Fuel pressures and WUR questions

Hello all,

1981 US 308 GTSi

Car has always run well, as I go through things it is running better and better. Passed CA smog a month or so ago so it couldn't be too bad... right? Starts great cold but I have been chasing a warm start issue (always starts, just depends on how long and how much throttle I give.) Has never had the cold start fast idle (whether it just doesn't work or has been disabled I don't know). Cold light on dash lights for first few min of running.

Had a bad check valve in pump. Fixed.
Had a leaking Fuel Accumulator Fixed
Had leaking Injectors. Fixed.
Replaced the o-ring on the outside end of the fuel pressure regulator on the side of the fuel dist.

After replacing the injectors I found that there were incorrect vacuum line connections so I had a vacuum leak and vacuum was not getting to the digiplex system. With Steve's help here I was able to get routing correct and readjust the AFR (at operating temp.) Really changed the character of the car... much more fun. Still, warm starts (even 5-6 hours later) were not great.

I finally bought one of the cheap CIS fuel pressure test kits. I am really not sure if I am using it correctly so if that is my issue hopefully someone will point that out. Here's what I did.

65F/18C temps car cold for over 12 hours.

Disconnected the output line (that originates at the top of the Fuel Dist.) at the larger of the 2 banjo's at the top of the WUR. Plumbed my pressure tester between that line and the WUR with the valve on the WUR side. Unplugged the electrical connection to the WUR, turned the key to "on" and pulled the plug to the switch on the fuel dist. With the pump on and the valve closed to the WUR I got an almost instant 5 bar pressure.
Shut off pump to test supply side:
Dropped to 3.2 Bar immediately
3.0 Bar at 5 min.
2.9 Bar at 10 min.
2.85 Bar at 20 min.

I'm thinking supply side is looking pretty good.

Ran the pump again and opened the valve to the WUR....

Exactly the same pressures... exact same leak down. (well at least this tells me my injectors aren't leaking anymore?)
Was unsure about the vacuum test so independently tried pulling 16 in of vacuum to the top WUR vacuum line and then to the side vacuum line. No change whatsoever.

Plugged in the electrical connector to the WUR No change at 1, 3 or 5 min. Still 5 bar.

At this point I started the car (started right up quick) and let it idle for 5 min. Still 5 bar.

IF (and that's a big IF) I am testing correctly I guess that means my WUR is not working. How is the car running so well?

What tests (if any) am I missing? I previously thought I was only electrically challenged.... but I'm definitely adding CIS to that list.

Thanks.

 

OK, re-reading I see that other than "is my test procedure correct?" My other questions are more implied.

With my WUR acting like this what are the effects? I seem to have a good AFR at idle so would this go crazy lean in the higher revs? Crazy rich?

Are there any obvious things that would cause my WUR to malfunction like this? Would I need to remove and disassemble? If I went that far and there were no obvious problems (clogs? Leaking membranes?) can it just be reassembled or is a rebuild kit necessary? Can it be adjusted from the bottom? or only opening it up each time? (I see a popular "mod" from the VW crowd is to drill a hole in the bottom of the housing to access the allen adjuster.... The Porsche guys drill and tap the top plug for a set screw.... but those don't seem to have the same vacuum fittings ours have.

 

I had what seemed to be a similar warm/hot start issue (1980 GTSi), though for me when I disconnected the thermo-time switch it was instantly rectified suggesting a bad locked open TTS. Maybe give it a try on yours. I just disconnected the blue connector circled and warm start issue vanished.
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Thanks Plutonium, I live in sunny SoCal so its never cold enough that I've seemed to need it. At one point I left the cold start injector disabled for a couple months and could never tell a difference.

 

That is pretty bizarre. One sanity test you could do is:

1. When you've got the valve on the pressure gauge set-up closed = there is no fuel flow thru the WUR (so the gauge measures the system pressure) = so there should be no fuel flow coming out of the small banjo fitting on top of the WUR and its line going back to the tank.

2. When you've got the valve on the pressure gauge set-up open = there is (or should be) fuel flow thru the WUR (so the gauge measures the control pressure) = so there should some fuel flow coming out of the small banjo fitting on top of the WUR and its line going back to the tank.

You could test to see if you get some fuel flow in the line coming out small banjo fitting in condition 2 -- if you don't, you have a blockage.

The vacuum is only applied to the nipple on the top of the WUR (the nipple at the bottom side of the WUR is just left open to atmosphere). Always having a high control pressure could contribute to difficult warm restarts as during starter motor cranking on a working system = engine vacuum is low = the control pressure is lower = adds enrichment to aid starting. While cold starting gets a squirt of fuel from the CSI, and may not be so impacted from having too high a control pressure (in your warm environment).

 

I should've written: "The vacuum is only applied to the nipple on the top of the WUR (the nipple at the bottom side of the WUR is just left open to atmosphere -- or is connected to somewhere that is just always at atmospheric pressure upstream of the throttle plate).

 

Im also in Southern California have an 81 GTSI, & I just recently had an issue with the WUR. After reading & watching lots of You Tube videos, I decided to remove it & disassemble it. Most of the videos I saw dealt with single diaphragm WUR’s, ours have two. Had I only disassembled the top half & cleaned out the inlet micro filter, I’m confident that I would have resolved my issue, but curiosity got the best of me and I damaged the secondary diaphragm by disassembling the bottom half. The secondary diaphragm is riveted to the lower housing The diaphragms were pliable with no stiffness. I subsequently sent it to www.specialtauto.com where they rebuilt it with a 3 week turn around. I re installed it & my 308 is purring like a kitten again. I did have to have the air/fuel mixture re adjusted at the fuel distributor which was professionally done. If you decide to try and fixit you self, just disassemble the top half to clear the inlet micro filter which is usually the issue with the WUR and if you mess it up like I did, it can be rebuilt for $350.00 at Specialtauto in Texas. Good luck & hope you resolve your issue


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Ok. So I took off the return line from the WUR where it enters back in to the dist. Running the pump and it’s a very small dribble… maybe a drop or 2 a second. Not even 1/10 of what comes out the supply side. But more than I was expecting with 0 drop in pressures.

I went ahead and pulled the WUR. There is crud in the filter but the inside looks brand spanking new (and I had been told that the entire fuel system had been rebuilt about 3 years ago… I believe them.

are there any bench tests I can perform?
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So I cleaned out the filter on the inlet side of the WUR… hoping against hope. The only bench test I could think of was to hook up without installing. So I hooked the pressure tester to it as I had before but this time with the WUR return line going into a bottle. 5 bar with the WUR side closed off and then when I open the line it drops for a second and climbs back to 5 bar and then the return line starts to drip out fuel. I never deal with this kind of stuff but seems like the WUR is set to 5 bar or more? Grrr. I’m still not ruling out that I’m missing something obvious…

 

Hope you guys don't mind my stream of consciousness updates as I think of and try something every few minutes.... But I decided to try the pressure test again with only the top half of the WUR. That means no bimetal strip, no springs nothing acting on the diaphragm. Control pressure should be very low... nope. Still 5 bar. Damn these screws holding the diaphragm etc are in there tight. I'm afraid I might strip the heads of the screws....

 

Now I'm getting somewhere. After trying a few things with no luck I connected the bare top, no diaphragm no nothing, to the pressure tester. Set it in a bucket expecting (hoping) gas would come gushing through.... just a dribble and the difference between system pressure and control pressure is now 5bar to 4.95 bar.

So the top part (meaning the round black disc that the fuel banjo bolts thread into) Is it removable or serviceable in any way? I cant get the filter out from the outside... I was hoping that the offset hole on the inside (supply side) went straight to the filter so I took a small nail, ground the point off and tried to poke from the inside hoping it would push the filter out. No luck. I'm out of ideas guys. I'm gonna dump this thing in my ultrasonic cleaner and pray.... hoping someone that knows how this top is assembled can shed some light.

Thanks.

 

Well, it seems my WUR just needed a little self care. I treated the top to multiple hot bath massages care of my ultrasonic cleaner. after 2 or 3 attempts I hooked it up to the pressure tester attached to the car and when running finally got more than a trickle coming through into the bucket. Still just the WUR cap, no internals at all, was giving me over 2.5 bar pressure.. Back in the ultrasonic cleaner a couple more times until it was under 1 bar. Checked the resistance of the bi metallic strip and it was in spec so I re-assembled the unit. I did not test with vacuum, as I was beat, but the cold and warm control pressures were for the first time A) changing at all and B) In spec. Low end cold and high end warm but I'm calling that a big win.

Re-assembled everything properly and that first start was VERY hard starting 3 or 4 tries and if finally caught enough to slowly chug up to an idle. Guessing that with the new control pressure it was probably rich I turned down the mixture screw 1/8 of a turn and she became much happier. After she reached temp I (using the method I mentioned in the "Fuel mixture access" thread) leaned it out another 1/16 of a turn and started working my way back richer until the air meter flap stopped increasing the idle speed when lightly touched. That took me almost exactly back to my original 1/8 random turn. Right way? Wrong way? Its all I know.... hopefully we find out a better way in that other thread. Shut it down for 30 minutes and a warm start was 8 ish seconds of cranking. Better than before? Hard to tell. maybe I'm just being optimistic. Took it for a drive around the neighborhood. I honestly can't tell if its any different as I still haven't gotten used to how much better everything feels with all the vacuum lines properly routed.

Thanks everyone for your help yet again.

 

My guess would be that this will put you in a rather rich condition as a cylinder typically makes max torque at something like 12:1 AFR while the F idle spec is more like 14:1 AFR. I think you could try going a bit more CCW (lean) and see if that has any impact on warm restarts with little risk (the idle adjustment has little AFR effect at higher RPM -- which is sort the genius of the CIS "funnel").

 

Forgot to add -- now that you've got it working correctly (well done!), if you could measure the volume of fuel that is returned out the return line, say in 30 seconds, when cold and when warm = that could be some useful information for others (that is nowhere in the F/Bosch documentation AFAIK).