View Full Version : Am I hitting fuel cut on my gen4 3s-gte?

07-24-2012, 04:24 PM
There seems to be a wide array of answers for the stock boost levels on the gen4 motor. I've heard 12psi, 14, 16, 19, etc.

Last two days I hit what I pretty sure is fuel/boost cut (like a brick wall, the motor just starts hesitating/bucking like I'm out of fuel).

Sadly there's not a lot of people with the gen4 motor around. There's a lot of gen3 stuff though (and the gen4 stuff I'm finding is in Jamaica, europe, etc). From what I can find on the st215, fuel cut kicks in around 1.3 or 1.4 bar and stock boost is about 1.1 - 1.2 bar (15-17bar). When I have the problem, it happens around the 19-20psi mark (fuel cut levels).

What could be causing the issue that I'm boosting up to fuel cut without problems? Is there something I may of mis-connected or missed that is letting it do that? I know if I remove the line off the turbo VSV I can boost to the moon but I don't want that, I'd like to keep it around 13-15psi without any chance of hitting fuel cut.

07-24-2012, 07:35 PM
Fuel cut at sea level is ~19 PSI. I know youre not quite sea level, so maybe a little bigger.

If youre hitting fuel cut without a boost controller then you have a problem with your wastegate or plumbing. Check the line coming off the turbo to the wastegate, and the line from the wastegate to the TVSV solenoid. Ill bet you got a crack or something somewhere.

If youre still overboosting but you have checked that stuff and its OK, then remove the line from the turbo to the VSV, cap it on the turbo end, cap it on the VSV end, and see what that drops you down to. Should put you at wastegate yield. If youre still overboosting there, your wastegate actuator is not functioning properly or youre getting whats called boost creep.

Try my first 2 suggestions first.

07-24-2012, 07:46 PM
Yeah now that I'm thinking about it I'm wondering if I blew a line from the wastegate to the TVSV. I didn't think about checking that until about 10 minutes after I posted it. I bet one of the lines off the TVSV popped off. I never over boosted before and it just started happening lately (2 days ago).

07-24-2012, 08:06 PM
The last time I was overboosting it was because the bolt with the round plastic knob on my cheap eBay mbc came out.

07-24-2012, 08:15 PM
The last time I was overboosting it was because the bolt with the round plastic knob on my cheap eBay mbc came out.

I'm all stock though. No controllers, nadda. Just clocked the turbo and installed a boost gauge.

07-25-2012, 03:59 PM
Had a quick glance at it last night before I left the station, I didn't see any lines disconnected and everything seems to be in good shape (the hoses are all new).

Driving home I pushed it (maybe held back a bit?) but I didn't hit cut. It seemed to hold at 15 or 16psi. This morning though, I gassed it a bit and in 3rd gear it cut.

Luni, if I understand you you're saying to cap the line from the turbo --> the VSV? Mine's plumbed up turbo --> wastegate --> vsv --> some random container behind the intake manifold --> VSV.

Could I of mixed up the lines on the VSV where I connected them?

07-25-2012, 06:21 PM
I guess you could have.

Your wastegate actuator should have 2 nipples on it. One goes from the turbo to the actuator. The other goes from the actuator to the TVSV. That one is the one Im saying to cap off. On both ends.

07-26-2012, 05:03 PM
I've been running 19-20 psi for going on two years. I only hit fuel cut when it's really cold out. My vsv is removed all I'm running is a Mbc.

07-26-2012, 08:19 PM
Tecker what elevation do you live at? Elevation plays a role in fuel cut. If youre at sea level its ~19 psi. The farther up you get from sea level the higher it goes. In Utah, Im at 4200-4800 feet depending where in the valley I am. My fuel cut value (on a Gen3, which is the same as a Gen4) is around ~23 psi.

07-27-2012, 04:39 AM
I'm in upstate ny 12803 is my zip.

08-01-2012, 10:35 PM
I hit fuel cut w/ an open 2.5" down pipe on a stock 94 MR2 Turbo which I think is 17.4psi or something? Regardless, hit it while in 2nd gear going up a hill w/ no controller.

I love how cars drive at or near sea level. At 4500ft everything feels like ass comparatively lol.

08-02-2012, 04:43 PM
Yep Brian, and fuel cut on a 94 USDM MR2 Turbo is 17 psi. So you were right in line with where you should have been.

08-02-2012, 05:11 PM
I need to work out some kinks with my turbo plumbing (namely at the throttle body). I'm wondering if that's causing my overboost stuff. No clue though, gotta work it out one thing at a time.

(anybody have some 2.5" aluminum pipe about a 18" long straight section?)

08-04-2012, 12:04 AM
ive had a similar problem with my st215 swap also. i found that plugs always went out. this was with the cheap ngk. i went with the iridiums and problem solved. seems like you have a stuck wastegate..

09-07-2012, 04:14 AM
Yeah, all the lines seem fine. This weekend I'll have some time to actually start removing/capping lines and figure out whats going on.

Right now, it goes from the compressor housing --> wastegate actuator --> canister on the under the intake manifold --> top port on the TVSV. The bottom port then goes to the throttle body. Wonder if these lines were mixed up at all.