CIS Journey / Rabbit hole

[ducatiroger]

Hello All,

Working on dialing in the CIS system on my 76 911s with a 83 3.0 SC engine. I say 83 as it doesn't have a sump plate.

Picked up the car a month ago and had a great drive home ( 76 911s Hotrod First Drive PHX to SEA ). I had drafted a list of things to change with the car but 49 yr. old cars have a way reshuffling the priority list as they see fit. Queue the fuel pump failure.
Old pump looks to be the original 911-608-110-56 style that had been leaking based on the build up. Decided on the much more affordable Bosch 69430 at a tenth the price.


Car started running rich (back fires at partial throttle) so that meant it was time for a fuel pressure tester kit. Not sure if the change in fuel pumps affected system pressure but the new pump was delivering CSP of 2.8 bar, so time to get familiar with the fuel distributor. After running the pump the CCP (with WUR unplugged) max'd out at .9 bar. CSP stayed in the 2.9 bar range.



Okay time to mess with the fuel distributor system pressure.


Had to work my way up to four washers (several tries later) added to the check valve/pressure screw (only three copper washers shown) and ended up at 4.9 bar. Success! I am a little concerned with the number of washers required. Is that an indication of something wrong with my fuel delivery system?


Checking the CCP pressure with the WUR element unplugged I saw 1.6 bar with a WUR temp of 7 C. That seems out of spec. Anyone care to chime in?

Also checked the CP with the WUR plugged in for four minutes with no change in CP. Not ideal (I think). Getting 11.6 vdc to the WUR plug and the WUR element is showing 24 ohms resistance. Pulling a vacuum on the lower port didn't change the CP but it did hold a vacuum. Forgot to chech the upper vacuum port.

Once warmed up the car runs pretty well with a nice regular 1K rpm idle. Still has a hesitation between 2k-3K and occasional exhaust backfire but fewer back fires at partial throttle after adjusting the SP. The butt dyno is saying the car doesn't pull quite as hard in the lower <3K rpm range.

So, am I rebuilding my WUR? It's a 045 if that is relevant. Any suggestions on next steps would be appreciated.

Cordially,

Roger

[boyt911sc]

Roger,

Could you post a picture of the fuel distributor showing the Bosch ID #?. Thanks.

Tony

[ducatiroger]

Originally Posted by boyt911sc

Roger,

Could you post a picture of the fuel distributor showing the Bosch ID #?. Thanks.

Tony

Hi Tony,

Photo of plate. The printed numbers are 0 438 100 031. The stamped numbers are easier to read.



Thank you,

Roger

[3rd_gear_Ted]

The fuel tank filter should to be cleaned before changing the pump.
The pump mechanism doesn't like grit whatsoever.
Add an inline filter, not easy but needed.

[ahh911]

I'd suspect a blockage on the fuel tank return firstly. Remove the accumulator return line and blow into it. Then I'd suspect a blockage between the fuel distributor and fuel pump.

The fact that the fuel pump showed leakage is maybe an indicator it's under back pressure, so maybe the latter is more likely. Check fuel filter and path.

There is also a min spec on fuel delivery unloaded.

Phil

[ducatiroger]

Originally Posted by 3rd_gear_Ted

The fuel tank filter should to be cleaned before changing the pump.
The pump mechanism doesn't like grit whatsoever.
Add an inline filter, not easy but needed.

So install a filter between the tank and pump? There wasn't one previously so I didn't think to do it while installing the new pump.

Originally Posted by ahh911

I'd suspect a blockage on the fuel tank return firstly. Remove the accumulator return line and blow into it. Then I'd suspect a blockage between the fuel distributor and fuel pump.

The fact that the fuel pump showed leakage is maybe an indicator it's under back pressure, so maybe the latter is more likely. Check fuel filter and path.

There is also a min spec on fuel delivery unloaded.

Phil

Thank you for these suggestions. Just to confirm, if I can't move air through the return line I have a blockage?

During the whole adding spacers drill there were a couple of times where the system pressure spiked to 7.5 to 8 bar. I attributed that to my hand modified copper spacers being slightly too large. Filing down the OD seems to have addressed the overpressure situation.

I'll be sure to check the engine compartment fuel filter and collect a unloaded fuel system delivery performance.

My weekend calendar is filling up.

Thanks for the troubleshooting help.

Roger

[boyt911sc]

Roger,

Test the FP delivery rate before the fuel accumulator. You should get at least 2 liter per minute. Or 90+ psi. with delivery valve closed. Make sure the FP has both volume and pressure in spec.

Tony

[Schulisco]

Tech spec book
https://de.scribd.com/document/736191799/911-all-78-81

[ducatiroger]

Originally Posted by boyt911sc

Roger,

Test the FP delivery rate before the fuel accumulator. You should get at least 2 liter per minute. Or 90+ psi. with delivery valve closed. Make sure the FP has both volume and pressure in spec.

Tony

Thanks for direction. I'll report back this weekend.

Originally Posted by Schulisco

Tech spec book
https://de.scribd.com/document/736191799/911-all-78-81

Yes, I do have the SC Tech Spec book. If only the print wasn't so small.

[ahh911]

Originally Posted by ducatiroger

So install a filter between the tank and pump? There wasn't one previously so I didn't think to do it while installing the new pump.



Thank you for these suggestions. Just to confirm, if I can't move air through the return line I have a blockage?

During the whole adding spacers drill there were a couple of times where the system pressure spiked to 7.5 to 8 bar. I attributed that to my hand modified copper spacers being slightly too large. Filing down the OD seems to have addressed the overpressure situation.

I'll be sure to check the engine compartment fuel filter and collect a unloaded fuel system delivery performance.

My weekend calendar is filling up.

Thanks for the troubleshooting help.

Roger

I made up a little BS, it's not the return, if the return is blocked you'd have high pressure. Anyhow, you'll be checking the fuel accumulator for a membrane tear, I'd blow into the return while there, you'll hear the tinkle tinkle back into the tank. The rest of the statements I put out are correct.

Phil

[BoxsterGT]

For those who might like a washable Filter between the Tank and Pump,

I offer this.....


It is also available with a Shut-off valve that allows periodic cleaning without draining the Tank.

For info, please email me: len.cummings @ verizon.net but without the spaces.

Please, NO pm's as my box is almost always FULL.

Thanks.

Len

[3rd_gear_Ted]

Len,
That is good fix for a known Porsche design flaw. (gasping sound goes here)

[BoxsterGT]

These filters were intended for the original Dansk Fuel Tanks that had internal sediment and caused multiple Fuel Pump failures.

Dansk has since corrected this issue and they now seem to be a good choice as a replacement.

I am happy to help with any fuel hose / line questions. Been doing this since 2004, and now retired.

With my wife Susan helping and keeping me on my toes we are doing what we can to help preserve these wonderful vehicles for generations to come.

Have a great Porsche day everyone.

Len

[Schulisco]

Originally Posted by BoxsterGT

These filters were intended for the original Dansk Fuel Tanks that had internal sediment and caused multiple Fuel Pump failures.

Dansk has since corrected this issue and they now seem to be a good choice as a replacement.

+1

Never seen before. interesting! Is there a part no. available for these filters?

Thomas

[ducatiroger]

Originally Posted by BoxsterGT

For those who might like a washable Filter between the Tank and Pump,

I offer this.....


It is also available with a Shut-off valve that allows periodic cleaning without draining the Tank.

For info, please email me: len.cummings @ verizon.net but without the spaces.

Please, NO pm's as my box is almost always FULL.

Thanks.

Len

Thanks for sharing this. Couldn't figure out how I might squeeze a fuel filter into the feed line. Looks like a elegant solution.