RPM lags MAP by 0.4 seconds

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jsmcortina
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Blown88GT wrote:All that work to confirm that the default DT of 1.0 is an acceptable value?
Well yes... but given the way the VE table was before, it really seemed like something had to be horribly broken.

James
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Blown88GT
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Re: RPM lags MAP by 0.4 seconds

Post by Blown88GT »

Jim_Blackwood wrote:If by injector DT you mean the time required for the injector to open, I have that set to 1ms, same thing that I've always used in every install. All standard injectors, no peak and hold. I had the impression that they generally didn't vary from that much. Anyway, bog standard mid- 1990-2010ish Ford injectors or possibly a little later. I suppose the newer ones might be a little faster...
All the Ford injector calibration data is available online ready to be plugged-into the online calculator. Usually pretty close to what you measured.
You can find links in other threads.
http://www.msextra.com/forums/viewtopic ... 34&t=66558
1988 Mustang GT, 59k miles, Orig Owner
ProCharger 600B I/C, 12psi, FRP Hdrs, Flwmstr F2, 3G Alt, Contour Fan & DCC, 3.55's, Prog Sprg, Subfms, UCA, LCA, FCA, Tokico 5's, Bridgestone RE-71R 245/40R17, Crane HI-6, Kirban FPR, MS2, DIYPNPF60, Spartan 2, C&L76mm blo-thru MAF, 47lb FRP-LU47
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

Sure, that's the standard figure for the injector. From the VE table, my expectation was an electrical fault causing a 2.0ms deadtime of the like. The physical test has confirmed that this is not the case and that the injectors and electronics are behaving as expected.

James
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Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

It was a bit more than that. It also turned out that my small body "42lb" injectors that all flowed the same when saturated, had significant variations at the other end of the scale. As much as 20-25% possibly. Not the best thing when trying to tune the idle, and that was what we were trying to sort out. We also changed the number of squirts from 2 to 4. And then the "old" fat body set of injectors flowed 37.7 saturated and were within a few percent otherwise so they went back in and got remapped. That's the set that was at 1.0 DT and the new ones could have been off by more. So at this point it's impossible to say how much the change really was.

I went back to an earlier tune that had a slightly better idle and copied over the start/warm-up/accel and other settings and it helped some, but now the fast idle is way high so I'll need to work on that. Then I began deforming the maps to try and get the oscillation to move down in speed. Right now I have a fairly stable 1100 rpm idle which is a big improvement and I think I might be able to do a bit better. At the moment though I'm adding a coolant recovery bottle to stabilize temps before doing any more tuning. I also need to install the new wideband so I have a gage I can see while driving. (the old one has no external indicator)

Essentially, the timing map now has a trough at idle speed and when the rpms drop it gets significantly more advance. That has helped more than anything else so far but I may be as far as I can go with it. The VE map is still pretty flat in that area so that is something to work with. I hope that finely tweaking those two might get me below 1000.

Jim

EDIT: I still don't know that my VE table won't look broken to you guys when it's done, but we did find some corrections. The injectors were either flowing less than their rating or were non-linear both of which would have thrown the table off, and my FPR was set at idle rather than with the engine off and fuel pump on. Since it is referenced to manifold pressure that also threw the map off.
Blown88GT
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Re: RPM lags MAP by 0.4 seconds

Post by Blown88GT »

1988 Mustang GT, 59k miles, Orig Owner
ProCharger 600B I/C, 12psi, FRP Hdrs, Flwmstr F2, 3G Alt, Contour Fan & DCC, 3.55's, Prog Sprg, Subfms, UCA, LCA, FCA, Tokico 5's, Bridgestone RE-71R 245/40R17, Crane HI-6, Kirban FPR, MS2, DIYPNPF60, Spartan 2, C&L76mm blo-thru MAF, 47lb FRP-LU47
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

True but the curve is pretty flat except at the ends.
Without more data points I'm not sure exactly what was up with those small body injectors, I may do more testing of them later on, provided I find the time to redesign my injector bench. Bigger fish to fry right now though.

Jim
Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

Got another data point that might shed some light. I've been chipping away with only minor improvements, currently I have a stable idle only above 1100rpm under ideal conditions. Otherwise it begins to oscillate just as described above. I was able to get down to 1100 by retarding the idle advance to -4 degrees and cannot go further without modifying the trigger wheel.

So the new data:
I took the car out, put it in 5th gear at a crawl and let the clutch out to an engine speed between 200 and 300rpm. It ran smoothly and pulled strongly from that speed. No bucking, spitting or any other bad behavior. No sign of this oscillation I've been fighting. It just brought the engine speed up smoothly.

I was not running a datalog. That will be my next to-do.

For your general edification. I certainly do not know what it means. But I'd love to hear your impressions.

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by billr »

Being able to run at a lower rpm under load is quite normal. I'm guessing the higher MAP when under load results in less reversion of the intake charge and better combustion (more consistent) of what charge does get into each cylinder.
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

Here's the latest datalog, really nothing different from before though that I've seen. I backed off the idle stop until it started oscillating and then at the end screwed it back in some. I can sometimes get a 1000 rpm idle but it is unstable.

Jim
2018-04-10_16.40.14.msl
(355.55 KiB) Downloaded 40 times
TurboBob
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Re: RPM lags MAP by 0.4 seconds

Post by TurboBob »

I've read thru all the posts, and looked over the latest log. I think the issue that you are battling is the intake manifold volume. At idle it fills and empties so slowly that air related controls are too late to stabilize things. PID on the idle control may help some, but thats going to act slowly also.

I'm wondering if some sort of PID on the idle spark advance might make a difference. most specifically some derivative gain to give some "anticipate" to the control loop.

I don't think this is built into the current firmware, but shouldn't be too hard to add.

There may be ways to work around using one of the generic PIDs, or some sort of RPM-dot compensation.

Note: this is a non-scientific analysis, just a SWAG. (scientific wild-assed guess)

Thoughts gentlemen?

Bob
Jim_Blackwood
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

Just a quick question:
In the megalogviewer which corresponds to the injector pulsewidth, DutyCycle or PW? Probably seems obvious but maybe not so much.

Jim
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Re: RPM lags MAP by 0.4 seconds

Post by jsmcortina »

The firmware log fields are covered in the manual.
http://www.msextra.com/doc/pdf/html/Meg ... .4-50.html

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

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Re: RPM lags MAP by 0.4 seconds

Post by whittlebeast »

Jim_Blackwood wrote:Just a quick question:
In the megalogviewer which corresponds to the injector pulsewidth, DutyCycle or PW? Probably seems obvious but maybe not so much.
Jim
This may help. See https://youtu.be/gyFOkxit8gA
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Re: RPM lags MAP by 0.4 seconds

Post by Jim_Blackwood »

OK, that was helpful. Is there a way to copy and save a small section of a datalog as a different file? I have something I'd like you guys to look at if you would.

Jim
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