14.2 volts possible.......

[5.7 hemi]

Having a tough time getting 14.2-14.5 volts on my dads 70' Challenger. All factory wiring, dual field alt., and no ballast due to the FAST EFI set up. Still has the ammeter, it's working, but he has 11 volts at the coil, 14.3 at the alt., and the fuel pump has 11.2 volts.

He replaced the VR as volts were jumping from 10-11.7, and now has a steady 14.2 volts. I'm not much help to him with this, but I did recommend the ammeter bypass, but not sure if that will help get full voltage to the fuel pump.

I'm in need of some help, DESPERATELY!

 

[jenkins71]

Why not run a big *** wire from the Alt straight to the fuel pump? Then put a relay in to control it.
Plenty of people run a wire straight from the Alt to the battery post on the starter relay.

 

[5.7 hemi]

I'm not quite sure that is the answer to his problem. The FAST has a relay already for the fuel pump, so I need to figure out why/where the voltage drop is occurring.

 

[Hemi Rebel]

Focus on the fuel pump circuit. You have 14.3 at the alt and 11.2 at the pump. Start measuring back from there. What does it have on that circuit at the relay? Then coming into the relay. Just keep measuring back at each connection till you get to the source

 

[dpstark2]

If your alternator is putting out 14.3V but your fuel pump is only seeing 11V, then you have a wiring problem somewhere. You need to do an extensive voltage drop test, not only on the positive side but also the negative. Without seeing a wiring diagram of how the car has been updated for the fuel pump, ballast eliminated, etc., it's hard to give specific advice. In general, you'll need to check for a voltage drop from your battery to the positive supply of the fuel pump, then trace that circuit back to the battery. You should have near 0V of drop (i.e., full voltage to the pump), which you do not have now. Once you see that the voltage drop goes from the 3V you are currently seeing to near 0V, you will have found where your wiring has high resistance.

Two more points regarding EFI and wiring. You mention an ammeter bypass, so I assume that hasn't been done. If you are running your fuel pump in addition to stock wiring through the ammeter, that is almost certainly accounting for some of your voltage drop. If your coil is seeing 11V, that further concerns me that your ammeter, it's wiring, and the bulkhead connector are soaking up a lot of voltage. Second, you must absolutely make sure your grounds are good. If you measure 11.2V at your fuel pump, which is grounded to the frame at the back of the car, you can't tell if you're getting 3V drop across the connection from the fuel pump ground to the battery, or at the positive side of the fuel pump. Ideally, everything should be grounded to one reference point. I know this is usually not possible, so you have to make sure you have a good battery to engine, battery to frame, and frame to fuel pump ground. Also, that your computer and sensors all reference the same ground.

Good luck, and please let us know what you find.

 

[Pops1967GTX]

informative video on voltage drop

[video=youtube;XhRPLgH6uZg]https://www.youtube.com/watch?v=XhRPLgH6uZg[/video]

http://www.classicwinnebagos.com/forum/index.php?topic=3424.0

http://www.mopar1.us/charge.html



From my testing manual
Feed Circuit Test - Voltage Drop Test


The starter feed circuit test (voltage drop method) will determine if there is excessive resistance in high-amperage feed circuit. For complete starter wiring circuit diagrams, refer Wiring Diagrams. When performing these tests, it is important to remember that voltage drop is giving an indication of resistance between two points at which voltmeter Example: When testing resistance of battery positive cable, touch voltmeter leads to battery positive cable clamp and cable connector at starter solenoid. If you probe battery positive terminal post and cable connector at starter solenoid, you are reading combined voltage drop in battery positive cable clamp-to terminal post connection and battery positive cable. The following operation will require a voltmeter accurate to 1/10 (0.10) volt. Before performing tests, be certain that following procedures are accomplished:

Battery is fully-charged and load-tested.
Fully engage parking brake.
If equipped with manual transmission, place gearshift selector lever in Neutral position and block clutch pedal in fully depressed position. If equipped with automatic transmission, place gearshift selector lever in Park position.
Verify that all lamps and accessories are turned off.
To prevent a gasoline engine from starting, remove Fuel Pump Relay.

1. Connect positive lead of voltmeter to
battery negative terminal post. Connect negative lead of voltmeter to battery negative cable clamp (Fig. 2). Rotate and hold ignition switch in Start position. Observe voltmeter. If voltage is detected, correct poor contact between cable clamp and terminal post.
2. Connect positive lead of voltmeter to battery positive terminal post. Connect negative lead of voltmeter to battery positive cable clamp. Rotate and hold ignition switch in Start position. Observe voltmeter. If voltage is detected, correct poor contact between cable clamp and terminal post.
3. Connect voltmeter to measure between battery positive terminal post and starter solenoid battery terminal stud Rotate and hold ignition switch in Start position. Observe voltmeter. If reading is above 0.2 volt, clean and tighten battery cable connection at solenoid. Repeat test. If reading is still above 0.2 volt, replace faulty battery positive cable.
4. Connect voltmeter to measure between battery negative terminal post and a good clean ground on engine block Rotate and hold ignition switch in Start position. Observe voltmeter. If reading is above 0.2 volt, clean and tighten battery negative cable attachment on engine block. Repeat test. If reading is still above 0.2 volt, replace faulty battery negative cable.
5. Connect positive lead of voltmeter to starter housing. Connect negative lead of voltmeter to battery negative terminal post. Rotate and hold ignition switch in Start position. Observe voltmeter. If reading is above 0.2 volt, correct poor starter to engine block ground contact.

 

[5.7 hemi]

Fella's, thanks for the info. I'll pass it along to my dad so we/he can start looking for the drop. The ammeter bypass is gonna get done first thing.

Thanks again!!!