G4+ Fury - 1.5JZ - Suddenly losing power

[Dean]

Hi everyone,

I thought I'd ask here to see if anyone can help with the issue before we book dyno time. This is a friend's car I helped wire a number of years ago. We've chased some ignition issues over the years, but there were many trouble-free events. The most recent event showed a pretty massive problem with the engine cutting out and not responding to throttle inputs.

1.5JZ - R35 GTR coils - 350Z E throttle - standard CAM and CRANK sensors

You can see the issue at multiple points in the log, but a couple of good ones are: 19:02.003, 19:20.200, 20:07.670

There's a bit of a misfire, which could be anything spark/coil related, but the weirdness happens are that. You can see the driver is applying throttle, and the throttle body is opening, but the engine is not responding at all. It's still showing a steady RPM, and there aren't trigger errors, fuel/ign cuts or faults being recorded. 

 

Can anyone see what could be the issue? Or do we need to log some different parameters to get a better idea?

Thanks!

 

Dan 370Z

[Adamw]

I think there is an issue with the throttle/throttle position.  All of the time points you mention show evidence of the same issue, but the last patch at 20:07 to 20:12 is especially convincing.  The log shows the TPS is wide open at 3000RPM, yet the manifold pressure is sitting at only 33-48kPa, there is no way an engine like this would be pulling overrun levels of manifold vacuum if the throttle really was wide open/unrestricted. 

The MAP appears to be correct as the differential fuel pressure is reasonably flat at the same time, if it was the MAP sensor that was reading low the diff FP would be much higher than normal in that area. 

Since TPS sub and the throttle error accumulators arent logged its hard to confidently say that it is actually the throttle causing this restriction as there are a few puzzling observations:  1) If it were just the TP main sensor failing then I would have expected the throttle control system to trip into safety mode, it only allows about 2% error for a max of 2 sec.  2)The throttle motor DC is sitting at about 30% in the restricted areas which looks similar to other areas of WOT when it was working correctly, so that kind of suggests TPS was actually in a similar/normal position.  I dont know how the TPS is connected to the throttle shaft/butterfly internally, but it is almost like the motor is moving the TPS, but not the throttle butterfly?  Broken shaft maybe?  Or perhaps the throttle actually is opening fine but the "throttling" is coming from something else - like a rubber coupling or air filter collapsing, something floating around inside an intercooler pipe etc.  I would have thought to pull the MAP down to 33kPa however it would need to be a pretty well sealed "restriction".

Anyhow hopefully that gives you some clues what to concentrate on.   

[Dean]

Thank you for the detailed response Adam! That gives us somewhere to start. 
I appreciate your time. 

[David Ferguson]

That reminds me of a car that was modified to have an inlet restrictor.  First, they sealed the original cowl opening (bottom of the windshield) in the aluminum air box.  Then they welded on a pipe to attach the inlet restrictor.     I ran it on the dyno, and it only made 275 hp, previously 425-450 unrestricted.    They were really upset -- until they discovered they hadn't actually cut the hole to the intake pipe/restrictor.   The airbox was collapsing the 1/8" aluminum top and allow air in the very tiny gaps.   So it was making 275 hp with essentially NO air.   Once the airbox was properly modified, the engine was restricted to something just under 400 hp I believe.

So, check you don't have a clogged air filter, rag in the intake, broken throttle plate or similar.

[Dean]

We may have found the issue! The intake on the turbo is a relatively long 45deg silicone hose that has lost its rigidity. 
It’s only had load on the hoist with the handbrake and brakes providing resistance, but it has improved so far after removing the intake!

I went over the whole loom and fixed a few nicks and dodgy repairs too, but we’ll see how it goes at the next track day.