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Discussion Starter · #1 · (Edited)
I'm thinking of building a fuel mixture control mod to richen my mixture. Before you ask why, see the attached dyno chart. The chart is the before and after of my exhaust mods. Originally, these cars run too rich for best performance. My car flows so much more, that I actually run too lean for optimum performance. I want to use the old in-line resistor trick that many people normally scoff at. Normally, I would agree with them. However, with my "lean" engine conditions, I'm thinking I can add some power back by richening the mixture. Any thoughts?
 

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I think your below 4500rpm mixture needs some serious richening, but above that you're good. According to my Bosch Gasoline Fuel Injection K-Jetronic manuall, ideal for max power is lambda = between .85 and .95, which IIRC is somewhere around 14:1. I'm surprised your not pinging down at the 16:1 range.
 

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JMatt,
I have built such a device, but have not done enough testing with it yet. It has a switch so I can go either rich or lean by tricking the PCM via bogus IAT sensor inputs. It is used only for wide open throttle runs when the fuel injection is in the open loop mode. Here's a few threads where it is discussed. On the first thread, my post describing it is on page two. The last thread was my first shot at it. After seeing rich dyno results I added the switch and rewired everything so I could go lean also.
http://www.300cforums.com/forums/performance-modifications/11930-stupid-air-fuel-ratio-question.html
http://www.300cforums.com/forums/pe...10020-experimenting-the-races.html#post116204
http://www.300cforums.com/forums/pe...5-mixture-control-wide-open-throttle-wot.html
 

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Discussion Starter · #4 ·
Magnuman! You da man!! That is EXACTLY what I am trying to do. Can you post some pictures of your install? I really think I can add some power by richening my overly lean mixture during WOT. Your results are very intriguing. PICTURES PLEASE!!!
 

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JMatt,
Here's my first post on this mod. from another forum. It has a reference and picture from yet another forum. The picture is the way it looks now, except there is a double pole single throw switch now mounted above the potentiometer.
http://www.lxforums.com/board/showthread.php?t=11491

If you go to the races after doing this mod., you may also want to do our 25 cent fan mod. http://www.lxforums.com/board/showthread.php?t=18678.
Also, I see, on the other forum, you were trying to find out how to run the wires through the firewall. I posted the how to for that. Here it is:
http://www.lxforums.com/board/showthread.php?t=19930
 

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JMatt,
I hope there was something wrong with the graph. You’re dangerously lean.
Your PCM has to be pulling some serious timing out to prevent detonation from damaging the engine.



Here is a quote from this Article

Since having the right air/fuel (A/F) ratio will be the difference between making power and grenading your engine—though modern EMSs will almost never let an engine damage itself—tuners spend a lot of time getting it just right. Too lean and the engine pings, too rich and you lose power. All tuners rely on a wide-band UEGO A/F meter for fuel tuning. Wide-band A/F meters provide rapid and precise measurement of A/F ratio by sampling the exhaust gas composition as it exits the engine.

For the naturally aspirated M5, Powerchip claims to target an A/F ratio of 12.9:1 at WOT for optimal power before detonation becomes a problem. I keep mentioning WOT because when the throttle is held open, the engine becomes loaded and the ECU will think the driver is asking for power, not economy. The ECU will kick into a power enrichment (PE) mode which uses a separate map providing a richer mixture and not bound by closed loop operation or long term adaptive corrections (see below). By performing several WOT runs with the stock software, the tuner can determine how much fuel to take out of the stock PE map, which is usually rich to prevent damage to the catalytic converters. Knowing what the stock WOT A/F is and what cells need to be changed, Powerchip will go in and change the values of the target address proportionately to get a leaner mixture to make more power. There’s a lot of guessing and checking involved, but the goal is to have an A/F ratio of 12.8 to 13.0 throughout the power band at WOT.
Doesn't solve your problem but the article is vary informative about the goals of tuning PCM controlled cars.


How many miles have you put on the car with exhaust changes installed?
The computer can adjust the WOT references to richen the mix, but its range is limited.
 

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Discussion Starter · #7 ·
maneval69 said:
JMatt,
I hope there was something wrong with the graph. You’re dangerously lean.
Your PCM has to be pulling some serious timing out to prevent detonation from damaging the engine.



Here is a quote from this Article


Doesn't solve your problem but the article is vary informative about the goals of tuning PCM controlled cars.


How many miles have you put on the car with exhaust changes installed?
The computer can adjust the WOT references to richen the mix, but its range is limited.
Actually, the air/fuel ratios were reported to Mopar, who indicated that they were still fine. Additionally, most of the time the car uses the O2 sensors to adjust mixture, which should keep the engine rich enough. However - at WOT I definitely want the car running richer than it is, hence the desire to "trick" the car into thinking it's colder, thus richening the mixture. I've done the mode, now I need to do some testing.
 

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JMatt said:
Actually, the air/fuel ratios were reported to Mopar, who indicated that they were still fine. Additionally, most of the time the car uses the O2 sensors to adjust mixture, which should keep the engine rich enough. However - at WOT I definitely want the car running richer than it is, hence the desire to "trick" the car into thinking it's colder, thus richening the mixture. I've done the mode, now I need to do some testing.
My point was that the PMC can adjust open Loop(WOT) settings based on long term closed loop information. (only small amount of adjustment)
In closed loop it should run exaclty 14.7:1 no matter what you change. WOT should run a lot richer than that.

How was this reported to Mopar?
Did they see that graph?

Hopefully what Mopar is saying is that this is with in the control limits of the PCM to prevent Detonation.(by removing timing)
If they where saying this is an acceptable tune, get a second opinion.
(I hope they where just saying you would not hurt your engine running that lean.)

At any rate, you’re defiantly missing out on some power especially at the low end.
Let us know how the IAT sensor trick works.

I get my 5.7 dynoed Monday. We will see how much leaner it gets now that it has headers and high flow cats.
 

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JMatt, another alternative might be to get slightly bigger injectors. The current injectors at 59 psi fuel pressure are at 34.9 lbs on 05' 6.1's. I assume they are the same for 06' models. Adjusted down to 3 way at 43 psi they are 30 lb injectors. If you go slightly higher, say 10-15%, you should be able to richen the mixture at WOT. The challenge now is to find a source for these. I know that the Ford Cobra injectors at 42 lbs will work with a harness to make it fit the Hemi's, but the harness is expensive. I'm wondering if there is an alternative at or around 38 lbs. Anyone have a source?
 

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I'm almost positive the lean condition you see is bogus and your A/F is fine. I can see it just in the even 2 point A/F curves.

1. If you already have a bung installed then the Wide band sensor was not calibrated properly and is giving you a false lean run.

or

2. The wide band sensor was hooked to the rear of your "new" exhaust and was savaging fresh air pulses throwing false lean A/F readings.


I've looked at your graphs, I've done similar mods on a SRT-8 and tons more. I own wide band A/F monitors and I can tell you the lean dyno run is false with 99% certainty.

If you have a bung installed then go get another dyno run done but not at the same dyno facility. If you don't have a bung then get the dyno guys to weld one on and retest. I would not go to the same dyno facility.
 

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Discussion Starter · #12 ·
300C_AWD said:
I'm almost positive the lean condition you see is bogus and your A/F is fine. I can see it just in the even 2 point A/F curves.

1. If you already have a bung installed then the Wide band sensor was not calibrated properly and is giving you a false lean run.

or

2. The wide band sensor was hooked to the rear of your "new" exhaust and was savaging fresh air pulses throwing false lean A/F readings.


I've looked at your graphs, I've done similar mods on a SRT-8 and tons more. I own wide band A/F monitors and I can tell you the lean dyno run is false with 99% certainty.

If you have a bung installed then go get another dyno run done but not at the same dyno facility. If you don't have a bung then get the dyno guys to weld one on and retest. I would not go to the same dyno facility.
99% of the time I would believe you. However, the dyno facility is probably the best facility within 500 miles. It's primary purpose is dyno tuning of Nascar engines. The testing was done by the exhaust manufacturer (one of the more prominent drag-racing related companies in the country).

Finally, I just posted one example. In reality, I have 30 dyno runs. 4 with the stock configuration, and 26 with the headers back mods. The lean condition is definitely there in this case. (with 99% certainty. :wink1: )
 

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JMatt said:
99% of the time I would believe you. However, the dyno facility is probably the best facility within 500 miles. It's primary purpose is dyno tuning of Nascar engines. The testing was done by the exhaust manufacturer (one of the more prominent drag-racing related companies in the country).

Finally, I just posted one example. In reality, I have 30 dyno runs. 4 with the stock configuration, and 26 with the headers back mods. The lean condition is definitely there in this case. (with 99% certainty. :wink1: )
Just to clarify things,

I was the second guy to supercharge a SRT-8. I sort of kept this a secret here :) This includes using a Spit second controller and I did my share making custom fuel maps on the SRT-8 and I've done custom Thermistor mods and tricks on the SRT-8. I have dual wide bands with data logging and tons of Dyno runs. I also record enhanced drive train data and I can see and modify pulse width and injector duty real time. and I've run many types of racing fuel.

Everything you've done to your car has already been done. I know what it takes to lean out your motor and your not there yet. Stop kidding yourself and get a bung installed. Go to a competent dyno that can get things done in 3 runs not 26!

Your headers are not going to give you 80-100HP. That's the type of gains needed to tax your Fuel system and lean it out 2 points.
 
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