e21 w/weber, have spark, have fuel, and it was running - then died. Help

Can't for the life of me figure out why it won't fire.

I replaced the fuel pump (and relay) a while back, and it ran for about 20min, then died and wouldn't restart.

This is the same phenomena that happened when it died before - except that it was the fuel pump then.  I had no pressure that time.

Will run a bit on starting fluid.

Now I can crank it and watch 3lbs through the regulator, it has spark.  Coil is good (I thought it was bad, bought a new coil - which ohm tested same as the one I replaced... oh well).

Thoughts?

Help. 

Which Weber and which regulator? Street or race car?

Webers can be a bit finicky about fuel pressure I generally ran no more than 2.5 psi on the 32/36.

some kind of fuel line obstruction downstream of the regulator? If it's running on starting fluid, seems like the *only* real answer is fuel not getting there. I don't know Webers very well, so not sure if it would be carb-related or fuel line related. 

38, Holley regulator I think?

It reads 3lbs while cranking, and it ran really, really well before it just shut off and died. 

I suppose it wouldn't hurt to pull the carb and run some cleaner through it. 

With the engine off:

Hold the coke open and look down the bores.

Work the throttle linkage and see if you get a strong squirt of fuel.

No squirt means no fuel in the carburetor.

No fuel in the carb means something after the fuel pump is blocking the flow.

Usually a crappy regulator, needle and seat sticking shut or a dirty filter if you put one after the pump for some reason.

For a quick fix, try giving the float bowl area of the carb a couple whacks with the handle of a screwdriver to see if you can jostle the float loose. If that works, you still need to open the carburetor and sort out the problem.

How well did it run before the fuel pump died?

Stuck float, then accelerator pump was leaking. 

Each time the car has died, and it just died again now, it runs flawlessly for about 20 min, then just shuts off. 

After it dies I can start and idle for a few minutes at a time, but it won't stay running. 

LS swap wouldnt have those issues.... just saying

K swap neither, but then need a higher pressure pump.

How is it dying? Does it sputter to a stop or does it just drop dead?

If it is stopping dead, it does sound ignition related (as you where guessing, like a bad coil).  How is the spark triggered?  Points? Pickup etc.  Almost seems like something g is overheating.

In reply to aircooled :

Just up and dies.  Absolute charm while it's running, then shuts off. 

Electronic distributor, so no points or condenser.   In between the last time it ran really well and it running nicely this time (and shutting off) I've swapped distributors and ignition modules that I had lying around.  No change. 

 In the old days there was a ballast resistor on some cars, but I haven't ascertained of this car has one. 

I need to find a wiring schematic and chase down anything ignition related.

It's just dumb spark and dumber fuel, this shouldn't be that hard.   Then there's the dumb guy trying to diagnose it, so I've got the hat trick, and that's a positive, right?  Or is that backwards?

And, I'm starting to think a motor swap would be easier at this point.   More expensive, to be sure, but still easier. 

TurboFocus said:

LS swap wouldnt have those issues.... just saying

mdshaw said:

K swap neither, but then need a higher pressure pump.

How many Formula 1 world championships have these engines won? Right, none, I'd stick with the almighty M10 

I don't have anything add but I hope you get sorted it quickly so you can enjoy the car with the nice spring weather. 

Have you checked fuel in the carb and spark immediately after it dies? Certainly seems most likely heat-related, and probably ignition, but I think checking when everything is at temperature and the fault has just occurred is going to be necessary.

E21 wiring diagrams here: https://web.archive.org/web/20160320174252/http://www.jtresto.com/e21info.htm

Are those 12v (sometimes called high performance) coils?

If the ballast resistor was removed (full 12v to the coil) and those are "standard" points coils, they will overheat and fail at idle (at least in my experience) then come back when cooled down.  Check voltage to the coil with the ignition on to see if there is a resistor. With a resistor it will be more like 6v.

I had a similar thing happen to me when I went to an electronic pickup (which needed to be wired with a full 12v).  The car would run fine for a while but would die at low RPM, until I put in a high performance coil.

In reply to adam525i :

lol imagine how many F1 championships would be won if the rules allowed LS and K-motors, M10 doesn't stand a chance!

In reply to aircooled :

Factory electronic ignition,  early cars did have points, but mine is a later car. 

TurboFocus said:

In reply to adam525i :

lol imagine how many F1 championships would be won if the rules allowed LS and K-motors, M10 doesn't stand a chance!

LS and K motors are 20-30 years of upgraded engineering knowledge. 

For the time, a factory 4 cyl block (obviously not factory stock internals though) that would hold 1500hp was pretty impressive. 

Some years ago somebody had a complete M10 F1 cylinder head and exhaust for sale.  Whoever found it posted the link on bfc. 

We all drooled...

In reply to OldGray320i (Forum Supporter) :

Those M12s sound insane

Ok, so I've been through the grounds, the fuel system is working, gets spark, runs absolutely flawlessly for about 20-25 min and dies. 

If it fires and runs after the initial death, it will rev at light throttle opening, but die under greater throttle opening, so that says vacuum advance, or advance period, is part of the issue?

That's either distributor or ignition module, right?

I've swapped both with old parts car stuff, and it's died either way - except that I can't remember if I threw the old ignition module back on because that didn't seem to make a difference at the time it was previously not running (that was the fuel pump issue).

The distributor is definitely the swapped one. 

I'm inclined to think it's the ignition module (it's a later car, no points/ condenser). 

In reply to OldGray320i :

I wouldn't expect advance issues to cause it to die at greater throttle openings.

I've just gone back and re-read some, and I'm unclear on whether any of the checks for spark, pressure, etc have been done right after the car dies.

And am I correct in understanding that without changing any parts, it will run badly after dying and restarting, but after sitting for a while (cooling off) it will do another 20 minutes of running great followed by sudden shutdown?

That sounds an awful lot like an ignition module overheating.

In reply to Jesse Ransom :

Car died a mile from home, so I went and got the spare ignition module, swapped, made no difference.

Didn't think to bring a plug wrench, but, it's given spark when dead before.

Correct me if I'm wrong, it should be a nice blue pop, though, right?  It's looked distinctly weak and yellow before, and then stronger/ bigger at other times. 

Either way, it's a completely dumb system, so if I have fuel and spark, it should run. 

Fuel pump set just shy of 3lb, and it will maintain as the car sputters.

That leaves spark,  so it has to be distributor or module, right?

Distributor would seem to fairly dumb as well,  so that would point to a module, wouldn't it?

Or is there something in the distributor which could still cause an issue?

It was a non running parts car,  could be a bad module that made it a parts car.

I haven't found a way to test either one, I'll see if I can Google it, but I haven't found anything yet.

OldGray320i said:

In reply to Jesse Ransom :

Didn't think to bring a plug wrench, but, it's given spark when dead before.

Next time you take it out for a drive, bring a spare spark plug and stick it on one of the wires. Easier than removing one with a hot engine. 

I'm not ready to bet money on anything in particular.

It may be all dumb stuff, but if you've got fuel, and you've got spark, and it's still not running right, then... something has come up with extra dumb.

3lb of fuel pressure doesn't let the carb off the hook. (You've had float issues before, yes? Do we know everything's clean inside?)

Spark that varies from fat and blue to weak and yellow suggests something is unreliable there. (Got any other ignition modules? Coils? Ready to do something crazy like swap in a Pertronix? I'm not saying go parts cannon, but when there's a weak-ish spot that wouldn't mind an upgrade anyhow... If you happen to be inclined.)

There's always a reason. I want to be very clear that I'm not suggesting that this is your issue (it's not; it's really not) but I've had the spray tube in the primary venturi on a DGV come loose in its casting and rotate until it wasn't facing the right direction. Weird stuff can happen, but it's *still* a reason.

Maybe something very simple is behaving variably. Maybe something that shouldn't be an issue is having an esoteric meltdown (Esoteric Meltdown is now my Dr Teeth and the Electric Mayhem cover band). But there's a reason.

Electric fan causing a voltage drop as the car gets 20-minutes-hot? Not on an E21 I'm guessing, but it's been a while... Triple-check whether this car *should* have a ballast resistor? Sounds like there's some uncertainty there, and if it should have one but doesn't that might be making the coil toasty...