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Rev Dip/Hesitation on snap TPS adjustment during cold start - How to correct?

EFI Tuning Fundamentals

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Hello Team HP Academy Students! (this is all jolly fun isn't it!)

Complete noob here, ploughing my way through the lovely HP Academy (Andre's my new best virtual friend)

Anyhow... I have an Naturally Aspirated MX5 mk1 1.8 that I've installed an ME442 ECU on and is running on MAP, with the existing MAF installed still for IAT's.

I will be fitting a turbo kit soon and then mapping for Fi, but want to be a lot more proficient than I am now.

I've been looking at Accelerator Enrichment as the revs drop whilst the engine is cool at idle when I press the throttle... it's annoying, and I'd like to learn how to correct this but have no idea how!?

Here's a view of the data log showing what I think are the relevant factors, and you can see the AE/TPS delta where the manifold pressure and TPS change quickly...

I believe the result is the combustion running lean momentarily and preventing combustion, causing the revs to dip?

I've put a pic of the AE tables in at the bottom for reference.

Any ideas how I can correct this AE/TPS delta, presumably by tipping in more fuel to correct the injection...?

It may not be possible due to fuel atomisation at this temp?

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Thank you,

Vince

I'm not seeing the issue. The cursor in your data is at a point where you lift off the throttle at almost 3000 RPM. The MAP drops due to a closed thorttle, and the AFR goes rich slightly, but you aren't asking for torque so it really doesn't matter.

Have you tried adding more acceleration enrichment at lower coolant temps? I am assuming you have your base VE table and AE tuned correctly at operating temps.

I'm not really understanding the AFR in the log data, and but the engine seems to react with a gain in RPM when the pedal is pressed. May not be 'crisp' feeling which I think is what you're after.

The fuel will atomize, just not as quickly as when the manifold is warm. You just need a bigger wall wetting pool when temps are cold.

Andre always suggests making larger changes when experimenting, I can't see any harm here in doing that.

Exactly that Tyson... I'm not sure whether the issue is coolant related though. It dips even when the engine is hot...

So it looks like it could be TPS related!?

It's weird... only at idle and initial throttle pressing the engine dips and sometimes even stalls.

I understand the port wall issue and lower atomisation of fuel under cooler conditions.

I'll try increasing the TPS AE table, although I've no idea what numbers to put in and where... Can anyone recommend some numbers please and explain what the adjustments will be doing?

Thank you kindly...

Vince

Can you pause the live data in the ECU and scroll back through it? If you can, use this function to see the load points that the engine is transiting through when the issue occurs and make changes in those locations.

I can indeed pause the data... not in the ECU though, I've got data logs and use MegaLogViewerHD to review the data... It could be that the AE/Tip in is too much? I've no idea what AFR's/Load etc the car should be producing in order to remedy the idle dip. It drops down to around 700rpm after each throttle blip...

Surely this must be a known phenomenon?

Are there any folks out there who could review my mecal & data log to see if there's anything glaringly obvious? if not, I'll have to take the car to a proper rolling road tuner and pay keen attention and ask a lot of questions whilst they map the car properly :)

Data log file attached, can't send mecal files via HP Academy website :(

Attached Files

I can indeed pause the data... not in the ECU though, I've got data logs and use MegaLogViewerHD to review the data... It could be that the AE/Tip in is too much? I've no idea what AFR's/Load etc the car should be producing in order to remedy the idle dip. It drops down to around 700rpm after each throttle blip...

Surely this must be a known phenomenon?

Are there any folks out there who could review my mecal & data log to see if there's anything glaringly obvious? if not, I'll have to take the car to a proper rolling road tuner and pay keen attention and ask a lot of questions whilst they map the car properly :)

Data log file attached, can't send mecal files via HP Academy website :(

Attached Files

I can indeed pause the data... not in the ECU though, I've got data logs and use MegaLogViewerHD to review the data... It could be that the AE/Tip in is too much? I've no idea what AFR's/Load etc the car should be producing in order to remedy the idle dip. It drops down to around 700rpm after each throttle blip...

Surely this must be a known phenomenon?

Are there any folks out there who could review my mecal & data log to see if there's anything glaringly obvious? if not, I'll have to take the car to a proper rolling road tuner and pay keen attention and ask a lot of questions whilst they map the car properly :)

Data log file attached, can't send mecal files via HP Academy website :(

Attached Files

When it comes to the tuning of Fuel Film/Transient behavior, I do not concern myself with getting the lambda trace to be flat as would happen in an ideal situation, I work more on the feel of the engine and its drive ability through that region. Some times this will result in an apparent lean spike, or a rich trough.

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