hello, 1980 635csi Euro w/ L-jet no start

[rockreid]

since the 5-series and the early 6's like mine share many aspects, I thought this would be the best forum for trying to get my 1980 635csi Euro running and sold. My early 635 has the Euro engine and dogleg 5-speed. The car has sat for about 3 years now and is pretty rusted, but was my daily driver for a few years back in 2004-2006.

I have confirmed the fuel pump works and used it to pump all the old gas out. Using a test light I confirmed the fuel pump gets power when the engine is cranking, but not when the key is simply On. I want to replace the fuel pump relay and the main relay but need to know where exactly they are in my car and the best place to find parts. Since this is an L-Jet, I'm not sure if my test light was pointing to a bad relay or not. I do know that while it was running it suffered from the typical rough idle, probably a vacuum leak somewhere.


Thanks,
Rocky.

[Karl in KS]

When the key is in the run position, the fuel pump relay is only energized when the air flow meter door is open--at least a little from idle air flow. So take off the elbow between the air filter and the air flow meter, turn your key to the run position, and push the air flow meter door open. The fuel pump should energize as you open the door.

Then check for spark as you crank the engine. The old mechanic told me "90% of all fuel problems are really the ignition."

Wish you well with your car, the six is still the best looking car BMW made.

[Mike W.]

When the key is in the run position, the fuel pump relay is only energized when the air flow meter door is open--at least a little from idle air flow. So take off the elbow between the air filter and the air flow meter, turn your key to the run position, and push the air flow meter door open. The fuel pump should energize as you open the door.

Then check for spark as you crank the engine. The old mechanic told me "90% of all fuel problems are really the ignition."

Wish you well with your car, the six is still the best looking car BMW made.

Agreed. I will add, there is no main relay like on Motronic cars, the Combo or double relay is the closest, but it only runs the FI, not ignition. Check for spark and go from there.

[rockreid]

how common is it to have a fuel pressure valve seize up? I am getting gas to the engine cranking now but when I take the fuel line off the cold start valve, nothing comes out indicating the whole fuel rail is dry, yes? The only thing in the way is the fuel pressure valve, possibly seized from the old gas.

[Mike W.]

No, it would be the other way. The fuel pressure regulator is like a plug on the output side of the fuel rail, so even if it was wide open, you would still have some flow, even if you didn't have any pressure. And if it was stuck closed, you would have ~100PSI and be in danger of blowing off fuel lines. If you think the fuel pump is running, and sure you have gas in it, check or replace the filter, it's the most likely plug in the line.

[Karl in KS]

How old are the fuel lines from the gas tank to the pump? If that hose is cracked, your pump will suck air.
How did you use your fuel pump to pump the old gas out, just dump the pump outlet into a bucket? If so, disconnect the line again at the fuel filter outlet and the cold start valve and see if you can blow through the line. It should be open. Then before connecting things again, see if your fuel pump will pump gas through the filter.

It's possible that in pumping the old gas out of the tank you stirred up the sludge in the bottom and plugged the pickup. In which case you'll need to pull the tank unit and clean it out. If your car has an access plate in the floor of the trunk like e12, you don't need to drop the gas tank to remove the gas pickup from the tank.

[rockreid]

I think fuel delivery is fine now, I have spark, but the engine now fires for 1/2 second and quits...and I have to have the pedal floored for it to even fire up.

I checked around and there are no fuel leaks..I had to run a new flex fuel line from the back of the car because the old lines were corroded. This setup is just to get it started and confirm the engine works..

I don't see any hoses that immediately could cause a big air leak... anything else i should check.... this car ran fine before sitting for so long.

[Karl in KS]

Let's review the ignition. The 12v feed uses a different circuit when starting, bypassing a ballast resistor. When switch is in the run position, that resistor limits current to the primary side of the coil. It's not unheard of for that resistor to fail, shutting down the engine when you move the key from start to run.

And a funny thing I had happen once was the fuel filter got really plugged even though it didn't look dirty. Conjecture is a little water in the tank caused the filter paper to swell. The car would barely run. This was a different car in my past with a carburetor on which I added a glass in-line filter just ahead of the carb.