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

kinda....not really
dizzy should have a vacuum pot. but since L-jet does not have injector trigger points inside teh dizy, it can be made to work with a VW type 009 or an 050.

no vacuum signal on fuel reg or even a d jet fuel psi reg will run the car

i speculate acceleration to be flat

Thanks for the info. The dizzy s/n is 0 231 178 009 which I believe is a generic VW part. PO probably replaced correct one way back when. Not having the vacuum signal on the fuel reg bothers me a bit, but that's and easy fix....I have plenty of hoses.

George

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

That was GREAT Dave. Well put.

Well done ,always DD comes in, cheers to you for your help on here and on pelican, time someone said it........

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.

I believe you have that backwards Dave.
FP is higher at idle with L-jet set up correctly.

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

Don't know about L-jet, but D-jet should have fuel pressure reg referenced to manifold pressure.
This insures that the injectors see a constant pressure drop and fuel flow is metered solely by pulse width.
Dave is correct that at idle with manifold pressure at a vacuum the injectors will see a greater pressure drop and higher fuel flow for a given pulse width

On my 74 1.8 L-Jet I have an auxiliary fuel pressure gauge hooked up the diagnostic port of the fuel rail. I notice a slight drop in pressure as the rpm's go up. The fuel pressure is around 29 to 31 at idle.

In a 914, D-jet fuel pressure is constant, not referenced to any external signal.

D-jet does not reference its fuel pressure to manifold pressure, there is no vacuum line connected to the regulator. (Perhaps they hadn't given that aspect any thought when they designed it?)

Since the pressure in the manifold is highest at WOT, I am pretty sure that the fuel pressure in the L-jet cars is higher at WOT than at idle. The object of the manifold-referenced fuel pressure regulator is to keep the pressure drop across the injector constant.

The original distributor on an L-jet car should have a vacuum dashpot on it. If there is no provision on yours for a dashpot, it may not be the right one. (I could be wrong about the part number.) That said, you don't specifically need the correct distributor to run the engine, the way you do with D-jet. Since L-jet takes its "time to inject" signal from the ignition points, it can work off a standard distributor.

If you have the (cheap) "009" distributor, you might wind up having to replace it or modify the advance curve in order to get everything working as well as possible. (The stock 1.8 distributor also has a Bosch part number ending in "009", hence my possible confusion.)

--DD

The manuals all say the pressure goes up as manifold vacuum decreases, as you said Dave.
However, I vaguely remember making measurements on a car where the opposite was the case, and the engine ran properly.
(Maybe it wasn't an L-jet Type 4 and I'm mis-remembering.)

Dave: Now I am confused. According to the PET and Haynes Repair Manual, the proper Bosch distributor for a '75 1.8 FI is 022 905 205 series which has a dashpot. I agree that my 0 231 178 009 without a dashpot is probably a VW replacement though.

George

That's the Porsche part #.
Bosch has a different number for the same part.

Chris;
I stand corrected.
D-Jet does not reference fuel pressure to manifold pressure, but L-Jet does
Sorry for the confusion.

OK. I yield. It's beer thirty here on the east coast. Tomorrow's another day.

George