Idle too high. How do I adjust

[Dan Griffin]

Bottom line: Does ecm use vss to determine eng. load?? If so I dont see how
a car/truck ecm could be made to easily work on a boat..I say 14.7 to 1 is
way to lean, even at steady cruise, ( 19-23 mph hull just planing)...eng
load for a car is much less...If only map, tps and rpm are used I think I
could see how this might work though...
what/how to send vss a signal though? mount a speedo cable to prop? Or the
magnetic sensor type, I dunno if  that'll work underwater though? prop rpm
is same as eng rpm (I think)...In neutral prop shaft is the only shaft not
in motion..You want neutral switch hooked to gear selector..somehow...
All unused tables in the bin would have to be zeroed...I see lots and lots
of chip burning here unless you get really lucky, ( if its right the 1st
time Id buy a lottery ticket)
Dan
----- Original Message -----
From: Jay Vessels <jwvess00 at home.com>
To: <gmecm at diy-efi.org>
Sent: Tuesday, September 11, 2001 6:59 PM
Subject: RE: Idle too high. How do I adjust


> Hi there!
>
> On my truck ('87 2.8V6 TBI 1227429 ECM) you can set base idle speed with
> the following method:
> Key off, short ALDL pins A&B.  Key on for 30 seconds or so, then unplug
IAC
> with the key on.  IAC pintle should be fully extended here.  Start engine
> and adjust base idle speed (minimum air).  Turn engine off.  Key on,
adjust
> TPS voltage to spec. (0.50 volts +/- .05V seems to work for most cars).
If
> the voltage was way off (i.e. you moved the idle screw a long ways) then
> you might want to repeat the process until you get a base idle speed you
> like and a TPS idle voltage in spec.  This also seems to work for Dad's
'86
> Caprice ('85 F-body TPI system, '85 ECM number slips my mind).
>
> This did not work for my '84 Cavalier Type 10 convertible (2.0I4 TBI,
> unknown ECM).  It had a plug that you were supposed to install in the air
> horn of the TBI to block the IAC before you set minimum air.
>
> When I got the car, it idled at about 2000 RPM and slammed into gear.  I
> replaced all the gaskets, vacuum lines, and the IAC to no avail.  I could
> not adjust the speed lower with the idle speed screw.  In a fit of anger,
I
> removed the IAC and pulled on the pintle.  It almost came all the way out.
> I threaded it back in so that the TBI's pintle seat itself would push the
> pintle in as I reinstalled it.  Started the car, idled fine.  I guess the
> IAC was somewhat retracted and the ECM never commanded enough steps to
> fully seat it.  Either that, or it was stuck (albeit new) and my brute
> force method fixed it.  Try this at your own risk.
>
> On my truck, I don't have the VSS connected at all and the ECM is wired
> such that it is always in Neutral.  It idles fine and fuel economy is
> decent.  What benefits would I gain from attaching the VSS signal (didn't
> have a VSS when I converted to TBI, now I do since installing the cruise
> control)?  Currently set up like it is to disable EGR complaints.  Would
> pulling EGR code out of the chip and connecting the VSS signal be a better
> solution, or just more work?
>
> Jay Vessels
> 1982 Chevrolet S-10 Sport, 2.8V6 TBI
> 1994 Chevrolet Cavalier Z24 Conv., 3.1V6 MPI
> http://www.vessels-clan.com/jay (now W3C compliant)
>
> At 05:22 PM 9/11/01 -0500, you wrote:
> >
> >> As far as connecting a VSS, Couldn't I just connect it or would I have
to
> >> mechanically power it as well?
> >>
> >> I dont see the connection logically between the VSS and idle, as it
idles
> >> perfectly, other than too high for the boat. In the vehicle, 800 would
be
> >> very suitable.
> >
> >You could likely connect it once and give it a signal > 36 mph (isn't
that
> >right, fellas?) to allow the IAC to reset itself, then disconnect it.
> >Problem is that the IAC baselines itself to certain numbers of "steps"
> >from being closed...then after some period of time the ECM attempts to
> >adjust to a particular RPM, given other parameters. Other parameters
> >include stuff like decel, dashpot, temp, A/C, PNRDL, etc. My car would
run
> >at 2500 RPM for a few minutes before it idled down, and it never did make
> >it to true idle speed. IAC didn't know where "closed" was after I took
> >the TBI apart for cleaning. Sounds like you don't have that
problem...yet.
> >
> >If you don't have the ability to burn an EPROM, that idea of blocking IAC
> >and adjusting idle speed with a screw looks better and better. I won't
> >pretend to be anyone that is worthy of burning chips for people (can you
> >say engine go poof?), but if your calibration (the 4 letter code) is one
> >of those listed in the bin_library email me directly and I'll give it one
> >shot in the name of neighborly help. Today seems like a good day to offer
> >some of that.
> >
> >-greg
> >

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org