revD

iTrader: (2)

new to the RX world, and just picked up an 88 TII

liking the car but it doesnt seem to get full boost, maybe gets 1/3 of the gauge. I swear when i test drove it got double the boost i get now. is this correct? the cars seems pretty slow right now.

thanks!

FelixIsGod29X

iTrader: (50)

The stock boost gauge in the cluster is absolute garbage. It reads 0-40? psi. The stock turbo doesnt like more than 12? psi. Check the condition of your turbo and compression test your motor. If all turns out well then buy a aftermarket gauge and a MBC.

KhanArtisT

iTrader: (2)

Also check that the boost control solenoid is hooked up b/w the compressor reference line and wastegate actuator.

And the stock gauge doesn't read in psi IIRC, I'm pretty sure its mmHG

yudaya

sorry but your wrong the stock guage doesnt read in psi(american mesurements) it reads in mmgh, like a murcury pressure reading im not sure but around 10 psi is equal to the top to the guage, thats why when you hit fuel cut its ussually right at the top of that guage.

revD

iTrader: (2)

yeah its in mm HG,
I asked another guy about it and he said there might be a flapper door that directs air at low rpm to biuld boost, then should open -- this could be my issue.

so -- i looked under the turbo where the rod for the wastegate control(?) is, and i could not move the rod with a set of pliers. I did not put too much force in but expected it to move easily -- could that be what my friend and you guys are talking about?
im looking for some more info now...

KhanArtisT

iTrader: (2)

lol you'd have to be a strong **** to be able to move the wastegate arm/rod with your hand with it installed.

Thats not the right place to start though (but close), if you're hitting low boost its obvious that the wastegate isn't stuck closed which is unlikely anyway. I guess the arm being hard to move rules out a faulty diaphragm which is also uncommon.

Follow the rod to the actuator (big circular thing mounted on the compressor) and to the rubber line coming out of it. Check to see if this line is hooked up directly to the compressor or to a solenoid (small box thing).

I suppose the twin scroll could be stuck in the low RPM position, I don't know if thats common though and you should be able to wire it open for a test drive. I'd search more on that topic.

revD

iTrader: (2)

ha, woops...
well, i didnt find a pic of the twin scroll deal to help find/understand it, and need to chase down that line, I see where its connected to the actuator, but not the other end.

(need to get myself a manual on the car)

RotaryRocket88

iTrader: (7)

The stock gauge is actually in cmHg or mmHg x10, so 40 cmHg = 7.7 psi. A stock S4 TII should be hitting 5.5-6 psi in the 3.5k to 7k RPM range, which would be 28 to 31 cmHg (3/4 of the gauge).

The gauge may just be inaccurate, or something could actually be limiting boost. A big boost leak could do it. Maybe the BOV, a popped off vac line or loose intercooler coupler. The twin scroll actuator seems unlikely since the door will only close off one passageway in the turbine if vacuum is applied to the actuator. The twin-scroll solenoid is responsible for switching the actuator on/off, but solenoids rarely fail. If the actuator were stuck open (no vacuum applied), low end boost (under 2700 RPM) would come on a little bit slower, but midrange/topend boost would still be maximum.

revD

iTrader: (2)

well, the car feels pretty slow, i have checked for vac leaks, and the car runs pretty smooth. so ill keep checkin stuff.

KhanArtisT

iTrader: (2)

FYI you can find the manual in the FAQ (top of this section) under "MANUALS AND LINKS"

yudaya

i was going to mention boost leak as well, or dirty filter could limit intake for the turbo,ive moved the waste gate accuator arm a few times while installed ,its supposed to be very hard. a while back i made a restrictor for my intake , i was boost spiking really bad(damn s4 wastegate) and didnt have the time to swap out my turbo so i limited theair intake and ended up with low low boost while without the restrictor i was hitting fuel cut every time i barely hit boost itd jump to 10psi and cut like a **** but definitly check that

FelixIsGod29X

iTrader: (50)

Alright guys im sorry! I havent looked at a T2 gauge cluster in a few years.