Need help to find boost leak.

[bosco659]

I have an '89T with the following upgrades: Lexus AFM, 550's, Walbro, AFPR, SAFC 1, Spearco I/C, CT26 54 trim. I drove it to a local club meet the other night and it ran great. 15 lbs solid boost with no issues. I parked it for about 4 hours, had dinner, did the show and shine thing. When I left and got on the highway I started to hit fuel cut at about 10 to 12 psi. I had to dial back the boost to about 10 psi to keep from hitting fuel cut again.

Yesterday and today, I checked the following: boost leaks = none, switched AFM's, checked CT26 waste gate actuator = ok, vacuum at idle = 20 in, engine code 34 - turbo pressure, found one vacuum line disconnected at the thermostat housing thanks to some idiot at the meet, fuel pressure 29 psi at idle with vacuum attached, no vacuum leaks. Bottom line is I can't find anything wrong.

Any thoughts about what might be causing this issue? Car pulls really strong at 10 psi, idles well and everything is great other than the fact that fuel cut keeps on coming back. Previously I could boost up to 17 to 18 psi before I hit fuel cut. Could my SAFC be causing this? Maybe it is pooched and is not correcting as much as it is supposed to. I will hook up the wideband and check AFR's later this week.

Any thoughts would be appreciated. I can only think that the jack a$$ that pulled my vacuum line and disconnected one of my relays also did something else to that car that I haven't figured out yet.

Thanks!

 

[Nick M]

Either you missed the pin hole in the intercooler piping/coupler, or the turbo produces more volume than TCCS will allow.

That is making assumptions when you say everything else is right, such as the bypass screw length.

 

[bosco659]

I will check again for boost leaks in the intake between the throttle body and the head. I read other forums that talked about looking for boost leaks and they advised to make sure that the crank was positioned such that there would not be any valve overlap ie: intake and exhaust valve partially open at the same time. Makes sense to be sure that this doesn't occur since all of your test pressure would leak thru the head.

Anyone know what the best crank angle would be to avoid having this condition occur?

Thanks

 

[rayall01]

I will check again for boost leaks in the intake between the throttle body and the head. I read other forums that talked about looking for boost leaks and they advised to make sure that the crank was positioned such that there would not be any valve overlap ie: intake and exhaust valve partially open at the same time. Makes sense to be sure that this doesn't occur since all of your test pressure would leak thru the head.

Anyone know what the best crank angle would be to avoid having this condition occur?

Thanks

Another route to go, would be to isolate the piping before the manifold, and take that possibility out of the equation. Just test the piping first, and if it holds pressure, it would indicate a manifold leak. You could always reconnect it and try it the hard way after, if it made you feel better.

 

[bosco659]

Another route to go, would be to isolate the piping before the manifold, and take that possibility out of the equation. Just test the piping first, and if it holds pressure, it would indicate a manifold leak. You could always reconnect it and try it the hard way after, if it made you feel better.

I have already tested the intake piping and am 99% confident that there are no leaks before the throttle body. It's my intention to test the manifold etc this w/e.

Thanks