I'm wondering if anyone has advice about an issue I am having with my 1972 BMW 2002. The car is almost completely stock. It has a Weber 32/36 carburetor. It was running fine until it began having an issue where it would run for about 20 minutes and then start to miss, stutter, and ultimately die. My dad is somewhat of a BMW expert (raced/owned 2002s for years in the SCCA), and has changed the distributor and coil to electronic, disconnected the vapor recovery system to vent the tank, changed the fuel pump, alternator, done a valve adjustment, put new spark plugs and spark plug wires, and performed a general tune-up. Still, the issue persists! It has been a long time, and he still can't figure out what the problem is. Anyone have any ideas?
Thanks in advance!
02Pilot will be along here shortly; he will likely have some wisdom to share. Reading your post, it really reminded me of vapor lock. But that thought is based on ancient experience with carbureted Chevy V8's that made a whole lot of heat underhood.
Chris Powell
Racer and Instructor since, well. decades, ok?
Master Auto Tech, owner of German Motors of Aberdeen
BMWCCA 274412
German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471
It sounds like a fuel problem, so let's look at that first. What's the fuel state of the carb when it dies? Is there fuel in there? If you pump the throttle after it has died can you see fuel pumping into the intake from the accelerator pump? Is the fuel still running through the stock plastic line and straight to the carb, or did you reroute it?
What do the plugs look like? Does it matter if you're driving or idling, or does it only die in one condition or the other? How long does it take before you can restart it? Had you changed anything on the car immediately before the problem started occurring?
Let's get some of these questions answered, then maybe we can nail down what's going on.
Life's tough. It's tougher when you're stupid. -John Wayne
Thanks, O2Pilot. The answers to your questions:
Yes, there is fuel. Accelerator pump works correctly. Fuel is still running through the stock line. The spark plugs are pretty new so we haven't pulled them out lately. Would imagine they look normal. The car will die no matter what, does not depend upon driving vs. idling. It seems to restart almost immediately, but it seems that it used to take longer... when you do restart it, it wants to die right away and doesn't run well. We had not changed anything on the car immediately before it started occurring.
Sure sounds heat-related to me, and probably fuel, so vapor lock as Chris suggested is certainly possible, though ambient temperature would probably be a factor here. Possibly overheating in the ignition components as well - check those for excessive heat. Do you have a ballast resistor or a resistor wire? If the former, that's a possibility.
Now here's a really odd possibility: if the fuel tank vent is blocked, you could be getting a vacuum in there as fuel is removed. This will eventually counteract the pump to the point that it won't run until the vacuum is relieved. I know you said you disconnected the vent, but did you check that no blockage remains? Try running the car with the filler cap removed and see if the problem goes away.
Life's tough. It's tougher when you're stupid. -John Wayne
We did try running the car with the filler cap removed, but the problem didn't go away. Also took the vent line off to make sure it was clear...There is neither a ballast resistor nor resistor wire. We live in a pretty cold place (San Bruno, California), so my dad has a hard time believing it's vapor lock..it's baffling!
It sounds like fuel delivery is OK. If you had an oxygen sensor and AFR meter in there we could monitor it, but failing that or a tailpipe sniffer, we can only go on visual evidence.
So you have a resistor (blue) coil? Or some other arrangement? Check the spark intensity with the car cold, then again immediately after it dies. See if the coil is getting really hot. I know you changed the ignition components, so this is unlikely, but we need to be methodical.
Have you checked the timing when both cold and hot? Could something be moving around in the distributor and throwing the timing off?
Another thing to consider is electrical grounds. They are often problematic on these cars. If something is loose and gets looser when it heats up it could be enough to compromise a connection. For that matter, check the fuse box too - I've seen old fuses cause some strange problems.
These are long shots, but we're clearly deep into long shot territory already.
Life's tough. It's tougher when you're stupid. -John Wayne
It had a Bosch blue coil without a ballast resistor, but now it has a Pertronix 40511 3 ohm flamethrower coil. We will check the spark intensity like you said when the rain lets up here.
Haven't checked the timing, but since it will immediately start again and run great for about 20 mins, seems the timing would be the same? Just to note, the distributor used to be a #0231180008 (the usual for a 73' 2002), but my dad had switched it to one he bought on ebay at some point before the issue began. Beginning to wonder if this is related.
Also to note, it has an EGR valve and a fuel pressure regulator. You think those might be suspect?
Why does it have a pressure regulator? Are you using an electric pump? You don't need one with the stock pump. Is there a gauge on it? Webers need very low pressure (~2-3psi) or the needle valve will be overwhelmed.
I'm not a fan of aftermarket coils, but they're easy to test, and if it's new it should be fine. Running the Bosch blue without a resistor is correct, as there is an internal resistor in the coil. Some people run the blue coil plus a resistor, resulting in weak spark.
I know almost nothing about the EGR - I've never had an 02 with one. It's certainly something to look at though, since it's function is definitely affected by heat.
The distributors are pretty simple and robust. The fiber washers disintegrate and cause the timing to flutter around (take the cap off and lift up on the rotor - if there's vertical play in the shaft it will never hold timing correctly). To find one bad enough to be affected by heat would be a new one for me, however. No harm in swapping the old one back in though.
Life's tough. It's tougher when you're stupid. -John Wayne
Supposedly the pressure regulator is stock, maybe it has something to do with the fact that this is a California car? No gauge on it, it's vacuum-controlled. I think our next step might be the EGR valve...
Can you post a photo of this pressure regulator? I don't recall ever encountering a factory FPR on a 2002. Are you sure it's not the EGR control valve? Do you have an air pump too?
If it were me, I'd rip every last piece of emission-control equipment out of that thing and then start over. The whole system is a train wreck.
Life's tough. It's tougher when you're stupid. -John Wayne
The sad thing is that the car will soon be moved to Reno (my new residence), and it will be smogged there, so I'm not sure if removing all of the emission-control stuff would be prudent right now...
No air pump.
Here's that photo you asked for:
IMG_9143.jpg
Where do those other lines go to? A simple FPR should have fuel in and out and a single vacuum line. Have you tried bypassing it?
Life's tough. It's tougher when you're stupid. -John Wayne
Will try to bypass next and let you know how it goes! Thanks for all of your help so far!
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