[Lemming]

Below is the AF ratio (from a dynotune) for my 924S3. As you can see, the mixture is quite lean in the lower RPMs. I would like to add a chip, but am afraid that the chip may lean an already lean condition. What are your AF ratios? Are they similar?



Specs: '95 engine with 67k miles; KN filter (8" base, 7" length).



Would adding an adjustable pressure regulator help. I should mention that I did upgrade the fuel pump to a new stock 968 pump. The pressure regulator came with the engine.



I should also mention that if I stab the throttle while at idle you can hear the inrush of air but it seems to take a while for the fuel to get there and therefore there is a hesitation. This does not occur if the engine is at say 3K and you nail the gas. I swapped AFM with my daily driver and this did not correct the condition.

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[Greimann]

I don't have any AF ratio charts, but can confirm that an adjustable fuel pressure regulator allows you to bump the mixture a bit to take care of some of the holes in the throttle response. A chip typically also fattens up the mixture too. Between these two mods, my lean hesitation is gone, especially at low RPM.

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[Lemming]

[quote name='Greimann' date='Oct 4 2005, 09:12 AM']A chip typically also fattens up the mixture too.[/quote]



Hmmm, I was told the opposite by a tuner, he said that most off the wall chips increase HP by making the mixture leaner, especially at the higher RPMs. In fact, based on the chart above, he suggested that I not go with an off the wall chip, but to send the information to someone who can custom program one.

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[tedwright]

[quote name='Lemming' date='Oct 4 2005, 09:58 AM']Hmmm, I was told the opposite by a tuner, he said that most off the wall chips increase HP by making the mixture leaner, especially at the higher RPMs.  In fact, based on the chart above, he suggested that I not go with an off the wall chip, but to send the information to someone who can custom program one.

[right][post="10665"]<{POST_SNAPBACK}>[/post][/right][/quote]



Actually most aftermarket chips for normally aspirated cars make more power from advancing ignition timing. That is why many of them will require that you run a higher octane fuel.



PS- May I ask to see the dyno sheet? If you prefer to email me, it is trwright@gmail.com



Thanks!

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[Lemming]

Here they are.

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[flash]

ok - i've been trying to stay away from this one because i don't want to get into yet another chip thread, so please do not ask me to post any more charts - besides, the charts i have are too large in increment to be able to do any real comparison of value - based on past experience, and with all due respect, it will only spur on further argument from those who don't really have the basic understanding of what they are looking at, and potentially fuel another round of "mine is bigger than yours" - i'm done testing chips and having those arguments



all that being said, ahere is a summary of what we found:



based on testing at the tailpipe, the Racer X and Promax chips actually run essentially the same mixture as stock all the way up to about 4k (a tenth up in a couple of areas and a tenth down in others) - all variations to that point could easily be attributed to variance in atmospheric conditions at the moment



after that, the Racer X chip has slightly richer mixture (and i do mean slightly) which directly corresponds to where it exceeds the Promax in power



i can't speak to the differences in timing amongst the chips, because i didn't look into that



also, in setting up other cars, we always sought the fattest possible mixture for maximum power, attempting to stay somewhere in the 12:1 range - there is a good little section on this in the book "Super Power" - bottom line, leaner for emmissions and mileage - richer for power



hope this helps more than it hurts

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[Lemming]

[quote name='flash' date='Oct 4 2005, 11:21 AM']ok - i've been trying to stay away from this one because i don't want to get into yet another chip thread, so please do not ask me to post any more charts - besides, the charts i have are too large in increment to be able to do any real comparison of value - based on past experience, and with all due respect, it will only spur on further argument from those who don't really have the basic understanding of what they are looking at, and potentially fuel another round of "mine is bigger than yours" - i'm done testing chips and having those arguments[/quote]



Flash, nowhere in my original post did I ask for specifics on a chip or which one to buy. Instead, I'm interested to know if my AF ratios are on target with a stock 968. I have no history with this engine and have a custom air intake and exhaust installed. I'm concerned that my AF is high across the board and that I need to do some troubleshooting prior to trying to increase power with a chip.



Surely someone on this board has a dyno showing AF mixtures on a fairly stock 968.

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[flash]

i didn't say you did - i wasn't really directing that to you specifically - somehow though every time i make any comment on any chip related item, it ends up in the same discussion, and i was only trying to avoid that



moving on to the issue at hand - i've looked closely at your graph, and compared it to my chart - you are running lean by about .5 across the board (i.e. where you should be 13:1 you are 12.5:1)



i would take a look at a couple of things:



check your MAF to see that it is clean

check your O2 sensor for the same thing

maybe it's time to clean the injectors?



if you still get the same results, try a different probe - we had a similar issue and a new probe resolved it - the other one had ben used too much and was coated and therefor giving false readings



your exhaust could be causing the problem - these things are very tricky on these cars - it appears that the resonant induction intake manifold has a lot to do with the exhaust and that they seem to work together - weird things happen when you change one and not the other to compensate - it has been causing us a lot of problems in trying to squeek out every last bit - i'm not sure we can increase the throttle body size for that very reason - we'll see



the bottom line though is that an aftermarket chip will not make you run leaner, in fact, you will run slightly fatter in a couple of spots (it isn't enough to cure your problem though)

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[Lemming]

[quote name='flash' date='Oct 4 2005, 12:01 PM']moving on to the issue at hand - i've looked closely at your graph, and compared it to my chart - you are running lean by about .5 across the board (i.e. where you should be 13:1 you are 12.5:1)



i would take a look at a couple of things:



check your MAF to see that it is clean

check your O2 sensor for the same thing

maybe it's time to clean the injectors?



if you still get the same results, try a different probe - we had a similar issue and a new probe resolved it - the other one had ben used too much and was coated and therefor giving false readings[/quote]



Ok this helps, so although I'm running lean, it's not as much as I thought. I have looked at the MAF and it looks fine (the tuner also looked at it). I popped the MAF off of my daily driver and still had the low RPM hesitation but this was not done at the dyno (too bad). The O2 sensor came from my 924S so I'll check it. As for the injectors, I don't know, they came with the engine, so that is also worth looking at.

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[Aus968]

Lemming,

I would suggest changing your 02 sensor to a 968 type, from memory I think it is different than the 924s. The MAF is self cleaning so I would not worry about that, you'll know when your MAF goes out , Also i guess you have checked for vac leaks.







[quote name='Lemming' date='Oct 4 2005, 02:07 PM']Ok this helps, so although I'm running lean, it's not as much as I thought.  I have looked at the MAF and it looks fine (the tuner also looked at it).  I popped the MAF off of my daily driver and still had the low RPM hesitation but this was not done at the dyno (too bad).  The O2 sensor came from my 924S so I'll check it.  As for the injectors, I don't know, they came with the engine, so that is also worth looking at.

[right][post="10681"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[RS Barn]

An exhaust probe is not a good way to test air fuel ratios. There is not enough volume at low rpm to get an accurate reading. They get closer as the rpm's go higher. The best way to test is at the OE location just after the header. The good dynos use a $1000.00 Professional O2 for accurate readings. That could explain the variance between low and high rpm readings. That doesn't mean they are different though. You should have a steady 12.8 to 1 ratio across the board.

One other comment was that power gains were from advancing timing. That is part of the mixture. The combination of timing and A/F ratio is where the power is.

Pete

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[Lemming]

[quote name='Aus968' date='Oct 4 2005, 05:44 PM']Lemming,

              I would suggest changing your 02 sensor to a 968 type, from memory I think it is different than the 924s. The MAF is self cleaning so I would not worry about that, you'll know when your MAF goes out , Also i guess you have checked for vac leaks.[/quote]



I just checked the PET and both cars use the same sensor (944 606 135 02), however, I will pull and clean it.

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[Aus968]

Wow, i was thinking that the 924s had one two pin plug and one single pin plug, I can clearly remember changing them out and disconnecting two separate plugs, Maybe its an Australian delivery thing, sorry for the bad info, <img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" />



[quote name='Lemming' date='Oct 10 2005, 03:06 PM']I just checked the PET and both cars use the same sensor (944 606 135 02), however, I will pull and clean it.

[right][post="11018"]<{POST_SNAPBACK}>[/post][/right][/quote]

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