CIS Fuel pressure question

jebbach911 · 12-22-2011, 03:49 PM

I have zero cold control pressure and zero warm control pressure but normal system pressure. This happened after my overboost cutout switch turned off my fuel pumps several times while I was trying to get my boost controller adjusted. Could the fuel pumps turning on and off abruptly have jammed the pressure regulator inside the fuel head? I just had a few minutes to check pressures before running out the door for Christmas/Family stuff.

If anybody can think of anything else to check, please chime in!!

The car is 1991 911 Turbo
Mods are BL WUR, CIS modded fuel head, Fabspeed headers and exhaust, Synapse BOV, GReedy EBC, GT35 turbo,

mark houghton · 12-22-2011, 04:45 PM

A couple of obvious questions first come to mind. Is your car running? If the answer is yes, that's just not possible with zero control pressures. Do you have your test gauge hooked up to the WUR correctly?
If the car aint running, and you have tripped several times the overboost cutoff switch as mentioned, then perhaps the switch is now toast - thus, your pumps won't run at all. If that's the case, simply unplug the single wire to the switch and connect it to ground somewhere. If the switch is at fault, that simple maneuver will take the switch out of the equation.

A little more detail...car running, not running, soradic, running kinda-sorta but crappy, starts briefly but quickly stops , stuff like that.

jebbach911 · 12-22-2011, 06:49 PM

Thanks Mark!

Car not running , had to trailer it home . It was running like a champ right before it did this. AFR's went to 10's at idle when they were at 13.9. The fuel pumps are running as I am checking pressure, I jumper the terminals at the main fuse block. System pressure is still 6.5 bar like before. Could the disc inside the BL WUR have moved from the fuel pressure abruptly stopping?

mark houghton · 12-23-2011, 05:11 AM

Quote:

Originally Posted by jebbach911

Thanks Mark!

Car not running , had to trailer it home . It was running like a champ right before it did this. AFR's went to 10's at idle when they were at 13.9. The fuel pumps are running as I am checking pressure, I jumper the terminals at the main fuse block. System pressure is still 6.5 bar like before. Could the disc inside the BL WUR have moved from the fuel pressure abruptly stopping?

Hmm...stranger things have happened, so I guess anything is possible though I've never heard of this occuring as a result of overboost shutdowns. Does sound like the WUR is at fault, though. Know anyone with a spare you can swap out with to confirm the problem?

DSPTurtle · 12-23-2011, 05:44 AM

It sounds like you might have the gauges hooked up backwards. The WUR should not completely stop fuel. That is not a failure mode I have ever read about. Unless your screen is clogged... really, really, badly. Thats easy to check though, just look down the input fitting on the WUR.

JFairman · 12-23-2011, 07:27 AM

It does sound like the gauge fittings are connected backwards and your reading the open and closed position of the ball valve and what it does backwards.

The ball valve should be after the T in the hose that branches off to the pressure gauge. Ball valve open shows control pressure and closing it shows system pressure.

jebbach911 · 12-23-2011, 09:09 AM

UPDATE: I did have a spare WUR from a 79 SC N/A, I installed it and came up with 4.3 bar CCP and 6.8 bar SP. I reinstalled the BL WUR to verify symptom with hoses in same position and still have 0 CCP and 6.8 SP. So it is definitely the BL WUR. It doesn't appear that the settings have moved from a visual inspection and there was no evidence of fuel coming from the vent.

I'm getting ready to shoot an e-mail to Brian but do you guys think I should attempt to disassemble and inspect the BL WUR?

Thanks for any input, sure would be nice to drive this baby during the Christmas holidays! This was my Christmas present to myself was to get it running for the holidays while work was out!!

JFairman · 12-23-2011, 10:07 AM

Then your BL Wur is returning all the fuel used for hydraulic control pressure to the tank. System pressure fuel goes through a tiny orifice in the fuel head before going to the control pressure chamber above the control plunger.

The restricted fuel flow through that small orifice is what enables the WUR to regulate it's pressure by returning some of it to the tank while using it as hydraulic "control pressure" pushing down on the control plunger against the force of the air flow meter linkage pushing the control plunger upwards as you open the throttle.
With zero control pressure your fuel heads fuel flow to the injectors would probably go full rich a little ways above idle speed.

The metal disc in the top of the WUR is stuck in the lowest possible position below the fuel orifice it seats against or it's ruptured or something.

Brian Leask may fix it for free since he modified it if you send it back to him. If you take it apart first he won't know if your doing that caused the problem and... it's your call.

You could put your SC WUR back on and lower the CCP by tappping the adjustment down with a hammer and brass drift punch or use a C-Clamp to squeeze it down slowly so you can drive the car.
It won't have any boost enrichment so just don't go boosting it alot like that.

jebbach911 · 12-23-2011, 10:34 AM

Thanks JFairman for that excellent "laymans terms" explanation.

I've sent Brian an e-mail about the situation and I think I will box it up and air-freight it to Brian today instead of "monkeying around" with it.

I've waited this long to get this car together, another week or so won't hurt too much.

Thanks for all the input guys!!