View Full Version : Stump the mechanic/electrician


Z28Roxy
05-06-2012, 11:30 AM
Ok some of you joked when I made a post about getting the fuel pumps / sender arm into the tank correctly without breaking it because I'm just about to throw a fucking match in the gas tank.

Let's see if any of you guys are smart enough to figure this one out...

This is a Lonnie's dual pump kit / including wiring harness too. And yes I will be calling Lonnie on Monday.

I got the pump in the car before but had to take it back out because while the pumps ran (checked both by switching the hobbs switch back and forth), the gas gauge read infinite fuel. I had to mess with the ground and power connection on the sending unit a little. I checked it with my multimeter, everything was fine. 0ish ohms with the arm all the way down 90ish with it all the way up.

I put the whole unit back in the car and check the wiring harness with my multimeter. Like 7 ohms which is about right (tank is low on fuel). Fuel gauge reads totally empty and pump doesn't run. I go check the electrical connections and now the gauge reads accurate but the pump doesn't run. I check the connections AGAIN and get the pump to run but now the gauge reads infinitely full. I check all the fuses and grounds. No blown fuses, no frayed wires, no loose grounds, etc. I can only think maybe the wires are getting tugged (anyone who has that kit knows the connection from the top of the sender to the plug and play wiring kit is short). So I try soldering/extending all the wires. My multimeter still reads everything correctly. But now the gauge reads infinitely full AND the pump doesn't run either.

Any electrical geniuses have any ideas here?

EDIT: Just tried unplugging the wires and plugging back in, pump runs, gauge wrong (infinite full)

CLIFF NOTES:

1. Lonnies dual pump / wiring kit
2. Get pumps and sending unit in tank. Pumps work, gas gauge reads infinite full.
3. Take sending unit out and plug connectors back in. Ohms fine.
4. Put pumps and sending unit back in the tank. Check ohms again. Fuel gauge reads totally empty and pumps don't run.
5. Unplug wires. Ohms read fine again. Plug back in. Fuel gauge now accurate. Pump doesn't run.
6. Unplug wires. Plug back in. Pump runs but gauge reads FULL FULL.
7. Try extending wires. Ohms still fine. Now pump doesn't run and gauge reads FULL FULL still.
8. Checked all grounds (none loose), all fuses (none blown), all wires (none frayed or broken).
9. Tried unplugging wires and plugging back in, pump runs now, gauge still FULL FULL.

gjohnsonws6
05-06-2012, 12:05 PM
Pins/ wires in correct cavities on connector? Ground wire/ sending wires mixed up maybe?

Z28Roxy
05-06-2012, 12:09 PM
Pins/ wires in correct cavities on connector?


Yep and not damaged.

Ground wire/ sending wires mixed up maybe?

Nope.

93 LT1 Vette
05-06-2012, 12:50 PM
Cold solder joints? Try environmental splices/aircraft wiring splices instead of solder for the wire extensions.

guppymech
05-06-2012, 12:56 PM
Make sure the pins and sockets are locked in the connector. If one is pushed back it will look and check good when the connector is disconnected but will not make a solid connection when the connector is reconnected. Also check how tight the male pins fit in the sockets (with a spare pin check the friction on the pin when it's removed from the individual sockets).

Z28Roxy
05-06-2012, 03:34 PM
Cold solder joints? Try environmental splices/aircraft wiring splices instead of solder for the wire extensions.

It's not my splices/soldering since it is essentially behaving the same as before I rewired (now that I got the fuel pump to run again).

I am using these FWIW, I had to google environmental splices.

http://www.fastronixsolutions.com/assets/Terminal%20Products/p400-420.JPG (solder filled connectors).

Z28Roxy
05-06-2012, 11:35 PM
Make sure the pins and sockets are locked in the connector. If one is pushed back it will look and check good when the connector is disconnected but will not make a solid connection when the connector is reconnected. Also check how tight the male pins fit in the sockets (with a spare pin check the friction on the pin when it's removed from the individual sockets).

Now that I look, the pin for the ground on the "harness bracket" that comes out of the rear of the body could be bad.

http://www.jegs.com/InstallationInstructions/100/182/182-102151.pdf

See figure 1. The thing that the fuel pump/sender plugs into. How do I replace that thing though, and part # if so?

guppymech
05-07-2012, 10:14 AM
Looking at the wiring diagrams in the GM Service Manual for my 1994 Trans Am (don't know if your '95 is same or different).
The 'harness bracket' that passes through the body is connector C405B, P/N 12092789 (10-way M metri-pack 150, 280 series)
Cavity A1 is for fuel pump motor feed, gray wire.
Cavity A2 is for fuel gage sensor signal, purple wire.
Cavity A3 is the ground, black wire. The chassis ground for this wire is G305 which is also the ground for the power seats.
G305 is one or two ring terminals bolted to floor pan bar #2 under drivers seat near the rocker panel.

Fuel tank harness connector is C405A, P/N 12092859 (4-way F metri-pack mixed series)
this side of the connector has the same A1,A2,A3 coding.

I will post more info if I find it. I think you should be able to buy individual pins and sockets for the wires that you'd crimp on after unlocking the wire from the connector.

http://order.waytekwire.com/productdetail2/M50/31076/METRI-PACK%20150%20SERIES%20%20MALE/
http://order.waytekwire.com/products2/M50/320/550/400/1/Delphi%20Packard%20Metri%20Pack%20150/Multi-Pin%20Connectors/Terminals%20And%20Connectors/
http://order.waytekwire.com/products2/M50/320/550/450/1/Delphi%20Packard%20Metri%20Pack%20280/Multi-Pin%20Connectors/Terminals%20And%20Connectors/

quik95lt1
05-07-2012, 10:46 AM
yea its a pretty simple setup with the GREY power wire, PURP signal and Black Ground........your issue is screaming ground issue.....if you loose ground the gauge will peg and pumps wont run.....im not sure of the exact design of the gauge system however if it was me heres how I'd do it and heres why i think its a ground problem.....

id ground the middle leg of the potentiometer (gauge piece in tank) and run the other leg to the gauge, send 12v down the gauge wire and using a current monitoring circuit is how i would actuate the gauge based off of the resistance being encountered at the end of the circuit in the tank....being high resistance lowers the current delivery to the gauge and raises the gauge to full, and low resistance increases the current delivery to the gauge and brings it down to E........so.......if you have a bad ground your current delivery is aweful regardless of the position of the potentiometer so you see pegged full at all times....even a poor connection will do it anything over 90 OHMs and your gauge is going to peg......90Ohms is small compared to what a bad connection can cause for resisitance in a low level monitoring circuit like a fuel gauge...........also the lack of ground will make the pump not run........or even if the pump can find enough ground to turn it self on it is probably still feeding through that bad 90OHM+ ground connection lowering the current delivery to the pump and making the fuel gauge have a shit fit......shut the pump off and the load dissappears from the bad ground connection.....the gauge now works because its a very low level signal (id assume <50ma) try jumping the black wire directly to a verified 0OHM chassis ground and i bet you the whole thing works fine......


also FYI id look into those butt conectors......im not sure how those are going to react to being submerged in fuel for long periods of time.........as for that bulkhead i doubt thats ur issue but you can check your voltages and ground on respective sides to make sure......to check the ground send 12 volts to the red multi meter lead and then check tthe ground wire on each side of the bulkhead with the black multi meter lead....you should read the same voltage on both sides as you do if you went across the battery posts with the leads.......

if it makes you feel any better i went through this gauge bullshit when i went to add another pump in my tank i was sucking the walboro 255 dry around 7200rpm......then i saw the little swizzle stick they were trying to pump fuel through, got pissed off threw the old pump and pickup in the garbage and ran an a1000 externally.......best move i ever made lol

Z28Roxy
05-07-2012, 01:00 PM
snip

Thanks!

yea its a pretty simple setup with the GREY power wire, PURP signal and Black Ground........your issue is screaming ground issue.....if you loose ground the gauge will peg and pumps wont run.....im not sure of the exact design of the gauge system however if it was me heres how I'd do it and heres why i think its a ground problem.....


Yeah I'm going to try grounding the black wire directly to my chassis ground (same place I grounded the racetronix).


snip, regarding in tank stuff


No, no no the stuff inside the tank itself is fine. ;) and those solder filled butt connectors aren't in gasoline I used them to extend the harness outside the tank.


if it makes you feel any better i went through this gauge bullshit when i went to add another pump in my tank i was sucking the walboro 255 dry around 7200rpm......then i saw the little swizzle stick they were trying to pump fuel through, got pissed off threw the old pump and pickup in the garbage and ran an a1000 externally.......best move i ever made lol

Believe me I'm close!

WS Sick
05-07-2012, 02:13 PM
Open the glove box and set it in there problem solved.

Z28Roxy
05-08-2012, 12:07 PM
Tried regrounding.

Pump works, gauge still reads full............ :mad: