fuel pump voltage now with new readings 7/10 !
06-10-2007, 07:19 PM
#1
fuel pump voltage now with new readings 7/10 !
ok peeps finished fitting my group A fuel pump and re-wire but not 100% happy i have got 13.9 volts at the battery but 12.8 at the pump drops to 12.6 when cooling fan on etc? 
earth has been fed straight back to battery so cant be a earth probs!would u expect this voltage difference?forgot it on a 2wd sapp cossie
earth has been fed straight back to battery so cant be a earth probs!would u expect this voltage difference?forgot it on a 2wd sapp cossie
06-10-2007, 07:41 PM
#4
Football Cwazy
Join Date: Oct 2004
Location: Redditch, Worcestershire
Posts: 9,553
Likes: 0
Received 0 Likes
on
0 Posts
i'd say that was quite good compared to most cossies 
i rewired mine in the week, it was 13.6v at the battery, but 9v at the pump
it's now about 12.9v at pump, although i haven't checked it on boost yet
i rewired mine in the week, it was 13.6v at the battery, but 9v at the pump
it's now about 12.9v at pump, although i haven't checked it on boost yet
Trending Topics
06-10-2007, 07:48 PM
#9
Football Cwazy
Join Date: Oct 2004
Location: Redditch, Worcestershire
Posts: 9,553
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by mechanic28
cool i thought it was quite low would not expect to loose a volt could abit difficult to check voltage under load leads not long enough stu so u think 12.8 at idle is ok when volta at battery is 13.9?
bud-weis 9v jesus thats low
could abit difficult to check voltage under load leads not long enough stu so u think 12.8 at idle is ok when volta at battery is 13.9?bud-weis 9v
jesus thats low
i know luckily it's never seen full boost in my ownership
06-10-2007, 07:54 PM
#11
Originally Posted by bud-weis
Originally Posted by mechanic28
cool i thought it was quite low would not expect to loose a volt could abit difficult to check voltage under load leads not long enough stu so u think 12.8 at idle is ok when volta at battery is 13.9?
bud-weis 9v jesus thats low
could abit difficult to check voltage under load leads not long enough stu so u think 12.8 at idle is ok when volta at battery is 13.9?bud-weis 9v
jesus thats low i know luckily it's never seen full boost in my ownership
good job as well fella
06-10-2007, 08:31 PM
#13
PassionFord Post Troll
iTrader: (1)
Join Date: May 2003
Location: Cleveland
Posts: 2,815
Likes: 0
Received 0 Likes
on
0 Posts
I'd expect your voltage to be higher at the pump than you've measured. If all your wiring is new then all being well I'd expect your voltage to be higher.
Did you wire it as described in our PM's?
Neil.
PS If I recall, my wiring drops 0.1V from pump to battery. (i.e. I have .1V less when measuring at the pump compared to across the battery)
Did you wire it as described in our PM's?
Neil.
PS If I recall, my wiring drops 0.1V from pump to battery. (i.e. I have .1V less when measuring at the pump compared to across the battery)
06-10-2007, 08:46 PM
#14
yer the same way fella bit mythed to be honest not happy just want it all right before i get it live mapped can not figure out y i have lost over a volt might take off all the connectors which i soldered and put some new one in and crimp them instead
just want it all right before i get it live mapped can not figure out y i have lost over a volt might take off all the connectors which i soldered and put some new one in and crimp them instead
06-10-2007, 08:50 PM
#16
Advanced PassionFord User
Join Date: Mar 2006
Posts: 1,686
Likes: 0
Received 0 Likes
on
0 Posts
if your cable is only rated for about 27A then i would guessyou have used 2.5mm2 cable. you really need to know the exact cable size as it sounds like the cable may just be suffering from abit of volt drop.
06-10-2007, 08:53 PM
#17
Originally Posted by Neil S
So it's as per mine only with a direct earth back to the battery?
Do you have any idea what current is flowing in the circuit?
Do you have any idea what current is flowing in the circuit?
06-10-2007, 08:57 PM
#18
Originally Posted by rssteve
if your cable is only rated for about 27A then i would guessyou have used 2.5mm2 cable. you really need to know the exact cable size as it sounds like the cable may just be suffering from abit of volt drop.
06-10-2007, 09:31 PM
#22
Advanced PassionFord User
Join Date: Mar 2006
Posts: 1,686
Likes: 0
Received 0 Likes
on
0 Posts
im not suprised its so low. Not a bad guess was it 2.5mm2. Not big enough tbh it might have a rating of 27A but when you add lenght you get volt drop. not sure what a fuel pump draws but id put in a 6mm minimun to decrease the resistance of the cable. or you could run a couple of your 3mm2 in this will halve the resistance so less voltdrop.
06-10-2007, 09:55 PM
#24
Norris Motorsport
Pump should be earthed to the chassis using as short an earth cable as possible, and not returned to the battery via a cable. (Unless I mis-understand what you wrote above)
06-10-2007, 10:07 PM
#25
ok just checked got 13.4 volts at terminal 87 of the relay using the original fuel pump earth so can only be 2 things 1 bad connection in the wire from term 87 to pump or voltage drop due to running my earth all the way back to my battery wot u think?
or voltage drop due to running my earth all the way back to my battery wot u think?
06-10-2007, 11:18 PM
#29
Advanced PassionFord User
Join Date: Mar 2006
Posts: 1,686
Likes: 0
Received 0 Likes
on
0 Posts
its fine to use the cable as the earth providing its big enough. the earth of the body work is only as good as the small earth strap thats go from body to battery(neg terminal) and remember these also have to take all other power back from other electrical bits. If you got some spare 3mm2 cable run another and join them together. thus giving 6mm2 cable this will make the volt drop alot less. For the size of cable the voltage you are getting at the pump currently is what i'd expect.
07-10-2007, 06:08 AM
#30
Too many posts.. I need a life!!
You need to volt drop it all properly. Test the voltage between the pump negative and a good earth on the body. Volt drop each side of the relay, volt drop everywhere!!!!! Simple checking the voltage between the pump positive and earth is an almost meaningless figure as it wont tell you if, and where you are losing the voltage.
07-10-2007, 07:13 AM
#31
20K+ Super Poster.
I like some of the theories here!!
Cable too small, resistance of copper wire is 0.000999 OHMS per foot@20Celcius.
Group a pump draws max 13amps@12 volts, so cable carrying capacity of 27 amps not big enough!!
For all people use the formula,
R=pL/A.
If you want to go even more overboard use Silver wire as resistance is only 0.000944 Ohms/foot.
I assume you used thinwall wire(?), as 44/030 will carry 27.5amps continuous.
This is 3mm(2) which is almost the same as 12 gauge.
over 30 feet, or 9.1440 metres, at 13 amps and 77F this wire will drop 0.6318 volts.
As you can see this is more than capable of the task in hand, so you have to look elsewhere.
Solder can build a resistance, did you use PURE silver solder, or with ROSIN(flux), or std 60/40 lead tin ?
tabetha
Cable too small, resistance of copper wire is 0.000999 OHMS per foot@20Celcius.
Group a pump draws max 13amps@12 volts, so cable carrying capacity of 27 amps not big enough!!
For all people use the formula,
R=pL/A.
If you want to go even more overboard use Silver wire as resistance is only 0.000944 Ohms/foot.
I assume you used thinwall wire(?), as 44/030 will carry 27.5amps continuous.
This is 3mm(2) which is almost the same as 12 gauge.
over 30 feet, or 9.1440 metres, at 13 amps and 77F this wire will drop 0.6318 volts.
As you can see this is more than capable of the task in hand, so you have to look elsewhere.
Solder can build a resistance, did you use PURE silver solder, or with ROSIN(flux), or std 60/40 lead tin ?
tabetha
07-10-2007, 12:12 PM
#32
Too many posts.. I need a life!!
Join Date: May 2004
Location: in the garage fixing yet another oil leak
Posts: 925
Likes: 0
Received 0 Likes
on
0 Posts
as tabetha says 3mm plenty thick enough. one way forward is to wire a 100watt headlamp bulb in parallel with fuel pump to simulate the current draw at full boost and allow you to establish voltage at the pump under actual road conditions. it will also make it easier to find where the problem is. my money is on tired relay / old connectors
07-10-2007, 03:31 PM
#34
Advanced PassionFord User
iTrader: (1)
Join Date: Dec 2004
Location: Bristol
Posts: 1,660
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by tabetha
I like some of the theories here!!
Cable too small, resistance of copper wire is 0.000999 OHMS per foot@20Celcius.
Group a pump draws max 13amps@12 volts, so cable carrying capacity of 27 amps not big enough!!
For all people use the formula,
R=pL/A.
If you want to go even more overboard use Silver wire as resistance is only 0.000944 Ohms/foot.
I assume you used thinwall wire(?), as 44/030 will carry 27.5amps continuous.
This is 3mm(2) which is almost the same as 12 gauge.
over 30 feet, or 9.1440 metres, at 13 amps and 77F this wire will drop 0.6318 volts.
As you can see this is more than capable of the task in hand, so you have to look elsewhere.
Solder can build a resistance, did you use PURE silver solder, or with ROSIN(flux), or std 60/40 lead tin ?
tabetha
Cable too small, resistance of copper wire is 0.000999 OHMS per foot@20Celcius.
Group a pump draws max 13amps@12 volts, so cable carrying capacity of 27 amps not big enough!!
For all people use the formula,
R=pL/A.
If you want to go even more overboard use Silver wire as resistance is only 0.000944 Ohms/foot.
I assume you used thinwall wire(?), as 44/030 will carry 27.5amps continuous.
This is 3mm(2) which is almost the same as 12 gauge.
over 30 feet, or 9.1440 metres, at 13 amps and 77F this wire will drop 0.6318 volts.
As you can see this is more than capable of the task in hand, so you have to look elsewhere.
Solder can build a resistance, did you use PURE silver solder, or with ROSIN(flux), or std 60/40 lead tin ?
tabetha
do you mean 44/0.30 as 44/.030 will give you 0.0311mm2.
07-10-2007, 04:04 PM
#35
Originally Posted by tabetha
I like some of the theories here!!
Cable too small, resistance of copper wire is 0.000999 OHMS per foot@20Celcius.
Group a pump draws max 13amps@12 volts, so cable carrying capacity of 27 amps not big enough!!
For all people use the formula,
R=pL/A.
If you want to go even more overboard use Silver wire as resistance is only 0.000944 Ohms/foot.
I assume you used thinwall wire(?), as 44/030 will carry 27.5amps continuous.
This is 3mm(2) which is almost the same as 12 gauge.
over 30 feet, or 9.1440 metres, at 13 amps and 77F this wire will drop 0.6318 volts.
As you can see this is more than capable of the task in hand, so you have to look elsewhere.
Solder can build a resistance, did you use PURE silver solder, or with ROSIN(flux), or std 60/40 lead tin ?
tabetha
Cable too small, resistance of copper wire is 0.000999 OHMS per foot@20Celcius.
Group a pump draws max 13amps@12 volts, so cable carrying capacity of 27 amps not big enough!!
For all people use the formula,
R=pL/A.
If you want to go even more overboard use Silver wire as resistance is only 0.000944 Ohms/foot.
I assume you used thinwall wire(?), as 44/030 will carry 27.5amps continuous.
This is 3mm(2) which is almost the same as 12 gauge.
over 30 feet, or 9.1440 metres, at 13 amps and 77F this wire will drop 0.6318 volts.
As you can see this is more than capable of the task in hand, so you have to look elsewhere.
Solder can build a resistance, did you use PURE silver solder, or with ROSIN(flux), or std 60/40 lead tin ?
tabetha
no fella used standard cable
07-10-2007, 04:12 PM
#36
07-10-2007, 05:37 PM
#38
Originally Posted by smidsy
Originally Posted by glennshute
I just drilled a hole in my spare wheel well for the earth and used a nut and bolt.
It's used to earth something else in my boot too!
07-10-2007, 05:45 PM
#39
I'm sure others are wondering this as well....
I'm going to rewire mine over winter...... now how do ya do it with an idiots guide...lol (I'm ok with the earthing bit)
Is it a case of from the battery to the std relay then onto the pump or more complicated than that??
Cheers
Steve
I'm going to rewire mine over winter...... now how do ya do it with an idiots guide...lol (I'm ok with the earthing bit)
Is it a case of from the battery to the std relay then onto the pump or more complicated than that??
Cheers
Steve
