Why No Cel?

imp · Jul 31, 2017

Recently acquired (May 1) '94 GT 5.0 HO, 5-speed. The vapor canister is gone. The smog pump lies idle, belt bypassed. According to previous testimony here by accepted expert knowledge, there should be at least CEL for canister missing. No CEL.

My '04 Explorer, OBD-II, on the other hand, stranded me when the ABS Module "bought it". That threw

"P2106 FORD
Throttle Actuator Control System - Forced Limited Power", as well as flashing 4X4 HIGH, BRAKE, Wrench, and ABS icons. Reacting to the ABS, the great whatever-his-name-is Makurko or something, Ford Super Technician, video showed him going right to the rear differential housing, and pulling out a mangled ABS speed sensor. That fixed it. I never went that far, but rather bought into other opinions regarding the Drive by Wire problem. They unanimously recommended replacement of the Throttle Body. I did. You can guess the result. Problem unchanged.

Here's my point. The DTCs are intended as a guide, but are not Gospel. At any rate, the OBD-I earlier system is I think far more misgiving. But, nonetheless, how did the guy who threw away my canister convince the PCM to not throw a code?? Car runs perfectly, but eats too much fuel, IMO. No DTCs. No CEL.

Help!! imp

90sickfox · Jul 31, 2017

Does the CEL light up when you turn the key to run ?

Mustang5L5 · Jul 31, 2017

OBD-1/EEC-4 is just a more primitive system. It's not going to operate like OBD2 simply because OBD2 didn't exist yet, so we can't backward-apply the same logic to it.

To sum it up, MOST of the trouble codes associated with OBD1 will not trip a CEL. IIRC, only the 13 most critical in terms to how the engine runs will display the light.

Charcoal canister is not one of them.

General karthief · Jul 31, 2017

The obdl is like the government, it knows about it, you just have to force it to tell you.

imp · Aug 1, 2017

90sickfox said:
Does the CEL light up when you turn the key to run ?

@90sickfox
Yes, all the icons behave normally on prove-out, including the meat-bag, go out after eng. starts. One post stated there was a code for "Canister Missing". I ain't got that one. imp

General karthief · Aug 1, 2017

Are the 94-5 charcoal canister is the same place as the fox?
I thought they moved them inside the fender on the opposite side of that same frame rail.
Purge canister, excuse me, no code 85?

Mustang5L5 · Aug 1, 2017

karthief said:
Are the 94-5 charcoal canister is the same place as the fox?
I thought they moved them inside the fender on the opposite side of that same frame rail.
Purge canister, excuse me, no code 85?

It's a different code for Sn95's. I'm actually not too privy on EEC-4 in the Sn95 cars, but yank a canister in a fox and you get a code 85.

imp · Aug 1, 2017

Mustang5L5 said:
It's a different code for Sn95's. I'm actually not too privy on EEC-4 in the Sn95 cars, but yank a canister in a fox and you get a code 85.

@Mustang5L5

Well, someone yanked out mine, and no code(s). Now the question is: how would PCM detect a "no canister" present?
All it knows is it sends an electrical signal to the purge valve, which admits vapor into the engine via a vacuum line. With programming trickery as in later OBD-II, it could detect no current flow to the valve, and throw a code. But whether or not actual vapor flow takes place, rather doubtful, IMO. imp

General karthief · Aug 1, 2017

I think you're looking in the wrong place, it's behind the inner fender liner, look up into the cavity between the front wheel and the bumper cover.

Mustang5L5 · Aug 1, 2017

I honestly think it's just detecting a change in resistance of the solenoid to verify the valve opens and closes. I doubt it's conforming flow.

Is the harness plugged into a purge valve left hanging?

imp · Aug 1, 2017

karthief said:
I think you're looking in the wrong place, it's behind the inner fender liner, look up into the cavity between the front wheel and the bumper cover.

@karthief

Am pretty familiar with that hole, actually, since there is an opening in the inner fender apron, through which the guy had put a long, curved 3-1/2 inch tube, with a small K&N stuck inside the cavity. Could not get it out to service withoiut disassembling the entire inlet ducting. That's gone now. imp

imp · Aug 1, 2017

Mustang5L5 said:
I honestly think it's just detecting a change in resistance of the solenoid to verify the valve opens and closes. I doubt it's conforming flow.

Is the harness plugged into a purge valve left hanging?

@Mustang5L5
Yes, that makes sense. Every one of those "self-checks" requires quirky added circuitry and programming within the PCM. Some are easy, like displacement (movement of a part), this is done in the DFPE which detects and measures movement of the EGR valve.

The harness has no connection left for the purge valve. I suspect it's been cut off and hidden within the harness from which the MAF extends. There is a round rubber grommet surrounding the MAF wiring, about 6" from the MAF plug. There must have been a bracket, which is gone, and right below, the TFI Module is screwed to the fender apron, kind of cock-eyed, not like Factory installed. imp

jrichker · Aug 1, 2017

The computer uses current sink technology; it does not supply power but it does supply ground.

The computer controlled ground circuit has protection via an op amp comparator that measures the voltage drop across a low value resistor of known resistance.

As current flow through the resistor increases, the voltage drop across the resistor increases: Ohms Law states E=IR. When the op amp comparator detects a voltage greater than its trip point, it turns off. That turns the power FET or transistor that supplies the ground off.

The turn off signal can either trip a D-Flop to shutdown the circuit until the computer power gets turned off, or it can run in PWM mode and provide a lower power level that won't damage the power FET or transistor that supplies the ground. Everything that drives a coil, relay or some other feature uses this principle.

imp · Aug 2, 2017

jrichker said:
The computer uses current sink technology; it does not supply power but it does supply ground.

The computer controlled ground circuit has protection via an op amp comparator that measures the voltage drop across a low value resistor of known resistance.

As current flow through the resistor increases, the voltage drop across the resistor increases: Ohms Law states E=IR. When the op amp comparator detects a voltage greater than its trip point, it turns off. That turns the power FET or transistor that supplies the ground off.

The turn off signal can either trip a D-Flop to shutdown the circuit until the computer power gets turned off, or it can run in PWM mode and provide a lower power level that won't damage the power FET or transistor that supplies the ground. Everything that drives a coil, relay or some other feature uses this principle.

@jrichker

Very informative. But, what is your point, Grandma? imp

jrichker · Aug 2, 2017

imp said:
@jrichker

Very informative. But, what is your point, Grandma? imp

Mustang5L5 said:
I honestly think it's just detecting a change in resistance of the solenoid to verify the valve opens and closes. I doubt it's conforming flow.

My point was to clarify how it works...

General karthief · Aug 2, 2017

I don't know about you guys but that cleared things up for me, explains what happened that night my resistor needed draining and I d-flopped causing my circuit to shut down for 5 or 10 minutes. My resistor was ok after I had a cup of coffee. I'm just glad I didn't damage my op amp comarator!

imp · Aug 2, 2017

karthief said:
I don't know about you guys but that cleared things up for me, explains what happened that night my resistor needed draining and I d-flopped causing my circuit to shut down for 5 or 10 minutes. My resistor was ok after I had a cup of coffee. I'm just glad I didn't damage my op amp comarator!

@karthief

Any problem, real or just perceived, lends itself to the exclusive use of left-handed tools! imp

Why No Cel?

imp

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90sickfox

Wasn't a pretty sight...and I've got big hands

Mustang5L5

That is…until I whipped out my Bissell

General karthief

wonder how much it would cost to ship you a pair

imp

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General karthief

wonder how much it would cost to ship you a pair

Mustang5L5

That is…until I whipped out my Bissell

imp

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General karthief

wonder how much it would cost to ship you a pair

Mustang5L5

That is…until I whipped out my Bissell

imp

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imp

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jrichker

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General karthief

wonder how much it would cost to ship you a pair

imp

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Why No Cel?

Mustang Master

Wasn't a pretty sight...and I've got big hands

That is…until I whipped out my Bissell

wonder how much it would cost to ship you a pair

Mustang Master

wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

Mustang Master

wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

Mustang Master

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