Supercharger starting problem

[Slow Old Poop]

I have a '96 318ti with a '97 M3 motor (built by a shop in Jacksonville, FL). Engine mods include a M50 manifold, cats removed, Shrick cams and Turner Stage 3.

A local BMW shop installed an Active Autowerke supercharger (thus replacing the Turner Stage 3 stuff). The car runs very strong--except when I shut it off, it won't restart.

We discovered, when checking fuel pressures, that if we cut power to the fuel pump, it starts! By watching the gauge, we see that the engine cranks for a few seconds until fuel pressure at the fuel rail drops to 20 psi, and then it starts. So now I have a switch to turn off the fuel pump and I'm getting by.

But I'd sure like to make it right. Before the supercharger, the car ran like a clock.

We've been working with the Active Aerowerkes experts, and their opinion is that it's something very simple--like something is mis-plumbed--but nobody can figure it out. We wonder if there's something different between 318ti and E36 fuel plumbing that could be causing this. Or if the M50 intake manifold is different from the E36 M52 manifold the supercharger is designed for.

Here's some data:
45 psi at the fuel pump and fuel rail.
New fuel pump installed per Mike Miller's suggestion.
Seems to run rich.
82000 miles on M3 motor

Any ideas? Is there anybody in Iowa that REALLY knows BMWs?

[vollosso]

What injectors? What tune?


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[XnWarden]

Plenty of FI cars run the M50 manifold. So unless they didnt reroute all the vacuum lines properly, that isnt your issue.

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[jskicet]

I had starting issues with the Walbro from day one. After a year of long starts I tried putting a new stock one back in. Been fine ever since.

[Randy Forbes]

Only time I have had starting problems, it always traced back to dribbling injectors (partially clogged and/or leaking when they shouldn't be open).

For the little it costs, I'd send the set off to Injector Rx, and you'll have them back 3-days later. I'm very satisfied with their work, and I have no financial interest.

[1000hp]

I have the same issue. The car cranks forever before re-starting when hot. Seems to be flooded.

Only time I have had starting problems, it always traced back to dribbling injectors (partially clogged and/or leaking when they shouldn't be open).

For the little it costs, I'd send the set off to Injector Rx, and you'll have them back 3-days later. I'm very satisfied with their work, and I have no financial interest.

Randy, did your issue occur during hot-start only? I have been thinking clogged or leaking injector, but the fact that it only happens during hot start makes me wonder if it's a DME or tune issue.

[Slow Old Poop]

Reply to all

Thanks guys

Vollosso asked: What injectors? What tune?
Whatever Active Aerowerkes (AA) sent with the kit. We've doubled checked it, read it out, and AA verified it was correct

JSJICET said I had starting issues with the Walbro from day one. After a year of long starts I tried putting a new stock one back in. Been fine ever since.
No Walbro. We put in a new BMW pump

Randy Forbes said Only time I have had starting problems, it always traced back to dribbling injectors (partially clogged and/or leaking when they shouldn't be open). For the little it costs, I'd send the set off to Injector Rx, and you'll have them back 3-days later. I'm very satisfied with their work, and I have no financial interest.

How did you know it was dribbling injectors? We noticed that at least one of the sparkplugs had gas on it.

100HP said: Randy, did your issue occur during hot-start only? I have been thinking clogged or leaking injector, but the fact that it only happens during hot start makes me wonder if it's a DME or tune issue.
E
Dunno about Randy, but mine is a hot start only issue. AA thinks it might be a DME (what's that?) issue too. Of course, I haven't heard from them in about a week now.

Rich

[Randy Forbes]

DME = Digital Motor Electronic, aka, the computer.

Wet gas on plugs the first time, pulling them out and watching the spray-pattern the 2nd time.

Interestingly enough, the first time it was cold-start issues. The second time, it was (black tailpipe) smoke! I guess that was more of a running than a starting problem...

[1000hp]

I suspected the DME initially, because I experienced this problem with other software (Conforti) on this same DME before the car was supecharged. After that I switched to a different DME with FI software, then changed back to this DME with the current software, and the issue returned with this DME. But I also changed injectors when I put this DME back in, so it could be an injector issue as well.

I will swap DMEs when hot and attempt a hot start and see what she does.

[vollosso]

Hot and cold start have different fueling tables.

If the pressure is good at crank and it’s not firing until it drops then it’s likely too much cranking fuel.




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[1000hp]

I will swap DMEs when hot and attempt a hot start and see what she does.

Actually no I won't because the other DME is tuned for much smaller injectors

- - - Updated - - -

Hot and cold start have different fueling tables.

If the pressure is good at crank and it’s not firing until it drops then it’s likely too much cranking fuel.

Interesting. Do you know if that is something that can be adjusted with, say, Rom Raider without having to save and re-flash the entire tune?

[vollosso]

- - - Updated - - -


Interesting. Do you know if that is something that can be adjusted with, say, Rom Raider without having to save and re-flash the entire tune?

Anything is possible.



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[Slow Old Poop]

Hey guys--I 'splained Randy's theory about the dribbling injectors to Active Autowerke, and they want us to do a "rest pressure" test. This involves getting the engine up to operating temperature with a fuel pressure gauge attached to the fuel rail, shut the engine off, and remove the fuel rail and injectors whilst the fuel rail remains under pressure. Watch it for 30 minutes to see if anything leaks.

Thanks for all your help so far. I'll keep yez posted.

[Braymond141]

You need to rev to 2k rpm and turn the key to off every time you shut the car off. Rev and turn the key off while it is at that rev. It will restart every time.

This is not an uncommon issue, but proper tuning will fix it. I dealt with it for years running easy mode 10psi by installing a 4.0FPR on a standard Dinan 6.5psi kit/tune. You're not the first person to post about this on this forum.

[Slow Old Poop]

Wow Braymond! I'll definitely try that while I await my wrenching buddies to return from the Michigan 500 and do the test (I am a terrible mechanic--I'm only good for working on stuff under the car--my wrenching buddies don't let me anywhere near the motor or electronics).

You said "This is not an uncommon issue"--if so, I wonder why Active Aerowerkes hasn't heard about it? They seem to be as confused as we are.

Meanwhile, I'll search the forum to find some of those other posts you mentioned. Didn't find them the first time, but I didn't look very hard. Now that I know they are there, I'll be more diligent.
Thanks, mate.

[Braymond141]

Why do you need to wait for your buddies? Drive the car. When you go to shut it off, just blip the throttle (to about 2.5k rpm) and turn the key off soon as it hits 2500rpm.

[Slow Old Poop]

That's what I meant. But we still want to do the resting pressure test when they get back.

[vollosso]

Resting pressure test is a waste of time.


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[Braymond141]

Resting pressure test is a waste of time.


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Agreed. This is a tuning issue.