I've had this posted at the "club" for a few days and no one can help (or no one cares)...



Transition is supposed to occur at 4500rpm, right? So what senses the rpms and sends the signals to the solenoids? the ecu? something else?



And the reason I'm asking this, of course, is that my transition occurs at 5500rpm



Any help would be much appreciated.

 

the ecu controls it, but its also needs to see a certain amount of boost to start the transition. do you have a boost guage?



mike

 

Thanks for the response .



Yeah, I have a boost gauge. I actually had a thread on here a while ago when I was troubleshooting my boost problem - turned out to be just my altitude (7000ft), and I cured it with manual boost control in wg and pc (I now get pretty close to 10-8-10, but with transition at 5500). The only remnant of that boost problem is the late transition. Maybe it's the altitude also, but I don't see how. I figure it's most likely the ecu (since you say that's in charge of the transition) or the rpm signal that the ecu sees. Does the ecu see the same rpm signal as the tach? I heard somewhere that the tach gets its signal from the speedo and calculates rpm from gear ratio (or something like that). My tach seems fine. No bouncing or anything.



Any ideas?

 

the tach is fired from the ecu? (they fire it right from the trailing ignition on everything else), so i think the ecu does see the same signal as the tach (i think). the tach could be off however (unlikely). what rpm does the car hit 10psi on the first turbo? when does it drop to 8? it could be an altitude problem but it would be nice to eliminate other possibilities first



mike

 

I don't know for sure when it hits 10. It seems pretty soon (like almost immediately) after I floor it in 3rd at about 40mph. It drops to 8psi at about 5200rpm, then I feel the surge (and it goes back to 10) at about 5500. The link in my sig that says "My boost problem" contains alot more detailed info about lots of tests where I T'd into various vacuum hoses. The summarized version is as follows:



1) charge relief valve closes at 3500rpm

2) precontrol valve opens at about 4000rpm

3) turbo control valve opens at 5000rpm (probably just a little higher than that)

4) charge control valve opens at 5200rpm.



I determined whether valves were open or closed by using a vacuum pump to see what pressure/vacuum was necessary to open (or close) each valve, and then by T-ing into the vacuum (or pressure) hose to see if/when that pressure or vacuum was reached. I never spliced into any wires to check exactly when the solenoids were getting signal. I didn't think my cheap multimeter would make sense of the pulses. I did check that all solenoids work correctly, so I think (?) it is fair to assume that they are getting the signals very close to when the valves are opening/closing. Correct me if I'm wrong there.



Sorry if this is all a bit messy. This stuff tends to get very complicated very quickly. Any insight is much appreciated.



Has it ever been known for an ecu to make transition occur later than 4500rpm?

 

wow that is wierd. the only thing i can think of is to verify that the tach is right. that is bizarre



mike

 

Hmm. But if the tach is reading from the ecu, and if the ecu wants to transition at 4500, then the tach should be at 4500 during transition, even if the true rpms are somthing different, right?



Well, anyway, it's not a really big problem. The car still drives well. Just bugs me. Eventually I'll get an aftermarket ecu, and maybe that'll fix it.



Thanks for the help .