Stalling Issue

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Stalling Issue

Unread postby wickedsnake00 » Wed Aug 01, 2018 7:33 pm

With a little tweaking of spark gain and injector timing I've got it idling nice and smooth at cold start. But it will randomly drop RPM, sometimes saving itself, sometimes stalling out, as seen in the log. Any ideas?

Note that fueling has been dialed in when hot. And it's not one specific airflow where it occurs. I've tried adjusting cold start RPM up and down and it doesn't happen at one particular airflow; it seems to be more time based, usually in the 90-120s range.

The only thing I noticed is that load (and consequently fueling) seems to jump up about 250ms before RPM dips. Is this just a consequence of how PIDs are calculated/reported, or could something be causing this?

RPMdrop_datalog_080118.zip
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wickedsnake00
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Re: Stalling Issue

Unread postby svt4cobra6 » Thu Aug 02, 2018 10:26 pm

I had a similar issue but eventually the car stopped running. I had several issues but runs great now, had a short in the ECM harness, had a blown pickup in the distributor, probably from the short, had a short in the power wire to the alternator. Ended up replacing alternator power wire, new ECM harness and distributor as well as engine harness but I think it was OK. Also replaced the power relay located near the passenger speaker in the dash. Also checked my computer in another fox body, checked out ok.
Sounds like your issue is probably tuning, make sure you have around 40 psi fuel pressure
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Re: Stalling Issue

Unread postby decipha » Fri Aug 03, 2018 2:42 am

csv files are a pain for me to view

first verify you have the throttle stop set correctly by ipsibr being at 0.000 at a warm stable idle as well as the isckam correction at 0

then dial in dashpot

if load spikes up and it stalls then most likely you have a corrupt value in the maf transfer or elsewhere, make sure the maf values are all in chronological order else each time it hits that point it will stall
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Re: Stalling Issue

Unread postby wickedsnake00 » Fri Aug 03, 2018 10:54 am

What format do you prefer them to be in?

ISC air has been dialed in the same way you outlined. IAC integrator is 0 at hot idle. Throttle bypass air is dialed in based on how you outlined (MAF - IAC flow from transfer function).

I'm using close to the values you defined for dashpot. I'll have to double check the tune but it's got a very soft slow decay rate. Is dashpot used during idle control? I thought it was just when transitioning from throttle control to idle control.

MAF values are in order. I know the signal is noisy but that's the best I can get given my limitations.

I will say that it's got an odd non-linear step in that area from about 60-100 cts, likely due to the odd intake characteristics. It seems to hold fine for the ~ 10 seconds preceding the dip though. And I've tried playing with startup RPM to get me outside that non-linear area, but the behavior is the same.

How would I go about hunting down a corrupt value? I'm using SCT PRP so I don't have quite as much flexibility as BE.
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Re: Stalling Issue

Unread postby decipha » Fri Aug 03, 2018 5:39 pm

xdl compressed tunerpro log files

no dashpot is to decay down to idle, its not contributing to base idle

just go through each function and verify nothing at the top left or top right x axis min and max has been altered
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Re: Stalling Issue

Unread postby wickedsnake00 » Tue Aug 07, 2018 1:14 pm

I guess I'm kind of SOL using SCT. If I were to do it again, I'd definitely go Moates.

I'll have to go through them and check. I think there's a few functions I rescaled using the normalizers, including the ISC multiplier.

A few other thoughts regarding the data-

How critical is "smoothness" in the MAF transfer function? Is there a certain amount of change in slope between points that shouldn't be exceeded?

Does the EEC use simple linear interpolation between points for most functions, especially MAF transfer? Or is there anything else that could cause perceived airflow to deviate from the MAF transfer function?

I notice just before RPM drops, not only does load come up but injector pulsewidth jumps up a LOT. The IAC doesn't seem to add air until well after it's starting to recover. If I can't resolve the cause of the RPM drop, is there any way to tune the response to RPM drop at idle to help it save itself better?
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Re: Stalling Issue

Unread postby decipha » Wed Aug 08, 2018 1:49 am

no SCT is fine no prob, all the SW is the same basically, its just an editor

but yea moates QH is far superior the realtime tuning itself is worth its weight in gold

as long as the maf is linear its smoothness isnt really a concern, usually tho if theres non linearities its due to poor injector dial in or bad maf measuring no worries tho

nope its all direct interpolation

yea pw and load should come up for a drop in rpm at the same mafv since VE is going up, just think about it, moving the same amount of air at a lower rpm means a higher volumetric efficiency

u can adjust the drop thats called dashpot, you need more preposition - FN882A and less decay, would also be wise to increase the minimum dashpot clip as well so u dont decay out less than whats ideal for a given rpm
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Re: Stalling Issue

Unread postby wickedsnake00 » Wed Aug 08, 2018 10:52 am

Is there any way to utilize tunerpro without some sort of Moates hardware? I'm logging through the OBD port via an Xcal3 into SCT Livelink, and that's why everything I have is in CSV.

It's not too linear in one spot where there's a steeper slope, but I think it's a red herring since the stall appears to occur in different spots on the transfer function, including linear portions. I think it's primarily due to the intake pipe geometry. The MAF is barely 12" downstream of a merge pipe with a less than ideal configuration due to space constraints. But I digress.

That's what I would expect, but the load and pw increase 250ms before the RPM drop, where RPM and airflow are stable. That's what makes me scratch my head.

This is occurring stationary with no throttle input. I start it up, don't touch anything, and let it ride. Despite things like AFR, spark, airflow and RPM being stable, out of the blue RPM will rapidly plummet to 400 (<1 second) or even die. Does it use dashpot if it is at idle and sees a big RPM drop without any throttle input? Or is it just relying on the ISC neutral idle air, ISC multiplier, and IAC transfer function?
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Re: Stalling Issue

Unread postby decipha » Wed Aug 08, 2018 12:17 pm

if nothing changes and it randomly stalls you have a mechanical problem
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91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
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98 Camaro SS - Bounquisha
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Re: Stalling Issue

Unread postby Paulie » Wed Aug 08, 2018 12:50 pm

Looking at your log your maf counts are very unstable. I see a maf count of 36 at 1204 rpm and a few rows later maf is 112 at 1208 and this is at a relatively stable idle well before the surging
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Re: Stalling Issue

Unread postby wickedsnake00 » Thu Aug 09, 2018 8:14 am

decipha wrote:if nothing changes and it randomly stalls you have a mechanical problem


I'm open to that suggestion, although it only does this in a very specific region: at idle >90 seconds after cold start, and below 150 deg F ECT. Outside of those parameters it's perfect.

Any ideas on what mechanically could cause a random stall or make injector pulsewidth/load jump? It seems to have spark and idles smooth. Fuel pressure is steady. FPDC is pretty low. I've tested for vacuum leaks.

I will add that the one thing that seems to remedy it is more air, whether it's by cracking the throttle, or I even tried intentionally leaning out the region from 97-140 cts by 15% and forcing open loop. It ran lean like you would expect, but never dropped RPM or stalled.

EDIT:
And maybe just for the sake of my curiosity, how does the PCM handle a sharp RPM drop like that? Looking at the logs it seems like it tries to immediately dump in a ton of fuel with a high pulsewidth to save itself. But I would have thought that fueling would be more dependent on airflow, and the mechanism(s) it would use would be the idle air integrator to add air based on delta from desired idle speed and reserve spark. Of course air integrator is fairly slow responding and spark is going to get clipped as load goes up from RPM decreasing so rapidly.

Paulie wrote:Looking at your log your maf counts are very unstable. I see a maf count of 36 at 1204 rpm and a few rows later maf is 112 at 1208 and this is at a relatively stable idle well before the surging


I'm aware of that, and I'm not surprised. The location is less than ideal, and the merge pipe upstream of it is pretty well, hideous. I tried a flow screen but that turned the noisy signal into a sine wave and made things even worse.

It smooths out at higher flow, and somehow the engine seems happy with it outside of this specific region of >90 seconds after cold start at idle, before warmed up.
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