help! engine dies after coming off a blip
 

this one is mainly for you Ken,
Engine starts and idles fine. we blip the throttle, and it seems to speed up fine, then when we come back down to idle it will die if we don't hold the throttle open a bit...even if we do this, it still usually dies as soon as we close the throttle all the way. i thought it might be because the alternator starts to load the motor after the motor hits 3000RPM after starting, but we disconnected one of the terminals from the alternator, and this STILL happens. it seems like MS is going into some other mode that the engine doesn't appreciate after it either:

1) revs up to a certain rotational speed
2) detects a certain rotational accell (with delta TPS)

but it may be something completely different.
any thoughts?

Do you have decel turned on? Meaning are you leaning out the mixture at all during decel?

What's your timing like in that area?

Do you have the dash-pot enabled? BAC valve?

The main reasons I've seen for this behavior are timing, removal of the dash-pot, and running too lean at the low extremes of the map, and having fuel-cut enabled and at too low an RPM.

Ken

yes, the dashpot and BAC are both currently out. that must be the problem. although i was under the impression that the BAC valve only did anything when on fast idle. does MS open this up during decel too?

Unforturnately we've got a bigger problem now, we can't even get the motor to start. it will start 1 times out of 20, but only for a few seconds. we are getting fuel, and we checked our plugs, they seem very weak. we are using a really old ignition coil, but i have a new MSD two tower coil in the mail (40k volts). i am hopeing that this fixes our problem.

The stock computer doesn't use the BAC for dash-pot functionality, but the MS can.

On the weak spark, you could probably increase cranking dwell and see if that helps any.

Ken

ok, i ordered a "GM style" two-tower coil from MSD and 2 new plug wires. the sparks look amazingly strong now compared to what we were seeing. :shocking: once we hooked up the new coil the engine started up after only about 10 seconds of cranking (which is good compared to what is normal for us). we idled the engine for a long time and ended up perminantly fouling a plug. this is becasue when we had our original issue the plugs got soaked, then after we got the motor working again, all the fuel up in the plug coked out. this is no big deal and was sort of expected. we put in a fresh set of plugs and now we are big-time back in buisness. We have since hooked up our radiator fans to MS and they seems to be turning off and on fantastically. we hooked up our BAV, but only to a human controled switch for now. my electrical engineering buddy needs to make some circuit if we want to attach the BAV to MS, but he'll have that ready by next weekend. over the next days of working on the engine i will be trying to get our cranikng duration as short as possible in this cold weather and do a little more tuning at idle. after that we may being working on putting the turbo on the engine (yes we are turbocharging an NA S5!).

The next question is, should we build a friction break dyno to load the motor, or just focus on getting the motor in the car? does anyone have any suggestions? keep in mind that this engine is going in a Nissan 240sx, so putting the motor in the car will not be a walk in the park.

by the way thanks for all the help guys, especially to Ken.

If you've got access to a dyno, especially if it'll hold load... as tuning that way is a lot easier, and result in the engine running much better during transients, etc..

Ken