Boostedhat

I would like to ask you gentlemen for some help. I have an 1995 Sc300 with a GTE swap. Mods include HKS to4R single turbo setup, Greddy type R 47mm wastegate with a 14psi spring, all swapped to usdm electronics, and a 1994 Supra 6 Speed TT OBD1 ecu and Greddy Boost cut controller, HKS SSQ new version. Greddy front mount kit, usdm supra injectors and a wally 255 fuel pump.

Finished the swap about 6 months ago and the car ran GREAT. Gradually over time the car started breaking up under boost off and on. Now the car never boosts right and always breaks up. Currently running 14psi. The car starts breaking up around 10 or 11 psi. Did a search and thought maybe the spark plugs were gapped wrong, pulled them out and they were about .44 and kind of white, so I purchased new plugs and gapped them to about .30. But this did not change anything. Strangely the cars gas tanks has been overpressuring, so we we drove it with the gas cap off and it seemed to help just a tad, but still broke up some. We have considered that maybe some of the coilspacks were going bad but, would that not cause the EGT to run cooler because of unburned fuel?We smoke machined the gas tank and the charcoal canister and purge valve are working fine. Pulled the codes on the ECu and it showed a "lean exhaust" code. Strange thing is the A/F Ratio guage says that the car is running fully rich, while the EGT guage climbs to about 1400 deg. All O2 sensors are new with the swap. The car runs perfect in normal driving with out getting into full boost. Checked all the couplers for ripps but have seen none. We have been racking our brains for a while and that is why I made this thread for help. Greatly sorry for the long post and thanks in advance for help.

2jzlex

iTrader: (3)

Hmmm, what is your fuel pressure? Always start out with the simple things. Might even try resetting the ECU.

eric_r_ho

iTrader: (9)

Did you check your engine vacuum? Don't know what the proper Hg is for that motor. Check for any vacuum leaks for the various lines on your motor..most likely its that if its throwin' you a lean code. Do you have some sort of ignition retarding for spark knock? I'm not too familar w/ your ECU mapping but I'm sure its the same concept as the K-Pro I had in my RSX..

cbrasian

whats controlling your fuel? ecu only ...

Boostedhat

Fuel is controlled by stock OBD1 Supra TT ecu.

TTSC3

I had this problem with my car about 6 months ago, but I went through everything pretty thoroughly. Obviously, I gapped the plugs down to .028, then I checked for vacuum leaks, and fixed any that were present. Before I went any further, I did a leakdown test, as from my previous experience, this can easily cause a break up, and you'll be chasing your tail trying to find the problem. Anyway, it passed the leakdown test perfectly, yet the problem still persisted, so I dug further and started checking the wiring at the coilpacks, the connectors, etc. I had a few connectors that were a bit shady, and some tiny breaks in the wiring as I pulled back the harnesses on each one, so I fixed/replaced all of them. I also swapped the ignitor and put a DLI on the car, and after that, the problem was solved. This process will probably work for you too.

Boostedhat

My Harness is brand new, none of the clips look bad at all, and no cracks on the coilpacks.

TTSC3

Swap the ignitor and do a leakdown test.

cbrasian

leakdown test wouln't do anything to do with break up its spark...... i would say you prolly need something to control fuel like a afc2 also gap your plugs down to .26- .28 check your wires and coils and hook it up to a dyno..... with afr the egt would be high as the unburned gas is getting burned in the exhaust

Dew23

iTrader: (1)

Check your coil packs and what plugs are in the motor.

TTSC3

Are you serious? Of course it would. If it fails leak due to w/e reason, whether it's a broken valve spring, or any other odd things, it would most certainly break up. I've had this happen on many race cars I've worked on, and I just went through this on my GTE. Usually it's spark, but you can't rule out anything when dealing with issues like this.