More fuel pump information. If you own an S10, Astro, Safari, Blazer, Jimmy or Bravada (are there more?), You're probably familiar with fuel pump problems or will be soon.
I dissected my old fuel pump and found surprises. I found that behind one of the two carbon brushes in the electric motor, the metal spring was heavily carbonized, shortened and weakened by apparent overheating. The carbon brush itself was fractured and jammed in it's socket. I'm just guessing, but if the brush couldn't move freely it wouldn't continue to make good contact with the commutator, which would inhibit current flow. Current flow would likley also have been inhibited by all the carbon buildup on the spring, since the current flows from brush to spring to contact to power or ground wire or vice-versa. I've included an image where you can see that the burnt spring (top of picture) is about 2-mm shorter than the good one. Also the burnt carbon brush is in 2 pcs in the photo. It broke apart as soon as I removed it from it's socket in the motor.
SYMPTOMS:
1. Engine cranks fine but won't start. (Easy to confuse with ignition problem).
2. Engine runs fine once started.
3. Hooking up battery charger or jump starting may help get it started.
4. Turning Ign. Key On and Off several times may help get it started.
5. Starts fine in warmer weather or soon after it was last running.
6. Won't start in cold weather or after sitting for 24 hours or more.
7. You can hear the pump running and it's quiet and consistent sounding.
8. Fuel pressure test reveals a steady but LOW fuel pressure.
I would expect that no two pumps with a similar failure mode would produce exactly the same symptoms, but if your symptoms are similar, the cause may be the same. You need to hook up a fuel pressure gauge and perform a pressure test and make sure that your problem isn't a bad fuel pressure regulator before replacing the fuel pump.
You can verify fuel pump condition further by performing a current draw test or better yet hooking up a Digital Storage Oscilliscope but I don't know the testing procedures for that off-hand.
NOTE: Fuel pressure should be 60-66 psi on CSI injection systems (VIN# "W" at the 8th digit) and 56-62 psi on SFI injected engines.
P.S. Seems kinda counterintuitive to take a DC motor with sparking brushes and immerse it in gasoline, I mean the gas is pumped right straight through the innards of the motor itself. I guess I'm no physics professor, because I wudda predicted a massive fireball!
Image (Click to make bigger)
Thursday, August 21st, 2008 AT 12:58 AM
