Using TBI on moded 5.7

[Mike Vannorsdel]

First I'd like to thank all the listers since the responses have been
outstanding.
    The volts from the TPS are measured at the TPS with a digital volt meter.
The power supply to the TPS reads 4.5v.  The idle problems are with an up then
down idle.  It seems to be from a rich condition.  I have removed the idle
screw plug and have attempted to adjust the IAC but can't get the idle to be
stable enough.  I haven't tested fuel pressure yet.  The distributor doesn't
show any problems in base mode at idle but I haven't checked at different
RPMs.  I can actually see puddling on the throttle plates at idle.  I'm
thinking the high TPS idle reading is causing this.  The only problems are with
hesitation and erratic idle.  Otherwise all is great.  Could leaving out the
PCV cause problems?  I'll look over the wiring to the TPS and do some ignition
and fuel pressure checks.

Walter Sherwin wrote:

> 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?
> >> >> >> >
> >> >> >
> >> >