy at all. I've posted a log of one run here . Not that I expect anyone to go through it but it may be faster if there is a certain thing you are looking for to confirm a suspicion.

Anyways, O2s were right around 800 throughout second gear. In third the O2 reading starts off around 820 or so, sits at about 800 at the 1000' and gets down to 780 by the end of the run.

MAF readings sit around 245 through second gear and then fluctuate in third gear between 215 and 235. I am guessing the undulations seen on the MAF scope correspond to the undulating boost gauge.

RPM at 2-3 shift was 4875.

Fuel pressure gauge is not installed yet. I'll tape my test gauge to the windshield as soon as I lengthen the hose and confirm a rise of 1 PSI per pound of boost. It is a Racetronix fuel pump and hot wire kit, although I didn't find it seemed to pump any more than the old pump I took out when pumping out fuel through the Schrader valve. I have the AFPR set to 45 psi without the vacuum line attached per recommendations for the Thrasher chip.

Thanks for the input guys.

 

[Nick Micale]

Originally posted by ALBERTAN
........MAF readings sit around 245 through second gear and then fluctuate in third gear between 215 and 235. I am guessing the undulations seen on the MAF scope correspond to the undulating boost gauge.

RPM at 2-3 shift was 4875.

Fuel pressure gauge is not installed yet. I'll tape my test gauge .......

Well, that's more like it!

Would say the shift point does not indicate weak valve springs causing this problem.

The MAF readings could be the MAF itself. A known unreliable piece these have given me fits in trying to tune out a high RPM miss. Certainly possible to have a weak actuator too?

If the spark plugs are not very recent, would change them first as that is the most common high speed miss problem. The very "scientific" way to work through this is changing parts, tuning and data recording.

 

[ALBERTAN]

Thanks Nick. Was thinking of grabbing an extra set of plugs and taking them to the track Friday since I know I've been running it rich since I got it. The current CR43TS plugs are gapped a tight .035" and have maybe 200 miles on them.

I'll try the MAF test and see what shape my stocker is in. An LS6 MAF and Translator/Extender package is in the works with a friend selling his TTA. Looks like another project that may not be put off until the snow flies.

Is there a way to determine if the actuator is weak rather than just replacing it? I looked into an actuator from a SyTy for the GN since they came with an adjustable rod, but the dealership told me it was integral and would require the purchase of the entire turbo. So I went next door and bought a die and said to heck with stock appearing.

Thanks again for your time Nick.

 

[TurboDave]

I took a look at your file, and the only things I saw out of the ordinary were of course the MAF "rollercoastering", and naturally the O2's were following that! Maybe one thing to try would be to attempt to find a friend to borrow a MAF off of, for some more testing. Or borrow one off the TTA
Nice thing about have two closely related turbo cars is borrowable parts

Run looked pretty good other than that. I had to pick my jaw up off the floor when I saw the timing curve!! But then remembered you were running a Thrasher.

 

[ALBERTAN]

Thanks Dave. Sounding more and more like the MAF. One other thing I want to do is put the front screen back in. I know that's messed up vehciles in the past so I'll make back to back runs with and without it tonight. Thanks guys.

 

[ALBERTAN]

In the interest of keeping this forum useful for those scouring the archives for info down the road, I thought I'd throw out another possibility. A friend with a Syclone just cracked his header on the weekend and reported the same fluctuating boost afterwards. Not 100% sure of the logistics of how a cracked header would affect it...someone with more knowledge may want to comment. But if you happen across this thread during a search for info on a similar problem on your car, here is one more avenue to explore. I'll post the solution in my case once I actually find it.