Elevation related bogging/hesitation?

[Silber]

Hey everyone, seeking some help diagnosing an issue.

 

I went to meet up with fellow forum members @kayentaskierand @rider for a drive on some great mountain roads, however I didn't make it to the meet-up location due to the car losing all driveability as I drove up a canyon, gaining over 3000 ft in elevation (~8000 total) from where I live and drive the car around. The engine would basically bog/hesitate even to the point of stalling with almost any throttle input, but would start and idle fine. After realizing I wasn't going to join the drive, I nursed the car back out of the canyon, and the engine ran better and better with lower elevation, to the point that it ran normally by the time I got home.

 

Any suggestions as to what I can do to overcome this apparent elevation-related issue?

 

Here are the specs on the car:

• 2009 Birkin w/ 2.0L Duratec
• AT Power ITB's
• Crower Stage 2 cams
• FAST XFI 2.0 engine management

 

I have been watching @KnifeySpoony's thread about hesitation with his 420R, as I did notice slight hesitation sometimes at low RPMs/part throttle in first gear on my first few drives after I bought it, which the previous owner never reported having. I'm able to mostly negate it just with driving style, but my gut feeling with that was also elevation, as I'm at ~4800 ft whereas the previous owner was at ~1900 ft.

 

Also worth noting I had this car out at auto-x a couple of weeks ago (elevation ~4300 ft), and other than my first easy launch on my very first run, I had no bogging/hesitation issues at all and the car ran like a top.

 

Thank you for your consideration.

 

Gregory

[MV8]

Unless there is a common runner tube connecting all the intake ports to a vacuum line to a MAP sensor, then you are running the "alpha-N" option with the MAP providing barometric pressure (no vac line). There is an internal correction factor applied based on the baro input but speed density offers better driveability overall.

 

I expect you need to lean the load table across the board and probably washing down the cylinder walls with fuel for rapid bore wear. I expect it was running rich at 1900ft. I recommend not driving it anymore until you get this resolved.

 

You can park it for a month, equip yourself and spend many hours studying to make logical changes or to minimize down time, have it tuned now on a local elevation dyno and plan to equip yourself in the near future.

Emphasize to the tuner that you are looking for max driveability for local elevation and temps, and are not concerned with peak hp numbers and keep the original tune file as a backup. A few pictures of the various tables of the new and old tables would be nice to see posted and give you more info later if you don't install the software on your pc in order to see the old tune.

 

I would consider fitting vac ports to each runner to tee together for a MAP source, then switch to speed density mode for better performance all around. Just cutting brake line, flaring the end, cutting to about an inch long, drilling a slight smaller hole in each port around the top or side, then pressing the brake lines in to provide a vacuum port. The ports are connected with three vacuum tee's with the third in the center, going to the MAP sensor being used for baro if it is the same part number. The MAP should be mounted very close(short hose) and the lines/hoses kept thin/small for rapid response to changes. Easily reverted to alpha-N by capping the ports.

 

 

 

 

Edited August 13, 2023 by MV8

[Silber]

MV8, thanks for the reply. For the short term I am going to see if I can find a tuner who can re-work the tune for my elevation, and hopefully provide some altitude compensation, even with the alpha-n type mapping.

 

Long term I may start down the rabbit hole of learning how to do my own tuning, incorporate a system like you described to take actual MAP readings and tune it via speed density, or sell the ITB setup and acquire an intake manifold, sacrificing a little hp and the "cool factor" of the ITBs for better driveability.

 

Hopefully I haven't caused too much damage driving it around...

[Silber]

Update on this issue. Some digging around in the engine bay revealed that the car does have a MAP sensor, which answers the question of speed density vs. alpha-n. I found a tuner who was willing to work with the FAST ECU (which is apparently quite unpopular) who discovered that the ignition timing was pretty good, but the fuel mapping needed to be bumped up across the board; the engine was running lean.

 

The result of the tune was a safe 176 whp/144 torque, and a engine that feels much happier. Next steps are to order a cable from FAST to do my own data logging, replace or upgrade the old, inaccurate wideband O₂ sensor connected to a dashboard AFR gauge, and take the car back up the canyon to see if the ECU can handle the big elevation changes.

Edited September 6, 2023 by Silber