ECM fault? Ignition ????

[Programmer]

>>PS: Idle fluctuation is about 50..80 RPM, but when it falls it is causing
roughness and shaking the whole body<<

Along Davids' suggestion about the pickup signal being lost -- that's
EXTREMELY plausible--minimum signal RPM to the module must be at least
700mV. A weak magnet (reluctor) or cracked magnet is often the cause. The
centre brush of this HEI system must also be 3000 ohms--there can be enough
RFI to confuse the PCM into false triggering. Most aftermarket brushes are
lower in value. Another thing--if the MAP value follows RPM--the PCM
commands rich as the RPM drops--and idle worsens. Even though the O2 may be
cycling rich/lean at idle and you get a corresponding roughness--you may be
chasing the wrong thing. Ignition is critical to everything...

My last word...about this thread

Lyndon.


-----Original Message-----
From: Akselrud, Boris <AkselruB at moodys.com>
To: 'gmecm at efi332.eng.ohio-state.edu' <gmecm at efi332.eng.ohio-state.edu>
Cc: 'n5xmt at bellsouth.net' <n5xmt at bellsouth.net>
Date: November 10, 1999 11:27 AM
Subject: RE: ECM fault?


>1. I am dealing with the problem for three years
>2. I've done all the
>scanning/scoping/replaising/maintanence/doublechecking/dealership/shop
>3. I do have bought a service manual from Helm Inc and have it memorized
>4. I've done everything that was suggested so far by the mail list and done
>it multiple times in past
>
>I have stated in my original post that I have done all that you are talking
>about before I even though of posting on the mail list. What we were doing
>so far is reiterating things that have been done by me with the engine.
>
>The objective of my post was to see if there is a commone experience with
>that particular engine and ECM which woudl cause such idle behaviour.
>Apparently there is not and I have an abnormal case.
>
>If there is nothing that I have not tried so far and nothing new can be
>suggested, then the thread is over.
>
>I am greatful for everybody's input.
>
>PS: Idle fluctuation is about 50..80 RPM, but when it falls it is causing
>roughness and shaking the whole body.
>
>-----Original Message-----
>From: David Cooley [mailto:n5xmt at bellsouth.net]
>Sent: Wednesday, November 10, 1999 11:50 AM
>To: gmecm at efi332.eng.ohio-state.edu
>Subject: RE: ECM fault?
>
>
>Boris,
>Blunt and to the point:
>You said the vehicle has done this for 3 years.  Why suddenly it's a
>serious issue?
>You haven't said how many RPM's the idle hunts up and down, you haven't
>provided *ANY* scan tool data IE: block learn/integrator (Fuel learning)
>values, recomendations have been made and you change the subject in the
>next message and skip over the suggestion.
>Troubleshooting *MUST* be done in an orderly manner if it's to turn up any
>problems.
>There is a wealth of info on this list and people that are willing to bend
>over backwards to help other list members out, but you have to be willing
>to take that advice and apply it or you'll get no where.
>The first step you need to take is to buy a service manual so you can check
>the basics, Plugs, Wires, PCV valve etc.  the ECM/sensors should be the
>last thing checked after all the normal mechanical/vacuum related items.
>
>
>At 11:19 AM 11/10/1999 -0500, you wrote:
>>I am wondering if there is anybody on that list who is doing engine/ECM
>work
>>for living, has seen 5.7 TBI run smoothly at idle and has experience with
>>these, within drivable distance of New York City and don't mind looking at
>>my case?
>>I feel I've done everything I could myself as well as dealership/auto
shop.
>>
>
>===========================================================
>David Cooley N5XMT Internet: N5XMT at bellsouth.net
>Packet: N5XMT at KQ4LO.#INT.NC.USA.NA T.A.P.R. Member #7068
>We are Borg... Prepare to be assimilated!
>===========================================================
>