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Fuel problem in 1979 bmw 528i


I posted this same question a few years ago. The problem went away (really!) for 3 years and but has resurfaced. I have since moved back to the east coast and cannot find a mechanic that knows how to fix older cars.
When the car starts, it runs pretty well, but feels as though there is something wrong with the fuel line. Its sputters and spits if I don’t let it warm up and sometimes when accelerating or doing so uphill it will surge and hesitate. Sometimes it will not start. It feels as tough the fuel is not getting where it needs to go. If it doesn’t start on the first try, I have to wait until the next day to try again, as even just the one attempt will flood it. The fuel pump and fuel pressure have been checked, the fuel filter replaced. i suspected the fuel injectors and ran some seafoam through about 4 tanks of gas. This seemed to help a bit, then not so much. Also put some Heet through it as it feels like there is moisture in the fuel. I have been buying the highest grade gas form several fill ups. It really feels like moisture in the tank to me, but Heet didn’t seem to help.
Question: Could it be the fuel injectors?
My other suspect is the catalytic convertor, but would that cause it to not start?
Thanks for any help.

34 yr old bimmer. Fuel injection? How is air flow metered? Maf? Is the device more mechanical in nature or somewhat electronic? I bet the fuel injection control parts are a good place to start.

@lealea - you need to find a (likely older) mechanic who is experienced with these cars, there are a number of possible problems.

I don’t know how air flow is metered. I don’t know what maf means.
Texases, there aren’t any such mechanics where I live.
I really don’t want to say goodbye to this car. I feel the problem is simple, albeit difficult to find, but I need a daily driver I can depend on.
Is there anyway water could be getting into the gas tank when it rains? The problems seem worse in damp and wet weather.

Sorry, but a '79 BMW is way down the list of ‘dependable daily drivers’. If Heet hasn’t cured it, I doubt it’s moisture in the gas, unless the tank’s rusted out.

But you just gave us a BIG hint. It’s worse in wet weather - it might be old/worn spark plug wires, cap, and rotor. When’s the last time those (and the plugs) were changed.

All new plugs, wires, cap and rotor within the last 4 months.

I’ve had this car for six years and has only recently failed me. It only has 141,000 miles on it. It sat for 11 years before I bought it, so the tank was rusted out. I replaced the tank and fuel pump right after I bought it in '06. Thanks for continue to troubleshoot with me. I appreciate your help. I love this car.

The 528i is a great car, I thought of buying a used one several years ago.

Ok, not likely ignition, so it’s back to the fuel injection system. Have you run a double dose of Techron through it?


The last time I posted about this car I remember you telling me that you wanted to buy a 528i a while back.
I’ve been running the premium fuel through it for the last several fill ups. We don’t have Chevron up here in Maine. :frowning:

You can buy Techron fuel additive at most parts shops, put in 2 bottles and see.

You might want to find a BMW forum, I bet there is an area for the “E12” (that’s how they refer to that body style). Yours has the Bosch L-jetronic fuel injection system, which I think is mechanical. Maybe a BMW forum member could direct you to a knowledgeable German (doesn’t have to be BMW) car mechanic.

I ran some stuff called Seafoam through it several times. It is an injector cleaner. I filled it up Wednesday night and put some Stabil in it for the first time. I didn’t get a chance to see how it ran with that, since it didn’t start today. :frowning:
Thanks for your help!

Have someone check the hose that runs from the air vane meter to the throttle body for cracks. If no cracks are found then the air vane meter may be the problem.


"Yours has the Bosch L-jetronic fuel injection system, which I think is mechanical."
What was that sign at the entrance to Hell?
Wasn’t it, “Abandon hope, all ye who enter here”?

Having experienced the pure hell of a Bosch mechanical FI system, I can only wish the OP good luck.

Seriously, however, unless the OP can locate a mechanic who is really skilled with 30+ year old German cars, the OP may be better-off just disposing of this car before it becomes an even bigger money pit. And even if there is an appropriate mechanic available, this car is not really fit for daily driving.

I’m afraid you’re right. But before getting to that point, I would have a mechanic go over the basics, looking for any vacuum leaks, cracked hoses, plugged injectors, etc. Did BMW use those rubber O-rings to seal the injectors to the intake manifold? In my '83 GTI those would harden and shrink, creating air leaks.

Problems that get worse when going uphill and accelerating are often caused by a blockage somewhere. When the engine is asked to really put out the power, it must take in loads of air and fuel and throw out loads of exhaust gas. Any constriction on either side will show up as poor performance on acceleration and hill climbs.

Suspects would be anything that limits flow of air & fuel and exhaust. The air filter, fuel filter, fuel pump, fuel injectors, or cat. Since it shows up on starting too, my first suspect would be an obstruction in the exhaust system. On newer cars they can remove the upsteam O2 sensor to measure for cat obstruction. You may not have this though, so the first measureemtn would be intake manifold vacuum at idle. Is it to spec? Second would probably be to temporily disconnect the cat and see if that fixes the problem. Best of luck.

Any chance of getting to Portland? This shop might be able to fix it up.

If you really want to keep the car, you can surely find a capable mechanic in the Boston metro area. That could mean driving a few hours and leaving the car, but it might be required to get the job done. If you live way up north, Quebec City might be a better alternative.

@lealea did your mechanic have a fuel pressure gauge hooked up when it had difficulty starting?

Is the cold start valve functioning correctly?

Has the ECT sensor been checked?

Does the fuel pressure hold for the specified amount of time after the engine is shut off?

There’s checking and there’s checking

You state the problem is worse in damp weather. Maybe what is happening is that based on atmospheric conditions you’re shutting off a warmed up engine and the warm engine is attracting moisture inside of the distributor cap. Heat will attract moisture and as an analogy, think of a window sweating on a cold, damp winter day.

You might try spraying the cap and wires down with WD-40 to see if this problem goes away. I’m assuming here, right or wrong, that the distributor shaft bushings are not worn and causing a problem with the new rotor and cap.

Very nice looking car by the way.