RB26 needs throttle to start | AEM
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lightspeed_32
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Last seen: 11 months 2 weeks ago
Joined: 08/19/2014 - 10:41
RB26 needs throttle to start

I’m finding my RB26 always needs a touch of throttle to start. I’ve wound the idle valve screw out a fair bit and recalibrated the idle base settings and when I start it’s looking to 90% duty on the idle valve. Still needs a prod of throttle to fire up. Any pointers on what else to change?

 

AEM_SB
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Last seen: 2 weeks 1 hour ago
Joined: 06/07/2014 - 14:29
First, double-check the idle

First, double-check the idle valve is actually hitting 90% duty when the engine is at zero RPM. I've seen some calibrations that disabled the idle valve below 1 RPM, presumably to avoid the 'whine' sound from the IAC that can be heard when the engine is off.  Look at the breakpoints and table values of the LS_Duty table to see if duty cycle would be allowed at 0 RPM. Our RB26 base map uses LS3, and the default calibration looks OK for using the IAC at 0 RPM.

 

It's also a good idea to double-check the solenoid is getting 12V power from the car harness when the key is in the start position. Some circuits get disabled when the starter is engaged, make sure your harness was not modified to pull power from one of those circuits. The ECU sends a switched ground duty cycle,  other side of the IAC solenoid needs to be receiving 12V power from the harness.

 

90% should be at or near maximum flow, you won't get much more from 95 or 100% duty cycle.  If the Idle Position is above 35% when the engine is fully warm, I would adjust the base idle screw or throttle stop to allow more air all the time. Then decrease the IdleBasePosition table in the ECU as needed to avoid idling too high when warm.

 

It's also possible you need to adjust the cranking fuel. Try less fuel, that would be higher numbers (leaner AFR target when cranking) in the 'LambdaCrankingTable'. Be sure to only adjust for the 'cold' temperature, don't change the table numbers if the engine starts well when warm. Remember you only get one or two real cold starts per day; even if you start and then shut off after just a few seconds the engine will re-start much more easily than if it had been sitting for 5+ hours.

Hope that helps,

SB

lightspeed_32
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Last seen: 11 months 2 weeks ago
Joined: 08/19/2014 - 10:41
Yes, that does help my

Yes, that does help my thinking. I have stock BNR32 harness that was brand new 3 years ago...basically as new so 12v should be good. I am running a 710 Infinity but have used as many settings as possible from the 508 base map to build my own base map. It does get the 90% signal at start. One other thing that has crossed my mind is just how long should it take to fire. I have an ATI damper Infinity 24 tooth wheel and use an AEM trigger disc (although you guys sent me the wrong one and I had to drill it to fit the CAS, ended up with the cam slot 350degrees (175deg) out of sync). Anyways looking at the logs it starts about 3 and a half crank revolutions, 2 of which are to find cam sync. I’m now thinking that is probably optimum.