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2s2mad

Hesitation when lightly pressing the accelarator after a complete stop

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Hi guys,

 

I have a MS2 V3board.

Map sensor, 240SX TPS (not currently used but connected)

AEM Wideband

fuel only

L28, N/A, Ported and polished head, Turbo injectors, stage 1 Isky cam, walbro.

Complete inox Header with 3 inches exhaust system.

 

I have 2 issues I would like to share with you.

 

1/ The first one is a light hesitation / stumble when I start from a standing point, after a trafic light for example.

When I press lightly the gas pedal, the engine will stumble and then act normal.

The AEM will read a lean condition for a second.

(If I floor the pedal I will also get the same problem)

 

My idle is pretty rich and goes between 13.5 - 14

Timing is OK and was modified (advanced or retarded) without effect on this particular problem.

 

Should I use TPS enrichment?

If yes, what kind of settings?

 

2/ When I bring the 3rd gear to 5000rpm (for example) and then release completely the gas pedal and coast (keeping the clutch engaged) MS will cut the fuel injection (which is normal).

My problem is if I stay in 3rd gear, let the RPM go down to 2500 and give it a little gas again then I will shoot to lean and the engine will hesitate for a couple of seconds and then back to normal.

 

Is this coming from the fact that the MAP sensor is getting the information with some lag in certain condition or that the information it receives is not relevant?

What should I do to correct this behaviour?

Can I use the TPS information to prevent this from happening?

 

Thanks

Cheers

Simon

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Surprised you haven't got a response yet since you have a question about real tuning on something that you're actually working on. Have you looked through the Megasquirt site? Down on the left menu, there's a link to tuning instructions for MS-II. There's a whole section on using MAP or TPS to add acceleration enrichment. Looks like it fits your first issue.

 

http://www.megasquirt.info/ > Tuning Megasquirt-II on the left menu > about 2/3 down on the page is "Setting the Acceleration Enrichments"

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Tuning accell enrich has been one of the most challenging things for me too. Ive gotten it pretty good by messing around with it for a long time, but its still not as crisp as it was blipping the throttle when carburetted. I am running a blended map/tps, but my tps signal is noisy as hell. I am also suspecting that my map sensor lag time is too high. It responds fine to rapiddly rising boost, but that instantaneous transistion from vacuum to positive pressure seems to cause a hiccup.

 

Ive read a lot about accell enrich, but most of that is with older firmwares. Almost everyone ive talked to with a newer megasquirt version has some issues with hesitation when blipping the throttle. Im interested to see if anyone has a good solution too.

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Hi Guys,

 

Thanks for the replies.

I knew I would have to play with the AE but I cannot get it right for the moment.

When I blip the throttle it is still going lean for half a second and then goes to super rich because of my AE!

I am currently trying with 100% TPS.

My TPS is getting erratic readings sometimes so I put the TPS threshold to 200 to avoid shooting rich without touching the pedal.

My grounds look good to me but there may be room for improvement.

 

Anyway if someone has some starting points for AE I would gladly try them.

I am using thelatest version of TunerStudio

 

Thanks

Cheers

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I did some more messing with my AE today. I changed the MAP averaging lag factor from 50 to 90, then set my AE to 100% MAP based, and it still shoots lean for a split second then goes rich. I then changed TPS and RPM averaging lag factors from 50 to 90, and tried changing the AE to 100% TPS based, and then a blended AE, but no matter what I do the AFR will still shoot lean momentarily causing a slight hesitation.

 

So I'm at a loss, my car is still drivable and runs great, but the AE hesitation is just a slight nuisance that I can't make go away. Me and 2s2mad are in the same boat, at a loss for AE ideas.

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 I also have the issue.  I think it's just the timing of the injection pulse versus when you tip in the gas pedal.  Using X-Tau improves it but I can't get it to disappear.  I improved it with iterations of AE, X-Tau, and ignition timing, but it's still there.  I need to try again with a fresh set of plugs. 

Edited by cygnusx1

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I have had a similar problem the whole time I've had my MS (MSII v3.57 board) running (~2yrs). I've always chalked it up to my own poor tuning ability, which is a definite possibility, but it does seem common, based on this thread. FWIW I'm running a stock 83zxt engine, Ford 370cc injectors, around 70/30 MAP/TPS enrichment (noisy TPS like Cannonball). I've never been able to get rid of the lean stumble at throttle tip-in. Embarrassing when easing away from a group of admirers <_<:angry::)

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How long and big is the hose from the MAP port on the manifold to the MAP sensor on the MS board? I've wondered about that. Maybe there's a lag in response time due to pressure equalization at the hose ends. Small manifold port, big hose would lead to a lag in pressure equalization in the hose.

 

 

Just thinking...

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I finally upgraded my stone-aged laptop for a decent tuning rig and put my nose to the grindstone again. I was able to really improve throttle response by first verifying that my MAP and TPS signals were very clean with low noise. Then I set my thresholds very low, raised my lag factors to 90, and made sure that the AE curves were not coming on too strong. In other words, you want very little AE pulsewidth at low MAPdot and TPSdo rates, and ramp it up richer and richer for the higher rates.

 

My problem was rooted here: Because my AE was too rich at tip in, due to me trying to "improve" throttle response, I had gone back and raised my thresholds and lowered my lag factors to prevent "over AE". Not correct!

 

You should allow AE to happen at very light throttle/MAP inputs, just dont' let it be too rich at very small inputs.

 

 

 

 

Here is what I ended up with today. My lag factors are all at 90. See image.

 

 

post-457-094849300 1344804854_thumb.jpg

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I know this thread is a little old, but I thought I would put my knowledge in here so that others with off-idle hesitation issues might find it later.

 

My car (MSII/3.57/Fuel Only) was having a noticeable hesitation off idle. The culprit was related to RPM spikes at low RPMs. No issues above ~1500RPMs. Just tapping on the throttle was causing my RPMs to shoot briefly to 8K or 10K.

 

By turning on noise filtering, as well as tach period rejection (set at 2ms/30%), virtually all of my off-idle hesitation issues went away.

 

This would only be helpful to people who either see RPM spikes in their data logs or, as I first noticed it, saw my RPMs jump wildly off-idle when viewing Tunerstudio/Live VE Analyze.

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Cygnus you are the man! Your post got me thinking

that my stumble might not be the lean miss I was

focused on.

 

I paided closer attention to my cruise pulsewidths, and

realized that my gently tweaked AE map was way too

much. I had been concentrating on getting the trigger

points set and had not given enough thought to the

amount of fuel to be added. I ended up reducing each

amount by 75% and now have absolutely no stumble

at all. I may end up further trimming the larger pw addrs,

and then ponder x-tau...

 

post-3640-085717600 1346993190_thumb.png

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Just wanted to grab some info from the megasquirt site and post it here since it seems applicable:

 

"If the car does not buck under acceleration, you are close to correct settings. If it bucks and stumbles, then it is going too lean and you need to richen that part of the table. Before tuning decel [or accel], make sure you have your VE table close to correct first!"

 

"You will have to go back and forth between the various accel setting to hone in on the optimal settings for your engine and driving style. Note that you should not use the EGO O2 sensor feedback to tune accel enrichments, this will only confuse your tuning efforts. "

 

I did a lot of my AE tuning with the car not moving, just sitting in the driveway stomping on the gas at various rates like they say in the manual. Then drive around with it and take data and record the stumbles. Ignore the EGO reading as it says in the megamanual, but use the data to figure out what AE bin was used for that event so you can adjust it. I'll post my settings when I get a chance just for comparison but they seem generally close to the last post by Dan_Austin. i haven't changed them in years and they were good for my 2.8 and 3.1L motors. No hesitation or anything.

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