So with almost all of my engine upgrades completed, it was off to the dyno to see what I had, and so I could map the fuel curve into a Lamda chart for building custom software.
I was hoping for around 225hp/tq so that with software I would have right around the same numbers as an ///M3 of the same year.
Appoitment at 1pm, couldn't get to it until 3pm, and once they did, they felt the car was running too lean to feel safe to run a pass. At 3800rpm the car was running 15:1 air to fuel. ghead ghead
To add insult to injury, they still felt the need to charge for the time and adding the MAF probe interface, so for nothing, I was charged $136 and change.
If that wasn't bad enough, upon returning back to town, I went to investigate this fuel/air ratio more in depth. As the shop I went to was a Mustang shop, I thought I would see if Bimmers were just that different (eventhough the guys at the speed shop said this was a universal ratio that should be around 13-13.2:1). My local Bimmerhead tech said that it was indeed a universal ratio, but that ratio was 14.7:1. they gave me a number to a performance Bimmer shop, and upon talking with them, they asked me enough questions to where I am now totally confused
So maybe the addition of an adjustable fuel pressure regulator, or is it fine as it is...I just don't know. But damnit I'm gonna find out! Anyone out there have any ideas?
What do I think? I'm not sure. Hell, I don't even know if it really is running lean. My tech said that Bimmers run lean and that 14.7:1 is about right (I'm at 15:1 which isn't far off from that), but he also said he didn't know much about dyno numbers. The guy he told me to call, said that 15:1 isn't necessarily bad unless your getting that with the gas pedal to the floor. The guys at Delk Performance (Mustang shop with the dyno--and they are a very big outfit, and well respected) said that this was way off.
I do know that my car was running a little rich when I got it, so I went with a hotter plug and that screwed things up, so I went back to oem, but it did seem to run a bit better with new plugs. Then with the addition of the CAI, I'm sure it is running a little leaner, but I thought the MAF would correct for the new CAI.
The car runs great with the exception of a few small flat spots in the power band, and this is why I wanted to Dyno, and add software. I figured a new ECU program would take advantage of all these upgrades, but I need to map the fuel curve so the guys at Turner can hook me up with a new chip!
14.7:1 is stoichiometric ratio of air to gasoline for all combustion. In naturally aspirated cars, you typically tune to a ratio of about 13.5:1 during WOT. With a turbo, you're usually in the 12:1 range for resistance to knocking and the like.
15.1:1 isn't too bad, certainly not too lean to dyno. is that A/F at normal or WOT? if that's at normal, then it would be a problem, because all cars run leaner at WOT, unless you have an aftermarket ECU that allows for seperate WOT maps (bosch motronic only has an 8 bit proc, not that powerful, whereas a Link has 16 bit and a TEC 3 has 32 bit) Plus the motronic doesn't compensate for pressure differentials, so altitude makes a massive difference. just stuff to keep in mind.
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Originally posted by uiuc240+Nov 18 2004, 10:56 PM--><div class='quotetop'>QUOTE(uiuc240 @ Nov 18 2004, 10:56 PM)</div><div class='quotemain'>14.7:1 is stoichiometric ratio of air to gasoline for all combustion.
In naturally aspirated cars, you typically tune to a ratio of about 13.5:1 during WOT.
15:1 is lean.* Time to figure out why.
So if the stoichiometric ratio is an intended constant regardless of most variables, then how can I reach this effectively?
If I pick up an adjustable fuel pressure regulator, is this my smartest move?
Originally posted by triggrhaapi@Nov 18 2004, 11:53 PM 15.1:1 isn't too bad, certainly not too lean to dyno. is that A/F at normal or WOT? if that's at normal, then it would be a problem, because all cars run leaner at WOT, unless you have an aftermarket ECU that allows for seperate WOT maps
I was watching, and he shut it down in fifth at 3800rpm because the mix wasn't changing.
So when I get new software, how can I have different proms?
<!--QuoteBegin-Kevin325i@Nov 19 2004, 12:11 AM Oh man I was hoping for a dyno plot finally. 15:1 sounds too lean at idle.
Ok... in my opinion.. this all has to do with your originial OBDI software.. which is set to meet a certain fuel curve...
This is how it works... your computer reads how much resistance your MAF sensor is giving... if you change your MAF sensor.. to a different one.. then that resistance signal might be different.. thus giving your computer system.. and then your fuel curve false information. Reason why I think this.. : Your fuel pump.. depending on the condition of your pump.. is going to put out a schedualed amount all through a fuel curve... with a variable ratio of air. Now if your fuel curve is getting false information.. Meaning a different data word from your OBDI system than it was getting from its old OBDII system. (which, if your running lean.. means your sensor is saying there is less air than there actually is.. ) Your computer works in data words.. and if that so data word is large.. then it will tell your fuel pump to send an respectable amount of fuel to meet your ratio. Thus it is telling your fuel pump not to send as much fuel.. becuase it only thinks there is little air coming in...
Fix... get software that enables you to modify either your MAF or your fuel curve accordingly...
I also understand that your OBDI system is thinking its reading the right MAF and such... but does it have the same injectors... and does it have the same coil pack and spark? And does your computer send the same signal to your fuel pump telling it to send more fuel? Might be a different signal meaning less fuel.
If I was you... being that you have an OBDI set up.... I would look into a stand alone fuel system.. which might be a pain in the ass.. but start adding new manifolds and cams.. and you will thank me later.
I would also invest in a fuel pressure gauge.. and a ratio gauge. Both will help you figure your problem out.
I will be out of town till Monday.. not sure if I will have internet connection where I am going...
Cars run *richer* at WOT, not leaner. The ECU is programmed to dump fuel to allow the engine to handle the load without pinging. Sometimes at cruise (light load) the engine can creep up to 15:1 or 16:1, but it should NEVER happen on a dyno. THis is apparently not the most "performance-minded" website for Bimmers. You should seek help from another site that has more tech-heads. I'm new to Bimmers, so I'm not sure how to fix your problem.
However, the simple answer is "You Need More Fuel". You could try to band-aid this by bumping up fuel pressure, but that's not usually a good answer. It can cause it to run rich all the time, not just at WOT. Basically, either your injectors are not big enough to handle the flow (you should have 24# injectors!) or your ECU isn't mapped properly to tell them what to do.
14.7 is the stoichemetric number but it is not the number you want. Sure thats when you get complete "combustion" but you just dont get the power you want out of it. I would say you would want something around that for when you are at idol "completely forgot how to spell it" but the second you get on the gas you want to to drop into the 13's and when you go WOT for the best power you would want it to drop into the 12's for NA of course
But then again I am a mustang guy and our cars are different, but my thinking is they are somewhat similar atleast in Air/Fuel ratios
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