Big Blue's Transformation

[85lebaront2]

I mostly agree with what Jim said. The only difference might be "just semantics" (but an aside here, since "semantics" is defined as "a branch of linguistics... concerned with meaning", and since the entire point of talking or writing back and forth between people is to communicate meaning, then isn't saying "just semantics" equivalent to saying "just the entire point"?). Anyway...

Yes, the VSS is the vehicle speed sensor on the rear axle in stock form. But a sensor elsewhere (like on the speedo gear at the transfer case output) can do the same thing.

In my '97 the VSS signal is used by the PCM, the RABS and the PSOM. If one or more of those three weren't there the VSS would still be needed and would still be read correctly by the other(s).

Can the PCM correctly understand the signal from a different VSS than the stock one? I don't know. But I'm sure that info is out there.

The one semantics issue I have with what Jim said is that I'd say the PSOM converts the VSS signal to a signal for the gauge rather than say it essentially is the gauge. The gauge is just one thing that uses the PSOM output. The speed control is another. And the PSOM should be able to happily provide a signal to the speed control even if the gauge isn't there.

The PSOM can be reprogrammed up to 5 times. This ordinarily only be needed to compensate for changing the tire size, but it should be able to compensate for a different VSS rate. But be careful as it can only be reprogrammed 5 times. Then you apparently need to get a new PSOM.

Ok, let me run through this. Starting in 1987 the truck EECs started using the VSS signal that already existed for the speed control if installed. There was also a rear axle sensor for the RWABS system added in 1987, this was a tone ring on the differential that is simply pressed on in the Sterling 10.25". The tone ring has a ring of small teeth, I don't remember the actual count.

Ford used a transmission or transfer case speed sensor or an in-line in the speedometer cable from 1987 through 1991 for the EEC and speed control. In 1992 with the last body update to the basic chassis dating to the 1980 trucks, Ford elected to go to an electronic speedometer and use either the existing RWABS signal or on 4W ABS, the ABS composite signal. This is a 100 + pulses per revolution signal. Since the EEC-IV along with the speed control were designed to use a different signal, either both systems needed to be changed, OR the signal needed to be converted to match the old speed sensor output. With the introduction of the E4OD and the later 4R70W transmissions, the EEC now controlled them and definitely needed a speed input.

This is what the PSOM does and it is only needed IF you are not using a cable speedometer. If you are using a cable speedometer, the in-line or transmission/transfer case speed sensor is used instead.

[Gary Lewis]

Ok, let me run through this. Starting in 1987 the truck EECs started using the VSS signal that already existed for the speed control if installed. There was also a rear axle sensor for the RWABS system added in 1987, this was a tone ring on the differential that is simply pressed on in the Sterling 10.25". The tone ring has a ring of small teeth, I don't remember the actual count.

Ford used a transmission or transfer case speed sensor or an in-line in the speedometer cable from 1987 through 1991 for the EEC and speed control. In 1992 with the last body update to the basic chassis dating to the 1980 trucks, Ford elected to go to an electronic speedometer and use either the existing RWABS signal or on 4W ABS, the ABS composite signal. This is a 100 + pulses per revolution signal. Since the EEC-IV along with the speed control were designed to use a different signal, either both systems needed to be changed, OR the signal needed to be converted to match the old speed sensor output. With the introduction of the E4OD and the later 4R70W transmissions, the EEC now controlled them and definitely needed a speed input.

This is what the PSOM does and it is only needed IF you are not using a cable speedometer. If you are using a cable speedometer, the in-line or transmission/transfer case speed sensor is used instead.

Let me see if I can summarize. (I was in the middle of summarizing Bob and Jim's input when the phone rang and my brother, who has a broken ankle, informed me that his wife has COVID, albeit with a mild set of symptoms. Which then allowed Bill's input to come in.)

I have the VSS signal available currently from the speed control sensor in the speedo cable, but can fairly easily put the VSS device in the t-case and get a VSS signal from there, which might be better as it may not be subject to any variations due to speedo cables. And it will work with the EEC-V ECU. Right?

But will that signal work with the electronic speed control in place of the PSOM output? I'm not sure I understand that part.

[85lebaront2]

Let me see if I can summarize. (I was in the middle of summarizing Bob and Jim's input when the phone rang and my brother, who has a broken ankle, informed me that his wife has COVID, albeit with a mild set of symptoms. Which then allowed Bill's input to come in.)

I have the VSS signal available currently from the speed control sensor in the speedo cable, but can fairly easily put the VSS device in the t-case and get a VSS signal from there, which might be better as it may not be subject to any variations due to speedo cables. And it will work with the EEC-V ECU. Right?

But will that signal work with the electronic speed control in place of the PSOM output? I'm not sure I understand that part.

Gary, the answer to your question is yes it will, the 1992/93 aeronose trucks had the electronic speedometer and a vacuum speed control system. All the PSOM does is provide the speed signal in a format the rest of the electronics can use.

Here is an aeronose speedometer disassembled:

First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use, provides a signal to the speedometer movement (a magnetic gauge) and stores the mileage (up to 999,999.9 miles).

Second, the meter (back side) of the board.

Third, the actual meter portion of the speedometer.

Fourth, the odometer display with it's ribbon cable.

Extra, here is the chip from the electronic cruise unit.

If anyone comes across a Lightning I would love to get one of those speedometers, they go to 140 mph!

[Gary Lewis]

Gary, the answer to your question is yes it will, the 1992/93 aeronose trucks had the electronic speedometer and a vacuum speed control system. All the PSOM does is provide the speed signal in a format the rest of the electronics can use.

Here is an aeronose speedometer disassembled:

First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use, provides a signal to the speedometer movement (a magnetic gauge) and stores the mileage (up to 999,999.9 miles).

Second, the meter (back side) of the board.

Third, the actual meter portion of the speedometer.

Fourth, the odometer display with it's ribbon cable.

Extra, here is the chip from the electronic cruise unit.

If anyone comes across a Lightning I would love to get one of those speedometers, they go to 140 mph!

Bill - Thanks for all of that.

But, your statement of "First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use..." worries me. Are you saying the EEC-V can't use the pulse signal from the speedo cable?

I thought we'd said it can. I'm pretty sure the EEC-IV can because Huck, the 1990 half-truck, had a vacuum speed control, a speedometer cable, and EEC-IV w/o a PSOM. But can the EEC-V?

[Gary Lewis]

Bill - Thanks for all of that.

But, your statement of "First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use..." worries me. Are you saying the EEC-V can't use the pulse signal from the speedo cable?

I thought we'd said it can. I'm pretty sure the EEC-IV can because Huck, the 1990 half-truck, had a vacuum speed control, a speedometer cable, and EEC-IV w/o a PSOM. But can the EEC-V?

Bill - Don't miss my question in the previous post.

As for what I did today, not a lot. But I did get a start on the bracket for the fog lights. I cut an 18" piece of the aluminum channel but needed to cut it down the length at the 1" line to effectively make a piece of angle. But not having a good way to do that with a saw I did it with the mill. (When all you have is a hammer everything looks like a nail.) Here's the tail end of the "cut":

Then I drilled the holes for the 7/16" bolts to go through the bumper and spot-faced them on the back side to be flat and take a washer. Here you can see the spot-face on the left and a washer set in on the right, but what you can't really tell is how deep the relief is toward the top. It took removal of a lot of aluminum to make that spot parallel to the bumper.

Tomorrow I hope to get the holes drilled and spot-faced for the lights, the corners rounded, and the angle that Bruce suggested cut. However, the bolts that attach the bracket to the bumper protrude quite a bit so there's no need to take as much out of the bracket as depicted in the drawing since the nut & bolt would then be the tight spot. Still, I'll make it look better, for sure.

Then maybe I can get it powder coated and mounted. What color of powder? Black? Or the aluminum-looking powder used on several things under the hood, like the dipstick stay?

[85lebaront2]

Bill - Thanks for all of that.

But, your statement of "First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use..." worries me. Are you saying the EEC-V can't use the pulse signal from the speedo cable?

I thought we'd said it can. I'm pretty sure the EEC-IV can because Huck, the 1990 half-truck, had a vacuum speed control, a speedometer cable, and EEC-IV w/o a PSOM. But can the EEC-V?

Gary, you are overthinking things again. You remind me of my former department manager at NNS, whose initials are CES. We referred to him as Complicate Everything Snyder. The PSOM converts the pulses from the rear, I think it is 120 per revolution, into a format the EEC and speed control can use, ie, same as the older speed sensors. I don't know whether the Ford speed sensors generate a positive pulse of do like Chrysler and pull the signal wire to ground. Whichever it does, the PSOM emulates it.

In 1993 Ford trucks had the electronic speedometer and the vacuum cruise control, 1994 is when the electronic one came out. Since the vacuum cruise control works with either a speedometer cable/dummy sensor (I ran Darth that way until I got the later dash installed with it's wiring) or the PSOM, that would indicate to me that the PSOM outputs a signal equivalent to the unit on the transmission or transfer case.

You also have to remember that (a) OBD-II was mandatory for cars and trucks under 8500 GVWR for the 1996 model year, the same weight break applied to air bags and (b) the over 8500 GVWR trucks for California and I believe Massachusetts had OBD-II which is why the 460s stayed with EEC-IV except for trucks sold in those states. Since all of Ford's pickups had RWABS from 1987 on, it meant that the rear axle speed sensor was there, but used only for the ABS system until 1993 when it was used for the speedometer. Since the EEC-IV system needed a speed input the PSOM was used to provide it.

[Gary Lewis]

Gary, you are overthinking things again. You remind me of my former department manager at NNS, whose initials are CES. We referred to him as Complicate Everything Snyder. The PSOM converts the pulses from the rear, I think it is 120 per revolution, into a format the EEC and speed control can use, ie, same as the older speed sensors. I don't know whether the Ford speed sensors generate a positive pulse of do like Chrysler and pull the signal wire to ground. Whichever it does, the PSOM emulates it.

In 1993 Ford trucks had the electronic speedometer and the vacuum cruise control, 1994 is when the electronic one came out. Since the vacuum cruise control works with either a speedometer cable/dummy sensor (I ran Darth that way until I got the later dash installed with it's wiring) or the PSOM, that would indicate to me that the PSOM outputs a signal equivalent to the unit on the transmission or transfer case.

You also have to remember that (a) OBD-II was mandatory for cars and trucks under 8500 GVWR for the 1996 model year, the same weight break applied to air bags and (b) the over 8500 GVWR trucks for California and I believe Massachusetts had OBD-II which is why the 460s stayed with EEC-IV except for trucks sold in those states. Since all of Ford's pickups had RWABS from 1987 on, it meant that the rear axle speed sensor was there, but used only for the ABS system until 1993 when it was used for the speedometer. Since the EEC-IV system needed a speed input the PSOM was used to provide it.

Bill - I'm sure I'm overthinking it. But, to paraphrase another Okie, all I know is what I read in this forum and in Ford's documentation.

You said ""First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use...". That says to me that the EEC can't use the signal from the speedometer cable sensor. That's what got my attention.

But now you are saying "Since the vacuum cruise control works with either a speedometer cable/dummy sensor (I ran Darth that way until I got the later dash installed with it's wiring) or the PSOM, that would indicate to me that the PSOM outputs a signal equivalent to the unit on the transmission or transfer case."

That says to me that the EEC's, both IV and V, can use the pulses from the speedometer cable sensor awa the PSOM. I hope I'm reading that correctly!

[85lebaront2]

Bill - I'm sure I'm overthinking it. But, to paraphrase another Okie, all I know is what I read in this forum and in Ford's documentation.

You said ""First, the PSOM board on the speedometer, it does three things, converts the pulse signal to a format the speed control and EEC can use...". That says to me that the EEC can't use the signal from the speedometer cable sensor. That's what got my attention.

But now you are saying "Since the vacuum cruise control works with either a speedometer cable/dummy sensor (I ran Darth that way until I got the later dash installed with it's wiring) or the PSOM, that would indicate to me that the PSOM outputs a signal equivalent to the unit on the transmission or transfer case."

That says to me that the EEC's, both IV and V, can use the pulses from the speedometer cable sensor awa the PSOM. I hope I'm reading that correctly!

Exactly, the PSOM simply generates the pulse format that the EEC and cruise control need.

[Gary Lewis]

Exactly, the PSOM simply generates the pulse format that the EEC and cruise control need.

Ok Bill, thanks.

Now on to a different subject - the placement of various things on Big Blue's driver's fender. And for this I'm pulling some info from this post in the EFI For Big Blue thread.

You might ask why I'm worried about this now since I don't plan to go to EFI until late next year. The reason is that I need to make new #2 cables to connect the aux power relay (the old aux battery relay) with the battery isolator and the aux battery. And given the price of that cable and connectors I don't want to have to do that twice. So I need to figure out where the battery isolator is going to go as it is the key that, literally, ties everything together.

First, here's Huck's 1990 driver's fender with the bracket for the EFI air box bolted on:

And here's the fender w/o the bracket showing the bolt holes that it uses:

Then here's Big Blue's driver's fender. I'm pretty sure the hole circled in the upper right is where the bracket will go, and I think that will work as the leg of the bracket will go behind the battery. And, there's a circle below that roughly where the bottom screw goes. Further, I've put a circle about where the rear screw will need to go. But, I've drawn straight lines on a bit of a problem as that piece protrudes into the engine compartment and will hit the bracket. So some changes will have to be made.

However, that picture of BB's fender does not include the battery isolator that currently sits between the coolant recovery/windshield washer reservoir and the fender, right where the black ground cable is shown in the picture. So both the coolant recovery/windshield washer reservoir and the battery isolator will have to be relocated.

And. the EFI PDB goes on the fender behind the air box but ahead of the speed control servo, so there's no room on that side for the reservoir so it'll probably have to go to the passenger's side. But I do need to find a place for the battery isolator on that side of the engine bay as the cable running across the radiator has to bring the power from the primary battery to the EFI PDB.

So, if anyone has suggestions please offer them!

 

[kramttocs]

Ok Bill, thanks.

Now on to a different subject - the placement of various things on Big Blue's driver's fender. And for this I'm pulling some info from this post in the EFI For Big Blue thread.

You might ask why I'm worried about this now since I don't plan to go to EFI until late next year. The reason is that I need to make new #2 cables to connect the aux power relay (the old aux battery relay) with the battery isolator and the aux battery. And given the price of that cable and connectors I don't want to have to do that twice. So I need to figure out where the battery isolator is going to go as it is the key that, literally, ties everything together.

First, here's Huck's 1990 driver's fender with the bracket for the EFI air box bolted on:

And here's the fender w/o the bracket showing the bolt holes that it uses:

Then here's Big Blue's driver's fender. I'm pretty sure the hole circled in the upper right is where the bracket will go, and I think that will work as the leg of the bracket will go behind the battery. And, there's a circle below that roughly where the bottom screw goes. Further, I've put a circle about where the rear screw will need to go. But, I've drawn straight lines on a bit of a problem as that piece protrudes into the engine compartment and will hit the bracket. So some changes will have to be made.

However, that picture of BB's fender does not include the battery isolator that currently sits between the coolant recovery/windshield washer reservoir and the fender, right where the black ground cable is shown in the picture. So both the coolant recovery/windshield washer reservoir and the battery isolator will have to be relocated.

And. the EFI PDB goes on the fender behind the air box but ahead of the speed control servo, so there's no room on that side for the reservoir so it'll probably have to go to the passenger's side. But I do need to find a place for the battery isolator on that side of the engine bay as the cable running across the radiator has to bring the power from the primary battery to the EFI PDB.

So, if anyone has suggestions please offer them!

Old aux relay? Are you running both? If so, why? I know I sent you that power stud since we talked about this quite awhile ago but I don't recall the details.

I would mount the isolator where the aux relay/power stud goes on the firewall only have it. Will require a little more length but nothing terrible.