86 in dash vss

[sandrock]

CEL/SES/MIL lamps, from my understanding anyways, only come on when the code set is emissions related. Which means every engine sensor that is under the computers watchful eye will set a code if something is wrong. But anything else outside of that, if the computer sees it, will set code but not throw the light on. A good example of this are misfires...the CEL (at least the PCMs I've dealt with) will flash the corresponding cylinder the PCM picked detonation up on, and will set a code and illuminate the CEL continuously until the engine is restarted, then it goes away.

[jameslleary]

CEL/SES/MIL lamps, from my understanding anyways, only come on when the code set is emissions related. Which means every engine sensor that is under the computers watchful eye will set a code if something is wrong. But anything else outside of that, if the computer sees it, will set code but not throw the light on. A good example of this are misfires...the CEL (at least the PCMs I've dealt with) will flash the corresponding cylinder the PCM picked detonation up on, and will set a code and illuminate the CEL continuously until the engine is restarted, then it goes away.

Only on OBD2... the only OBD1 system that I know of that will give you anything with cylinder specific ID is Ford EEC4, when you activate the compression test feature.

[1project2many]

OBDII has to follow specific rules regarding when the light it on and when it's not. Emissions levels 1.5X the vehicle's allowable max will illuminate the light, and anything determined to be catalyst damaging will cause the light to flash. OBDI had no such specific rules so the mfgrs did what they wanted. Early Mopars, Volvos, and a few others had a time interval counter which would illuminate the light for no other reason than "It's time."

Some OBDI GM code will give cylinder specific issues. As OBDII approached, GM started implementing misfire detection and injector voltage monitoring code.

[jameslleary]

I would think that would only be the LT1....its the only obd1 (v8, anyway) that i know of that had cylinder identifying capabilities, as it didnt batch fire the injectors.

Anyways, I just spun the speedo cable by hand, with the volt meter hooked to the yeller wire, and i got some readings from it. must work, pretty good for a 25 year old unit.

[EagleMark]

Early Mopars, Volvos, and a few others had a time interval counter which would illuminate the light for no other reason than "It's time."

That would be a code #1 "Check Engine Light" check engine light!

[jameslleary]

ok, so...has anyone figured out what this crank signal wire is for? the truck starts without it.

[1project2many]

Some of the early code used the crank input. Later calibrations don't and the wire is unused.

[Six_Shooter]

ok, so...has anyone figured out what this crank signal wire is for? the truck starts without it.

You mean the wire fused at 3 amps?

That is just a signal to the ECM to tell it that the vehicle is in a starting procedure (ignition key turned to the start position).

IIRC, the ECM uses this for starting parameters, such as retarding the timing.

[jameslleary]

Cool, thanks. I'll go ahead and hook it up. Running ASDU, dont know if it requires it or not. I dont have a PC available to me to look...Is there any way to find out which bins have air injection commands programed into them? TBI truckzs are wuite confusing in Ca.
All of the TBI squarebody trucks 87 to 91 have A.I.R., and then you get to the NBS GMT-400 TBI trucks, and sosme do have A.I.R. and some do not. what gives?