I recently tuned my Evo IX at Carz using ecuflash and mitsulogger.

Baseline was 270whp/266wtq
Tuned was 290whp/272wtq - while heatsoaked

The problem is, after dyno run 13, my car suddenly, out of nowhere was getting lean on the top end. On dyno run 13, I had a perfectly flat AF from 5,000-7,400 rpm. ~11.4 AF

On run 14 and every run there after, the car leaned out starting at 6,000rpm getting as lean as 12.6AF @ 7300rpm.

No matter what changes I made in ecuflash, the af up top stayed the same. I rescaled the injectors which REALLY richened everything up, EXCEPT 6,000-7,300 rpm. I went as low as 8.5 target AF in the cells it was using past 6k which still made NO difference (on run 13, target was around 10.7 which made 11.4AF)

Nothing I did mattered. I ended up pulling 4 degrees of timing up top as extra protection against knock, and gave up the fight.

If I can get back to the nice af ratio, and add that timing back in, I could be making close to 300whp

Any ideas?

 

I would suspect that either the wideband got too hot and started showing erroneous values or the car has a cat, and the cat got too hot which caused the wideband to read strange.

 

Could be fuel pump, fuel regulator. If you had a fuel pressure gauge you would be able to monitor pressure as you make a pass to see if there is a pressure drop.

 

Fuel pump could have been over worked, from the 13 first runs, and got hot and work less the perfect.

 

Sayno, if you do not have a wideband the stock narrow band once it gets hot will read lean when you are not lean.

best thing to do is once you see that happening is to let the car cool down and make a few more pulls to see if it is just a heat soaked nbo2.

 

I was on a superflow dyno with Dual AEM UEGO widebands

 

fuel pump if it's not changed .. I experienced the same problem on the dyno with a IX .. we suspected the problem to be the fuel rail but couldn't confirm .. I had walbro and a regulator fitted, fuel pressure steady at 67psi throughout ..

the IX made 295whp with just intake and exhaust and AFR just kept increasing run after run by about 0.3AFR

problem went away after the rail change to an ATP rail .. but still puzzling as to why that happens ..

 

I had a fuel pump on a IX do the same with 5k miles. Would drop pressure up top. Put a 255hp in and it was fine.

 

Overworked stock fuel pump. Go put in a walbro.

 

Could also be the IPW Step or Lean Spool trigger, as well. This has been discussed and I thought the IX was showing a start RPM of 6k. Not a lot of detail regading this but it could have caused an issue, as well.

 

Things that can make it lean:
1) FP
2) Knock
3) knock + forgotten values on low oct maps
4) Misfire
5) Exhaust leak from flange heating up
6) anything else mentioned in above posts
7) My car allways runs leaner if boost increases or it gets colder outside
This is not an ECUFlash problem

Good luck, keep us informed

 

it sounds like your fuel supply isn't adequate and if that's the case you're ipw/idc is going to rise as you attempt to add more fuel yet the AFR isn't going to richen up.

most commonly it will be:
fuel pump
dirty filter

 

A friend had a similar issue and it ended up being the FPR hose wasn't holding its seal as well from the very heatsoaked engine compartment at the end of long hard pulls on the dyno. The tuner suspected it so he put soapy water on the FPR nipple and sure enough as the pull would reach the top end...bubbles. He gave us the $.05 zip tie for free (what a guy!lol). Problem was solved. Not saying this is the case but it is an area to be addressed regardless. I hear too many stories about the FPR hose popping off, especially on the dyno.

 

that's a good point...I have a zip tie on mine there because it blew off one time. My boost guage taps into there and I noticed the boost was awfully low during a pull...that's the only way I noticed it because I wasn't logging at that time.

 

What were the mods you made to your car right before the dyno? I am having this very same issue right now,(especially the attempted fuel increase at high RPM's) I think I've figued out the answer, but I'm curious to yours to solidify my theory. FWIW, I just installed my Green, Walboro and 750cc FIC injectors. Right now the car also, loads up then, a huge backfire occurs, car falls on its face. (once during a log) I do not have a wide band to monitor, so I can't comment on the AFR's on the street.

...and all my vacuum lines are zip tied.

Okay, I just realized this thread was brought back from the dead !