CIS System problems

[JSZ]

Finally completed the top end rebuild and installed the engine to have problems with the fuel management system.
A little history, the car is a 82 911 SC, last on the road in 2004. When I acquired it it had 5 or so head studs broken, so I removed the engine and rebuilt the top end. The fuel tank was cleaned also.
The specifics:
- New Bosch pump, matching the PET and Bosch number
- New Mahle Fuel filter
- Injectors thoroughly cleaned and tested
- Fuel distributor cleaned

The car starts up very quick and runs for 30 seconds and dies. If you attempt to open the throttle it dies. With a pressure testing harness on, the engine starts and has about 4.5 bars and then climbs to 7 bars and dies at that point. Return line is open and air was blown through it. Something is elevating the pressure. Wondering if I have a Bosch pump out of spec. I did change the fuel distributor with another that came from an operating car. It ran better and would stay running however it still over pressurized after startup.
I have read the CIS primer, however it does not trouble shoot higher pressure.

Any help or thoughts would be most appreciated.

[boyt911sc]

Jeff,

Since you have a pressure gauge kit available, the first thing you should do is measure the control and system fuel pressures before even attempting to start the engine. Based from the initial information you have posted, I suspect you won't be able to measure them because you have fuel flow anomaly in the system. Keep us posted.

Tony

[T77911S]

check the inlet screen on the WUR it may be clogged.

are gauges connected correctly

[tirwin]

If you’re measuring a fuel pressure of 4.5 and then 7 bar on a running engine something is way wrong.

With the engine off what is the system pressure? By that I mean fuel pump running and the valve closed on the pressure gauge. Then open the gauge (engine still off) with the electrical connection on the WUR unplugged and measure cold control pressure. Finally, plug in the electrical connection and measure WCP after about 3 minutes. I’d just line to see if you’re getting the same result on a non-running engine. That should be a baseline for fuel pump, WUR and fuel distributor.

4.5 bar would be fine for system pressure but absolutely too high for normal warm control pressure operation. You’d be WAY lean.

A friend of mine tested a really high WCP reading. Had me scratching my head. Turned out he had a kink in a soft fuel line when he rebuilt the line and re-installed it.

[JSZ]

OK, a little more information......
Checked fuel pump pressure with disconnected WUR and no start, started to register on gauge around 2 bars or so and then pegged the gauge above 7 bars almost instantly.

When I get back again, I am going the check the check valve in the pump and check volume. May also replace with a known working used Bosch pump.

Also, I also changed the drain and strainer on the fuel tank.

I will update as more information becomes available.

Thank you to all for the suggestions.

[boyt911sc]

Originally Posted by JSZ

OK, a little more information......
Checked fuel pump pressure with disconnected WUR and no start, started to register on gauge around 2 bars or so and then pegged the gauge above 7 bars almost instantly.

When I get back again, I am going the check the check valve in the pump and check volume. May also replace with a known working used Bosch pump.

Also, I also changed the drain and strainer on the fuel tank.

I will update as more information becomes available.

Thank you to all for the suggestions.

Jeff,

I am assuming you have a good working pressure gauge. If this is the case, your fuel pump is good and working. There is nothing wrong with the FP. There is a flow restriction to the return line going to the fuel tank. Break the return line by take runner #3 and place the end of the fuel line in a suitable container. Turn the FP on with gauge installed. I bet you, the gauge won't register that high. Keep us posted.

Tony

[JSZ]

Tony, after an afternoon of diagnostics, you were right, a clog in the return system. So at the no 3 bank, disconnecting the return fuel line, excellent flow. I next removed the return line at the tank and again excellent flow. At that point I noticed a small flow from a the tank return line, which ultimately was no flow. After testing the pressure on the supply side without engine running, and within specifications. We decided to start the engine with the return line in a gas can and not in the fuel tank. Engine started right up and ran, pressure was within spec, though will need tuning and more diagnostics. The fuel tank has been removed and now will be cleaning the obstruction.
Stay tuned more to come. Thankful to hear run at this point..
Thank you.