83 sc backfires won't run help please

[boyt911sc]

Michael,

You don't need to remove the metal/rubber fuel line between the WUR and FD to check the fuel pressure. You could either install the pressure gauge kit at the FD or at the WUR. But it is more convenient to use the WUR side. Why? There is more room to work at this area plus the fitting (12-mm x 1.5) at the WUR is the same as the one on your gauge. At the FD side, you need 8-mm x 1.0 fittings. My suggestion to you at this point, is try the WUR side because you got the needed fittings in your set. Keep us posted.

Tony

[roadster49]

Hi Tony and Bob,

I hope I did this correctly: the temperature in Troy, MI was 39 F which is 4.4 C

Hooked up pressure meter to the WUR and to the rubber line disconnected per Tony's description.

System pressure, with valve closed was 6.6 bar

control pressure with WUR plugged in and valve open was 6.6 bar at 8:47,
At 8:57 it was 5.9 bar and stayed at that number till 9:04 when I went to open the return fuel line.

With the return fuel line open the pressure was 5.0 bar

Next step please?

[timmy2]

Post a picture of your hook up. Here is how to do it:
Remove line from fuel distributor to WUR at the WUR only.
Connect removed line from FD to gauge side of shut off valve. (No valve between removed line from FD and gauge)
Connect line with shut off valve after the T directly to the WUR fitting.
With valve closed pump running is system pressure.
With valve open pump running, WUR power disconnected is cold system pressure.
Pump running, valve open, electrical connected to WUR for 5 minutes is warm pressure.

[Bob Kontak]

Originally Posted by roadster49

Next step please?

Your pump is designed to deliver 5.2 bar. I can't deliver 6.6. Replaced with a different type?
(That said, I do not think the Accumulator is a pressure regulator - it's just a fuel flow "shock absorber" - I may be wrong)

You removed the return line to the tank (downstream of WUR?) and control PSI stayed at 5 bar with test valve open from dist to WUR?? Clog in WUR? This is getting into the area where you need to be real nice to Tony.

This is the basic hook up. Is yours like this? Let's make sure you are hooked up correctly like Timmy says.

[tirwin]

My understanding of the fuel accumulator is that it does two things. It acts as a sort of check valve to help maintain residual pressure after shutdown and it acts as a smoothing function for fuel delivery rate. The fuel pump has some small amount of variation in the rate of fuel delivery at a certain pressure. The FA smooths out the variation to make the fuel pressure more consistent. In a telecom network we would call this a shaper, buffer or a queue.

[Bob Kontak]

Originally Posted by tirwin

My understanding of the fuel accumulator is that it does two things. It acts as a sort of check valve to help maintain residual pressure after shutdown and it acts as a smoothing function for fuel delivery rate. The fuel pump has some small amount of variation in the rate of fuel delivery at a certain pressure. The FA smooths out the variation to make the fuel pressure more consistent. In a telecom network we would call this a shaper, buffer or a queue.

Thanks. Well, it sure does seem the check valve is working fine.

Your thoughts on the 6.6 bar of system pressure?

[roadster49]

Post a picture of your hook up. Here is how to do it:
Remove line from fuel distributor to WUR at the WUR only.
Connect removed line from FD to gauge side of shut off valve. (No valve between removed line from FD and gauge)
Connect line with shut off valve after the T directly to the WUR fitting.
With valve closed pump running is system pressure.
With valve open pump running, WUR power disconnected is cold system pressure.
Pump running, valve open, electrical connected to WUR for 5 minutes is warm pressure.

Per the above here is my test set up

[roadster49]

Here is the systems pressure

[roadster49]

Here is the pressure with fuel return open:



I am going to retest as the numbers seem out of boiunds.

[Bob Kontak]

Looks set up correctly.

If it is, you have a blockage between the inlet to the WUR and the return line connection.

Blow on the return line to the tank to make sure that will take flow (eliminate variable).

Pull the Porsche connector off the top of the WUR. The thing your gauge is connected to. There is a little screen in hole. Check if clogged.

[Bob Kontak]

Here is a simple test. Valve open and you are reading 5 bar. Crack the line (on the WUR) just to the rear of the big WUR connection. Your pressure should drop as gas leaks out.

If it does not drop, the blockage is isolated to the WUR.

[Bob Kontak]

Michael,

Can't tell from your first pic in post #49 what is disconnected.

Return line is the bottom of the two big green lines way in the back (well, front) of the engine compartment.

This is where you disconnected and got 5.0 bar?

[roadster49]

I retested it here are pictures
set up


valve closed

valve open
initial

after 10 with WUR plugged in

[roadster49]

Hi Bob,
It is the hardest connection to get to, way in the back with a 13MM on hose to green pipe in firewall and 17MM the hose going to the engine.

Yes this is where I got 5.0 bar with the hose disconnected.

Need to shut down for the day. I can check the screen and crack a connection next week.

Thanks,

Michael

[roadster49]

Well i am heading to the airport so will pick up from here next week.
Thanks all.

Michael

[Bob Kontak]

Good work.

There are two suspect places the flow can plug.

WUR and then at the fuel distributor aside from the line itself.

Check this diagram out. Pretty easy to follow.

911 CIS Primer - CIS Lambda

[boyt911sc]

Originally Posted by Bob Kontak

Good work.

There are two suspect places the flow can plug.

WUR and then at the fuel distributor aside from the line itself.

Check this diagram out. Pretty easy to follow.

911 CIS Primer - CIS Lambda

Michael,

I can't see well from your pictures if it was the return line or not. If the return line was opened and fuel pressures remained high, then the problem is upstream. Restriction is occurring some where between the the return line open section and the fuel distributor. There is a strong possibility that FD is causing the very high system fuel pressure.

If I were in your shoes, I would do this test to determine whether the high system pressure is caused by the primary valve or a restricted fuel line right after the FD. Leave the return line open but place it in a container. Loosen the primary valve and remove all the shims or washers. Tighten the primary valve and repeat the pressure test.

a). If the system fuel pressure remains at 6.6 bar after removing the shims or washers, the problem is not the primary valve. It could be a clogged FD or the return line after the FD.
b). If system pressure drops down significantly, you found the culprit.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

I can't see well from your pictures if it was the return line or not.

Hi Tony,

Same question I asked in post 52 and then he responded in post 54. He sees to have it correct.

I am going to call you tomorrow. I want to talk about the fuel distributor aspects of the probable clog.

What time does your wife wake you up from your beauty sleep?

[boyt911sc]

Originally Posted by Bob Kontak

Hi Tony,

Same question I asked in post 52 and then he responded in post 54. He sees to have it correct.

I am going to call you tomorrow. I want to talk about the fuel distributor aspects of the probable clog.

What time does your wife wake you up from your beauty sleep?

Bob,

I am on my way home from baby sitting and should be back home by 9:00 PM. I will wait for your call between 9:00 and midnight. Love to hear your voice again and reprimand you for being a naughty boy. Maybe you could update me about the reverse gas discussion......... you still owe me one over-cooked hamburger.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

Bob,

I am on my way home from baby sitting and should be back home by 9:00 PM. I will wait for your call between 9:00 and midnight. Love to hear your voice again and reprimand you for being a naughty boy. Maybe you could update me about the reverse gas discussion......... you still owe me one over-cooked hamburger.

Tony

This old coot is going to bed now.

Tomorrow in the afternoon.