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Old 03-06-2010, 01:24 PM   #1
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Default Lean after warm/hot restarting

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Hot and warm restarts cause me to idle lean, sometimes to point where the engine wants to stall. The fuelling eventually richens up after driving a few hundreds meters so what do I need to play with in order to sort this hot start lean idle issue? It's not ASE or WUE related as ASE is only active for 15 seconds after starting up and my coolant can sometimes still be well over 90degC and out of WUE temp parameters.

Cheers,
Craig
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Old 03-06-2010, 02:06 PM   #2
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I have the exact same problem as you in for helpas well
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Old 03-06-2010, 02:21 PM   #3
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@Craigo - where have you connected your map line?

I had the exact opposite - hot starts the car would go rich as hell. The solution was - the 99/00 has a valve integrated in the fueling system that closes the MAP line to the FP regulator off at hot starts. I t-ed up the Map line to this vacuum line and didn't see the real MAP at the startup - only the ambient pressure... so the MS was throwing in a lot of fuel. This was on a piggyback MS-2.

For your problem it could be heatsoak of the IAT? What is your MAT correction factor set to? AFAIK it overcompensates a bit and should be set to a value closer to 50% instead of 100%...

What did your MAT values look like? The log doesn't show them...

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Old 03-06-2010, 03:04 PM   #4
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My MAT was only 15degC when taking that log. The actual sensor is currently tie wrapped to my air filter as I still need to get the bung welded in to the intercooler hardpipe.

My MAP line is connected to the barb nearest the throttle body and I've looked for the MAT correction factor setting but can't find it in TS?

Appologies for my vagueness...
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Old 03-06-2010, 03:12 PM   #5
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Quote:
Originally Posted by CRAIGO View Post
My MAT was only 15degC when taking that log. The actual sensor is currently tie wrapped to my air filter as I still need to get the bung welded in to the intercooler hardpipe.
Sounds like sensor heat soak, or in your case sensor exposed to hot stagnant air, but you need to address this before moving on.
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Old 03-06-2010, 04:16 PM   #6
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Really? I had a run out today and let the engine idle for 20 mins at full temp and all I saw was a max MAT of 25degC with no ill affect? If I shut down the engine and immediately restart it, I get the lean idle until I rev it out so to speak In my eyes that doesn't really give it any time to heatsoak anymore than it was 10 seconds earlier while the engine was running. The IAT sensor is literally under the headlamp next the air filter (miles away from the charger and exhaust manifold).

I've a feeling if it heatsoak, I'm going to have a real battle with the problem when the IAT sensor is mounted properly in the intercooler outlet hardpipe.
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Old 03-06-2010, 07:39 PM   #7
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Try adding a little after start enrichment at the higher temps.
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Old 03-07-2010, 01:51 AM   #8
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Do you have the GM open element sensor or the OEM Mazda?

Greets
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Old 03-07-2010, 08:02 AM   #9
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I have the GM open element sensor.

I've been looking into coolant-related air density and made some changes there but have yet to load it up to the MS. My settings for this were all set to a flat 100% upto 37degC.
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Old 03-07-2010, 05:56 PM   #10
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Okay, today I ran the car up to full temp and let it stew for 30mins. After a warm re-start (Coolant was 68degC) with the tweeked coolant-related air density settings, the idle was still lumpy and lean AFRs ~18:1 which makes the engine want to stall. |The MAT figure was 30degC at this point and I immediately popped the bonnet and pulled the IAT sensor up and blew over it, the MAT temps dropped to 23degC within a second or two and the AFRs richened up to a nice 15:1 and the idle ossolation stopped.

Looks like Ben was right, it's the sensor heatsoaking in stagnant warm air. Thanks Ben.

Heatsoak is just that, Im guessing even a heatsoaked intercooler would adequately cool the open element sensor immediately upon restarting the engine as long as it's located in an optimum position merely because there will be a stream of air passing over the sensor element. (even if the stream is warm)
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Old 07-20-2010, 02:33 PM   #11
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this is interesting i've had the same issue for quite a while although my IAT sits just before the TB after the intercooler like instructed. Believe the problem only really came about after fitting some Rx7 550cc. Did you managed to resolve the issue?
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