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Old 09-06-2016, 01:30 AM   #1
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Default NB8a cold running oddity

(Please move if inappropriatelocation)

TLDR, Cars fuelling is really odd when cold, to the point that it is undriveable, however when its warm it runs better than stock.



I have a customers 10ae, 1999 NB8a.
Its turbocharged with a very well engineered turbocharger kit.
It has a Haltech PS1000 plugin ECU.
It has been tuned on an Adaptronic PnP ecu.
The problem presents itself <30*c regardless of ecu.
The ecu is picking up the correct coolant temperature no question.

Ive posted this here rather than in the ecu section because I believe that it is mechanical.

My questions are as follows:

Does anyone have a link to a full vacuum diagram?

What is the acceptable place for ecu MAP?

What could cause fueling to change on this model, with temperature?

This is essentially a return fuel system like an early miata, correct?

Thankyou for any help I get, Im very difficult to defeat, but Im feeling close to defeated here.

Dann
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Old 09-06-2016, 01:33 AM   #2
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returnless on all NB's

e85 or pump?
oem cooling or reroute?

biggest effect, other than ait, is injector/fuel heatsoak. what injectors and fuel system?
what does odd mean? rich? lean?
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Old 09-06-2016, 01:44 AM   #3
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Pump.

It has a factory return fuel system.

RX8 Yellows.

The vacuum hoses, valves and butterfly actuator etc confuses me, making it difficult to diagnose.

Ill pull the pumo out right now and let you know what I find.

BRB
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Old 09-06-2016, 01:54 AM   #4
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Pump and intank filter is as-factory.

This issue is only during cold start/running, as soon as its genuinely warm, >60c its perfect like oem.

The fueling fluctuates, and it misses. Throttle response is non existant, it dies from running to lean, if I enrich the car to get the throttle so it can be blipped without stalling the car runs so rich the wideband cannot read it when its driven.

Dann

Last edited by nitrodann; 09-06-2016 at 02:05 AM.
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Old 09-06-2016, 07:03 PM   #5
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So it does it sporadically on the stock ecu/injectors when its dead cold, and the owner is from a much warmer state than here. He also lets it warm up.

Having tested everything outside of swapping looms or engines, its fair to say that its a latent problem within the car and that he will solve the problem as it worsens at his end.

But seriously, this one defeated me, I spent 2 weeks, 3 different ecu brands, 2 sets of injectors, etc etc etc etc

Dann
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Old 09-06-2016, 07:05 PM   #6
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if it does it on stock ecu then IMO it's fuel system. did y'all put a gauge on there to check pressure?

the OEM NB returnless system sucks and is very finicky sometimes
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Old 09-06-2016, 07:56 PM   #7
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Its a return system.

It has plenty enough consistent fuel pressure to make 220whp dead steady with a very flat VE table.

I havnt measured pressure or flow but the return is strong as ****, PLENTY of fuel and way way more pressure than is needed to start and run a cold engine.

It only does it cold, and clears itself right up when its hot.

Weird as.
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Old 09-06-2016, 08:08 PM   #8
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so australlia cars run a return-style system? cool
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Old 09-06-2016, 08:19 PM   #9
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Not NB8B
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Old 09-06-2016, 08:23 PM   #10
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that's really odd. what about o-rings? perhaps its got a leaky o-ring that expands with heat and stops leaking
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Old 09-06-2016, 08:26 PM   #11
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Ill replace them all again when I reinstall the RX* yellows, past that, headgasket or cracked something maybe valve clearances..?
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Old 09-06-2016, 08:38 PM   #12
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possibly leaky valves or rings that close up with heat. o-rings are real easy and cheap to start with tho
do comp/leakdown
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Old 09-07-2016, 07:18 AM   #13
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Comp/leakdown was good.

I reassembled it with yet another new set of seals and was super careful with everything and it seems to be fixed.

The fact that the temperature was repeatable right down to the last few degrees really threw me.

Dann
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