voltage variation at idle
- Thread starter MPGmustang
- Start date
FOUND IT, THE REGULATOR WASN'T PLUGGED IN 
yay! I mean, bummer about the frustration, but there's no fix like the easy fix.
Did you get your TBI calibrated to your engine yet? IE the IAC setting, minimum idle speed set 125 RPM less than the chips target idle speed. TPS voltage in the .58 to .59 volt range
currently my speedo is 10% too much... so I'm roughly calculated i'm 15.5mpg city and 20.5 freeway... and the ECM is untuned and I have the mech fan back on for summer... winter I hope to place the electric fan back on.
I do have the company sending me a new chip...
I think I still have a vacuum leak... I'm going to go through it tonight and really seal it up... I thought I was good with ultra coppper RTV but something is still leaking... I'll also check the MAP hose I have and unplug my vacuum guage from the engine. I'm going extreme to find my vacuum leak.
but back on topic, my charge is back up at running RPM's but at idle it goes down to 12.5, which is battery voltage. so it's not charging at idle. the old alt has a smaller pulley, I'm going to swap pulley's and see if I get my idle of 13.1 volts back... something is better than nothing. sadly as my ALT runs off the AC pulley I can't change my AC pulley size. I will have to find an alt that can charge at lower idle speeds.
I do have the company sending me a new chip...
I think I still have a vacuum leak... I'm going to go through it tonight and really seal it up... I thought I was good with ultra coppper RTV but something is still leaking... I'll also check the MAP hose I have and unplug my vacuum guage from the engine. I'm going extreme to find my vacuum leak.
but back on topic, my charge is back up at running RPM's but at idle it goes down to 12.5, which is battery voltage. so it's not charging at idle. the old alt has a smaller pulley, I'm going to swap pulley's and see if I get my idle of 13.1 volts back... something is better than nothing. sadly as my ALT runs off the AC pulley I can't change my AC pulley size. I will have to find an alt that can charge at lower idle speeds.
that is 'untuned', and that's the same with my 2bbl carb... it's the gearing that messed me up...
also the vacuum leak isn't helping.
also the vacuum leak isn't helping.
MPGmustang":2sdh9b3z said:
Good news is that you might be doing a lot better mpg wise.
The speedo reading in mph and the mileage distance reading are not out the same amount....when you have smaller tires or a final drive diff ratio/gearbox change which results in the 60 mph figure being 66 mph, the distance then reads the sotcke amount, but 10% lower , so your fuel consumption reads worse with smaller tires.
I know this because my Explorer runs smaller tires, and the speedo and distance gauge has the speed too high, the miles driven too low.
okay extacy, I'll give you a quiz...
3.2 (old) rear gear to 3.8 (new) rear gear AND 195/70-14 (old) tires to 235/70-14 (new) tires
what is my new speedo ratio?
I'm gussing somewhere around 55mph (speedo) to reach 50mph (actual)
oh and found my vacuum leak...
the head is leaking air between the metal and the putty build up... I think it's because it was done in less than 1 week... I didn't ask it rushed, it just worked out that way...
3.2 (old) rear gear to 3.8 (new) rear gear AND 195/70-14 (old) tires to 235/70-14 (new) tires
what is my new speedo ratio?
I'm gussing somewhere around 55mph (speedo) to reach 50mph (actual)
oh and found my vacuum leak...
the head is leaking air between the metal and the putty build up... I think it's because it was done in less than 1 week... I didn't ask it rushed, it just worked out that way...
MPGmustang":3phtx9nl said:
No contest, 10% is about right MPH.
3.2 with a 195/70 14 is 22.5 mph per 1000rpm in 1:1 top gear, or 2667 rpm at 60 mph .
3.8 with a 235/70 14 is 20.64 mph per 1000 rpm in 1:1 top gear, or 2907 rpm at 60 mph.
Overall indicated mph is exactly 9% higher than before
3.2----->3.8=18.75% lower geared
24.215 inches loaded verses 26.372 inches tall loaded is 8.90% higher geared.
Trade off one against the other by cross multiplication, and you get 9%.
But your distance recorder will be 9% less, and you need to find an output cog which corrects the ratio. Heaps of them to choose from for a T5, as Fords Fox car ratio step was always between 6 to 12% each ratio difference. Similar for the Chevy S10 and F cars.
eg common early 7.5/8.8 ratios
3.73 1.08115942
3.45 1.055045872
3.27 1.061688312
3.08 1.128205128
2.73 1.096385542
2.49 1.101769912
2.26
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