Speed limiter problem
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Speed limiter problem
A friend is working on a 94 f 150 4x4 351 E4OD. He did a gear swap 3.55 to 4.56. Along with a chip and assorted other things. The problem he is having is the truck is shutting down at 80 MPH. It used to shut down around 92 MPH. Could this swap cause the engine to shut off because of the top end /rev limit?? And would a speedometer recalibration fix this problem??
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Troger. As far as I know he did not. He was wondering if the speedo recal would do it. Who ever reflashed the chip didn't mention a rev problem. hence he is wondering if the speedo was the way to go. And why would you change the speedo gear? Is the 355-456 swap too much of a change for just the recal.
Posting Guru
Joined: Dec 2003
Posts: 1,483
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From: Northern California
The instructions in the tech section would be how you recalibrate the speedo, yes. If yours has already been calibrated 6 times before, it will lock you out though. In that case you will have to get a in line calibration module such as the TruSpeed.
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Joined: Dec 2002
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From: USA
Just a note: any speedomoter recalibrating will be on account of a different size tire, as the re-gearing doesnt have any effect on the speedometer since the speedometer gets it's reading from the rear axle speed sensor, which takes it's reading from the tone ring mounted on the ring gear.
Tire size change notwithstanding, a gear change from 3.55 to 4.56 increases engine rpm at any given vehicle speed, so it is not unusual that the engine would reach the rev limiter rpm at a lower vehicle speed since it is spinning faster now. If your friend also changed tire size and the percent change in gearing was greater than the percent change in tire diameter from stock size, the engine will reach max rpm at a lower vehicle speed.
I changed from 3.55 to 4.56 in my '92 Ford truck and also changed from 31.5" stock tire size to 33" tires, which resulted in a greater perecent change in gearing than tire size (I purposely over-corrected the gears for the larger tires). I have not run it all the way up to the rev limits of the engine though.
Tire size change notwithstanding, a gear change from 3.55 to 4.56 increases engine rpm at any given vehicle speed, so it is not unusual that the engine would reach the rev limiter rpm at a lower vehicle speed since it is spinning faster now. If your friend also changed tire size and the percent change in gearing was greater than the percent change in tire diameter from stock size, the engine will reach max rpm at a lower vehicle speed.
I changed from 3.55 to 4.56 in my '92 Ford truck and also changed from 31.5" stock tire size to 33" tires, which resulted in a greater perecent change in gearing than tire size (I purposely over-corrected the gears for the larger tires). I have not run it all the way up to the rev limits of the engine though.
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Post Fiend
Joined: Nov 2001
Posts: 14,947
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From: Topsfield, MA
The only thing stopping you from top speed is the speed and rev limiter. The rev limiter shouldn't be touched, because it's impossible for an engine like this to reach 5500 rpm at top speed (which is where the rev limiter is set near). The speed limiter is based on the speedometer reading, so if it is saying 80, than it's now being tripped at 80 instead of 92. Mine is set at about 92ish as well. I don't think it has anything to do with the speedo calibration or the gearing. I think it has something to do wiht the chip. Take the chip out and see what happens, but regardless you should correct your speedo (per the tech article instructions) so the reading is accurate.
I re-titled your thread to more accurately reflect the subject, it's important for other people who are searching through threads trying to find information.
I re-titled your thread to more accurately reflect the subject, it's important for other people who are searching through threads trying to find information.
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