At What temp will Fuel Pressure Up (FPU) system switch on the VSV?

[suprabee]

info on TEWD states that the system causes the VSV to come on for "high temp" starts.

I'm looking into the idea that my poor warm start idle (bounces from 500-650 rpms) for the first minute after start up is caused by my FPU not turning on. ie..the VSV circuit not being completed to allow the FPR vacuum port to vent to atmosphere.

the VSV is new (but I've tested it per TSRM), I have constant 12-13 volts at the one terminal of the VSV connector, other terminal has continuity to the VSV2 at the ECU. The ECU never switches on the VSV. Of course, I can unplug the vacuum line at the FPR and my idle increases to a stable 800 rpms. Wait a minute, then reconnect the FPR vaccum line and my idle drops to a smooth 650 rpms.


THW, THA, KS(using oscilloscope), and STA all tested at ECU and check OK. TEWD states that the ECU evaluates these sensors for determining FPU.
From what I see on the TEWD and comparing to the operation of the EGR VSV the ECU needs to pull VSV2 to ground, thus completing the circuit and opening the VSV.


My question is at what temperature should the FPU system turn on the VSV? Would it be normal operating temp or something higher?

OR... when has anyone experienced their FPU system working properly?

 

[jetjock]

THW is the dominant signal. Approx 100 C and higher. FPU is disabled 90-120 seconds after starting.

 

[suprabee]

^ thanks

I've been monitoring the VSV for days now and the ECU never switches the VSV to vent the fpr vac line. Again, all the sensor signals are there and in spec at the ECU , VSV is good, so it seems that the ECU has an internal fault.

Last year while I was replacing valve stems seals and had the intake off, I randomly checked the "old" fp VSV and it would not work with votage applied, I think I recall measuring it as open. So, I said..shoot, how about that..this VSV is bad....so, I bought a new one and installed it.

Since then, I've never checked to see if the darn VSV was actually switching on/off and so the other day while pulling the fpr vac line during the warm poor idle, rpm's increased and idle would improve, then slowly rpms would come down to 650 and remain stable even after re-attaching the fpr vac line. I've done this probably tens of times trying to resolve this issue, but I never checked to see if when at hot start up, I should have no vacuum on the fpr if the fpu system is working. I must have had some mental block or I'm getting old or something because I've read about the fpu system in many threads, but I simply never bothered to see if it was actually working. Looks like it is not.

I know I've read by many that the ECU's don't have failures, but without a schematic of the ECU I can only go with it being the fault here.

 

[3p141592654]

Well, I'd exhaust other possibilities first before I blamed the ECU. The FPU signal comes of the same MCU port as the ignition and injector signals and EGR.

Check for proper operation at the ECU itself to rule out wiring issues. The EGR signal is also worth checking, they share the same ECU internal ICs and components for the most part.

 

[Nick M]

If he flowed a little EGR at that time, it would act the same way.

 

[suprabee]

update...not the ECU...I was finally able to observe my fpu VSV working..that is...switching on to remove vacuum from fpr. I had to drive the car over into 90 degree temps to get it hot enough for the ECU to turn on the VSV. Seems were I live along the coast is just too cool and I guess my cooling sysyem is working very well also, so I was never getting it hot enough.

When I started the engine after sitting for @5 minutes after driving in 90 degree temps, the electric cooling fans came on, and the VSV was switched on, so fuel pressure increased. Also noticed that when the fans would shut off, so would the VSV. Observed this many times, so as JJ said previously, is seems the water temp is the leading sensor for VSV operation. At most I observed the fans and VSV operating 10-15 seconds and as soon at the coolant temp lowered, the fans and VSV shut off.

rick

 

[3p141592654]

So your poor warm starts problem remains, and is not the FPU VSV?

 

[suprabee]

So your poor warm starts problem remains, and is not the FPU VSV?

To clarify, I'm not having poor warm starts, starts fine, its poor warm idle only at start up. So, no the FPU system was not the problem because I found the system to be working.

That said, my poor idle at warm start-up seems to have been resolved. Here is the thread I started specifically for my loping/poor idle at warm start up. I started this thread only to answer the specific question about the FPU system, but it stems from my problem which can be read/discussed here:

http://www.supramania.com/forums/sh...idle-quality-at-warm-startup-for-brief-period

rick