[Gmecm] Two '747 problems

Sat Mar 12 17:33:48 UTC 2005

Well on your idle problem...
It sounds like you have a scan tool , so what are the IAC counts DOING when the idle cycling is present? If the IAC counts are also cycling then you have an input (TP,ECT, IGN REF etc) that is flakng out cold. If the IAC counts are fixed then you're getting air from somewhere else . Try carefully spraying some carb cleaner or varsol (I've also used a propane torch with a rubber hose on it for this) around the sealing points of your intake (dont forget the very back),thrttle body, including vacuum lines and fittings while it is acting up and see if you can find a spot where the engine reacts (speeds up or slows down) and you've found your leak.
HTH
WOT
  ----- Original Message ----- 
  From: David Haggard 
  To: nhromyak at comcast.net ; gmecm at diy-efi.org ; gmecm at diy-efi.org 
  Sent: Friday, March 11, 2005 9:51 PM
  Subject: RE: [Gmecm] Two '747 problems

  BLM's are between 125 and 130 all across the board.

  The fuel pump is a new in-tank unit for a 1990 TPI. Fuel filter is new. No vacuum leaks anywhere I can find. I even replaced the intake gasket to be sure. IAC shows no sign of sticking. There is no EGR, and the EGR routines are disabled by setting their thresholds at extremely high temps and speeds. (EGR is set to open at 254 mph.)

  I'll look into any and all suggestions. What I've received so far has been helpful in that it helps me think of different possibilities.

  David

------------------------------------------------------------------------------

  From: nhromyak at comcast.net [mailto:nhromyak at comcast.net] 
  Sent: Friday, March 11, 2005 3:53 PM
  To: gmecm at diy-efi.org; gmecm at diy-efi.org
  Cc: David Haggard
  Subject: RE: [Gmecm] Two '747 problems

  Stop and then restart and it is fine?!?!?  I am not familiar with the 747 tunning, do you have BLMs?  what are they like before and after the stop and restart?

  Could it be a lazy or plugged fuel pump/filter?

  Maybe the IAC is leaking.... or stuck?!?!

  EGR?

  Heh, I don't know...

    -------------- Original message -------------- 

    > Thanks, Nick for the thoughts. 
    > 
    > My manifold is Holley, but my TBI is a factory unit from a '93 454 
    > Chevy. I also failed to mention that the injectors are flow-matched 350 
    > Police injectors. 
    > 
    > The funniest part of my first issue is that after I stop the engine and 
    > restart, the idle is perfect from then on. 
    > 
    > David 
    > 
    > > -----Original Message----- 
    > > From: NICHOLAS HROMYAK [mailto:nhromyak at comcast.net] 
    > > Sent: Thursday, March 10, 2005 9:36 PM 
    > > To: David Haggard; gmecm at diy-efi.org 
    > > Subject: Re: [Gmecm] Two '747 problems 
    > > 
    > > I have the same problem with my TBI based 402 BBC. I keep thinking I 
    > have 
    > > an exhaust leak 
    > > But that should make it go more rich. When it is in open loop and a 
    > > little 
    > > rich, I get a smooth idle. 
    > > perhaps we have a lazy O2 sensor, or perhaps a vacuum leak. 
    > > 
    > > After chasing it down for the longest time, I changed my O2 voltage 
    > > readings 
    > > at idle. I am not sure if this can be done in the 808, but I think it 
    > can 
    > > be done in the 747, it certainly can be done with the 7730. 
    > > 
    > > I too have Holley TBI (4 barrel). To the best of my knowledge these 
    > > aren't 
    > > leaking, I have had them for six years now. 
    > > 
    > > Good luck. 
    > > Nick in Sacramento. 
    > > 
    > > ----- Original Message ----- 
    > > From: "David Haggard" 
    > > To: 
    > > Sent: Thursday, March 10, 2005 5:04 PM 
    > > Subject: [Gmecm] Two '747 problems 
    > > 
    > > 
    > > I have two tuning problems I can't seem to figure out. The ECM is a 
    > > '747, '88 305, moderately cammed, 454 TBI and Holley Pro-jection 
    > intake. 
    > > 
    > > 1. After cold startup, the idle will never settle down to a smooth 
    > idle, 
    > > even after driving and fully warmed up. The idle oscillates between 
    > the 
    > > target setting and about 1800 rpm. The throttle follower seems 
    > > overactive. But once the engine is warmed up above the closed loop 
    > > threshold, if I shut the engine off, wait ten seconds, then restart 
    > it, 
    > > I get a smooth idle at the target setting, and the throttle follower 
    > > acts perfectly. 
    > > 
    > > 2. I have a bad flat spot under gentle acceleration, between 1600 and 
    > > 1800 rpm. I experimented with lowering the PE TPS threshold to 20%, 
    > and 
    > > the flat spot is gone if I open the throttle past the 20% point and PE 
    > > is enabled. The flat spot is there under any acceleration below the PE 
    > > TPS level. The main fuel table has been tuned to give BLM's of about 
    > 126 
    > > in that RPM and throttle range, using WinALDL. The spark table has a 
    > > smooth, straight-line advance curve through that RPM range. 
    > > 
    > > Any ideas would be greatly appreciated. 
    > > 
    > > David Haggard 
    > > '88 Formula Firebird "SR-71 Black 'Bird" 
    > > 
    > > _______________________________________________ 
    > > Gmecm mailing list 
    > > Gmecm at diy-efi.org 
    > > http://lists.diy-efi.org/mailman/listinfo/gmecm 
    > > 
    > > 
    > 
    > 
    > _______________________________________________ 
    > Gmecm mailing list 
    > Gmecm at diy-efi.org 
    > http://lists.diy-efi.org/mailman/listinfo/gmecm 

------------------------------------------------------------------------------

  _______________________________________________
  Gmecm mailing list
  Gmecm at diy-efi.org
  http://lists.diy-efi.org/mailman/listinfo/gmecm
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.diy-efi.org/pipermail/gmecm/attachments/20050312/3c4d066f/attachment.html 