Recommendation, test fuel pump pressure under the truck. Either at the filter, or forward where the flex line is connected to the frame. The lines at the TBI should be bolted to the block, and don't want to "give" much to get a fitting in there.
CK5
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Lovely Fuel Pump replacement.....which one?
- Thread starter jeff in co
- Start date
Recommendation, test fuel pump pressure under the truck. Either at the filter, or forward where the flex line is connected to the frame. The lines at the TBI should be bolted to the block, and don't want to "give" much to get a fitting in there.
Ok, dropped in the tee just after the fuel filter....Great location thanks!
Truck decided to start after sitting for a few days.
At key on, pressure was 12 psi. After running, remained at 12 psi. Isn't 14 the minimum??
Truck decided to start after sitting for a few days.
At key on, pressure was 12 psi. After running, remained at 12 psi. Isn't 14 the minimum??
No, GM says minimum is 9PSI. Their spec for the range IIRC is 9-13, but many indicate you'll start to notice a difference around 9-10PSI. I played around with the stock parts on my Dads TBI truck, 14 was as high as I could get the stock pump to push.
If you can leave it on with no chance of fire, I'd do so just to confirm when it won't start you have pressure, but I'd have a noid light with me. Without an intermittent connection somewhere, the pump isn't going to be randomly stopping and starting.
If you can leave it on with no chance of fire, I'd do so just to confirm when it won't start you have pressure, but I'd have a noid light with me. Without an intermittent connection somewhere, the pump isn't going to be randomly stopping and starting.
Great, I can leave the tee in with no leaks so I'm good to go until it happens again. I'm just going to have to be a bit more strategic where I drive it. Hate to be stranded somewhere and have to call my wife. If something happens she always refers to the truck as the "$14,000 - $3,500 Blazer!"
It's been very reliable up to this point where I decided to do some "preventative maintenance"....
I also put on some new yellow stuff pads. Brakes way better! But getting a bit of squeaking. Hopefully that will go away once broken in.
It's been very reliable up to this point where I decided to do some "preventative maintenance"....
I also put on some new yellow stuff pads. Brakes way better! But getting a bit of squeaking. Hopefully that will go away once broken in.
some of those performance pads are noisier, that's one of the downsides of running them.
^^ Kinda hard to test when the vehicle isn't moving lately! 
I hope they will break in a little. It's probably twice the stopping power as the O'Reilly ones. But, after taking the rotors in to get a light turn, they decided the rotors were defective so they gave me new ones under warranty. Also, because the bearings and seals were in there, they gave me new ones for free too! All I had to do is buy new grease!
I hope they will break in a little. It's probably twice the stopping power as the O'Reilly ones. But, after taking the rotors in to get a light turn, they decided the rotors were defective so they gave me new ones under warranty. Also, because the bearings and seals were in there, they gave me new ones for free too! All I had to do is buy new grease!
Took another look at tank area and noticed that there was some leaking gas. Not sure where but I figured either the new hoses weren't all the way sealed or maybe the tank gasket seal.
I dropped the tank and put on new hose clamps (doubled the filler hose) and used the other rubber seal I got with the tank. Put it all back in and so far, no leaks....
Time will tell.....
I dropped the tank and put on new hose clamps (doubled the filler hose) and used the other rubber seal I got with the tank. Put it all back in and so far, no leaks....
Time will tell.....
Drove around for 2 days, all good and no leaks. Stopped last night and put in 1/2 tank of gas and drove home. Come out this morning and smell gas and see drips at bottom of tank. 
But it did start and run.
The filler neck is double clamped on each end, vent is clamped, pressure valve is clamped....I don't know.
Maybe a leak at the seam of the tank?!@? Only present if over half full??!?
Fighting me hard.
But it did start and run.The filler neck is double clamped on each end, vent is clamped, pressure valve is clamped....I don't know.
Maybe a leak at the seam of the tank?!@? Only present if over half full??!?
Fighting me hard.
with the symptoms at full tank it leads me to believe it's the pump seal (O-Ring). Also take a close look at the filler neck weld where it meets the tank.
OK, after feeling around the top of tank and it being dry, I started looking at the tank seam. It does look like it was leaking right out of the seam....almost a pin hole. As soon as the tank dropped below 1/2 tank, no more leaking.
So I got a replacement tank. Double and triple checked everything. One more thing I noticed, the fuel neck filler hose was too large (1-7/8). That could of also contributed so I went to Napa this time and got the correct size 1-3/4. Interesting how much better it fit!
Anyways, hopefully this is the solution for the leak. Not starting, well that's still a mystery but maybe I'm lucky with the leaks contributing. Fingers crossed.
Filled the tank past 1/2 and drove it home. No leak yet!
So I got a replacement tank. Double and triple checked everything. One more thing I noticed, the fuel neck filler hose was too large (1-7/8). That could of also contributed so I went to Napa this time and got the correct size 1-3/4. Interesting how much better it fit!
Anyways, hopefully this is the solution for the leak. Not starting, well that's still a mystery but maybe I'm lucky with the leaks contributing. Fingers crossed.
Filled the tank past 1/2 and drove it home. No leak yet!
Truck won't start
So good news first, no gas leaks from tank or hoses or pump o-ring. Added gas so it's now 2/3 full.....still no leak so that is a success.
Drove some more and sure enough, come out the next morning and just cranks.
Tested fuel pressure, zero. Even during cranking cycle. So I used my multi meter and it seemed to show around 5V. A little hard to tell the actual number. But I did hear a click sound up front after about 2 seconds with key on, and then the voltage dropped to zero. Thinking maybe the relay wasn't putting out enough, I picked up a new AC Delco Relay at the GM dealer, $20.
Replaced it and still no start, just cranks and cranks.
I did check the ground again, very tight. I unscrewed and tightened back again. No help.
Am I now looking at a bad fuel pump?
So good news first, no gas leaks from tank or hoses or pump o-ring. Added gas so it's now 2/3 full.....still no leak so that is a success.
Drove some more and sure enough, come out the next morning and just cranks.
Tested fuel pressure, zero. Even during cranking cycle. So I used my multi meter and it seemed to show around 5V. A little hard to tell the actual number. But I did hear a click sound up front after about 2 seconds with key on, and then the voltage dropped to zero. Thinking maybe the relay wasn't putting out enough, I picked up a new AC Delco Relay at the GM dealer, $20.
Replaced it and still no start, just cranks and cranks.
I did check the ground again, very tight. I unscrewed and tightened back again. No help.
Am I now looking at a bad fuel pump?
454Sub
5/8 ton status
Two ways to tell. See if your getting 12v at the pump connector. Test your ground next from the bolt head the strap is on to the pump connector. If that checks out pump is dead.
I still think its a bad wire from the fuse box to the pump...or something else in the fuel pump wiring like maybe the oil sender unit not letting power get to the pump at times..
OK, just ordered a new Bosch fuel pump from local Napa. I'll head home tonight and check the voltage at the plug again. If I get 12V, I'll then check the ground wire.
If not, I'll try jumping the pigtail to the 12V on battery terminal and test at plug again.
If I don't get 12V at the plug, I'll try looking upstream for any wire issues.
If I get 12V, I'll drop the tank and pull the whole thing out again (4th time now). Test pump and plug once out of the tank to verify it not working.
Finally, install new pump if all else fails. If I have to return the bosch pump, no biggie but want it in hand just in case.
Lots of research on AC Delco, Delphi and Bosch. A lot of folks point to Delphi but that's what I have now....so reluctant. Delco seems to be hit and miss and most made in China now. Decent reviews on Bosch.
If not, I'll try jumping the pigtail to the 12V on battery terminal and test at plug again.
If I don't get 12V at the plug, I'll try looking upstream for any wire issues.
If I get 12V, I'll drop the tank and pull the whole thing out again (4th time now). Test pump and plug once out of the tank to verify it not working.
Finally, install new pump if all else fails. If I have to return the bosch pump, no biggie but want it in hand just in case.
Lots of research on AC Delco, Delphi and Bosch. A lot of folks point to Delphi but that's what I have now....so reluctant. Delco seems to be hit and miss and most made in China now. Decent reviews on Bosch.
Remember you need something that'll put a good load on that power wire,like a headlamp bulb or even something like a blower motor,and leave it on several minutes--it may take awhile for any bad spot in the wire to heat up,and break the connection...
Using a test light or volt meter won't put enough load on the wire to make an accurate diagnosis..
Using a test light or volt meter won't put enough load on the wire to make an accurate diagnosis..
You aren't going to get 12V at the pump connector unless the engine is cranking or you measure IMMEDIATELY when the key is turned to run. The prime is only on for ~4 seconds, then it will go to nothing/near nothing voltage-wise.
Run 12V to the pigtail on the relay. Let it run as long as you want. That eliminates the pump and wiring as the problem. If it doesn't work in the morning, then I doubt it's a wiring issue. Should be the other way around, cold it would work, hot it would not.
rampage
3/4 ton status
Gray wire is power to the pump. Purple wire is the sending unit. Ground is any bare metal on the tank itself (I wouldn't use the ground that you have just in case its flakey).
Thanks Dyeager. Yea, I do know I only have a few seconds before it shuts the power off.....remember watching my pressure gauge go on, and then off (when it was working).
Still not working either. Morning or evening (engine cold). Wife and girl are going to a concert in Denver tonight so I'll be able to check it out better tonight after work without interruption.
Just LOVE the fact I was trying to do preventative maintenance on something that was working perfectly fine....now it's unreliable with new parts.
Thanks all for helping out....here is what I found.
Unplug connector and hook it up to the multi-meter. With key on, I get 12V for a few seconds, and then drops to zero (normal). Moving the ground from frame to pump ground, 12V. So that's all good.
So decide to jumper relay wire, I also get 12V (bypass relay). So that's good.
Reconnect pump connector. Try starting and no good. Check voltage at key on, get 10V now.
Jumper relay wire to battery, nothing. I don't hear the pump and it won't start, but get voltage (10V). Disconnect battery, try it again....thought I heard something. Disconnected and back again, I hear the pump running. So try to start truck and it starts and runs. With truck running, voltage goes to 14V.
Turn truck off, disconnect battery relay bypass wire. Try starting and hear pump again, truck starts up. Did it 3 more times and truck now starts just fine.
So, it seems the pump got a jolt of power from the relay bypass and woke it up. Does this mean still, weak/bad pump?
Note, I replaced the entire assembly. Delphi sending unit and pump all in one. If I replace just the pump, is there still a possibility the sending unit is causing or contributing??
Unplug connector and hook it up to the multi-meter. With key on, I get 12V for a few seconds, and then drops to zero (normal). Moving the ground from frame to pump ground, 12V. So that's all good.
So decide to jumper relay wire, I also get 12V (bypass relay). So that's good.
Reconnect pump connector. Try starting and no good. Check voltage at key on, get 10V now.
Jumper relay wire to battery, nothing. I don't hear the pump and it won't start, but get voltage (10V). Disconnect battery, try it again....thought I heard something. Disconnected and back again, I hear the pump running. So try to start truck and it starts and runs. With truck running, voltage goes to 14V.
Turn truck off, disconnect battery relay bypass wire. Try starting and hear pump again, truck starts up. Did it 3 more times and truck now starts just fine.
So, it seems the pump got a jolt of power from the relay bypass and woke it up. Does this mean still, weak/bad pump?
Note, I replaced the entire assembly. Delphi sending unit and pump all in one. If I replace just the pump, is there still a possibility the sending unit is causing or contributing??
Where are you measuring 10V? Nowhere in the system should there be 10V, I doubt even cranking it gets that low. Bad connections (corroded, poor contact, etc) will cause a loss of voltage.
I would speculate that it should run even on 10V, but starting may be a problem, especially depending what component(s) see 10V.
Sending unit will have nothing to do with the problem if the hose on it inside the tank is assembled right (would never run properly with an issue there) and the wiring/connections are good through it.
Until I hear more, that 10V is what I'm suspicious of.
