ECM fault?

[Akselrud, Boris]

I think that IAT sensor does differ from ECT by more than 5 degrees, because
air intake is made from outside, not from the hose close to the engine. The
valve that makes the switch between outside air and hot air heated by the
engine is disconnected. They told me it does not make any difference and it
would be just fine to always get outside air. But would it really cause the
idle to oscillate?

I don't have the numbers for long term fuel correction at idle right now,
I'll check and post it later.

The mechanical condition seems to be good, it runs quiet, the only problem
that exaust is kind of loud.

I don't recall the figures for vacuum, but recently we tried to connect a
reciever between MAP sensor and input manifold. We used a relatively rigid
plastic bottle. It squashed it right away.

I know that vacuum fluctuates along with idle fluctuation. Should it not???

I think charging is fairly consistend, I dont see any effects of lights or
other electrical load on the engine. I would have noticed.

A/C pressure switch was replaced with new and this past summer A/C system
was discharged/charged multiple times to correct pressure. I have also tried
to run without belt, which would eliminate this variable (needless to say
that it was without any effect on idle).

A/C on/off is working properly and scan tool is fine with that.

What's P/N switch???

-----Original Message-----
From: Programmer [mailto:nwester at eidnet.org]
Sent: Tuesday, November 09, 1999 4:13 PM
To: gmecm at efi332.eng.ohio-state.edu
Subject: Re: ECM fault?


If the O2 sensor is contaminated, it's usually coated with a white powdery
coating, and will result in a high but false O2 reading. This'll command
"lean" from the PCM and fuel will be reduced.

A sticking TPS (over 1.25V) will disable idle control from the ECM

If the IAT sensor differs from ECT by more than 5 degrees, check for high
resistance in the ECT circuit or the sensor itself. Cleaning the IAT probe
can help, too.

If your brother has a scanner--what's the long term fuel correction doing at
idle ? Has anyone confirmed mechanical condition of the engine ? Sure you
may have 20" vacuum--but is it rock solid steady ? Does it fluctuate with
the change in engine "idle" speed ?

Is charging voltage consistent ? If the voltage varies at idle, the IAC can
actually change position, which results in poor idle quality.

Make sure A/C refrigerant pressure isn't too high if "idling" in defrost or
A/C on. A defective pressure switch can cause an unstable idle.

IS the scan tool receiving an A/C "on" request, though the A/C is off ?

IS the P/N switch showing correct position via scan tool ??

Here's some more to chew on...

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>
Date: November 8, 1999 3:15 PM
Subject: RE: ECM fault?


>1. My brother owns an auto repair shop with all the tools including
>scanners. No trouble codes has ever come up, unless you disconnect
something
>on purporse.
>
>2. I don't know if such thing as fuel conditioner would make any
difference.
>Basically whatever my brother did in his shop with the engine did not have
>any slightest effect on idle behaviour. I could feel more power after new
>spark plugs, wires, distributor, timing set, fuel injector cleaner etc.
>However Idle behaviour remains the same: 2 sec or smooth running followed
by
>2 seconds of rough idle.
>
>3. I even was to a dealership with the intention to fix this problem. They
>responded that this is normal for that engine and even newer cars exibit
>stronger rougness (as well as charged me for the job they done and wich had
>no effect what so ever). However this is not the first V8 engine I drive
and
>I believe that this idle behaviour is certanly not normal.
>
>4. O2 sensor is new.
>
>5. Car has 110,000 miles.
>
>6. Could you explain what do you mean by was it "exposed to any silicone" ?
>
>Do these 5.7 TBI engines run rough at idle?
>
>Thank you for the responce.
>
>-----Original Message-----
>From: nacelp at jvlnet.com [mailto:nacelp at jvlnet.com]
>Sent: Monday, November 08, 1999 3:30 PM
>To: gmecm at efi332.eng.ohio-state.edu; gmecm at efi332.eng.ohio-state.edu
>Subject: Re: ECM fault?
>
>
>Try some good fuel system conditioner (ie Quaker State/Slick 50, only stuff
>that comes inna metal can).
>Has a complete tuneup been done?. All the electrical/wearable parts, at
>once?.
>Has it been on a scope, do you own a scan tool?.
>Personally I can't diagnose your car over the net,
>These are just a cople thing to look at.
>What shape is the O2 in, miles, was it exposed to any silicone?.
>Grumpy
>
>
>>Unfortunately no one answered my first post regarding what I think is ECM
>>related problem in 5.7 TBI in my 1993 Cadillac Fleetwood.
>>The problem is erratic or I would say unstable idle. Looks like ECM is
>>leaning the mixture (don't know for sure) causing idle to go below
>>comfortable level for 2..3 seconds followed by 2..3 seconds of smooth
>>operation
>>
>