My MAP goes way lower at mid range RPM than at idle

Zendalar · Post by **Zendalar** » Sun Apr 23, 2006 7:56 am

Can somebody read these files and tell me whats wrong with them, it seems that my MAP values go down when at mid range RPM.

The engine is 2.4 liter engine from a Porsche 911, no turbo, compression ratio is 8.

Whats wrong with my settings?

Bernard Fife · Post by **Bernard Fife** » Sun Apr 23, 2006 4:04 pm

Zendalar,

It's not usual to get lower cruise MAP than idle MAP, especially on engines that have high specific outputs (and lower compression doesn't help this either).

You may be able to lower the idle MAP by tuning the fuel and the ignition advance, but you may not, depending on how close it is to optimal right now.

Lance.

pb3 · Post by **pb3** » Mon Apr 24, 2006 12:17 am

I have just taken my first run and noticed the same thing. At idle, after full warm-up I am seeing about 43KPa (interesting that when I did a check before removing the carb I was seeing abount 50KPa), but at other times I have seen values as low as 30KPa.

Is this drop in MAP more likely to happen when you back off the throttle?

More importantly should the full range of MAP be mapped, ie my maps run from 30KPa up to 100?

Zendalar · Post by **Zendalar** » Mon Apr 24, 2006 3:52 am

Answering myself: Maybe my idle is not tuned as low (MAP) as it should. I will try adjusting the butterfly to get lower MAP at idle.

jsmcortina · Post by **jsmcortina** » Mon Apr 24, 2006 4:21 am

pb3 wrote:Is this drop in MAP more likely to happen when you back off the throttle?

Yes, if you lift off the throttle at high rpms in low gears you can see really low map figures.

More importantly should the full range of MAP be mapped, ie my maps run from 30KPa up to 100?

The lower kpas are only usually seen during over-run so don't worry about them - Megasquirt will use the closest bin - in this case your 30kpa row. Below that you may run a little rich, but you'll only be in that region for a tiny proportion of the time.

However, if you were running boost it is very important to map up to the highest kpa you'll see or you would likely run weak with engine-damaging results.

James

snillet · Post by **snillet** » Mon Apr 24, 2006 4:28 am

When i cruise in some roads at around 65-75km/h i have about 1500rpm and 35-45kpa.... when i go a bit slower yet again i touch the 30kpa bins.....

So some installations go down real low.

pb3 · Post by **pb3** » Tue Apr 25, 2006 12:08 pm

Ok, can you please confirm what I am seeing is correct.

Warmed engine, ~950rpm idle I see ~50KPa. I then went to the auto-tune screen and watched the graph with the moving point indicator. When I revved the engine, with no additional load I saw the pointer fall off the map. My VE map was based on my idle MAP value so anything less than 50KPa would be clipped VE wise, but fall of the graphic display.

So why does my engine produce more vacuum as the revs rise; in my mind it may be due to the hotish cam, I assume at idle I have a lot of overlap which causes a loss of vacuum, when the revs rise the vacuum increases when it comes on cam so to speak.

Bernard Fife · Post by **Bernard Fife** » Tue Apr 25, 2006 12:26 pm

pb3,

I think you are correct on all counts. The hotter cam can definitely cause lower MAP at cruise than at idle. Ideally your VE table will extend down to your cruise MAP, so you can tune your cruise fuel economy to be as efficient as possible.

However, you shuld base the MAP bins on the observed MAP while actually cruising, reving the engine in neutral doesn't tell you a lot.

Lance.

keithmac · Post by **keithmac** » Tue Apr 25, 2006 1:15 pm

My map with the cams is in the 65kpa region, cruising I can hit 40 or lower occasionally. As has been said closing the throttle at high rpms and engine braking causes the lowest maps.

Zendalar · Post by **Zendalar** » Wed Apr 26, 2006 10:34 am

On the log i put here, there is a switchpoint for lambda sensor, what is it? 0.7XX??

I will try to use autotune now that it works..well...pretty much allright...