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Lovely Fuel Pump replacement.....which one?

It's 12V when the plug is disconnected and I'm measuring at the plug pigtail. Once I reconnect the plugs back together, I get 10V when I turn the key on. Is there a pump draw/load that would pull it down 2V?

I would think all the wiring is good from the plug forward to the engine, because I get 12V without a load.
 
jeff in co said:
It's 12V when the plug is disconnected and I'm measuring at the plug pigtail. Once I reconnect the plugs back together, I get 10V when I turn the key on. Is there a pump draw/load that would pull it down 2V?

I would think all the wiring is good from the plug forward to the engine, because I get 12V without a load.
Click to expand...

To clean this up a bit:

When the relay is bypassed (so it's out of the picture) but pump is connected, you get 10V at the pump connector. There is a problem there. The battery should easily be able to run the pump with the engine off and voltage should not drop to 10. Based on wire diameter, connections, and length of the wire you may see a drop in voltage of maybe a few tents (given old factory wiring and connectors), but nothing as to what you are describing.

When you use the relay bypass, and are seeing 10V at the pump plug, what is the voltage at the relay bypass? Your battery would have to be bad (and at 10V) to see 10V at the pump plug under those conditions, because it would have to be ~10V at the bypass unless the wire between those two points is bad.

I'm assuming your ground is good when testing voltage since you see proper voltage under certain conditions. I like alligator clip end "jumper wire(s)" in these cases, so I can clamp the meter to a ground, which frees up a hand, and normally ensures I have a good ground on that probe and can trust the voltage reading.

If the pump is "stalled" I'm guessing it can generate a decent load, but if it were, that would almost certainly generate other issues.
 
Thanks for sticking with me on this!

I'm using alligator clips just as you are saying. Tried the ground on a few locations (including the tank grounding wire), all were solid, repeatable readings. I could place the meter on the floor and turn the key outside so I could see all the readings instantly.

Basically, I get 12V with and without utilizing the relay (pump connector unplugged).

Once I plug the pump connector in and put the alligator clip on the downside of the connectors, I get 10V with and without utilizing the relay.

My battery tested 12V and is an Optima Yellow top in good condition.

I don't know the voltage at the relay....didn't test that. I can do that as a next step, but it's going to be a few days until I can get back to it (heading to Vegas for Volleyball).
 
I would load test the circuit like mentioned before. I use a high beam headlight and a harness I made up. I just go buy a rectangle high beam head light and a pigtail for the back of it. I build a harness with two long leads maybe 5 or 6 feet coming off the headlight plug. I attach an alligator clip to one lead and the other I like to use a spade connection on it and then I can make up different adapters to plug into the spade and go to different size terminals for whatever I'm testing(ecms take real small pins some time, other stuff use round ones). I take the alligator clip lead and hook it to either positive or negative depending on if I'm testing a power or ground circuit and then the other lead goes to the circuit being tested. So like in this case attach the alligator clip side to a good ground since you are testing a power circuit and then insert the other lead using the appropriate adapter lead into the power wire connection at the fuel pump. You could test at key on with the relay in, but that will only be a few seconds, so I would remove the relay and install a jumper between pin 30 and 87 to bypass the relay and just run power through the entire circuit. The headlight should light up nice and bright. If not, then unplug it at the pump connector and check with a meter and then plug it in and if the voltage goes bye-bye then you have a bad connection or wiring causing your circuit to go open under load. Since yours is intermittent it might be tougher to find. You can also do the "wiggle test" while the light is hooked up and move the harness around and see if the light flickers to pinpoint a poor connection. Since your issue seems pretty random I would be leaning towards the relay being the issue if you haven't already replaced it. Or possibly something upstream on the control side like oil pressure switch or ecm, I'm not familiar with this exact system. Oh and just to make sure I didn't miss it, you have verified that the fuel pump not running is the cause of the no-start 100% right? I think I read that when you had the gauge hooked up. I hope this helps some and doesn't just confuse you more. Oh and the purpose of load testing like this to check to make sure your circuit will handle a "load". I have seen a ton of times when a test light or multimeter reads good on a circuit but as soon as I hook up my headlight tester power goes away(or ground). To test a ground circuit you just reverse things a little and hook the alligator clip to B+ and then the spade adapter to the ground circuit and it should light up. To get more adavanced there are ways to use it to test non-power/ground circuits also but I won't confuse you more with that. Good luck.
 
I'm leaning towards the wiring from the relay to the pump connector being the issue. If the battery stays at 12V, you are "losing" voltage somewhere along the line, and way more than should be happening under any normal circumstances.

If your pump was drawing so much that the wiring couldn't handle it (12V at battery, but 10V downstream) the wire would become the fuse, and burn.

It's far more likely that the problem is in the wiring itself, since you can bypass the relay and have the same result. But I'd want to verify that theory by measuring voltage at the relay bypass. I'd eliminate the relay as a variable at this point, since you say you get 10V at the pump with or without using the relay.

My memory stinks, do you have the GM wiring diagram for the truck to work off of (link in my signature)? The circuit isn't really that complex, but it might make you more confident of what you are seeing and where the problem might be if you are looking at the diagram. That relay wire bypasses everything. It is akin to hooking the battery directly up to the fuel pump. Oil pump switch, relay, fusible links, fuses, none of those are in the way when using the bypass.
 
^^^^ I'm now getting and understanding your thought process. I've been checking out some youtube videos and found one that is explaining exactly what I'm experiencing.

12V with plug disconnected, but once connected....that is the true way to test it properly. Wish I could do some more testing tonight but have to be gone for the weekend.

A good example explaining testing:
https://youtu.be/9aioZN33xsA

I finally looked up Roy. All this time I thought you were outside of Spokane. Looks like outside of Tacoma, actually. Man you guys have been hammered in rain/snow this year!
 
jeff in co said:
^^^^ I'm now getting and understanding your thought process. I've been checking out some youtube videos and found one that is explaining exactly what I'm experiencing.

12V with plug disconnected, but once connected....that is the true way to test it properly. Wish I could do some more testing tonight but have to be gone for the weekend.

A good example explaining testing:
https://youtu.be/9aioZN33xsA

I finally looked up Roy. All this time I thought you were outside of Spokane. Looks like outside of Tacoma, actually. Man you guys have been hammered in rain/snow this year!
Click to expand...

Heck, if you really wanted to test it, and have a bunch of spare wire (or spare battery), run a wire from the battery directly to the fuel pump connector. Since the problem is somewhat intermittent it may not prove anything, but you'd know 12V is getting to the pump, as close to it as possible.
 
I'm in the middle of Spring Gobbler Season, so my brain is fairly clouded. Normally I try to stay out of the more interesting stuff during this time because I often make a fool of myself.
However, I think I can help here.
I try to avoid blanket statements, but this time its called for.
The 10 volts is the problem. The pump will run on 10 volts, but there is no possible situation where you should be getting that reading if everything is good.
Assuming the ground you are using is good, then the problem you have is between where ever you are measuring the 10 volts and the positive terminal of the battery.
Bad wire, connection, partially blown fuse, somewhere you have a bad connection. But, before you start looking, you need to do one other thing. Troubleshooting stuff like this has certain rules to follow to make it easier.
One of the most important, is to reduce or eliminate the variables. Right now you have two. Which will cause enormous problems with tracking down the problem.
Get a piece of good wire, 12ga or larger. Connect it to the negative side of the battery, after you have removed and cleaned the terminal. Use that for a ground to hook your meter to.
If you still have the 10 volts, then its the connection between there and the positive post of the battery.

Just keep that load on, and keep moving toward the battery checking voltages until you get full battery voltage instead of the 10. When you do, the problem is between that point and the last point you got the 10.
 
Awesome, thanks all! Wish I could troubleshoot now but in Vegas all weekend watching volleyball. I'll hit it first part of next week.

A lot of great ideas that should help pinpoint problem!
 
OK, found one problem. Saw some tape around the electrical connector at the pump connection and it looked a little non-factory work....unwrapped tape and found this. Looks like PO clipped the wires and then soldered the very short pigtails.

Have not been able to follow the path or test some more (maybe tonight or tomorrow night), but this is certainly a start!

I've looked around and can't seem to find any replacement connector with pigtail ends. Asked Spectra Pumps, they said they don't make them.

So I could try to redo the existing connector and get rid of the solder joint, or redo the solder joint.

Ideas or is there a fix replacement connector??

IMG_20170405_173534417.jpg
 
Iupload_2017-4-10_10-51-53.png
Is that a 2 pin weatherpack like this? I have always just crimped on new terminals and seals and done it that way but you gotta have the crimper and know what you are doing to get them on correctly. If you search a little on the internet Dorman sells a pigtail if it is a weatherpack.
 
Weatherpacks are easy to make, but without the crimp tool they don't turn out real well.

You almost never need the housing, just the terminals and seals since those are one time use, but the terminals and seals plus the tool will probably run you $50 or so.

If you have no plans to use weatherpack elsewhere, makes little sense to get the equipment to make them.

However, I've gotten to the point that I prefer to run new connectors versus splicing when I can help it, just to minimize potential issues. When you damage the insulation (sticking voltmeter probes through it, splicing, etc) you end up creating the potential for tarnishing, corrosion, and weakening of the wire. Weatherpacks are pretty versatile if you deal with other 12V stuff, although there are smaller designs of connectors out there (even from Delphi), if current isn't that much of an issue.
 
I see two options from Delphi, 12 Gauge and 14/16 Gauge....but see some complain that the 12 Gauge is nowhere near capable of handling an actual 12 Gauge wire. Thinking about getting both sizes and see what they look like. I also prefer a nice, clean connection if possible. Soldering at a minimum on critical pieces.

So my standard solderless crimping tool is different than this special one?
 
If you are thinking of buying the terminals, they are so cheap I'd just buy some of each. I don't recall having any issues cramming whatever wire I wanted in there lol.

IIRC the weatherpack requires an "O" crimp (for the seal) and then one that bends the lock tangs for the wire folds them over.

Lets see if this link works:



This is the tool I have:

450_T-18-Crimping-Nests-WP.jpg


Don't forget, you need the depinning tool as well, they are cheap.
 
Great, thanks! Got some off of Amazon, $39 total for two different sizes of connectors (Delphi brand), the plyers and removal too. Be here Wednesday.

6128dWuK4UL._SL1500_.jpg
 
Replace connector ends with new ones, backprobed the connector with the pump connected....now getting 11.5 - 11.7V at key turn on, 13.5V after it starts and runs. Defininitely was losing something with those solder connections.

I also traced the wire up front and everything looks good and solid. So hopefully, that connector was the problem! Fingers crossed!

Truck now starts and runs.....

Thanks all!
 
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