Help with missfire - MSQ attached

[PaulO]

accelerating slowly (still getting the VE and AFR set) up through the gears. Once I hit 2600 rpms, starts to bog and miss. Bad enough through first and second but once in third - forget it. Stops accelarating. The question I have is - is it going too rich and causing a missfire leading to the lean O2 reading or is it really too lean? Tried moving the VE around rich and lean but not much difference. Perhaps I am not changing the tables enough? Anything you guys see that I am missing would be appreciated. MSII Ver. 357
Paul

[Matt Cramer]

It looks to me like it's just plain too lean under high load. Another thing is the MAP signal is a bit spiky; you may want to try getting it from a different point on the intake manifold.

[PaulO]

Thanks Matt,
This engine is a type1 vw aircooled engine with dual throttle bodies and 2 short intake manifolds. I am getting the map signal by combining manifold vacuum from all four seperate runners. Don't now of any better source. Is there a way to dampen the vacuum signal? Also, I have an idle map of 69-70 kPa and am wondering if this is too high (probably due to the cam) therefore neccesitating alpha-n tuning. What do you think?
Thanks,
Paul

[Matt Cramer]

I've seen low vacuum engines run on speed density, though alpha N may be worth considering. Try plumbing all four lines to a hollow cylinder, maybe about 2" long by 1.5" diameter, and from there to the Megasquirt.

[PaulO]

Matt,
You're a genius! I made the vacuum canister as you described and not only did it stop the MAP spiking it also lowered my overall MAP reading so that part throttle at low RPM does not generate a 100 kPa MAP reading. This gets my hopes up that I will be able to stick with speed density tuning.
Thanks again,
Paul

[lammmy]

Do you mind posting how you made this vacuum canister? I know I need one (ITBs) as my MAP is all over the place as well. I have a silvertop 4age but I'm just wondering where you plumb the lines to/from? It has a line going from each TB to the intake "manifold", do the lines go to the canister and then 4 more lines back to the manifold again and then one more to MS?

Thanks for giving me hope

[PaulO]

Iammy,
I simply got 1.5" PCV pipe from Home Depot, glued pvc end caps on it and drilled/tapped the endcaps for brass fittings to accomodate the vacuum line at each end. I placed the tube in line with the single vacuum hose running to the ECU. In my installation the tube is only about 12" from the ECU. I have seperate runners for each cylinder (4) so I tapped in fittings into each runner. I connected all four hoses together (actually 2 into one on each side then two into one again) and ran that to the ECU. Hope this helps.
Paul

[Matt Cramer]

Thanks but I'm just repeating a description of a mod I've seen on a customer's car. It was a Zetec powered kit car with Jenvey ITBs that managed to get a surprisingly good vacuum signal.