New fuel pump
 

Hello.
Really need help now.
Replaced fuel pump now for the third time, but the new one will not start, get power right up to the pump for a few seconds as it should, but there is no life in the pump.
Tried to connect power directly to the pump we just took out and it worked.
What can it be then?
It's a 1999 4.3 liter.
And we bought ACDelco to be on the safe side.

So you have power at the pump connector but the pump does not run?

George

Hello George

Yes, have 12.4 volts at the plug and then I measure both ground and positive in the plug. What is strange is that the old pump worked when we connected it straight to power after we had taken it out, but since we have heard so much negative about parts that are not ACDelco we chose to replace the old one anyway.
Per

Did you solder the new connector and how are you checking ground?

George

The new plug was already mounted earlier in the workshop when they replaced the first pump.
I only checked that it is ground and positive in the connector and there I got over 12 volts out on the multimeter.
Have read that there are some problems with splice pack 423, but tomorrow I will try to connect the old pump directly to the connector to see if it works the way it did when I connected it to the battery.

Per

You have to make sure that you have a good clean ground to the frame and no wiring issues. Both 12V and ground must remain in good shape under a load. Corroded or poor connections can read OK as open but fail under maximum current draw. Check the resistance from the ground at the pump to a clean spot on the frame. Then measure the net voltage across the ground and power as close to the pump as possible under a load.

George

Today I tried to connect the old pump straight to the connector, but it didn't work. Checked again right on the battery and then it worked.
Cut off the 2 wires grounded in point G402 and made a new grounding point and also mounted a new cable straight to the ground of the pump, but still dead.
Have to use the multimeter to search further or add a new positive to the pump from the fuse box.
Could there be something wrong with splice pack 423?

Per

The pump is only energized by the fuel pump relay control signal for a few seconds when you first turn the ignition key on. For constant power on that fuel pump power line use the prime connector at the fuse block and verify voltage at the pump connector. Once you have proven constant power at the pump connector supply a good ground to the pump with a jumper wire to the frame. I see that ground splice pack now so the ground is not just a straight shot to the frame. Did you measure continuity from the pump ground to the frame to see if there is a ground wiring/splice issue?

George

We have equal 12 volts both on the prime connector in the fuse box and on the plug of the pump as it should be for about two seconds when we turn on the ignition.
I also took a wire straight from the battery to the ground point on the frame without making any difference.
That's why I'm thinking about adding new wires from the engine compartment and back to the pump.
The fuel gauge works the way it should .

Your truck does not have G402 for the pump, that looks like a full size pick up thing. Assuming Blazer, your pump ground goes through S423 first then on to the frame at G416. What I dont understand is the wiring diagram shows S422/423 by the dash and G416 at the left rear frame which means the ground makes a long round trip. The labels might be wrong. For the S10 the ground is a straight shot to the frame at G416.

George

So you verify 12V at the pump for 2 seconds at KOEO? Is that with or without the pump connected? Where are you placing the negative probe?

Have you checked continuity from the pump ground to the frame or battery ground?

The best test is the pump connected and measuring net voltage from pump wire hot to pump wire ground at the pump with power applied. During this period of full load and high current any poor connections will cause a large voltage drop and reduce net voltage. If this is the case then we find the poor connection and correct. This assumes that the ground is active at the pump to start with.

George

We have 12 volts for two seconds with KOEO both with and without the pump being connected.

We have placed the negative in the connector when we have measured the current in the connector.

Haven't checked continuity yet, but that's what I'll do next.

Now I stand without a helper to turn on and off the ignition so I have to wait for him to return.
I'll be back with updates as soon as I get help again this weekend

Thanks for the help so far George!

Per

So you measure 12V at the pump, using the ground at the pump which verifies an active ground all the way back to the frame and 12V at the pump all the way from the fuse box? Have you done the same measurement with the other pump (at the fuel tank location) that verifies good at the battery?

George

Finally we got it to start again.

I do not know what has been the fault, because I installed a new ground wire, but it did not start then and I measured the continuity both on the ground cable between the frame and the pump and from the fuse box and until the pump was both good.

But, today it started suddenly after some attempts :)

Thank you very much George for all the help :)

Per

Glad you got it running.

George

Update on this.
The car went well at first, but the next day it refused to start again.

So today we have installed new wires both to the rear grounding point on the frame and new positive to the fuel pump, both laid from the engine compartment to be safe.

So then it finally started again so now it's just to cross our fingers and hope it will be fine.

Suspects that it might be broken somewhere in the old wiring harness or where they soldered the new type of contact for the gasoline pump.

Hi again George.

Since you seemed so well versed in this, I hope I can ask you again and maybe get some new ideas for solution :)

Back to start again, went well all day, started all the time with no problem, so yesterday when we were going to start it was just dead again.

Checked how many amps it pulls on the course, and it dipped 0.9 when we sat on the ignition and went down to 0.7 after about 2 seconds and stood on this until we turned off the ignition.
Removed the relay and at point 30 we had 12.6 volts and good ground at point 86.

Between points 30 and 85, 0.46 volts and between 30 and 87, 12.6 volts ie we had ground at point 87?

Put the relay back in and measured the voltage at the prime point and had 12.6 volts for about 2 seconds which is normal.

And the cables are new all the way from the engine compartment now so they are fine.

Per

The absolute best way to approach this is to first understand how much net voltage the pump is seeing during the initial key on period. Every element in the circuit has resistance and when the pump current passes through this resistance, there is a voltage drop across that resistance (voltage = current x resistance or V=IR). This is true for the portion between the battery and the pump and it is also true for the portion from the pump to ground. Any voltage drop on either side of the pump, reduces the voltage seen by the pump and hence reduces available wattage or power (current x voltage) because the net voltage is lower to the pump. The hardest part to understand is the ground side. If there is excessive resistance between the pump and ground then there is an excessive voltage drop across that resistance and the ground is "lifted" as seen by the pump. Lets say that there is a corroded connector or poor frame contact and the resistance is 4 ohms. If the pump draws 2 amps the the voltage across that resistance on the ground wire is V = IR or 4 ohms x 2 amps = 8 volts. Even if the positive side of the pump sees an ideal 12.6V, the pump only sees 4.6 net volts - the pump is part of a resistor divider network. Normally all of the resistance elements in the circuit are small and the wires are sized properly so that the net voltage to the pump is only slightly lower than battery voltage. The reason why you need to measure this during maximum load is because thats the only time that you will see all of these voltage drops since thats when current is at its peak. You can measure 12.6V with no load and an insufficient net voltage level at load. I use meter probes that are needles on the ends and pierce the wire insulation as close to the pump as I can get on both the positive and negative wires, getting into the wires as they enter the tank if possible to also measure the voltage drops through the connectors. Once we know that answer then we go from there. Since you ran new wires then consider this exercise checking your work.

In addition, if you have a DC clamp meter then also measure the current flowing during key on anywhere on the positive wire from the fuse box to the pump.

George

https://cimg3.ibsrv.net/gimg/blazerf...b03e9b76b9.jpg

Hello again.

Haven't had a look at it until today because it's been around 95F in the sun where the car is standing.

Beginning to wonder if the new pump is not working properly?

I got minus 12.3 volts in positive wire to the pump and when I unplugged the pump the ground fault disappeared and when I reconnected the pump the pump started right away but then the ground fault came back so the car did not start.

Both positive and negative wires are new all the way. So then only the wiring for the tank gauge that is old remains.

Per

What do you mean when you say ground fault?

It is literally not possible to have a negative voltage with reference to the trucks ground. Where are the meter leads (and what color) when you measure -12.3V?

Be careful because bad wiring can burn up a new pump. When the voltage to a new pump is too low, the pump overheats and can fail prematurely. On the flip side, these pumps are notorious for a high failure rate in all but a few brands such as AC Delco.

George

https://cimg9.ibsrv.net/gimg/blazerf...5c5c18fbd8.jpg
I have installed a new red color from the gray coming out of the fuse box and connected to the gray on the new pump connector as shown in the diagram that comes with the pump.

Furthermore, I have installed a new cable from the grounding point in the engine compartment and back to the grounding point on the frame, from this point I have added a new grounding cable to the pump connector.

When I measured the volt on the red wire that will provide power for about 2 seconds at the fuse box, I got 12.3 volts between this and positive on the battery, which should not be possible.

This changed when I unplugged the pump, because then I got 12.3 volts as normal for about 2 seconds.

So that's why I wonder if it might be the pump that has broken? It's an ACDelco.

Per

The entire truck frame is the ground for the entire system. As long as the main ground back at the engine compartment is clean ans solid then your frame is an exellent contact point for any ground. You need to remove that ground wire back to the engine compartment from the frame near the pump.

Why did you add a new ground wire from the pump to the frame? Did you remove the original ground wire from the pump to the frame?

You measured 12V between the battery positive and what red wire, located where?

George

The reason I laid a new ground wire was to make sure there is good ground all the way.

I added a new ground wire to the pump to be safe, and I removed the old ground wire.

I measured 12 volts between the battery and the feed wire coming out of the fuse box, it's originally gray but since I didn't have a gray wire I used a red instead.

I was out and measuring again now to be safe and then I measured between the prime connector in the fuse box and positive on the battery and had over 12 volts there when the ignition was off?

When we switched on the ignition it went down to 0 volts and then up to almost 10 volts for about 2 seconds and then back to over 12 volts when we turned the ignition off.

Per

Measuring voltage from the prime connector to the battery positive has no purpose. With the truck off that connector is connected through the pump motor windings to ground. The resistance from that connector to ground may be of value if a failed pump is suspected but that would be better checked at the pump.

Disconnect the new long ground wire from the rear frame to the front of the truck.

Make sure that your new ground wire from the pump to the frame is solid and has a clean connection to the frame.

Make sure that the old power wire from the relay box to the pump is disconnected.

Since your taking voltage measurements at the relay box, lets start there instead of at the pump where I suggested in post #18. We may end up back there later. Positive meter lead on the fuel pump prime connector and negative lead on the battery negative. What is the voltage during KOEO during the initial prime sequence?

George

Then I disconnect the new long ground wire as you suggest and measure continuity to make sure the grounding is good in the frame.

The old power wire is completely disconnected.

As I wrote above, it only went up to almost 10 volts at KOEO.

But I will measure again tomorrow after removing the long ground wire.

Per

You need to measure between the prime connector and the battery negative not the battery positive.

George

Disconnected the new ground wire, and the ground point on the back of the frame works properly.

KOEO - 12.3 volts in about 2 sec, but when we switch off the ignition it goes up again to 12.3 volts in about 2 sec

Only gets power at the primary connector, not the power wire that goes to the pump.

Measured between the postive on the battery and the power wire to the pump and then received 12.3 volts which should not be possible.

To be on the safe side and that the problem should not be in the fuse box, I dismantled the new power wire to the pump so that it is only connected to the pump, then still get 12.3 volts negative on this wire.

Per

How did you verify that the frame ground at the back of the truck works properly?

why do you keep measuring the voltage between the battery positive terminal and the power wire to the pump? This measurement has no purpose. As I said before, there are no negative voltages in your truck, only a negative reading on a meter if you reverse the meter wires. In this case the power wire for the pump is grounded through the motor windings of the pump with the truck off so it acts like a crappy ground with resistors and an inductor in the circuit. All measurements are with the black meter wire on the battery negative or a good clean frame contact point and the positive lead is on the positive voltage that you are trying to measure.

the pump priming terminal should be connected directly to the pump power wire. Why do you think that they are not connected?

you made sure that the new power wire is only connected to the pump. Where else was it connected?

once we straighten out how to measure voltages properly and what’s going on with these mew wires, we really need to get to the back of the truck and measure the voltages directly at the pump as I suggested many posts ago. I’ll hang in here for another couple of rounds but if you want my help I need you to follow my instructions. I want to help you fix your truck but You need to help me help you.

George

I measured continuity between the battery negative and the grounding point on the back of the frame and it was good.

I get 0 volts between negative on the battery and power wire to the pump at KOEO, only as I wrote over here 12.3 at the prime connector.

I use red on positive and black on negative, and if you change, you get the minus sign on the multimeter so it works properly.

The new power wire goes straight to the pump and is in the hose all the way so it is not near ground.

So that's why I think it's like you say, "In this case, the power wire for the pump is grounded through the motor windings of the pump with the truck off so it acts like a crappy ground with resistors and an inductor in the circuit" .

I get 0 volts at the back of the pump when it is connected, if I remove the connector then I get 12.3 volts between the rear grounding point and the power wire.

Per

See above. We need the test requested in post #18 to make any further progress.

George

Have taken out the pump and that was where the fault lay, short-circuiting between ground and positive.

Brand new AC Delco pump so I was promised a new one from the supplier.

Again, thank you George for your patience and help.

Per

Glad to help and glad it's fixed. Please perform the voltage test in post #18 to make sure that the new pump is getting strong net voltage so that the new one lasts for 100k miles

George

I'll do that test and I'll check all the wiring and connections before I put the tank back in.

Thanks
Per

Update on this.

Got a new pump in place and then it started right away and has since started every time, the only thing now is that the engine occasionally dies when we drive, but immediately starts again without any problem.
Don`t get any codes, so I'm not sure what that might be.

Has some problem with cylinder 4 misfire when idling, but it disappears when the revs go up, and we notice nothing else on the engine in terms of power and speed.

Per