3TGTE Flatspot Issue

[Daymoe]

Ive come to my first major hurdle with my 3tgte in my ra63 celica

When accelerating hard to get on the boost i find that it over boosts to around 10psi then dies/cuts out momentarily and comes back to life, sometimes kangaroo hopping down the road. the engine is all standard and on standard boost (bar pod filter and 2.5" exhuast). I never used to see figures above 7.5psi. Even though it is boosting so high i don't feel that its gaining all that much power even for that moment. So maybe the boost gauge is deceiving me. Basically i can't let the engine rev out with this issue and the car feels crippled because of it.

Is this an issue with the turbo? Waste gate? how can i test it?

Is this an issue with fuel delivery? I'm running an 18rg fuel pump as standard with the ra63 have a replacement VL turbo pump ready.

Is this an issue with ignition? plugs were changed 6 months ago, still running original plug leads

I could probly take a video of boost gauge tacho to help diagnose.

Any help/feedback is appreciated.

[dorifto_vip]

have you changed anything recently? it could possibly be fuel, is it fine off boost?
Also pull out the spark plugs and see what they looks like, if its been running rich or lean or if they are fouled.

[Daymoe]

Its had an oil change, and a variety of fuels, mostly premium though.

It runs perfectly off the boost.

Havent looked at the plugs yet, mostly because it doesn't miss a beat off boost.

[steve-O]

if i remember correctly the 3t-gte in standard form has a fuel cuttoff if it overboosts, which it seems to be doing. check that the vacuum line hasn't come off the waste gate actuator, or maybe the actuator is buggered

[The GW]

Mate my car did exactly this, almost as if it was surging...Ran fine off boost but as soon as it felt like it was kicking in itd carry on. (wasnt running a boost guage at the time) since i bought the car and didnt own it very long before it developed the problem i changed a number of things..
Mine was running a pre pump to a surge tank, then a vl turbo pump to the fuel rail. I mounted the pre pump lower so it was gravity fed. Replaced a couple of dodgy hoses, and made sure all clamps were tight. I also had a small hole in my petrol tank which i repaired, so do a comprehensive check of your fuel system for problems like this.
I put in new spark plugs, new leads, filters, all the general maintenance stuff that never hurts doing.
I also discovered a lot of dodgy wiring while working on the car which i had fixed up, so maybe look at this side next..
pm me if you have any queries mate ill give you more detail on what i changed

[The GW]

steve o does make a good point...check that out first mate

[Daymoe]

great suggestions guys. thanks heaps. +rep all round

GW: you found that all that work fixed the issue? or did u test it inbetween each job?

Stevo: Sounds like a sound suggestion, will check that for sure.

[TA22 GT]

The fuel cut sensor might also be poorly earthed, this will also cause your issue.

Its a single wire and the sensor is earthed to the body of the car. Check its all clean or to get rid of it just earth the wire out and the fuel cut is gone.
I have info on my site including the Toyota wiring diagram that may help too.
http://users.chariot.net.au/~stmezz/wiring.htm

Cheers,
Simon

[3t-RA40]

When I had my factory harness/computer made to suit the car I never had the fuel cut and boost cut sensors. The guy who made the modified harness,earthed (or what ever thay do) the sensor so the computer thought the sensors were there and working fine. Before I changed to the Haltech I was running nearly 14psi on standard computer and injectors (rebuild motor with forged pistons though).
Cheers,
Neil.

[Daymoe]

The hose had not come off the waste gate actuator, but how can i tell if its buggered?

[steve-O]

if you have access to an air compressor and a blow gun, attach the gun to the vac line and and give it a few quick bursts. but dont go nuts cause you might wreck the diaphram in the actuator or if you have enough vac line try blowing into it as hard as you can without passing out, it wont actuate but you shouldn't be able to blow any air through it. or maybe manually open the actuator with your hand and block the vac line, it should hold a little bit. then when you unblock it you should be able to feel the vacuum.
thats harder to put into words than i thought
steve

[TA22 GT]

The hose had not come off the waste gate actuator, but how can i tell if its buggered?

Its hard to say, but if its overboosting it sounds like the actuator is sticky or the diaphragm is faulty. Only way to know for sure is to remove the dump pipe so you can physically look at it and test its movement etc.

Cheers,
Simon