Today we were dynotuning for a few hours and with a few bars left on the fuel gauge the AFR was going from 11.4 to 12.7afr after 5000rpms. I put back the car to stock and instead of 10.3afr, it was peaking at 11.00.

After brainstorming a bit and verifying all fuel pressure and vacuum lines were attached, performing a boost leak test, I decided to add 5 gal of fuel.

First pull was richer, next pull was back into the 10's again.

It's worked fine since. This is a serious flaw that we can lose engines over.

We are posting this information as a warning that running your car hard on less than a half a tank of fuel can potentially harm your engine.

 

Good info.

Ill try and test this on my next tank of gas.

 

Have you tried to reproduce this on other vehicles or is it this one occurance you've noticed. I would think someone else would have noticed this before now, thats a big change in afr.

 

Did you try to drain the fuel tank and try it again on the dyno just to confirm?

 

Another good point.

What were the mods on the car? What tuning was being done and via what medium? Im assuming zchip?

 

Others have complained that in road racing and autocross, left hand turns they have fuel pickup problems also under a half tank.

We have not investigated the fuel pump pickup area as of yet as we develop our modification path for the Evo X. AMS has done all the fuel pump testing already which deemed the X pump to be the best of all the Mitsu production car pumps thus far. Fuel pump isn't the issue.

I have a blind theory that if the tank is anything like the CT9A tank, it is chambered and if the car is stationary on the dyno for example it will not disburse the fuel evenly in the chambers.

This is all hypothetical at this point until we can get in there and check things out.

 

We had to install a custom Surge Tank on 1 of our Road Race customers evo MR a few weeks ago due to fuel starvation.. It happens more often on hard left turns then anything.. in 2 seperate cases on an Evo X we have seen fuel starvation and a code thrown.. Here is some more information from a few weeks back about the surge tank systems..

https://www.evolutionm.net/forums/ev...urge-tank.html

 

https://www.evolutionm.net/forums/6317322-post14.html

 

Fuel starvation is normal in almost every car with a stock gas tank. I get it in my SE-R when the gas tank is at/below half. This is especially true in long sweepers that moves the gas in the tank to one side or the other, eg, the right hand sweeper (rabbits's ear) at Big Willow in CA and the left hand sweeper at Riverside @ Buttonwillow. When I race my car in a 30 min sprint race I make sure that I have at least 3/4 full gas tank. If the race is longer than I go with a full gas tank.

 

Not really..
It's common knowledge that AFR's will go lean with low amounts of fuel in the tank. Has nothing to do with the Evo specifically. I dyno bikes, and always start with a full tank for this reason. Heck.. Dynojet tells you about it in their training.

 

We are not talking about low fuel, we are talking about 1/3 to 1/2 a tank.

The Evo 7-9 has NEVER experienced this and we have tuned hundreds of them on the dyno.

It is a Evo X specific isssue.

 

Now we have two reasons to buy a surge tank. With under 5 mpg at a road course a full tank of gas lasts only about 1 hour. It is bad enough having to get gas after every other 30 minute session. Without a surge tank, you would need to get gas after every session to keep the tank half full, or just carry a 55 gallon drum of gas with you to the track. Any roof rack up to this task

Haven't had a problem in any other car at the track running down to empty light. In fact, have run the evo x down to empty many times at the track and have not noticed any adverse observable outcomes, but I have also not data logged anything. Track I run has very few left hand turns that would cause the other mentioned starvation issues. Surge tank is a good safety net mod. What exactly do you guys observe at the track with starvation?

 

when you get the fuel starvation, it's like hitting the rev limiter, but MUCH harder.

I think I was the first to post about it this summer.

I can't spend $600 on an antisurge kit, so I just fill up and keep the tank > 1/2 tank.

Or you can build one: http://www.geocities.com/hrayhouston/antisurgetank.html

 

Yes .. alot of AutoX guys are having this problem right now .. we get it even with 1/2 tank ..

And under hard acceleration after a turn .. it felt like misfire

really underestimated the ability of the car to turn corners

 

I'm assuming it was, because of you're writing that when you added fuel, the AFR went back to normal. As I wrote, dyno tuning should be done with a full tank.
Filling the tank, or asking your customer(s) to bring in their car that way is a very easy way to ensure you're not starting out with a base reading that's lean simply because the thing doesn't have enough fuel in it. Even if the X runs lean with more fuel in it than the prior gens, with a full tank, it won't, and your customer will leave with the proper A/F ratio. Problem solved