Anyone, anyone, Bueller, Bueller? I would think the tuners here that write code for these car would have to understand the ins and outs of these engines. No?

 

I think it is simply there to prevent intake surge to go back to the fuel tank or the charcoal canister. The pipe #19 on your drawing and C on this one is the tank ventilation at full load and the other #14 on your drawing and A on this one is towards the carbon canister going through the electric vent valve (the one you have to look at ;-) )

 

Correct JP. Check valve #16 has to be there otherwise you would be boosting the charcoal canister and the pre turbo intake track. I was more curious as to why even have the connection between the intake plenum and the "T" by the #14 valve (#5 and C in your picture) to begin with. What's the point?

As I said, I'm thinking that the reason the connection with the check valve is there is for the fuel vapors to get drawn into the plenum at idle when the plenum is under vacuum (but not pipe #19 or C in your picture). I'm thinking that if the check valve was not there and that pathway between the plenum and the "T" was simply blocked off, what difference would it make? If that was the case, fuel vapors obviously could not get pulled into the plenum (basically making a shortcut) but would simply go in the pre turbo intake track via #19/C. Since it's a closed loop, the vapors would still end up in the plenum (via the compressor, IC, Y-pipe, and throttle body) and get burned by the engine.

Also, curious when the purge valve #14 is being commanded open and closed via the ECU. I'm thinking it's closed with the engine off and open when the engine is open. It may be more complex than that however. I have actually verified that valve #14 is closed with the engine off as I can not blow through it. I will see if I can blow through it when the engine is running. I'm not sure if anyone knows for sure or if the working of that valve are explained anywhere. It would be nice to know as it would help me trouble shoot mine which in all likely hood is faulty.

Similarly, I have thought about deleting the sucking jet pump (E) and the hose going to the top of the plenum. I have the jet pump (E) blocked off on my engine as it is simply not needed in my application since I have a 997 engine driven pump providing vacuum to the brake booster.

JP, it seems like you know more than anyone here about the workings of these engines so thank you for your input.

 

I understand what you mean. Is it safer to take fuel vapour directly to the plenum instead of the turbo intake? Remember the turbo become red hot at WOT....When the fuel is return to the reservoir at wot may be the level of fume is high, even if it is cooled for us north american by the fuel cooler!!! It is also interesting to see two different lines take the fume to the intake, one from the carbon canister one from the fuel tank...

I was also curious of the function of this #14 valve, unfortunately the wiring diagram does not help since the wiring goes to the ecu (or dme) ....If you are saying it is closed power off, I would say it open at idle to clear the canister after refuelling per exemple and if you open the throttle you want to concentrate the vacuum to venting the tank... I will check later if there is a function to test this valve on Durametric or PST2....

The jet pump function seems to be only for the brake booster which is not useful anymore in your case....

We are learning every day John! Questions like yours help us to understand our car!!!

 

That's a great point JP. At idle, on the stock system you will have the most fuel return back to the fuel tank. As such, I can see why they are probably trying to divert that directly to the plenum and not the hot turbo.

I would assume that the #14 valve has to be open with the engine running (or at least open periodically) in order to vent the tank otherwise the tank would start to develop pressure.

JP, are you sure there are two ways to vent the fuel tank?? I'm not so sure. I thought the only way the tank vents is through the top hat (where the fuel line connections are) via the rollover valve. The reason I say this is that when my rollover valve failed a few years ago, my fuel tank suffered massive over pressurization basically blowing up like a balloon. The only way to release pressure was to unscrew the lid to the top hat. If there was another vent there is no way that pressure could have developed like that.

Here is a picture of an OEM top hat. The gun turret looking part is the vent that is part of the rollover valve and my belief that the fumes from here are routed to the charcoal canister and then on to the engine though purge valve #14.

 

I think we got a dedicated line for the carbon canister and one dedicated for the fuel tank vent. I am not familiar with the fuel tank and his components. Only open the cover once to inspect the wiring since some owner had burnt connector.... Roll over valve! Thats interesting to know! But why it did not depressurized towards the intake through pipe #19 (C) ??? Over the fuel tank you got three lines with release connector, one is pressure, one is return and one is vent (may be the green one). Also I was looking at the tank and it got a valve connected on the side for the vapour recovery system. Am I missing something here

 

Ok, so the plot thickens. Lol. This is what I know for sure. Under the gun "turret" in the top hat is a roll over valve. It is a simple ball valve that will close off the vent when you tilt the top hat past 60º or so. This prevents fuel from escaping from the fuel tank in case of a rollover. There is also a safety overpressure valve in the top hat (seen as a small red dot) which is not visible in your picture. This prevents a fuel tank overpressure situation an would simply vent to the atmosphere.

When I had my tank overpressure situation I was using an aftermarket billet top hat which had a faulty rollover valve (which failed closed shut) AND the top hat did not have the overpressure safety valve. Fumes built up in the tank to a very high level when operating the car. What is puzzling to me is why the fumes would not escape the tank via the vapor recovery route through valve #23 (in your top diagram) to the charcoal canister, and though #24 and #19 to the intake. This leads me to believe that valve #23 only opens allowing the tank to vent to the charcoal canister during fueling when you deflect the flapper in the filler neck (you can hear the click). When the engine is running, #23 must be closed (otherwise I would not have been able to develop such an overpressure situation in my tank while driving the car (unless of course #14 is closed while engine is running).

Which steers me back to the purge valve #14 on the engine (the one I'm going to change). This valve must only open for a certain amount of time after the engine is started in order to evacuate the fumes that have built up in the charcoal canister after fueling. While the engine is running, valve #23 and/or #14 may be closed and the fuel tank is vented through the gun turret in the tap hat and line #3 which terminates somewhere on the engine, but where??? Obviously it would have to be on the intake, UNLESS the gun turret is there to draw air into the tank to prevent a vacuum under some situations. Hmmmmmm..

This is all clear as mud now and pure conjecture on my part. Lol.

 

I think I need a rest now! Getting confuse with all those valves. I did not have all those on my Datsun 510 1970 But it is really interesting to try to troubleshoot a fault but difficult from a distance !

 

Im tempted to take out the #16 valve and see what happens.