US Spec 320i - Start issues

[joaocandeias]

Hi everyone!

My name is João, and i'm looking for some help with my '78 US Spec 320i. I'm sorry if issues like this are reported so many times in this forum, but i thought it was better to start from scratch, so here's an overview:

I have the car for a year now, and it didn't start when i bought it. We started by replacing the electric fuel pump, and eventually the car started running, although very roughly and would stall immediately after coming to a stop. We eventually replaced other parts like spark plugs and cables, distributor contact, ignition coil and fuel filter. The car now runs a lot better, and does not stall in Stop signs anymore like it used to do. A few tanks of fresh gasoline also helped.
But in the meantime, a whole year has passed and It still has some starting issues that i would like to address, as bad weather is coming and the car will be stopped for longer periods of time.

Below, is my best attempt of explaining the issues:

• When the engine is cold, the car starts at first try but stalls immediately. Most of the times i can start it at second try, as long as i keep my foot down on the accelerator until idle stabilizes.

• When the engine is on operating temperatures, it starts flawlessly. - for example: if i leave it parked for some minutes.

• The worst starting problems happen when the car is stopped for more than ~30 minutes (when it's not cold, but not operating temperatures either).
  The engine goes on cranking forever, and won't start for nothing. Most of the times i play the waiting game and leave it some more minutes until i eventually can make it start. Push start/popping the clutch also works if i'm in a hurry, but i avoid it at all costs.

Not sure if it's related in any way, but on the road, the car also hiccups quite a lot in low RPM's

I would really like to solve these issues in order to make my '21 a bit more reliable and enjoyable. Driving this car anywhere requires some managment in order to know if i'll be able to come back home . It's pointless to have such a great car in this state, so any help is appreciated
I can also make some video footage of the issues, so you guys can see exactly what i mean.

It's probably obvious, but i'm very very very far from being a mechanic. I'm a curious guy though...

Thanks in advance!






PS: here's a picture of the bad boy:

[Jeroen]

Looks good, and US versions are pretty rare in Europe!

There are a lot of things you can check, or have checked, as now it is uncertain what the condition is of engine, iginition and fuel management. For example:
- engine compression test
- check ignition timing
- exhaust gas analysis and mixture adjustment

That should give you some more direction. With the ignition work done I expect you have issues with fuel delivery, but you need to know if these basics are ok otherwise you are working around a maladusted setup.

[uwbuurman]

Like Jeroen says. After that, if you still have these kind of troubles, my suggestion is also on fuel delivery, WUR overhaul and adjustment, take a look at the coldstart injector (blue connector, on the intake manifold), and the time/temp switch, on the thermostat house

[Jeroen]

And the fuel accumulator might be at fault as well. It is fitted together with the fuel pump and fuel filter. If your issues persist you may want to try to bypass it to see if it makes any difference. But tests and checks first!