Where to get vacuum signal?

[AdmiralSenn]

Hey guys. Long time no post.

I've successfully MS'd my B28F - "successfully" as in "I can crank it and it starts and runs and sometimes I can even drive it".

I've just got a silly question. I'm still very new to tuning and there are big parts of engine theory that just haven't settled in my head yet.

http://yfrog.com/5nmiddle3j

There's a picture of the engine (not my car but gets the idea across). I'm using "vacuum line #1" for my MAP signal, but I think that using #2 might be better. I have weird lean spikes if I do anything but gently feather the throttle, and I think it might be the location where I've tapped my MAP line.

Would putting the line closer to the throttle bodies (as in almost right behind them) 1) solve any of this issue and 2) be a good idea in general, for the sake of accuracy/good practice/whatever?

It seems to me that with the tap closer to the throttles, the sensor would read fast shifts in engine vacuum more accurately. Am I on the right track here?

Thanks guys!

[crazy0000]

Any vacuum line behind the throttle body will give the same signal. You would need a degree in quantum physics to measure the difference in time that different vacuum locations in the manifold would portray.

Are you running a throttle position sensor? or just straight MAP throttle control.
I would be 100% certain to say any delay in fuel would be directly related to your tuning in the accel enrichment settings. Not your map signal location.

congrats on the b28f megasquirt, I want to see pics of this. where did you get your enrichment settings from?

[AdmiralSenn]

I'm running both MAP and TPS. The reason I started this line of thought in the first place was that shifting accel enrichment towards the TPS made a noticeable improvement.

I didn't get any enrichment settings - I'm doing it cold, and by myself. What's even better is that I can't really share my results with anyone because my engine uses the 3.0L Eagle Premier liners and pistons (don't ask why the previous owner spent so much money on this, but he did).

I'll try to get some pictures when it isn't raining.

[crazy0000]

I don't have a clue what you're talking about. If its MS'd then there is a thing called enrichment settings, you have to set those up with the TPS to make the car know when to ad fuel and how much depending on how fast or slow you pressed the throttle. and if you have a TPS you might as well just run the TPS 100% and not use MAP.

Did you install the MS? and did you get it running yourself?

[AdmiralSenn]

Yeah, I know about the various enrichment settings - I'm trying to get my VE table right first, though. What I meant is that I can't copy someone else's settings because my engine is, as far as I know, unique - higher displacement, higher compression ratio, and just generally all around different from both the other B28F setups and the later PRV setups.

Most people can copy and paste settings and get "pretty close". I'm on my own.

Right now it's about 75% MAP and 25% TPS control.

And yes, I installed it myself and got it running myself.

As of today the question is a moot point since I ended up starting over from scratch (long story), and in the process of re-doing my old settings the problem I was having went away entirely. So that's good. I think.

Thanks for the help! I really didn't want to carve up my nicely routed vacuum lines.

[AdmiralSenn]

FYI in case anyone finds this thread in the future: "Port #2" mentioned above is the factory charcoal canister purge signal line and is actually ported vacuum - making it useless and/or dangerous for use with MegaSquirt or any other MAP-using ECU - with the throttles closed it reads full atmosphere and then abruptly drops as the plates open, then rises back to atmosphere at WOT. On the B28F (and possibly other B28X series) it's under the throttles, but it feeds from before the plates so it's not a good idea to use this line. Save it for the factory emissions equipment or something more useful.

I was able to solve my MAP issues by rearranging my vacuum lines so that the MAP tee is on its own port and not sharing with anything else, and now it runs great!

[badvlvo]

For future reference- connect between to the intake, head or throttle body between the throttle plate and the intake valves, preferably at the intake plenum.

[AdmiralSenn]

Yeah, sorry I forgot to mention that I was using a factory vacuum port originally used for vacuum advance and K-Jet enrichment purposes.