Cliff notes: I can get the MAP sensor to read 0kPa through the entire rev range when going up a hill, but not on the flat.
I've been road* tuning my car using the software that comes with the ECU, a WB02 sensor and a hearing aid.
Everything was going well, getting the AFRs tidy through the rev range by driving up and down the dirty great hill that I live on. Driving up the hill, I could put the maps into any load cell by using a combination of steep incline, throttle and some left-foot brake.
I then did some further testing on a long stretch of highway far away from normal people.
I discovered that as the car accelerated through the rev range at WOT, the load cells would move up to the 0 kPa range up to about 4000rpm, and then would drop down to the -10kPa range until around 6500rpm, where it would return to 0kPa.
So back to the hill, and I can again get it to stay in the 0kPa range for the full run. wtf?
Initially I though that there may be an inlet restriction, but the intake path is extremely short. The factory throttle body is connected directly to a huge pod-style conical paper air filter. I'm not terribly keen on running without a filter, even for short testing.
The engine is a daihatsu HD-EG (1.6L detomaso, pretty much the same as an applause) with a monster Ivan Tighe cam in it. It's in a stripped out rally car with cage, total weight is about 800kg at a guess.
Is it possible that the engine is not being loaded enough when accelerating on flat ground?
ECU is an EMS Stinger, I'm using the factory location for the MAP sensor connection, using the MAP sensor internal to the ECU.
(The manifold connection isn't direct, but has some plastic chamber or somesuch between the vacuum fitting and the screw-in tail.. Should I remove this contraption??)
I plan to get the tune refined on a dyno eventually, just want to make sure that it's all good to go before I commit.
* Using private roads