Using TBI on moded 5.7

[Walter Sherwin]

Were any of these symptoms present before the mods, even mildly?  Your mods
are not overly extreme.

Your TPS voltages are way out of whack, and you should be expecting  around
.52 volts at idle and 4.8 volts at WOT.  If you have a non-slotted
autozeroing TPS then there is nothing you could/should do to effect better
"zeroing".  You would seem to have a problem with either a ground, or
wiring, or a ECM.  Are you measuring TPS volts with a scan tool through the
ALDL port, or via a digital multimeter?

What's your fuel pressure?

20"Hg and 30 IAC counts at idle are excellent, and pretty much confirm both
that you do not have a vacuum leak and that your IAC is working okay.
Hunting, or high/low idles, is a  sign of a bad IAC.  A rough idle is a sign
of poor ignition, or fuel, or engine mechanicals.  Which bad idle do you
have?

I would very seriously examine your distributor!!!!!  You would not believe
the weird grey hair promoting things that these distributors have been
responsible for.  Warm your engine, and disconnect the bypass timing
connector to force the system into fixed spark mode.  Watch the timing mark
with a timing light.  Is it unsteady and does it cut-out intermittently?
Raise the RPM slightly.  Again, is the mark steady?  Raise the RPM to 2000
RPM.  You should have noted a sudden +6 degree timing shift by 2000 RPM if
things are proper.  Pull the distributor and spin it in your hand.  You
should feel 8 very distinct magnetic "tugs" as the magnet/reluctor assembly
aligns.  If any of these tests failed, then your distributor is junk.

The distributor is the heartbeat of the entire TBI fuel/spark control
system.  I have gotten fed up with trying to rebuild these distributors.
Instead I usually purchase a new complete assembly from either GM (P/N
1103952) or from MSD.

Food for thought.........in addition to all the other good ideas/checks
presented by the other listers.

Walt.








>The voltage going to the TPS is 4.5v.  But for some reason at WOT it only
reads
>3.8v.  I'm pulling 20" vacuum.  I didn't reattach the PCV, is this a
problem?
>I'm getting 30 counts on the IAC.  From what I can tell is the TPS is
causing
>the rich idle and the hesitation.  Is there a special way to "autozero" the
TPS
>or just reset all of the sensors?
>
>Programmer wrote:
>
>> Check your engine grounds, and especially those that are sensor related.
The
>> TPS voltage "low" at WOT is a clue.  The TPS is "autozero" type--spec
should
>> be closer to .45 volts. Make sure the throttle plate is at rest when you
>> turn on the ignition. Like Shannon said, make sure the throttle plate is
>> opening fully. The TPS ground is also shared by the MAP sensor--and don't
>> overlook your EGR valve which could be leaking. If you have a scan tool
note
>> the IAC counts. Anything below 25 (and a higher than normal idle) with a
>> fully warmed up engine "indicates" a vacuum leak or wrong PCV valve.
>>
>> Pay close attention to what the BL numbers are doing--they're the self
>> diagnosing parameters you can use to see what the computer is commanding
at
>> the fuel end of things...
>>
>> Lyndon IPTECH
>> -----Original Message-----
>> From: Mike Vannorsdel <vannorsdel at rmi.net>
>> To: gmecm at efi332.eng.ohio-state.edu <gmecm at efi332.eng.ohio-state.edu>
>> Date: November 8, 1999 12:06 AM
>> Subject: Re: Using TBI on moded 5.7
>>
>> >Well the problems I'm facing now is erratic idle and poor throttle
>> response.  I
>> >have tried the timing at 0 and 10 with a little added power at 10 but no
>> fixes
>> >to the problems.  The TBI is used and I'm not sure on the condition of
>> IAC(it
>> >does work but I don't know how well).  The TPS reading at idle is .78v
>> which is
>> >high and at WOT it's 3.8v which is low.  I replaced the TPS and now have
>> added a
>> >hesitation, voltage is the same.  At idle the injectors seem to be
giving
>> way
>> >too much fuel(it almost puddles on the throttle plates).  The MAP is new
>> and
>> >there are no vacuum leaks.  The TPS doesn't seem adjustable.  I'm not
sure
>> if
>> >the problem is TPS, injector, or both.  The engine cruises fine.  I'm
just
>> >looking for smooth running and have faced the fact that I won't be able
to
>> get
>> >max performance from it with the stock ecm.  I have the data on the
engines
>> best
>> >performance level but am unfamiliar with prom programming and don't have
>> the
>> >equipment.
>> >
>> >CSH-HQ wrote:
>> >
>> >> If you really want it right, probably will take a chip (prom).
>> >> Might get by with jacking the timing via the dist/playing with fuel
>> >> pressure, but those are bandaids, but will tell you how far off you
are,
>> to
>> >> a degree.
>> >> Try reading tuning.txt, tuning.doc, and programming 101, then check
back,
>> and
>> >> you'll then have more of an understanding of where you are/what you
have
>> to
>> >> do.  The related material is off of the home page to FTP, and
projects.
>> >> Grumpy
>> >>
>> >> >No relation.  I don't have any reprogramming eqip either.  I'm aware
of
>> the
>> >> >needed settings for timing and fuel with the changes but really have
no
>> way
>> >> >to change the ecm.  I was just looking to see if the TBI at stock
>> settings
>> >> >will be a problem or not.
>> >> >
>> >> >CSH-HQ wrote:
>> >> >
>> >> >> You any relation to Kevin?.
>> >> >> Do you have a prom burner, or related equipment?.
>> >> >> Have you any prom burning experience?.
>> >> >>
>> >> >> More fuel, timing adjustments sound likely.
>> >> >> Have you read programming 101,
>> >> >> do you have a 1227747 ecm?.
>> >> >> Grumpy
>> >> >>
>> >> >> >I have a '91 K1500 with the 5.7 TBI.  I have just rebuilt the
engine
>> and
>> >> >> >made a few changes.  I have raised the compression to 9.5 and
added a
>> >> >> >CompCams XE250(250/260).  What, if any, changes should be made to
the
>> >> >> >timing and TBI to work well with the changes?
>> >> >> >
>> >> >
>> >