About 5 days ago the brake light starts flashing 8 shorts then one
long. Two days later, the wipers start cycling on the longest delay
setting whilst in the off position. It's an 88 so its got other issues
as well (gas guage always full, oil pressure reading at max), but some
things just get on your nerves. So I get this wild idea that since the
truck has a computer and my Winblows computers always need power
cycling to clear out ghost processes, why is a Chevy any diff?
I yank the fuses for the wipers and the one to the brake system, wait a
minute, then stick 'em back in. Wipers work fine and the brake light
Wonder if GM and Microsoft are in cahoots?
Those Functions have nothing to do with the Computer Circuit in any
1988 GM vehicle.
They only stuff the computer controls:
1A.Retard or Advancement from base timing (ESC or Electronic Spark Control).
1B. Spark Mapping;
1B-1. The Amount of Spark Energy Delivered.
1B-2. Duration of Spark.
1B-3. ESC Functions.
2.Fuel Flow Thru;
2A. Fuel Mapping software: which goes from these readings;
2A-1. Spark Mapping.
2A-2. Oxygen Sensor Readings (rich/lean).
2A-3. Open Loop vs Closed Loop (based off engine temperature).
2A-4. Throttle Position.
2B. Fuel Mixture; Also part of Fuel Mapping.
2B-1. Engine temperature.
2B-2. Engine RPM.
2B-3. Exhaust Oxygen Levels measured Via the Oxygen Sensor.
2B-4. Open Loop vs Closed Loop.
On Some 1988 GM Vehicles the ECM (Engine Control Module) may also
determine, power on or off, or control:
Electronic Cooling fan Functions (1994 Cavalier 2.2's have this)
Torque Converter Clutch Lock/Unlock.
EGR (Exhaust Gas Recirculation) (Have seen post 91 3.1 V6 FWD apps like
When someone has Replaced the E-prom or Reprogrammed a ECM:
They have only changed the Fuel and Spark mapping, as well as possibly
cooling fan operations on OBD-1 ECMs. On OBD-2 They may have changed
Electronic Speedometer Calibrations, Fuel & Spark Mapping, Cooling Fan
on/off Temps, Transmission Line Pressures (automatics only) and some
GM ECMs do NOT use any sort of Disk Operating System (MS D.O.S. which
Windows has to have to operate), or any sort of other Interface protocol
such us UNIX or derivatives of UNIX (Free BSD,Red Hat, Lixus, et-al). It
is Simple Binary Functions. On & Off (1=on, 0= Off).
As to your Problem, it's somewhere in the Dashboard Wiring harness or
at the fuse block. Get a Diagram, a Test Lamp, a Multi-meter, and a
Factory Service Manual that tells you what the readings should be.
Thanks for the info on what a computer really controls. An excellent
synopsis of ECM functionality. As computers go, and you pointed out,
its pretty rudimentary. I've had this truck since new and had the set
of manuals since then too. I don't want you to think this was like
intense scientific troubleshooting or anything. With over 20 years
experience in electronics and digital systems, that would be sort of
This little episode fall under "things that make you say "huh"? If you
are a long way from the shop and things start going haywire, you
In these two cases, it worked.
btw, neither symptom has recurred . . . yet.
My gas guage still reads full all the time so I'll look for a fault in
that circuit eventually. The guage always reading full is due to an
open (infinite resistance to ground) in the circuit. Probably some
corrosion in the ground or a loose wire due to the recent replacement
of the fuel pump, requiring removal of the tank. I mean really, with
the price of gas is it a bad thing to see it sitting on full? Yeah, I
know. It sux to be on the side of the road out of fuel.
The oil pressure guage always reading max is due to an open (infinite
resistance to ground) in the circuit. The sending unit has failed and
provides no resistance to ground so if it is connected, it reads zero
pressure. Personal preference is to look at max pressure rather than
zero until I get it fixed so the lead is hanging next to the sender.
Real pain that thing is to get to. About due for an oil change so I'll
be in the vicinity. Might git 'er done this weekend. Might not.
Doggone it! That's the problem with putting stuff on a ng. I start to
feel like I have to do something!
So today I replaced the oil pressure sending unit. There is something
to be said for lookgin at an accurate reading and it's working fine now.
I spent a little time with the fuel sender, cleaned the connections and
ground lug per the manual. According to their testing protocol, I still
have an open circuit. argh
Went throught the car wash and turned on the wipers again. Now they are
misbehaving again. . . . on the longest mist cycle even when off. Fuse
now out again.
At least I have clean oil and filter and reliable oil pressure reading.
PS: The front of the tranny and all is covered in oil. Don't tell me.
Main rear seal?
Your cluster is probably junk AS WELL AS your Dash Harrness. Commen
Problem on 10 to 20 year old S-Trucks.
Yet anyone who would think a OBD ssytem would run windows doesn't know
jack about cars.
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