02 Clamp and Dyno - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-04-2007, 12:11 AM   #1
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Default 02 Clamp and Dyno

So, I've got a digital voltmeter and a really small screwdriver. I know the two adjustments on the 02 clamp:

1. The actual voltage signal it sends to the ECU that translates the 02 sensor signal.
2. The psi where the clamp intercepts and transmits said signal (on the boost sensor).

So, what do I look for on the A/F graphs to help me sweeten those two adjustments? Should is see a jump or dip somwhere near the spot where I reach boost and the clamp kicks in? Will the clamp affect the boost curve in any way?
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Old 01-04-2007, 12:29 AM   #2
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PSI the clamp intecepts:

easy....you want it to "click" just as you enter boost. any later and you'll feel the hesitation, any earlier and you'll start dumping fuel in vacuum.

what to look for with voltage:

No clamp:



AFR fails to richen below 14.7 AFR untill the ECU enters an open loop.

Too lean:



Too high a voltage and when you hit WOT the AFR will spike lean or fail to richen up...(4.5 - 5.5 sec)

Tuned voltage:



Look at the dip (1.5 sec) as I floor it the fuel drops to 11:1 AFR and then levels back up...i could probably be a little less agressive with it.
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Old 01-04-2007, 09:08 AM   #3
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So, the clamp will kick in as soon as I go WOT. Is WOT on a dyno enough of a "heavy load" where it switches into open loop. I guess it is!

Brain, on that first graph, everything looks flat and safe and would seem to be the one that I want... but you're saying that's not what I want.

I understand the second graph.

The third graph show you going very rich... is that what I want? You dip down to about 11.1 there...
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Old 01-04-2007, 09:29 AM   #4
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The clamp is activated by a switch when you achieve boost, so yes, just as I hit WOT I go from 0~hg. to positive pressure. You want the clamp to activate just in boost, like .2-.5psi. You can see on the bottom two graphs where there is a split second lean spike just before the clamp activates.

The ecu wants to keep you at 14.7:1 AFR untill it enters an open loop, which is close to 4-5k. The first graph is flat at 14:1, unless you want to blow the engine, you wouldn't prefer that AFR. You can see that the ECU won't add fuel, even with a FMU untill it's damn ready to add fuel. If you look at the times, it doesn't add fuel till 3 seconds into the pull, in 3rd gear from 3k where I datalog from, that's close to 5000 rpms.

Tune for 12:1-12.5:1, I think I have since tuned the clamp to hit exactly 12:1. Either way on the posted log it dips to 11:1 for a total of 1 sec before it levels off at around 12.5:1, not a big deal.

The OEM ECU will want to dump in fuel after about 5.5k, it's the nature of the pre-determined maps and using larger injectors....do you best to tune your fuel pressure to prevent it from dipping. See why I'm going with MegaSquirt?
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Old 01-04-2007, 09:55 AM   #5
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Braineack has it pretty well explained, but don't confuse WOT with entering boost. You can enter boost slowly without going WOT like on a dyno. The O2 clamp should kick in based on reaching positive manifold pressure regardless of the rate of rise.

With the 305's in, the voltage on the clamp may need to be closer to Stoich (.47volts) to keep the ECU from throwing in too much fuel when it sees the lean signal.
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Old 01-04-2007, 10:04 AM   #6
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Quote:
Originally Posted by olderguy View Post
Braineack has it pretty well explained

Aww, that's like a pat on the back....
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Old 04-12-2007, 03:46 PM   #7
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