Car dies after foot off accelerator

jsmcortina · Post by **jsmcortina** » Mon May 22, 2006 1:01 am

What MAP reading are you seeing when you let off the throttle? If I'm reading that datalog correctly it says 118kpa ?! That is totally wrong for a closed throttle on a running engine - you should see <70kpa.

Where do you have you MAP hose connected? It isn't connected to a "ported vacuum" source on a throttle body by chance is it? Or the wrong side of the throttle plates?

James

arnold · Post by **arnold** » Mon May 22, 2006 10:28 am

MegaScott wrote:man, I forgot just how simple the old Megasquirt BG code is.
http://megasquirt.sourceforge.net/extra/

Yes, maybe, I want to change the minimum amount of things to keep it as simpel as possible for

MegaScott wrote: Have you tuned your idle bins properly? try richening up the idle bins a bit. Also maybe you can try to give it some decel enrichment right now you have it set to 100, try going to 125 and see of that helps.
http://megasquirt.sourceforge.net/extra/

Yes I tried the idle bins, not the decel enrichment (not sure what it does)

quote="MegaScott"]

You might want to upgrade to the MSnS-extra code, even if you aren't controlling spark there's alot of advanced features in that code that can help you out since you have a Wideband. Even if you don't use any extra features, you still get 12x12 tables, AFR tables, Better accell enrichment controls, the list goes on.

http://megasquirt.sourceforge.net/extra/[/quote]

Yeah I know but again, then I would have to change something again and that worries me a bit. I want to get things running with cuurent code and setup if possible. Then I will go on from a success basis, now I haven't been able to get it running the way I want it

James, the MAP is connected correct, you the Max MAP of the log (got a supercharged engine)

After thinking it over a bit, maybe I should use a 'dashpot' the damper the throttle closure? Moreover because stalling doesn't happen when I close the throttle slowly.... Could a mechanical dashpot be an option? Or is this THE reason to upgrade to the extra code?

arnold · Post by **arnold** » Mon May 22, 2006 11:45 am

like this

MegaScott · Post by **MegaScott** » Mon May 22, 2006 12:49 pm

I would try to richen up the idle bins just a little, say 10% and see if that fixes it, if not then add to Decel enrichment.

Decel enrichment does exactly what you want to do, adds or subtracts a little to your PW when tps is decreasing, this can prevent stalling or bucking when you let off on the pedal suddenly. 100% is the default which is no change, 110% is 10% more 90% is 10%less, it can't hurt to just give it a little, say 110%, and see if that helps, your engine won't blow up I promise.

The Dashpot will help, I know they put those on the old Throttle body Injection schemes back before more sophisticated software could do dashpot functions.

jsmcortina · Post by **jsmcortina** » Mon May 22, 2006 1:27 pm

The MAP signal still looks wrong.

When the line is you have TPS=20, MAP=98. When you open the throttle the MAP goes down. That's the wrong way around.

This is the behaviour of a "ported" vacuum source and is incompatible with Megasquirt.

James

MegaScott · Post by **MegaScott** » Mon May 22, 2006 2:58 pm

James is right, you need Manifold vacuum, not ported vacuum.

If you have ported vacuum the engine will most likely drown itself out with excess fuel when you let off the gas.

arnold · Post by **arnold** » Mon May 22, 2006 11:14 pm

Thx guys, well I am sure I connected it to the manifold. To be more precise: I use TBI of which I removed the thottle from. The throttle itself I moved upstream in front of the blower. So in fact the TBI has the injector and the FPR in it. I connected the MAP to this TBI unit (which has manifold vacuum in my point of view)

Maybe I forget something, I can try to connect the MAP somewhere else, I look closer at that!!

MegaScott · Post by **MegaScott** » Tue May 23, 2006 1:54 am

arnold wrote:Thx guys, well I am sure I connected it to the manifold. To be more precise: I use TBI of which I removed the thottle from. The throttle itself I moved upstream in front of the blower. So in fact the TBI has the injector and the FPR in it. I connected the MAP to this TBI unit (which has manifold vacuum in my point of view)

Maybe I forget something, I can try to connect the MAP somewhere else, I look closer at that!!

I read your post a third time and realized what you said. So I edited it.

The Map needs to be on the plenum of the intake, you could still be getting a venturi effect from the old TBI.

jsmcortina · Post by **jsmcortina** » Tue May 23, 2006 7:21 am

This is unlikely to be the problem here, but you are using a pressure sensor regulator aren't you?
Many TBI setups have the injectors above the throttle plate and regulate to atmosphere or use low pressure. With an enclosed setup that you now have you need to have a regulator referenced to the intake pressure.
(It should work without, but your VE table will look "wrong" with a far greater range of values.)

Concentrate on getting your MAP sensor reading right for now.

James

arnold · Post by **arnold** » Tue May 23, 2006 1:12 pm

I fully agree, but maybe this graph is less worrying. I just don't know what could be wrong. I must admit the engine is far from running perfect and often doesn't respond to throttle movement, especially when cold.