[Diy_efi] Projects

Fri Oct 19 12:46:29 UTC 2012

Clair, I've had a similar "fuel cut" feel before. It was at light-throttle, 
low load (like parking lot speeds) where at about 1500 - 2000 RPM the engine 
would cut out and in and out and in "roop-roop-roop-roop."

There were 2 things contributing to it. The aftermarket camshaft in this 
engine is very efficient around that speed, so it created a lower manifold 
pressure than the factory cam. This was causing it to give too much spark 
advance. At light loads, the engine couldn't detonate and set off the knock 
sensor. It would just missfire from too much advance. I lowered the "max 
advance relative to ref" value to reduce the advance. By "playing with" 
this, I was able to elimimate the parking-lot speed "roop-roop-roop" 
problem. The AFR display was all over the place when it was doing this. 
After adjusting the ignition advance, I was then able to see a stable AFR 
reading, and adjust the VE table to get it even smoother.

Then there was a similar feeling when driving down long, gentle downhill 
grades. It was a "waffling" kind of feel where the fuel was going lean. This 
was the "DFCO" decel fuel cutoff kicking in, because once again, the 
camshaft was more efficient than stock, and causing lower MAP and putting 
the ECM into DFCO.

These problems can be tricky! But there are really only 2 things the ECM is 
controlling - fuel and spark advance. You can eliminate spark advance easily 
by lowering the max advance. See if this makes it better or worse. If worse, 
then set that back to normal, and increase the overall advance (lower the 
bias). See if it is better or worse.  If during these tests you can make the 
engine run "better" in the area where the problem happens, then you are onto 
something with the advance curve.  If not, then look to fuel.

See if the fuel is too lean. Temporarily increase the fuel across the board 
(raise the base pulse constant) and see if this imporoves the engine in the 
"problem area" of the RPM and load. If this test helps in the problem area, 
then you are going to have to locate which cells in the VE table are low.

One very very powerful tool is TunerPro RT, with the data trace function. It 
highlights the cells in the VE table where the ECM is currently running. You 
can look at the laptop screen while the engine is operting in it's "problem 
area" and see the general area where the table is highlighted.

Basically, make an "across the board" temporary change to ONE thing (spark 
OR fuel) and see what this does to the "problem area." Then restore your 
original tune. You can narrow it down to a fuel or advance issue; and is it 
too much or too little advance, or too rich or too lean. Once you know what 
is happening; then you can narrow it down to the actual table calls that are 
incorrect for your engine.

Hope this gives you a few ideas!

Sincerely,
David

----- Original Message ----- 
From: "Clair Davis" <clair.davis at charter.net>
To: "'David Allen'" <davida1 at hiwaay.net>; <diy_efi at diy-efi.org>
Sent: Friday, October 19, 2012 7:24 AM
Subject: RE: [Diy_efi] Projects

> David,
> Thanks, it feels like I've been on the steepest part of the learning curve
> for the duration of this project.  It doesn't help that "real" life keeps
> getting in the way, but at least nothing is spoiling while it waits in the
> garage for some more attention.  I don't have any video, but I might have
> some data logging files - tied  up on my near-dead laptop.  I don't know 
> how
> useful they would be.
>
> The feel of the problem is like an abrupt loss of fuel - the car bucks and
> acts like a stall, and because it's a 4-speed car the feel is pretty 
> severe.
> AF ratios are also going very lean when this happens.
>
> I'm in the process of removing any "extra" bits in the fuel system - I 
> have
> a small surge tank that may be contributing, but I don't need that piece
> until I get in to a high-G + low fuel situation.
>
> I'm also going through the code and trying to switch off everything that
> doesn't look absolutely necessary to run the engine.  This is where my
> unfamiliarity with the code and the sophistication of the GM tuning effort
> are making things difficult.  They really did a great job and this novice 
> is
> a little overwhelmed...
>
> I'll see if I can dig my EFI files from the old laptop and get things
> running on this new machine so I can talk more intelligently now that the
> list is humming along again.
>
> Clair
>
>
> -----Original Message-----
> From: David Allen [mailto:davida1 at hiwaay.net]
> Sent: Thursday, October 18, 2012 12:32 PM
> To: diy_efi at diy-efi.org; clair.davis at charter.net
> Subject: Re: [Diy_efi] Projects
>
> Your engine setup looks very good. Nice 4-BBL throttle body setup.
> I've found out, as you, that part throttle is the worst part of it. 
> Multiple
> ECU's and different engines and the part-throttle is always the pain to
> tune!
>
> As for the part-throttle drivability, what is it doing? Do you have any
> videos of the drivability problem?
>
> Sincerely,
> David
>
>
>
>
>
> ----- Original Message -----
> From: "Clair Davis" <clair.davis at charter.net>
> To: <diy_efi at diy-efi.org>
> Sent: Wednesday, October 17, 2012 10:55 PM
> Subject: Re: [Diy_efi] Projects
>
>
>> Probably a good refresher for me to think about this again.  I've talked 
>> a
>> bit about my project with some of you in the past, most likely on the
>> GM-ECM
>> list.
>>
>> My project is installing a GM TPI-based MPI on a 1969 Plymouth Valiant
>> sedan.  The car was my daily driver for years, and I've been setting the
>> car
>> up as a fun cruiser and SCCA auto-cross / road racer as it becomes more 
>> of
>
>> a
>> toy.  I started the swap to EFI after fuel and oil control issues became
>> the
>> limiting handling factors.
>>
>> The system is based on a 7730, and includes a number of GM and
>> Chrysler-based parts.  I'm tuning with TunerProRT and Moates' APU1, and I
>> have some version of AUJP in the car now.  I have been able to drive the
>> car
>> some, but most of my tuning progress was made just before and shortly
>> after
>> my 1st son was born - 7 years ago.  I really need to get this car back on
>> the road and enjoy driving it again, and the tuning is all that is
>> preventing that from happening right now.   Idle is nice and WOT is
>> surprising, but that bit in the middle is trouble...
>>
>> I'm hoping that over the next few months I'll be able to sort out the 
>> part
>> throttle cruise problems enough to be able to drive it to a local dyno
>> shop
>> and do some more detailed tuning off the highways and side streets.  I'm
>> also seriously considering a move to a different control system if it 
>> will
>> significantly ease my tuning chores, but I've got quite a bit invested in
>> this OBD-I setup, so the benefit/cost has to be there.
>>
>> Here's some eye-candy for sticking with me so far...
>>
>> The car as she was right before the EFI project started, all the
>> suspension
>> goodies in place:
>>
> http://www.moparfins.com/clairdavis/webimages/69sedan/In_The_Park2-PS-Clippe
>> d.jpg
>>
>> And here's the engine after getting all the hard parts bolted down for
>> keeps:
>>
> http://www.moparfins.com/clairdavis/webimages/69sedan/upgrades/efi/TB_Serp_O
>> n-small.jpg
>>
>>
>> Thanks,
>>
>> Clair
>> DFWTX
>>
>>
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>> Diy_efi at diy-efi.org
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>>
>
>
> 