RPM lags MAP by 0.4 seconds

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Jim_Blackwood
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RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

Can someone *please* tell me what is going on here?
Ignore the TPS trace, it is unplugged due to noise.
What is important is that the engine starts and then dies.

RPM lags MAP by half a second. Duty cycle drops to 0.8
The controller just shuts down at 4.8 seconds despite the fact that the engine is still running.

Surely someone here has seen this before? Or should I just call DIYautotune?

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by billr »

Where did the VE table come from? No real engine breathes that poorly.
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

You're avoiding the question.

Why does the injector pulsewidth lag the MAP by almost half a second?

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Jim_Blackwood wrote:You're avoiding the question.
That's not the best way to get peer to peer help.
Why does the injector pulsewidth lag the MAP by almost half a second?
Where are you seeing this in the log? (Plus this wasn't your question, you asked about RPM.)

James
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Matt Cramer
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Re: RPM lags MAP by 0.4 seconds

Post by Matt Cramer »

There is often some level of lag for mechanical reasons, particularly when starting. Just how big is your intake plenum?

The reason the MAP reading temporarily froze (records 68 to 74) is that the MAP sampling is keyed to RPM. It will drop to a different sampling behavior once it is sure it has lost the RPM signal.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

It was not my intent to offend anybody.
But, I have asked before and I want to concentrate on this exact problem, not be deflected by other elements of the tune which are not affecting the start cycle. This issue *must* be resolved before anything else matters. A half second lag between MAP and pulsewidth changes means that the engine is going to oscillate no matter what else is done.

The size of the plenum does not matter. The processor is reading a bump in MAP and it takes .4 seconds for injector pulsewidth to follow it. That is in the CONTROLLER.

Yes, I asked about the RPM. The RPM trace closely tracks the PW trace. Both are a half second behind MAP! Why?

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Where are you seeing this in the log.

James
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Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

MAP begins going down at 2.977 seconds.
Injector PW starts down at 3.181s
RPM starts down at 3.384s

So I was off a bit, there is about .2s between each trace. The delay between the PW and RPM I can see as being mechanical but not the one between MAP and PW, and at .2s that's still way too high.

It's a short datalog and only shows one cycle which ends with the engine dying. So unless your display is clear on the left it might be behind the numbers.

I do have one showing the oscillation cycle which continues as a near sine wave for an indeterminate period. I may even have one where it eventually settles out. I can post that if you want to see it but it's the same thing just with lesser amplitude. I posted this one because the delay is pretty hard to miss.

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by turbo conversion »

I sent you a PM on your other post but I never got a response.

There are a few things in your tune that look very odd to me.

Example: VE table, ASE, WE, IAC idle cranking steps.

These can cause you the starting issue you are having.

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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Jim_Blackwood wrote:MAP begins going down at 2.977 seconds.
Injector PW starts down at 3.181s
RPM starts down at 3.384s
MAP is going down because RPM is going up.

The reported injector PW are only updated when the injector fires. At 1000RPM with 2sq alt, there are 120ms between squirts on each channel. Your datalog is recording approximately every 60ms, so you would expect to see between 1 and 3 records before the new value is seen.

As others have said, your VE table does not look correct at all. You'd expect to be approximately 100% VE at 100kPa, yours is around 30%.

James
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Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

I'm not sure what to tell you about the VE table except to say that you should ignore the outlying areas as I have yet to tune there.

Once started the car runs very well. Maybe a smidge rich but that's better than too lean.

I tuned the VE table to get the car to run. I did not try to go through the AFR table to do it, although I did try to enter sensible values in AFR. Not sure at the moment if afr correction is turned on or not, it may be on.

The table does seem to use overly large steps down in the idle and fast idle area, not sure why that is. And I don't much like the looks of the map either. But it does run good. Gets acceptable mileage and has great power.

So why you are saying I should have 100% VE I can't contest, as from what I've been seeing it has to be whatever amount of fuel the engine wants regardless of what the numbers are. If it isn't displaying what you expect to see perhaps you could suggest a way to make it conform? I will surely try it.
-----------------------------------------------------------------------------------------------------------------------------
But it does idle just fine once I get past the startup oscillations The idle is high, about 1200 rpm, when I've clearly demonstrated the engine has the ability to recover from below 300 rpm so it should be able to idle much slower. If I try to lower the idle it begins to oscillate again. I need to fix that. In terms of the way the engine runs that is the single biggest issue I am dealing with. I would like very much to cure that problem before I go off trying to even out the map.
Jim
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Jim_Blackwood wrote:So why you are saying I should have 100% VE I can't contest
Physics.

Unless your engine is thoroughly strangled it really should be near 100% at some point. If it isn't then you either have a severe mechanical problem or your ReqFuel is set very wrong.

James
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billr
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Re: RPM lags MAP by 0.4 seconds

Post by billr »

Let me try this from a different approach...

Have you flowed the injectors for rate and dead-time, using your injector drivers and fuel system? A weird VE table indicates the req_fuel may be far off, which in turn indicates the rate or DT are off. Those factors enter into the fueling calcs in several ways besides just the VE table scaling. We are encouraging you to find and fix a root problem, as indicated by the low VE, before wasting time on other tuning. Your tuning efforts will be more difficult, frustrating, and maybe even not fully-successful if the problem indicated by low VE isn't resolved.
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

I can appreciate that. It does coincide with my past experience.
I did flow the injectors, measure and time their fuel delivery, but it was on a prototype injector flow bench, running 40psi and with the injectors fully powered using a 12v battery and a switch. It's been awhile ago but they shouldn't have changed. They are 44lb injectors IIRC. Engine is 350cid boosted 5psi (Eaton blower).
I do agree that having the map values that low does suggest that either the req.fuel value is off or there is some other setting that is incorrect. What other setting could cause this?

If it couldn't be another setting then I probably have no option except to try a lower req.fuel setting and re-map the engine. It'd be pretty involved to remove and re-test the injectors and I'd prefer to avoid that if possible. Comments here would suggest that I need to reduce req. fuel to about 1/3 of it's current value.


I am willing to correct the VE table problem, but I still feel that this oscillation is going to be a problem if there is that much lag time in the controller. How could there not be?

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Jim_Blackwood wrote:that much lag time in the controller. How could there not be?
Did you read my reply above? The "lag" is because your engine is turning slowly and you are running 2sq alt.

You can mitigate that by running more squirts or fix that by upgrading to MS3 and running sequential.

This is not the reason your engine stalls.

More seriously though, at 5.012s in the log, your engine has stalled, but MAP is showing 52.2kPa, it then takes 1.4 seconds to return to 93kPa?! It should be instant. I can only assume you have a kinked or blocked MAP line. Ambient appears to be 97kPa.

James
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

One other factor that could cause the VE table to appear wildly low is if the injector drivers are damaged and the flyback isn't working, that results in an excessive closing time and you get more fuel than expected - you'd need a scope to test this.

I posted example scope shots on another thread here: http://www.msextra.com/forums/viewtopic ... 35#p509856

James
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Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

Sounds like the best but not the easiest solution would be to go ahead and convert to MS3. I do have the parts but I'm hoping to put that off until cold weather sets in, as the car is a convertible. It runs quite well except for idle. In the meantime maybe we can learn something.

I will try running more squirts as an interim solution, and should be able to put a scope on the injector outputs tomorrow.

Please try to keep an open mind about the possibility that latency could be a contributing factor in this idle oscillation, as I too am contemplating the effects of physical factors. At 1200 rpm that's 10 firing cycles per second per cylinder. 0.2 seconds is two complete firing cycles for the entire engine. That much delay is certainly going to affect the feedback loop. I was under the impression that the MS2 processor was fast enough that this sort of a delay would not exist. Admittedly I do not fully understand the additional factors you mentioned, I'm just going by what is displayed in the datalog.

As to the bleed-off at shut down, that is most likely due to the large plenum volume and doesn't show up when the engine is running due to the volume of air being sucked into the cylinders. Responses to throttle changes are essentially instantaneous I believe, though I can double check that. The throttle body and IAC are located at the inlet of the blower scoop/air cleaner, and the intercooler also has significant volume. The injectors however are located directly atop the intake ports at the end of runners which are several inches long. I AM concerned about the part the IAC is potentially playing in this oscillation scenario, however I unplugged it and still had the oscillation so I think I've ruled that out as a factor.

The one thing that has not been eliminated in my mind is the fact that injector pulse width drops, leading the drop in RPMs. Then if the engine recovers instead of dying, pulsewidth leads the recovery. That tells me that I'm dealing with a control issue, not physical factors.

If it's a control issue, then SOMETHING is causing the controller to oscillate. The engine is just doing what it's told.

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

The MS2 is plenty fast enough. The logged PW doesn't change because the MS2 is waiting for the engine to rotate.

Idle oscillation is often caused by too much timing.

That slow rate of MAP change is not normal unless your throtlle is sealed shut. If that's the case then no wonder the engine stalled. (All inlet valves would need to be fully closed too.)

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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

Good points James, as always. I will investigate further tomorrow and let you know what I find, including having a look at the timing advance, I'm very certain I have room to retard the idle advance significantly.
So I will go back over these last posts and do some testing.

Incidentally, yes the throttle plates were closed, down to the idle stop which was set for 1200 rpm with no IAC. But your point about the intake valves is well taken. I can't imagine any other place where that much vacuum could be accumulated though. But I will check the hose. It seems unlikely to be pinched but I will make sure.

Jim

Incidentally David, my apologies I haven't seen any PM.
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Re: RPM lags MAP by 0.4 seconds

Post by ashford »

there are quite a few wtf things i am seeing. the biggest i see is a 500% cranking pw. with your required fuel this should be around 55ms of fuel during cranking. but there is a limit to pulse width in ms2 and ms3(unless you enable 4x pw) i think but i am not sure it is 45ms. i looks like you are rolling over( starting from 0) the limit to where you are. aka 55-limit = cranking pw.

about that lag, there really is none or none outside of the parameters you have. you have a required fuel that matches the same pw as sequential aka each injector squirts every 720 degrees which means a bank squirt every revolution. this takes time. the ms has to calculate the pulsewidth in advance, wait till the time the engine is in position then do its thing and report it, it cant start squirting then do the measurement and call it time to quit. in your case it has to wait 1 revolution for every squirt. the calculation happens very fast, all that time is the waiting for the engine to come into position dont' belive me open up your log and look at pw2.

it appears that you think pw and map should be one and the same line. if it were fuel injection would be so easy. the example you posed cannot actually be used because it cannot be determined when pw started to decrease, it goes from cranking pw to whatever is calculated when it left cranking pw, it could of very well been falling off before hand if there was a log without cranking pw active
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