After mysteriously losing a few rpm in spool up the day before my live mapping and then discovering that I had an unbunged oil breather pipe in my intake, I needed to verify that these problems hadn't ruined my mapping. So after tightening a few clips and bunging up the oil breather, I headed down to a nearby rolling road (Westward - a MAHA RR) to see how the coop was running. The result pretty much confirmed what I felt on the road, power coming in approx 400 rpm sooner and an extra 9 ft/lb thrown in - see a comparison chart here . There was some bad news though, although the midrange fuelling is spot on, after 6K rpm it's running "dangerously lean". TBH, I'm not too bothered as I don't bounce it off the redline, but I see a few potential explanations:

1. New AFR reading is incorrect/less accurate (meter was in the exhaust not downpipe).

2. PTs map is less tolerant at the top end?

3. My injectors were having a bad day.

I'm guessing the answer is 2? In other words, the fuelling has been screwed but this matters less in the midrange i.e. mid range has probably gone from something like 11.2 -> 11.8 and the top has gone from 12.1 -> 12.9 or something like that?

All i would say is that if taking a wideband reading, the reading should be taken after the downpipe, to allow the gases to mix. Did you get a gas sensor up the exhaust or wideband lambda in the exhaust somewhere else?

As for the other options, dont know.

Ross

up the backpipe this time round, in was in the DP at PT. I couldn't hear the car deting, so it could be an inaccurate reading.

You cant always "hear it" according to the experts.

Did you get any afr figures or did the guy just say it seemed lean?

Ross

I don't have them written down, but it was in the 11s midrange, then after 6k heading to 13. If it was someone elses problem I'd say injectors/fuel pump but these were OK last time. However, if the map was screwed by the hole in the intake, I was expecting the it to be richer not leaner ..

No it would be leaner dude. Because there was less air meeting with fuel. Now there is more air meeting with fuel hence more fuel burnt and running more lean.

Ross

i thought the hole would lead to more unmetered air getting sucked in ... although the results would suggest otherwise.

Nah. Usually the opposite. Because of the pressure, the air gets forced out to the unpressurized region. So less air = richer. I had a hole in my intercooler and it was running MEGA rich. Have you tried resetting the ecu and allowing the ecu to re-learn with the hole not there?

Ross

the battery was disconnected for a different reason, so i guess i've had a reset. i can live with keeping it under 6 k rpm (which in 4th is 120 mph) ... next time i'm near PT i might get a remap then if they'll do me a deal!

edit - i guess the other option is to take the bung out!!??

Could it not be the fuel that was in the tank, ie if it wasnt Vpower or Tesco 99Ron at all??

All done on 95 RON!

that can t be healthy!!

i was told by claudio to use 99 ron from tesco!

Its been mapped on 95 ron tho, so he can run it if he chooses. Presume there is a reason for it aswell.

Ross

Id not let 95ron anywhere near my coupe, vpower at least, 99ron if i can get it(2 stations local to me sell it and another sells Vpower) and if i was really dire id use ultimate but my coupe has never liked it...

I do about 3 fill ups with 99ron and 1 with vpower to keep the system clean really

V-power is 99ron aswell.

Ross

Use 95 as that is all I can get, anyway, it's nothing to do with my lean top end! I sent an email to PT, I wonder if they'll get back to me

Thinking about this again, I think additional air would get sucked in. Would the pressure in the induction piping not be lower as the air is moving faster than outside? The pressure only gets increased after it hits the turbo compressor? So with your intercooler leak, your explanation is right, but as my "hole" was in the induction piping, the additional air would be sucked in rather than forced out?

Possibly, as that end is on a suction route. But its still after the afr meter, so it would be running lean previously if air was getting sucked in. Because the afr would only sense x amount and be providing enough fuel for x amount when you actually have x + y amount of air, hence it would run lean. But the results say different. You were running rich previously, and now your running lean.

Ross

This is the same issue as I had a while ago

A hole between the airflow meter and the turbo will cause unmetered air to get sucked in. The ECU will only give the fuel it THINKS is required, based on the AFM reading. Normally, this would result in running lean (more air going in that should be)

However, if the car has been mapped with the air leak, then the fuelling would be about right (mapping would overcome the extra air)

So - you end up with a car with an air leak that runs OK

However, if you then bung up the air leak, you'll cause less air to be drawn in, which should result in the car running rich.


I think.....

EDIT - the additional problem is that the ECU will try and make changes, so what is right one day may well not be right the next day.

Thanks for the posts h2ypr and Nigel, I also think I *should* be running rich. However it seems as though I'm running lean over 6k rpm in 4th ... but I'm not going to lose any sleep over it, in practice staying under 6k rpm in 4th and 5th shouldn't be an issue for me... it's annoying but I can live with it. Next time I'm down their way I'l try to get it sorted out.

Hmmm. Maybes your afr is needing cleaned to gauge more air properly?

Ross