[Diy_efi] Followup on 88 Corvette ECM

[Mark Romans]

I guess you answered your own question.  I've seen similar
failures and no codes.  The 165 ecm isn't that smart!
Mark

----- Original Message -----
From: "Perry Harrington" <pedward at apsoft.com>
To: <diy_efi at diy-efi.org>
Sent: Saturday, September 14, 2002 8:09 PM
Subject: [Diy_efi] Followup on 88 Corvette ECM


> Hello all,
>
> I wanted to followup on my Corvette troubles.  Seeing how I've spent a
considerable
> amount of time trying to solve my problem, I thought I'd share what I've
learned
> about GM ECMs.
>
> First, I have a 94 TBI 350 chevy truck as well as the 88 Vette, this will
become
> relevant later.
>
> Well, I don't drive my Vette a lot, and a while back (March) it started
having the
> ole injector blues.  So I swapped in a set of Ford 24lb injectors as
recommended by
> Vetters on the net.  The problem seemed to have cleared up, but I still
had a miss,
> and a dead spot just off idle.  Additionally the motor lacked power and if
you
> hit it hard it'd knock.
>
> So, I replaced the TPS sensor (looked kinda ratty) for good measure, since
the
> dead spot seemed to be throttle related.  That didn't fix the problem.
>
> Next I replaced all the ignition consumables.  Plugs, wires, cap, rotor,
since
> I hadn't done so since I bought the car in 99.
>
> That didn't solve the problem.
>
> I got the feeling that the fuel pump had something to do with it because
what
> initially caused me to park the car before March was a blown fuel pump
relay
> fuse.  I am told that when that happens the fuel filter and/or pump is to
blame.
>
> I'd already replaced the filter.
>
> So I replaced the pump.  The old one looked okay, the sock was kinda
grody, but
> rust was evident inside the sock.  Rust was also evident in the fuel rails
when
> I replaced the injectors.
>
> That didn't fix it.
>
> Now I've replaced everthing in the fuel system but the FPR and lines.  The
miss
> is still there.
>
> Now we bring the truck and the Vette together.
>
> I decided to hook up my AutoXray to see if the MAF was working correctly
and if
> the ECM was doing goofy things.
>
> I didn't have the AutoXray before March, so I hadn't scanned it yet.
>
> There was an EGR code, but that's it.  However, while scanning through the
realtime
> data screen I saw something parculiar.  The Coolant temp was 1.8 degrees
F, but
> the gauges on the dash said 180 when the gauge said 217, the CTS said
~21F.  Now,
> putting that info together with a problem I had with the truck I realized
the CTS is bad.
>
> I had the exact same failure mode with my truck.  It ran so pig rich that
it ran
> better on 1 injector!  I replaced the FPR diaphragm and that seemed to
help a little.
> Then on a whim I pulled the CTS connector and the truck started to run
better.
>
> I ohmed out the sensor and while in the engine it read 32Meg ohm.  Out of
the engine
> it read fine.  So I replaced the sensor with one I bought for it a long
time ago,
> problem solved.
>
> Back to the Vette.  Some time ago the puller fan stopped working.  I did
some research
> and found that the puller is entirely ECM operated.  It turns on when you
have the A/C
> on, and when the motor gets warm.
>
> So to test my theory I turned on the A/C and the puller turned on!  Wow,
that problem
> solved.
>
> Now I gotta pick up a CTS for the Vette tomarrow and see what happens.
>
> It's rather wierd that I'd have a CTS failure on 2 GM vehicles that are 10
feet from
> eachother.
>
> Anyhow, the purpose of this message is to give a little followup on my
problems, so
> that people will have a better understanding of failure modes.
>
> One last thing:  Why is the GM computer so stupid as not to notice the CTS
is bad?
>
> It has a MAT sensor and CTS sensor.  If the MAT sensor is reading less
than 100F, the
> CTS sensor should read hotter or near equal.  If the GM programmers had
thought about
> that piece of logic, they would have saved me a bunch of time.
>
> That is a CORE sensor that when failed should throw a code, not cause the
engine to
> run like crap.
>
> I don't mind replacing all the stuff I have, as they are consumables and
will
> ensure that those are causes of trouble in the near term future.
>
> --Perry
>
> --
> Perry Harrington Data Acquisition & Instrumentation, Inc
> perry at dainst dot com http://www.dainst.com/
>
> Those who would give up essential liberty to purchase a little temporary
safety
> deserve neither liberty or safety. Nor, are they likely to end up with
either.
>                              -- Benjamin Franklin
>
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>


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