High Block Learn

[Don Burns]

Shannen

I guess the signature is somewhat misleading so I'll clarify. The car
is an 86 Fiero GT that has a crate 350TPI with a 5-speed in it. As for
having the tools, I have always worked on my cars to some extent and know
enough about
engines to muddle my way through successfully. But, I have never ventured
into ECMs and the sensors that drive them, until now. My education and
background professionally is in RF circuit design, all analog. I am by no
means knowledgable when it comes to digital electronics. You guys leave me
in the dust when you talk about your compilers, assemblers, etc  ;-)

A guy in Chicago did the transplant for me a year ago but I have been out
of town so much I have not had time to dig in to it. He's built a couple
hundred of these things. The engine is set up so it is equivalent to
something like a 90 L98, Camaro/Firebird/Vette. I am using an AutoXray tool
- fairly cheap but seems to do the job. For this car the tool is configured
as a 90, 8th VIN=8, 4th VIN=F. This is how the builder told me to configure
the tool and I am following his instructions.

What I know about ECMs and EFI I have learned in the last several weeks out
of books, both from Motorbooks. One of the books was mentioned in a
bibliography on the DIY-EFI website and I have found both loaded with
information. Thanks for the recommendation. My actual experience working on
EFI? Almost ZIP.

I have replaced the O2 and MAP sensors, only because I happened to have
both in hand. There was no good reason to replace either other than to see
if there was any difference in how they worked with the ECM. There was no
difference. The O2 sensor was clean, no evidence of contaminants.

Here are some numbers from the scan tool I think are important. If I have
left something out that is important please tell me. All data taken at idle.

* O2 sensor toggles from 350 to 700 mv
* Block Learn is 160 and doesn't move
* Block Learn Cell = 4  (I don't understand this number or its meaning)
* Integrator  ranges from 128 to 135, sometimes a little higher
* Idle Air   10 to 13 steps (The idle is a little a little unstable right now
	and I suspect the IAC needs to be pulled and pintle and seat cleaned
* MAP   1.25 to 1.30 volts
* Knock sensor  5
* Knock retard  0
* Injection pulse width  2.0 to 2.1

The base timing for this engine is set at -8 degrees.

I have also run a can of throttle body spray cleaner around the top of the
engine looking for vacume leaks.

One more piece of data that might be telling: At highway speeds this car
does 21 to 22mpg, almost a 2:1 difference. No, I have not taken any scan
data at highway speeds simply because I have not had anyone to drive while
I am playing with the tool. Maybe this should be next, huh?

I am presently waiting for a guy in San Diego who sees 18mpg city with the
same car and engine to get back to me with comparative data. There is
nothing like seeing some numbers from an engine that doesn't have the
problem.

This was awful long, but I don't know how to come clean in 50 words or less.
Thanks in advance for any suggestions or tips.

Don

>There's more to this than you're mentioning.  I'd bet on it.  The
>first clue is that your siggy says "86 GT" and your post says "O2 and
>MAP sensors are OK".  86 tpi is MAF...
>Next clues are that you have a "mild chip", access to a fuel pressure
>gauge and a scan tool, and know enough about efi diagnostics to try
>forcing the ecm to substitute values for disconnected sensors.
>So tell us what you've done to the car, and what you've checked so
>far, and you'll probably save 2 days worth of cat-n-mouse games. ; )
>
>I may be mistaken, but if that fp reading is at idle, it may be a bit
>high for a stock 86 tpi.
>Shannen


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