'78 911SC Fuel Pressures Off - suggestions?

[F1LOCO]

Recent long start issues (hot/cold - doesn't really matter. Takes 2-3 longer cranks to get it fire right and then just a blip of the gas to stabilize it). Used to be able to barely make contact with key and it would fire strong and instantly). Now it will fire (when I get it fire) and instantly go to 1500 for a second or two, then drops to 900'ish pretty instantly. Electrical all updated - CDI (Ashlock), Bosch Cap/rotor, Clewett Wires and NGK plugs.

Fuel Pressure Gauges finally came in. I currently have a BOSCH 086 WUR with VAC port. From I can find this is for a 928 possibly? Hooked my gauges up, pumped VAC going in to 15 in/HG or 400mm/HG (at least SPEC in the shop manual for a '78) and got the following:

System Pressure valve closed 4.7 Spec 4.5-5.2
Cold Pressure valve open .85 Spec 1.7-2.1 (56F/13.3C)
Warm Pressure stabilized around 7' mark at 3.7 (spec 3.2-3.6)
Residual Pressures at 0 = 2.6; 10' = 1.4 (spec 1.3) and 20' = 1.3 (spec 1.1)

The specs I am pulling are from OE Porsche Shop Manual.

Any clues?
Seems like the two major off's are the Cold Pressure reading and higher residual pressure at 20'.

On a side note of discovery I noticed a bit of arching going on in the cap. Doubled checked all the wire connections, cleaned it up and after 40 miles, more arching on cap contacts and middle of rotor slightly black as well. Plugs looked good, though too new to really tell any signs. Timed at BTDC at 5 at 950 rpms (VAC disconnected) and pulling 25 now at 58000 RPMs with VAC disconnected. On a couple of hot kills, advanced mark on plug strap is about where it should be, just before the bend, and may even be on the low side a tad. The only thing I noticed today in running the pressures, the VAC would drop to 2-3 in/Hg every 2 minutes on the warm read outs. I would bump it back to 15, and would end up at 13 at end of two min runs all the way through 10 minutes. At idle, I am getting 15 in/Hg of VAC on the line going into the WUR at idle.

Thanks for any direction. Not sure if WUR is toast, just wrong one, or something else. Had been starting fine, though, since I got it a couple of years ago.

[RarlyL8]

Yes -086 WUR is for a 928, USA '78SC should have a -045 WUR.
Too rich at cold start would certainly delay the process and cause a rough idle until it climbs up out of it.

[F1LOCO]

So the 928 WUR could cause a rich start and low cold pressure reading? Easy fix, though price at $1K and not sure if Pelican will give me a core charge for a 928 WUR for the correct 045 WUR.

Thanks -

[boyt911sc]

Are you sure you have the correct Bosch ID #? Could you post a picture of your WUR showing the ID #? Thanks.

Tony

[F1LOCO]

[boyt911sc]

Originally Posted by F1LOCO

That is not the Bosch ID #. The numbers are located behind the post or beside “Germany “. Look for 0 438 140 XYZ. Try again.

Tony

[F1LOCO]

089 -

[F1LOCO]

Holding my breath BUT - while I had it out sprayed some carb cleaner on the screen side, let it soak, took a small brush an brushed it with fresh flush of cleaner. Reassembled and fired right up. Still need to sort out the 089 v. 045 WUR thing. Will hook some gauges up tomorrow and not sure if it really will matter on cold pressure rating (the main one that was off - but as to '78 045 specs),

SIDE BAR: No emissions equipment - No CAT, SSI headers, no SMOG pump. Not sure if it even came with it or not.

[boyt911sc]

Originally Posted by F1LOCO

Holding my breath BUT - while I had it out sprayed some carb cleaner on the screen side, let it soak, took a small brush an brushed it with fresh flush of cleaner. Reassembled and fired right up. Still need to sort out the 089 v. 045 WUR thing. Will hook some gauges up tomorrow and not sure if it really will matter on cold pressure rating (the main one that was off - but as to '78 045 specs),

SIDE BAR: No emissions equipment - No CAT, SSI headers, no SMOG pump. Not sure if it even came with it or not.

WUR-045/-069/-089 will all work for your motor. You just need a good working unit. The 0.85 bar CCP is too low even @ 0°C ambient temperature. You need to get the CCP closer to spec. Refer to WUR-045/-069/-089 CCP chart.

Tony

[F1LOCO]

Thanks. Is there way to adjust the cold pressure reading short of a rebuild? I think the unit was put in only 5K miles ago from the previous owners records.

[AFB24911S]

Check this out:

https://www.youtube.com/watch?v=PuELRd3gqgk

Although it should be a "set it and forget it" type thing, making the WUR adjustable can compensate for other problems later on.