fuel pump tips, warnings, and insight
DJSteve
01-16-2005, 02:59 AM
I just recently bought a 2000 Blazer 4-door 4wd with 118k... great shape, but it had "the" fuel guage issue. So I figured I would bite the bullet and buy a pump, spend an afternoon putting it in, and be on my merry way. Unfortunately it didn't quite work that way.
Warning 1: Everything on these pumps is plastic. Including the nipples the hoses hook to. Said nipples break easily. BE CAREFUL.
The ouput and return lines are easy to get off--just squeeze the clear plastic tabs just past the end of the hose. The center line (vent) uses a different style lock mechanism. Instead of having tabs there's an 0 shaped ring. The lock nubs are on the sides... you need to squeeze the top and bottom so the ring distorts enough to disengage them.
Warning 2: The Carter pump O'Reilly's lists for this application (P74789M) is wrong. The connections and internal pump mechanism are the same, but the locator tab that determines the rotation of the pump (and orientation of the hose connections) is in the wrong place and the lock ring will not fit over the pump. The o-ring gasket which is included with the pump is also incorrect--the original gasket extends down about 3/4".
Of course I found this out at 11pm on a Friday night after dropping the tank. We cut off the tab and machined out the lock ring on my dad's lathe. Everything was going well, I thought.
Tip 1: Make sure the rear tank strap is hooked in the frame before raising the tank all the way up. Hook up the hoses only after both tank straps are installed and the bolts started.
The tank was completely in, the blazer ran fine, and the fuel guage worked. Except I needed to get the rear strap hooked into the frame above the leaf spring mount. The hoses, specifically the return line, are not long enough to allow very much play. As mentioned earlier, plastic nipples are weak. Trying to gain clearance to install the strap may result in a popping sound (as the nipple breaks off) and a lot of cussing.
I took a picture of the original pump, put it back in, and took the Carter back to O'Reilly's. They agreed the broken nipple was a result of a wrong application (got lucky there) and ordered in a Delphi (OEM) based on the numbers from the picture of my pump. It appears to be correct, and only cost $9 more--$307 for Delphi vs. $298 for the (wrong) Carter.
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Insight: What causes the fuel gauge sender to fail?
There are metal fingers on the float arm mechanism which contact a printed circuit board. Fuel level is determined based on where these fingers touch the circuit board. The problem is that the fingers weren't designed to be long enough, and as the float pivot loosens up from wear, the fingers can come away from the board.
The Carter pump had a completely different design which used heavier contacts (similar to distributor points) that were attached to the float arm near the pivot so as to minimze the lever effect that might pull them away.
The Delphi appears to be the same design as before with considerably longer fingers. Hopefully it will do the trick...
Warning 1: Everything on these pumps is plastic. Including the nipples the hoses hook to. Said nipples break easily. BE CAREFUL.
The ouput and return lines are easy to get off--just squeeze the clear plastic tabs just past the end of the hose. The center line (vent) uses a different style lock mechanism. Instead of having tabs there's an 0 shaped ring. The lock nubs are on the sides... you need to squeeze the top and bottom so the ring distorts enough to disengage them.
Warning 2: The Carter pump O'Reilly's lists for this application (P74789M) is wrong. The connections and internal pump mechanism are the same, but the locator tab that determines the rotation of the pump (and orientation of the hose connections) is in the wrong place and the lock ring will not fit over the pump. The o-ring gasket which is included with the pump is also incorrect--the original gasket extends down about 3/4".
Of course I found this out at 11pm on a Friday night after dropping the tank. We cut off the tab and machined out the lock ring on my dad's lathe. Everything was going well, I thought.
Tip 1: Make sure the rear tank strap is hooked in the frame before raising the tank all the way up. Hook up the hoses only after both tank straps are installed and the bolts started.
The tank was completely in, the blazer ran fine, and the fuel guage worked. Except I needed to get the rear strap hooked into the frame above the leaf spring mount. The hoses, specifically the return line, are not long enough to allow very much play. As mentioned earlier, plastic nipples are weak. Trying to gain clearance to install the strap may result in a popping sound (as the nipple breaks off) and a lot of cussing.
I took a picture of the original pump, put it back in, and took the Carter back to O'Reilly's. They agreed the broken nipple was a result of a wrong application (got lucky there) and ordered in a Delphi (OEM) based on the numbers from the picture of my pump. It appears to be correct, and only cost $9 more--$307 for Delphi vs. $298 for the (wrong) Carter.
------------------------------------------------------------------
Insight: What causes the fuel gauge sender to fail?
There are metal fingers on the float arm mechanism which contact a printed circuit board. Fuel level is determined based on where these fingers touch the circuit board. The problem is that the fingers weren't designed to be long enough, and as the float pivot loosens up from wear, the fingers can come away from the board.
The Carter pump had a completely different design which used heavier contacts (similar to distributor points) that were attached to the float arm near the pivot so as to minimze the lever effect that might pull them away.
The Delphi appears to be the same design as before with considerably longer fingers. Hopefully it will do the trick...
ricksza
01-16-2005, 04:28 PM
On some GM vehicles, you can buy the fuel level sensor separately. Check with your dealer. There is a problem with the newer fuels eating the fingers off the old sensors.
97blazermadness
01-17-2005, 12:08 PM
Warning 1: Everything on these pumps is plastic. Including the nipples the hoses hook to. Said nipples break easily. BE CAREFUL.
The ouput and return lines are easy to get off--just squeeze the clear plastic tabs just past the end of the hose. The center line (vent) uses a different style lock mechanism. Instead of having tabs there's an 0 shaped ring. The lock nubs are on the sides... you need to squeeze the top and bottom so the ring distorts enough to disengage them.
I would add that patience goes along way towards dealing with these connectors -- that center line was a bear until I figured out to squeeze the O ring and gently but firmly pull straight back.
The ouput and return lines are easy to get off--just squeeze the clear plastic tabs just past the end of the hose. The center line (vent) uses a different style lock mechanism. Instead of having tabs there's an 0 shaped ring. The lock nubs are on the sides... you need to squeeze the top and bottom so the ring distorts enough to disengage them.
I would add that patience goes along way towards dealing with these connectors -- that center line was a bear until I figured out to squeeze the O ring and gently but firmly pull straight back.
DJSteve
01-17-2005, 12:41 PM
On some GM vehicles, you can buy the fuel level sensor separately. Check with your dealer. There is a problem with the newer fuels eating the fingers off the old sensors.
I had heard that, but also know that these pumps generally don't last forever, and when they die you're SOL if you need to get somewhere. I own a mobile DJ business, so dependability of vehicles is rather important--thus I'd rather replace the whole pump while I have the tank out so I don't have to worry about it.
I am fairly certain the sender problem was due to the metal fingers not being long enough to compensate for the slop in the pivot of the float arm. The contacts did not show any signs of wear or being eaten by the fuel. They looked to be stainless steel... if your fuel will eat stainless you may want to look into a different gas station. The contact fingers on the new pump are also longer, which I think supports my theory.
I had heard that, but also know that these pumps generally don't last forever, and when they die you're SOL if you need to get somewhere. I own a mobile DJ business, so dependability of vehicles is rather important--thus I'd rather replace the whole pump while I have the tank out so I don't have to worry about it.
I am fairly certain the sender problem was due to the metal fingers not being long enough to compensate for the slop in the pivot of the float arm. The contacts did not show any signs of wear or being eaten by the fuel. They looked to be stainless steel... if your fuel will eat stainless you may want to look into a different gas station. The contact fingers on the new pump are also longer, which I think supports my theory.
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