Distributor, Calling all L-Jet experts Options

[gfg3]

While I was trying to sort out possible vacuum leaks in my '75 1.8L FI (L-Jet) engine I noticed a couple of inconsistencies in the way the PO set up the system compared to what I believe is the correct vacuum setup:

1. The distributor in my car does not have any vacuum advance mechanism or vacuum hose connections. I thought all '75 EC code engines used vacuum advance. Am I wrong?

2. There is no vacuum line to the fuel pressure regulator. Normally there is a T in the line that connects the intake manifold with the decel valve and the fuel pressure regulator. Decel valve is hooked up correctly, but the fuel pressure regulator just has the in/out fuel lines, vacuum port is open. Can it work correctly like this?

George

[Dave_Darling]

The distributor part numbers sounds right. (That's a Bosch part number; there should also be a VW part number on it.)

Not all 75s had vacuum advance. All of the injected ones had vacuum retard. (I'm sure you don't have an AN-code carb'ed 1.8.) If you don't have the EGR system, then you probably never had a vacuum advance setup. The dashpot on the distributor may have a fitting on it for advance, but if so it was never hooked up.

The L-jet is designed to have the fuel pressure referenced to the manifold pressure. So the port on the FPR should be hooked up to manifold vacuum. If it isn't, the fuel pressure will always be as high as it would at WOT, leading to a rich idle and part-load mixture. That may have been a band-aid for a lean mixture from vacuum leaks.

--DD

[gfg3]

The distributor part numbers sounds right. (That's a Bosch part number; there should also be a VW part number on it.)

Not all 75s had vacuum advance. All of the injected ones had vacuum retard. (I'm sure you don't have an AN-code carb'ed 1.8.) If you don't have the EGR system, then you probably never had a vacuum advance setup. The dashpot on the distributor may have a fitting on it for advance, but if so it was never hooked up.

The L-jet is designed to have the fuel pressure referenced to the manifold pressure. So the port on the FPR should be hooked up to manifold vacuum. If it isn't, the fuel pressure will always be as high as it would at WOT, leading to a rich idle and part-load mixture. That may have been a band-aid for a lean mixture from vacuum leaks.

--DD

Outstanding info. Thanks Dave! I have an EC code 1.8 FI without EGR and no dashpot on the distributor, so it looks like the distributor is fine.

While I have this thread open, I also noticed that my decel valve just has two vacuum connections, a small line to the intake manifold and a large line to the S-duct. The third large tap that should also go to the intake manifold is blocked off as is the corresponding large tap at the intake manifold. Again, is this OK, or should I hook it back up?

Since the main reason I'm going through all this is part throttle surging and ratty idle, I guess it's time to replace all those vac lines....just wanted to do things correctly.

George

[AndyB]

The distributor part numbers sounds right. (That's a Bosch part number; there should also be a VW part number on it.)

Not all 75s had vacuum advance. All of the injected ones had vacuum retard. (I'm sure you don't have an AN-code carb'ed 1.8.) If you don't have the EGR system, then you probably never had a vacuum advance setup. The dashpot on the distributor may have a fitting on it for advance, but if so it was never hooked up.

The L-jet is designed to have the fuel pressure referenced to the manifold pressure. So the port on the FPR should be hooked up to manifold vacuum. If it isn't, the fuel pressure will always be as high as it would at WOT, leading to a rich idle and part-load mixture. That may have been a band-aid for a lean mixture from vacuum leaks.

--DD

Outstanding info. Thanks Dave! I have an EC code 1.8 FI without EGR and no dashpot on the distributor, so it looks like the distributor is fine.

While I have this thread open, I also noticed that my decel valve just has two vacuum connections, a small line to the intake manifold and a large line to the S-duct. The third large tap that should also go to the intake manifold is blocked off as is the corresponding large tap at the intake manifold. Again, is this OK, or should I hook it back up?

Since the main reason I'm going through all this is part throttle surging and ratty idle, I guess it's time to replace all those vac lines....just wanted to do things correctly.

George

I would recommend that you make sure all your hoses are correctly connected. I have a 75 with L-jet. I always make sure that my hoses are connected to the decel valve.

[gfg3]

I would recommend that you make sure all your hoses are correctly connected. I have a 75 with L-jet. I always make sure that my hoses are connected to the decel valve.

OK, here's what I get from all this:
1. Distributor is fine, no worries about no dashpot or vac hookups
2. Reinstall large vac line from decel valve to intake manifold, making 3 total lines at the valve.
3. Replace the line that T's into the fuel pressure regulator from the small decel valve/fuel pressure regulator line (i.e., rehook up the fuel pressure regulator vacuum).

I've got new lines on order, so once they come in.....off to work I go.

Thanks everyone.

George