I'm rather stumped here with my 1991 S600.

One of my ignition modules has an intermittent failure, so I am reliably only getting spark to one bank.

However, this failure seems to have interrupted the fuel flow. Most attempts at starting yield a spark but no fuel (I'm disconnecting the pump output line just at the FPR).

I can hear the fuel pump(s) running, but I have no fuel pressure or flow.

Is there an interface that prevents fuel delivery when there is a fault in an ignition module?

Cheers

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1991 Japanese S600
Resides in Kampala Uganda

the fuel pumps run, you should have fuel. there is no other part to interfere. ignition module failure CAN mean no fuel pumps running. sounds like 2 problems. good luck, chuck.

Are you sure the pumps are running? There is nothing to stop fuel flow if you disconnected the pressure line from the fuel rail.

Being you are disconnecting at the pressure regulator, that is the return side so fuel pressure must rise high enough for the regulator to open and excess fuel returned to the tank. If the pumps are weak or if one is not working, pressure will be too low and you won't see fuel.

Ok, that makes sense. I'm looking at a systems diagram that originally looked as if the output of the fuel pumps ran into the pressure regulator. That's why I was testing there.

If the FPR is at the end of the fuel rail, then it would make sense that I'm seeing no fuel output there.

But I cannot see where the output of the pumps connect to the fuel rail. I have to assume it's somewhere at the rear of the rail by the firewall.

Cheers

__________________
1991 Japanese S600
Resides in Kampala Uganda

To clarify, if the system is working properly, you should see fuel coming out of the FPR. If the pumps are weak, the pressure will be low but the engine still might run.

Regardless, check for fuel pressure at the pump outlet / fuel rail inlet.

Ok, I was just about to ask about this.

I see where the line from the fuel pumps coming in at the rear of the fuel rail. Just in front of the FPR is a cap fitted onto the rail. I'm assuming this is where the pressure would be measures.

What type of fitting is this? Is there a special Mercedes tool that has to be used, or can a regular gauge be hooked up?

Cheers

__________________
1991 Japanese S600
Resides in Kampala Uganda

That's the cap. It is likely a 1/4" flare just like older R12 AC systems. For various cars I use a AC charging hose and some fittings to attach to a regular gauge. The car side of the hose needs to have a valve depressor as it uses a tire valve core looking device.

In a real pinch the valve core can be removed. What ever you do, be sure to wrap a rag around the fitting when you take things apart, systems hold pressure even with the engine off to prevent fuel boiling, high pressure fuel is a real fire hazard.

That's what I thought. Car is at a shop right now for the non-start issue. So I couldn't start taking things apart.

I need to buy a tester while I'm stateside.

I think this might work: Fuel Pressure Tester & Fuel Injection Pump Tester

__________________
1991 Japanese S600
Resides in Kampala Uganda