1980 528i Possible Fuel Pump failure, but which one?

[brotherhay]

I have a 1980 528i with the 2.8L. I have had this same issue for years now, and have changed out many parts but it has yet to be fixed. Today was the nicest day of the year yet here in WI, so I fired the car up. Thats when I remembered this issue.

Basically, it doesnt seem as if the fuel has no pressure behind it when starting the car, but when its running it runs fine. If I turn the key to the on position, I dont hear the fuel pump engaging. If I turn it just barely past on, just before the starter engages I can hear the fuel pump running then.

So, it seems as if one of the pumps are working, but Im not certain as to which. I dont have a Haynes manual in front of me, so I figured Id ask here.

Should a fuel pump engage when the key is in the on position, and if so, which one is it? The one in the tank, or the one mounted to the underbody?

[T.Hanson]

From my best guess experience: Key on, ( take air cleaner off to access ) holding the air fuel meter flap open will let you hear the external fuel pump spinning. Think of the in tank pump as a helper, just to get the fuel up, out over the hump to the pump over the axle.

My external pump started getting noisy. Whether or not it would continue to pump, I replaced it, figuring the noise wasn't a factory fresh option. The in tank pump is next for me, having cleaned the little flat paddle screen, still buzzing. Full tank sometimes helps that.

Fuel pressure regulator ( little barrel on the front of the fuel injector feed rail ) can be tested, ( Google past posts or FAQ ), but I figured thirty years was enough to rate retirement and pension. Doing that cured my multi cranking start up problem.

If you've never replaced your fuel lines, pumps, filters, it's not difficult. Just a few patient hours to do everything. If you change components with old lines there's a good chance you'll find mushy ends.

True story: A rear line split lenghthwise and dumped at least three gallons of gas under the car, in the garage, engine running. Abject terror only saved by luck. Thirty years makes any notions of fuel, brake line safety non issues, a lit fuse to very large calamity.

[brotherhay]

So youre saying with the key in the on position, and flap open the external pump should engage. Seems flap open or not this is when the pump should engage. I dont think mine is doing that.

Might be time for a new/used pump.

[Mike W.]

Should a fuel pump engage when the key is in the on position, and if so, which one is it? The one in the tank, or the one mounted to the underbody?

As T Hanson mentioned, they should work only with the key on and the AFM flap open. IMO the in tank pump only allows you to fully drain the tank, I've put ~500K on M30 powered cars, mostly injected, and to the best of my knowledge I've never had a working intank pump. If your main pump isn't working, for further troubleshooting, key on, flap open, give the pump a whack with a screwdriver handle. That usually reseats the worn out brushes and it will run for a little while. That doesn't mean it's fixed, it's a way to troubleshoot or get home, it will not continue to run if that's what it takes to get it running.

[brotherhay]

Ill give that a shot after work here in a few hours. When the key was in the "almost start" position (just past "on") I could hear a pump running, but the sound was not a steady hum.

Ill test it out to see if I beat on that thing a little bit if it engages when it should. I believe this one is on its way out, sucks.

But, ill reiterate what I had initially found. This same problem was there for a while now. If I let the car sit, the longer I let it sit, the longer it takes to start. If I wait a day, takes maybe 5 seconds of turning it over to finally pop. Then when it does it starts out fine, then quickly lowers in RPM and then stalls out. A few more attempts and it will then stay steady rpms. I replaced alot of stuff, but still no fix yet. Fuel Pressure regulator, cold start combo relay, cold start valve.

Only thing besides this fuel pump that I can think of is leaky injectors. Ill check the oil for gas smell also. Other than the fuel pump, I really dont have much left that I can think would cause this.

[brotherhay]

Ok, so I did some adjusting of a few things, since once it is running its fine.

After it had ran for a bit, I went to test out the pumps with the AFM flap "all the way open". I dont even have to push the flap a quarter inch and the fuel pump engages.

Fuel pump works, so what could be the problem with the delayed starting after sitting?

EDIT: Id also like to add that I have replaced the Fuel pressure regulator a few years ago. It made no change from day one. The symptoms sure to point to that thing, but a bad one out of the box?

[T.Hanson]

You can Google search previous posts for the regulator testing procedures. Two or three years ago isn't very long, compared to mine lasting twenty five. Still, it's not the same as brand new.

Only because the same slow starting, lots of cranking before firing happened to me, and a new fuel pressure regulator fixed it, I pick that. Not that expensive and if it ain't it, keep it for a spare.

Google fuel pressure regulators to read how they work.

[brotherhay]

I agree, it just seems that the pressure regulator is the issue here.

Ill find another one, they really arent that pricey.


EDIT: actually I take that back. They are upwards of $80. Ill get to testing fuel pressure. I have the old regulator also.

[Mike W.]

How does it start once it does start, just fine or does it take a while to sort of clear it's throat? You could have the opposite of what you are thinking, you could have leaky injectors that are bleeding off the pressure into the manifold and flooding it. There is also a check valve in the fuel pump that is supposed to keep it pressurized when off, it's possible that has failed. If it is bleeding off pressure, it could be in a variety of ways, not just a bad FPR.

[brotherhay]

Yep, it takes a bunch of turns to get started, then once it pops over, it will die. Do that a few times, then it will run steady.
I checked the oil for a gas smell, and it kinda smells gassy, but not really too bad.

But, then heres another symtom that can also lead me to bad injectors. Once the car has been idling fine, if i back it out of the driveway, then floor it, the car just dogs right out like its flooding itself.

If the injectors were leaky, or just bad in general, it seems like this is exactly what would happen.

As most owners have dealt with, I too had leaky injector lines. I replaced those, but never really tested the injectors. I suppose maybe I should have those sent out and tested. Buying 6 new will really hurt, so maybe testing them out and weeding out the bad few would help.

[brotherhay]

Update:
So, after thinking some more of this out, I considered that the Fuel pump may have been bad. I was going to test it, but didnt have the correct connector to do it at the time. So, after more thinking, I figured it cannot hurt to purchase another Fuel Pump and give it a try.

New fuel pump installed, same problem.

Next stop just for fun, ill pull the cold start valve out and see if that thing sprays when trying to start. I suspect it is not. It was replaced a few years ago, maybe only has 5000 miles on it or less.

[brotherhay]

No better time than now to test out the cold start valve, since its 45F outside here in WI. Pulled the cold start valve, and wrapped the end in paper towel so that if it did spray, I could easily see it.

Nothing, not a drop. While I go through the book to diagnose whats up with that, feel free to add some comments to help me get this thing running the way it should be. Im sure its more than just this cold start valve...

[Peter Florance]

check the FAQ for combo relay; they get bad solder joints inside.
Also check thermal time switch which is what grounds the cold start valve

[Lenny D.]

No better time than now to test out the cold start valve, since its 45F outside here in WI. Pulled the cold start valve, and wrapped the end in paper towel so that if it did spray, I could easily see it.

Nothing, not a drop. While I go through the book to diagnose whats up with that, feel free to add some comments to help me get this thing running the way it should be. Im sure its more than just this cold start valve...

As Peter says, what controls the cold start valve is the Thermo Time switch. So called because its function depends upon both coolant temperature defining the time factor for which the CS valve sprays. It will also NOT energize the CS valve if the engine is started, stopped and restarted to prevent flooding. Pricey gizmo, but it does what it does. Also remember the coolant temp. sensor tells the ECU how warm or cold the engine is to allow the proper fuel/air ratio.

[brotherhay]

I wish bavauto had a way I could get a listing online of the items Ive purchased for this car. But, just by looking quick at the price tag of that sensor, Id be willing to bet I bought all of them but that one when I changed out the thermostat housing.

Ill test that thing out tomorrow, but, I also looked into this.

I tested the positive lead on the CS valve, and with the key on, its at about .06v. Turn the car over and it jumps to about 8v, although my battery is really fading.