High altitude + Pressure system + Incline = No Power?
04-21-2017, 12:51 PM
#1
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Thread Starter
High altitude + Pressure system + Incline = No Power?
Hi all, looking to share a story to see if a master mechanic / tuning guru can figure it out. TL:.DR below.
Story, driving over a mountain highway (Coquihalla, BC Canada), cool weather (6C/43F low that day) no crazy storms although quite a bit of rain and some sprinkles of snow. After two hours of normal performance I was approaching the summit and my rpms start to drop off, from say ~6000rpm to ~3500rpm, from around 110km/h to 70km/h. Any additional gas resulted in the car sputtering as it would not allow me to go past 3500rpm in any gear. So my first thought was air filter was soaked - not enough air, or the ECU was limiting me in a "default limp-mode" to protect engine if a sensor was gone or something. So I pullover, turn off car, let cool down 5-10min check air filter - dry, and try to start, doesn't start. Wait again and with pedal depressed the car starts. But it is still restricted at ~3500rpm, but now I'm going flat and it's not so bad. Drive for 30 minutes (no more big uphills) and the problem goes away, drives fine (THAT WAS WEIRD).
An hour later I'm much lower in elevation but I hit another long steep incline, no issues cruises up the hill - not pushing the car but 100km/h no problem. Another 45min later, I near the second summit of this trip and the car bogs down again, but this time it's worse, I can only go ~40km/h up hill, flat about 70km/h and downhill +100km/h again seems "rev limited" in all gears. This continues for what feels like forever (30-45min) of crawling. Finally I summit, and drive for remaining downhill and in town no issues (a 4 hour drive turned into +5 hour trip)...
Get to my friend's place (mechanic), plug in my tablet into ECU, check all sensors they seem to be OK. Engine temp engine shutoff - disabled. Tune looks fine, no abnormalities, good and bad news. He tells me it might have been a crazy pressure system combined with high altitude messed with base line atmos pressure on tune, causing car to over/under compensate under load, and there we have it... Seriously?? Told me nicer ECUs have a sensor for atmos pressure that re-maps tune to current outside pressure on ignition, which this one doesn't do. Could this be the case? Solutions? other Theories?
TL:.DR Can altitude and weather significantly affect forced induction performance? If yes has anyone purchased a barometric air pressure sensor (BAP) to adjust tune on ignition?
Car: AP2 (2004) w/ Kraftwerks supercharger kit - AEM series 2 ecu.
Thanks to anyone who read through all that mumbo-jumbo.
Cheers, Greg
Story, driving over a mountain highway (Coquihalla, BC Canada), cool weather (6C/43F low that day) no crazy storms although quite a bit of rain and some sprinkles of snow. After two hours of normal performance I was approaching the summit and my rpms start to drop off, from say ~6000rpm to ~3500rpm, from around 110km/h to 70km/h. Any additional gas resulted in the car sputtering as it would not allow me to go past 3500rpm in any gear. So my first thought was air filter was soaked - not enough air, or the ECU was limiting me in a "default limp-mode" to protect engine if a sensor was gone or something. So I pullover, turn off car, let cool down 5-10min check air filter - dry, and try to start, doesn't start. Wait again and with pedal depressed the car starts. But it is still restricted at ~3500rpm, but now I'm going flat and it's not so bad. Drive for 30 minutes (no more big uphills) and the problem goes away, drives fine (THAT WAS WEIRD).
An hour later I'm much lower in elevation but I hit another long steep incline, no issues cruises up the hill - not pushing the car but 100km/h no problem. Another 45min later, I near the second summit of this trip and the car bogs down again, but this time it's worse, I can only go ~40km/h up hill, flat about 70km/h and downhill +100km/h again seems "rev limited" in all gears. This continues for what feels like forever (30-45min) of crawling. Finally I summit, and drive for remaining downhill and in town no issues (a 4 hour drive turned into +5 hour trip)...
Get to my friend's place (mechanic), plug in my tablet into ECU, check all sensors they seem to be OK. Engine temp engine shutoff - disabled. Tune looks fine, no abnormalities, good and bad news. He tells me it might have been a crazy pressure system combined with high altitude messed with base line atmos pressure on tune, causing car to over/under compensate under load, and there we have it... Seriously?? Told me nicer ECUs have a sensor for atmos pressure that re-maps tune to current outside pressure on ignition, which this one doesn't do. Could this be the case? Solutions? other Theories?
TL:.DR Can altitude and weather significantly affect forced induction performance? If yes has anyone purchased a barometric air pressure sensor (BAP) to adjust tune on ignition?
Car: AP2 (2004) w/ Kraftwerks supercharger kit - AEM series 2 ecu.
Thanks to anyone who read through all that mumbo-jumbo.
Cheers, Greg
04-21-2017, 02:21 PM
#3
Registered User
Thread Starter
I have no idea, didn't capture any readings during stumbles. I didn't think to connect to ECU until I had someone who knew what to look for / experienced in tuning. We first thought it could have been a disconnected / erroneous MAP sensor but it read expected values later on when checked. No idea what it was reading during hill pushes though... Wish I had the foresight to have hooked it up.
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