Does gearing matter to EEC-IV computer?
Lead Driver
Joined: Jul 2017
Posts: 9,584
Likes: 1,168
From: San Jose, CA
Yes. (edit: but apparently not for '92 and later! See below)
It effects the shift points of the transmission, and likely some other things as well. I don't know all the details, but it's very likely to need something.
The speedometer will be off too, until you either change the tire height (taller) or re-tune the computer for the new speed it's seeing.
I don't know where the VSS is on your truck or what it takes it's signal from, but is this the '86 or '97 in your signature? Or another truck?
I'm a big fan of re-gearing, and in fact am planning to do it to my '93 if I keep it longer. It's just TOOO TALLLL and sluggish. Especially if I decide to go with larger tires in the future, but even with stock size tires it's a dog for towing.
Sorry I don't know the details you need. Just that it's a thing and someone else here likely has all the scoop.
Paul
It effects the shift points of the transmission, and likely some other things as well. I don't know all the details, but it's very likely to need something.
The speedometer will be off too, until you either change the tire height (taller) or re-tune the computer for the new speed it's seeing.
I don't know where the VSS is on your truck or what it takes it's signal from, but is this the '86 or '97 in your signature? Or another truck?
I'm a big fan of re-gearing, and in fact am planning to do it to my '93 if I keep it longer. It's just TOOO TALLLL and sluggish. Especially if I decide to go with larger tires in the future, but even with stock size tires it's a dog for towing.
Sorry I don't know the details you need. Just that it's a thing and someone else here likely has all the scoop.
Paul
Lead Driver
Joined: Jul 2017
Posts: 9,584
Likes: 1,168
From: San Jose, CA
Oh, and do you have smog checks in your area? Changing gearing and tire sizes can really mess with the testing as we found out not long ago.
Buddy's Bronco with Mustang EFI engine already had an approval and had passed smog the first time, but when he went to renew it two years later it kept failing for some unknown reason. Took months of head scratching before he realized that the engine rpm vs speed of the wheels was way off from that expected by the computer.
Did a quick speedo gear swap, to "correct" it and passed with flying colors!
After passing he just went back to the right gear to keep his speedo spot on.
Paul
Buddy's Bronco with Mustang EFI engine already had an approval and had passed smog the first time, but when he went to renew it two years later it kept failing for some unknown reason. Took months of head scratching before he realized that the engine rpm vs speed of the wheels was way off from that expected by the computer.
Did a quick speedo gear swap, to "correct" it and passed with flying colors!
After passing he just went back to the right gear to keep his speedo spot on.
Paul
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Cargo Master
Joined: Oct 2016
Posts: 2,738
Likes: 217
From: Northern VA
I scrounged the ECM from the F-350 I parted w/ 4.10. I guess it will be no use for my 88 F-250 w/ 3.55 . However, the 88 has a C6...so perhaps it would not matter ?
I know about those tall gears, my 3.08 4.9 couldn't get out of its own way.
I know about those tall gears, my 3.08 4.9 couldn't get out of its own way.
Lead Driver
Joined: Jul 2017
Posts: 9,584
Likes: 1,168
From: San Jose, CA
Yep, that's what I have as well. Almost thinking it would be worth going all the way to 4.10 or so, but might stick with a 3.55 or 3.73 range gear instead. Been holding off changing the gear lube until I make a decision.
I've mentioned it here on the forums before, but just for comparison my '68 with Explorer EFI 5.0 has 30" tall tires and 4.56 gears! It's a flippin' rocket ship!
Well, it's fast if you can keep from frying the tires. It's too much in fact, but does have it's fun side.
Have a built 4.11 third-member waiting to go in when I have time. I know if would run fine with 3.50's with these tires, but thinking of going larger someday, so had to compromise.
Paul
I've mentioned it here on the forums before, but just for comparison my '68 with Explorer EFI 5.0 has 30" tall tires and 4.56 gears! It's a flippin' rocket ship!
Well, it's fast if you can keep from frying the tires. It's too much in fact, but does have it's fun side.
Have a built 4.11 third-member waiting to go in when I have time. I know if would run fine with 3.50's with these tires, but thinking of going larger someday, so had to compromise.
Paul
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
On 1992 and later F-Series/Bronco trucks different gearing has no effect on the speedometer since the VSS in the rear axle is used to derive the signal for the odo/speedometer as well as the computer and Speed Control amplifier via the PSOM. I am not aware anyone has had issues swapping in different gears and still using the original computer on this vintage truck. Not even sure you can find a reference in the lookup data to determine computer with programming A and 3.08 gears is programmed different than a computer with programming B and 4.10 gears.
Taller or shorter tires will effect the VSS calibration constant, but not gearing.
Taller or shorter tires will effect the VSS calibration constant, but not gearing.
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Hotshot
Joined: Jun 2015
Posts: 12,802
Likes: 2,427
Yes.
It effects the shift points of the transmission, and likely some other things as well. I don't know all the details, but it's very likely to need something.
The speedometer will be off too, until you either change the tire height (taller) or re-tune the computer for the new speed it's seeing.
Sorry I don't know the details you need. Just that it's a thing and someone else here likely has all the scoop.
Paul
It effects the shift points of the transmission, and likely some other things as well. I don't know all the details, but it's very likely to need something.
The speedometer will be off too, until you either change the tire height (taller) or re-tune the computer for the new speed it's seeing.
Sorry I don't know the details you need. Just that it's a thing and someone else here likely has all the scoop.
Paul
I am not aware anyone has had issues swapping in different gears and still using the original computer on this vintage truck. Not even sure you can find a reference in the lookup data to determine computer with programming A and 3.08 gears is programmed different than a computer with programming B and 4.10 gears.
Taller or shorter tires will effect the VSS calibration constant, but not gearing.
Taller or shorter tires will effect the VSS calibration constant, but not gearing.
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