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Old 11-24-2013, 11:18 PM
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EFI question

Ok EFI guys need a little help. 88 5.0 speed density motor, runs perfect and purrs like a kitten until I reach about 60mph, then she surges and bucks.
Any throttle position up to that speed is fine and she pulls hard. I am leaning towards three options.. 1 speed sensor that I swapped out with the new speedo cable I got. 2 coolant temp sensor, or three MAP sensor.
I'm leaning towards the speed sensor because she was running fine before the speedo cable went in. It was a kit from a mustang place that included a new speed sensor with it.
Seems logical to me that she'll pull hard up to that speed and if I let off and hold her about 55 she runs fine..
I guess if that is my biggest bug that is fine with me. Thanks guys!
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Old 11-25-2013, 06:45 PM
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I was think it's more likely a timing issue.
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Old 11-28-2013, 01:23 PM
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Well I unplugged the VSS and viola I can no go way over 60. I called the place I got it from and all they could tell me was it is made for a mass air motor and mine is a speed density type. Either way one gremlin gone.
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Old 11-28-2013, 01:46 PM
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Not being a EFI guy, I didn't know what a VSS was, so I googled it. One of the hits was this:

What does a Vehicle Speed Sensor do?
The Vehicle Speed sensor or VSS measures transmission/ transaxle output or wheel speed. The ECM uses this information to modify engine functions such as ignition timing, AF ratio, transmission shift points, and to initiate diagnostic routines.


If this input does all this, it seems as though you don't want to run with it disconnected, but rather acquire the proper one, or one that works properly? Just wondering.......
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Last edited by SmithKid; 11-28-2013 at 01:54 PM.
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Old 11-28-2013, 01:58 PM
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Yep that's the same thing I found. I ran my 72 bronco with the same engine transmission combo for 10 years with no VSS. From what I gathered the speed density motor does not rely on the VSS as much as the mass air motor does.
Mine (speed density) mainly uses the VSS for cruise control and the speedometer for the year of mine. (88)
I will see if I can find the correct one however just to be safe.
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Old 11-28-2013, 02:58 PM
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Years ago when I had EFI on mine I called the ford motor sport people to ask questions and one was, what does the spedo sensor do for the cpu and he said so it knows when the car is moving, I ask why does it need to know that and he said he really didn't know . so there you go. what ever runs best...jh
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