MAP Signal Line Length
07-04-2011, 02:09 AM
#1
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MAP Signal Line Length
I have been experiencing leanness (12:1-13:1) which has been difficult to tune out.
It occurs when my MBC spikes. The spike lasts about a quarter second going from 14psi up to 25psi before settling down to around 21psi. Yes, boost builds that quickly.
The injector duty cycle indicates that I still have plenty of fuel left and despite richening up that row I am still seeing leaner AFRs than I should.
My map signal line is pretty long- about 15 feet or so. It is routed through a grommet on the driver's side of the firewall.
I suspect that the long signal line length results in MAP latency, just enough so that my ECU's MAP sensor is a step behind fast transitions like the boost spike.
I have experienced similar vacuum/boost "lag" before. When I sourced my MBC signal from my coldside IC pipe, my turbo spooled about 400RPM later.
I think that I will try running a short line through the passenger's firewall. Maybe one of the holes from the now-removed A/C. Another "fix" would be to drill out my MBC restrictor.
I searched the web about this and it's funny, the only thread that came up was a four year old thread from this site: https://www.miataturbo.net/megasquirt-18/length-map-line-11530/
It occurs when my MBC spikes. The spike lasts about a quarter second going from 14psi up to 25psi before settling down to around 21psi. Yes, boost builds that quickly.
The injector duty cycle indicates that I still have plenty of fuel left and despite richening up that row I am still seeing leaner AFRs than I should.
My map signal line is pretty long- about 15 feet or so. It is routed through a grommet on the driver's side of the firewall.
I suspect that the long signal line length results in MAP latency, just enough so that my ECU's MAP sensor is a step behind fast transitions like the boost spike.
I have experienced similar vacuum/boost "lag" before. When I sourced my MBC signal from my coldside IC pipe, my turbo spooled about 400RPM later.
I think that I will try running a short line through the passenger's firewall. Maybe one of the holes from the now-removed A/C. Another "fix" would be to drill out my MBC restrictor.
I searched the web about this and it's funny, the only thread that came up was a four year old thread from this site: https://www.miataturbo.net/megasquirt-18/length-map-line-11530/
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07-06-2011, 01:57 PM
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Some MS'ers (I think the developers?) tested MAP latency and showed that it is barely measurable through something like 100ft of vac line. Unless you're running a very large (VERY large) vac line it won't make a difference.
Have you tried installing a small lawn mower fuel filter in the line? That has been known to smooth out jittery MAP signals and it's what I have on mine.
I'd also check your accel enrichments. Maybe switch them to MAPdot if they're not already. (I'm assuming you run MS, obviously).
Have you tried installing a small lawn mower fuel filter in the line? That has been known to smooth out jittery MAP signals and it's what I have on mine.
I'd also check your accel enrichments. Maybe switch them to MAPdot if they're not already. (I'm assuming you run MS, obviously).
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