Fuel problem in 1979 bmw 528i

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Thanks for the list on where to start @georgesanjose. I think most of these things have been checked but I’m not 100% sure. I know the injectors haven’t been checked, which is part of the reason I suspect them. At $80-100 each I was hoping to not have to change them. I would definitely spend the money, though, if we were sure that was the problem.
Thanks for the suggestion, @kevin. I’ll try that next time it doesn’t start.

Not sure I followed Keith’s idea? Hold gas pedal to floor for 30 sec While NOT cranking, than hit starter? What does flooring gas pedal do if u r not cranking? No air is being sucked in while NOT cranking?

This one is hard to figure because the complaint could point in numerous directions.

The no-start might point to a thermo time switch/cold start valve problem that db4690 alluded to.

The bucking and jerking could be due to any one of a number of things so it’s near impossible to tell what’s going on based on what another mechanic has done and without car in hand.

Assuming (right or wrong) that the engine is mechanically fine, the secondary ignition is good, and the fuel system is as it should be there’s always the possibility of a vacuum leak which could be affecting the air flow meter.
It’s extremely simple to connect a vacuum gauge to the intake and know for sure in seconds whether or not things are good in that area anyway.

Popping the distributor cap loose and making sure there is no moisture inside the cap is a procedure that only takes seconds also. While the cap is off the distributor shaft could easily be checked to determine if there is any bushing wear which is then leading to rotor wobble. This should have been done, if not, when the cap and rotor was replaced.

The pics show a nice looking car and it would be a shame to give up on it over what is more than likely a minor problem.

Maybe even a stuck open thermostat contributing to the mix of issues…

Cavell, I don’t know, but it works. I think its because the excess raw fuel pools around the valves, which it will anyway, but with the throttle open, vapors are allowed to escape so that after the first crank cycle, the A/F mix is about right for starting and not too rich.

If you had a leaky injector say, one that dripped and dripped for hours after the engine was shut off, then yes, the gas fumes might well stay in the intake manifold area and opening the throttle plate would allow some to escape back into the air filter to intake manifold boot area, possibly lessening the richness of the mixture. For this condition (flooded) holding the pedal to the floor while cranking would be a good idea too I think. But given the ambiguous nature of the symptoms, and the age of the car, until someone starts doing some engine parameter measurements and taking things apart for a look-see, it’s pretty much a guessing game.

Yes, @texases. The car most likely has a Jetronic fuel system and finding someone familiar with it is probably difficult. My last effort to repair one resulted in installing a cold start injector over ride due to the cold start timer failing, with BMW offering no replacement, calling the part and the car obsolete. @lealea may need to be considering a new ride.

@RodKnox OP’s car has L-Jetronic. That is a regular EFI setup. Many Japanese manufacturers licensed this technology in the 1980s. So finding someone to work on it shouldn’t be like looking for that needle in the haystack.

A cracked coil was the culprit for the no start. I had the catalytic converter replaced and it’s still running rough. Next up: injectors.

@lealea

Congratulations on fixing the no start!

I would be tempted to attempt to clean the injectors before replacing them.

You need to hook up the cleaning solution directly to the fuel rail.

So a cracked coil was found, that makes sense. From what you were saying about some of the issues it sounded like an ignition issue to me. I doubt changing the injectors will solve anything but I could be wrong. If you do that at least you will know for sure one way or the orther. I would look more into something like an air intake leak or the air flow sensor as the trouble. The trouble may also be due to a faulty electrical connection somewhere used for the engine operation.

Have you checked the valve clearances, I once had all the fuel symptoms you mentioned except the starting problem on an 83 SAAB. I explored all the same fixes that you have. It finally came down to valve clearances on a car with 120,000 miles. On this car you had to use shims to adjust the valve clearances as the engine wore down with use. Adjusting the valve clearance solved all the issues. Just adding another avenue to explore. Good Luck, Beautiful white car you have.

+1, @bm - that’s a great idea. Here’s a description on how to do it on a slightly different model BMW SOHC engine:
http://www.pelicanparts.com/bmw/techarticles/E30-Valve_Adjust/E30-Valve_Adjust.htm

I experienced the joys of a cracked coil on my late 70’s VW Rabbit. Maybe both BMW and VW used the same Bosche coil, which might be prone to cracking. However if it has lasted all these years in the OP’s 78 BMW, there isn’t much room for complaint for THAT coil. The coil related symptom w/the Rabbit wasn’t that it wouldn’t start, or that it ran roughly. It started right up and ran like a top. But if I drove over even a small puddle it would completely stall out. I found myself in the middle of busy intersections at rush hour stalled out on a routine basis there for a while. I’d push the car to the side of the road. In about 5 minutes it would go fine again.

You know, that was a frustrating problem to solve. I knew it was water related, so I’d spray water from the hose all over the engine, and I could never get it to stall out. I put the car up on jackstands and sprayed water all over the underside of the engine compartment, and it would never stall then either. Finally I just decided to remove the coil from the firewall, and the crack, tho small, was immediatelyu apparent on the underside of the coil ceramic housing. How it was that I couldn’t short it out with all that water from the hose I sprayed on it remains to this day a mystery.

If the valve clearances are out, the valves may not be open long enough or closing too early, thus the feeling of fuel starvation or that plugged up sensation. Also when you cold start the engine, the metal has not expanded yet, the plugged sensation goes away as the engine gets to operating temperature and starts to breath more freely. Over time as the clearance increases the rough idle at start gets worse and last longer until the engine warms up. Without correcting the clearances, eventually the rough idle will continue even when the engine is hot, or something traumatic.

hi all,
i just saw these comments from June. Thanks for the new info. It is still running rough, haven’t had it in the garage again. It is sporatic and running well enough that I keep driving it everyday. It starts everyday, so I can get from A to B. When it runs rough I get crappier gas milage (15 -16mpg) and when it is running not as crappy I get around 18 – which is close to normal for this car. I’ll run this new info by my guy. Thanks again!
Thinking of buying a 2001 Audi tt. Thoughts?

Can you afford a Boxter. It’s more reliable than a TT. But with cars that old, how we’ll they were maintained is the most important thing. And you can get a 2003 Miata for the same price as the 2001 Audi.

Switching from a 79 BMW to a 2001 Audi tt? Out of the frying pan and into the fire maybe? I think @jtsanders is on the mark. If you like something sporty, a used Porsche Boxster or Mazda Miata will probably serve you better. Both are fairly economical as used cars, and rated fairly reliable too. Now if you want something that is really economical, and really reliable, a used Corolla or Civic is worth considering too. You can use the money you save to go to the movies more often.

Miata much better than the TT. 2001 was during a bad period for Audi and VW.

The old Bosch mechanical injection goes way back and many European cars used it. The MAF is a carefully balanced damper door moving on jeweled bearings that controls injector fuel volume…Finding replacement parts is probably getting next to impossible…As I recall, this system has no electrical connections at all. It’s 100% mechanical…They worked quite well as long as they were kept spotlessly clean. The movement of that damper door was delicate and anything that interfered with it would upset the fuel mixture…