Engine stalls when coming out of boost
 

ok so my car idles great, runs like a dream, and the new turbo is working great-
the only remaining bug is this- it occasionally stalls (turns off) when I come out of boost. It's almost as if the computer doesn't realize that the throttle has closed, and so the ISCV doesn't open soon enough. and the engine dies.

I do have a lighter flywheel (about half the weight of stock) is this the problem?

or,

is it the throttle position sensor? is it adjusted wrong?

currently, I have to set the idle at 1.5k rpms or it dies every time I come out of boost. ideas?
Thanks

Can your post be any more vague on what kind of a setup you're running?

Year of engine?
Type of ECU?
ECU Config file and datalog of the stall event happening, if applicable.

It's a 96, running 6 pounds of boost (from a turbo pulled from a 1989 ford thunderbird turbocoupe). intercooled. I have Flying Miata computers (the voodoo box 1 and the MSD)
I have a boost guage and a wideband gauge.

any more info you need?

It's the stock ECU- the Voodoo box just piggy-backs it. I do not have any data-log.

how do you have the idle control routed? Picture of engine bay would help.

With a Voodoo, the configuration of the idle control system should be unchanged.

I'm thinking this may be nothing more than a stock ECU not liking a super-light flywheel. Its idle algorithm is designed around the assumption of the dynamic properties of an engine with a stock-weight flywheel.

Does a '96 have that little shock absorber on the throttle body? Sometimes they seize up. It keeps the throttle from snapping shut, slowly closing the last ~5% or so.

lol I remember the days when people had to modify them because of the exact same problem... that said i also had this problem when i was trying to install the xede ecu i bought. No clue what the problem was but i'm glad i'm not running it anymore. Its definitely the ecu though.

I ran FM's 10.3lb flywheel with no issues, even using A/C, on my 97'. So something must be amiss for it to be stalling.


Is the voodoo box "tuned" correctly?

Yes, the voodoo box is tuned correctly. and even if it wasn't i cant see how that would cause the flaw.

i'll look at the spring- maybe hit it with some brake cleaner and see if it goes away.

the voodoo box only kicks in when it sees boost- how could this cause it to stall? as soon as i let off the gas, it should be turned off.

I very seriously doubt that the Voodoo box has anything at all to do with this, assuming it's installed correctly.

It is possible that the MSD box might be contributing to the problem. I don't know much about how this box works internally (the schematics and code were never published) however I can see two possibilities:

1: If the MAP signal feeding the box has been taken from a point before the throttle, then the box will still be seeing boost after you release the throttle and depress the clutch. In this case, it will still be retarding the ignition, and this will make it harder for the ECU to achieve idle.

2: If the box has a large degree of latency between when MAP actually drops below atmospheric and when the box "releases" from retard mode, it will have the same effect.

You adjust it so it knows when it sees boost. If the wrong light is coming on before boost, it's probably turning off late. It's a long shot, sure, but easy to check, and sounds like it's not the issue.

I should add: it's possible that the MSD box is malfunctioning, and causing ignition retard all the time, or at times when it should not. If you have a timing gun and a hand-operated vacuum/boost pump, you can test this rather easily.

Well it would make no sense why the xede would also cause this on my setup at 0 on everything. Well it also made no sense why it caused 18;1 afr at idle when everything was 0s but it was what it was. What does the wideband say when its stalling out?

where should my base timing be? should it be at 0 or advanced 6 degrees?

I adjusted the throttle position sensor, and it no longer stalls. I'm not sure if that was the correct fix or not.

tonight, i'm going to check the timing again, and make sure the voodoo is still tuned correctly. thx guys

With the voodo box doesnt the car still use the maf at least partially? If thats the case and you have a vta bov the lw fw might have just been enough to push it over the edge to make the car stall when you blow off.

With the engine at warm idle and a jumper in the diagnostic box between TEN and GND, timing should be at 10° BTDC.

great! thanks