I have a 86 with a 305 TPI and have had extremely annoying fuel pump issues. First, what i think was the original fuel pump, went out and confirmed that it was not working by doing a bench test. So I put a new kemso fuel pump in it rated for the car and it ran great for awhile. Eventually I stopped to get gas and after filling up it never came back on and never primed. After getting it towed home I assumed it was the ground on the sending unit as it the wire was a little finicky even tho it passed continuity. I then decided to replace the entire sending unit and put a recommended Walbro fuel pump rated for the car in. After a day and a half of it working fine and getting back from a long test drive today, it once again crapped out when i returned a few hours later for a ride. I have tested every circuit and the fuel pump relay and they all appear to be fine. I even ran straight power to the plug/bulkhead under the car that goes to the pump. And it still didn’t prime or engage. Although possible, i refuse to believe this pump or sending unit are faulty or bad from the factory.


Also worth noting, for the past month whenever accelerating the car staggers up and down rpm’s 1-2 times and then throws a code 33 SES light. after about 10 seconds the SES light goes off and the code is stored. I know this is related to the MAF sensor voltage but before moving on to that I would like to solve the fuel pump.

Any ideas?

 

You are correct in prioritizing the fuel pump problem. Consider any ground connections, including that at the tank unit.

 

To my knowledge the only grounds is first the one on the sending unit itself which is brand new. Second, the ground on the passenger side back of the engine block (which are also fine) along with the ground on the ECM that grounds the fuel pump relay circuit and prime stage.
All 3 of these appear to be fine but I still can’t figure out what’s causing the pumps to go bad. I’m out of town right now but my guess to check when I get back is the resistance of the power wire going to the sending unit. It may be going bad slowly and sending insufficient voltage to the pump causing it to burn out. But with that being said the 5 times i’ve checked voltage to the wire bulkhead under the car i’ve gotten 12 volts. This is really the most puzzling issue i’ve ever had with this car.

 

Did you inspect the connector C313 (and ground) between the rear seats? It should be under the rear seat cushion, almost on the rear pan.

 

hi all, i am having issues also with a new intallation of fuel pump and sending unit. I am getting 11.9 Volts at the back seat connector. everywhere else its 12.4 volts. I also use a testing prob which connects directly to the battery.
it spits out a resistance number when i test grounds. the ground at the back seat plug is 63 ohms like all other grounds i have tested. my question here is can i run the fuel pump at 11.9volts?

 

Years ago I had back to back fuel pumps go bad with less than 100 miles on them. Come to find out someone had put sugar in my tank. The sugar was like a thick molasses that clogged the sock and burned up the pump.

how did I know? After draining the fuel and washing the tank out with water there were ants everywhere taking advantage of this succulent delight.

should go without saying but always clean your tank out after removing a pump and replace the filter. I learnt that the hard way.

 

oh the car was sitting for 15 years. I have replaced the following injectors, fuel tank, sending unit, fuel pump, relays fuel pressure regulator diapram. But the pump has fail during testing. thats why i am wondering if 11.9 volts could have done that.

 

Generally, +/-6% voltage variance from nominal is acceptable. I've heard even 10% drop is acceptable. 11.9 VDC is well within both of this those acceptance values. I would venture to say the power source is not the problem.

I would check the G304 ground which is either under the carpet under the rear driver's side seat or just forward of the driver's front seat. Worth grabbing a 13mm and a #2 philips to gain access to both locations and inspect the ground for the pump.

Because the fuel gauge and fuel pump share the same ground is there any correlation for when the pump "dies"? Just make sure that you're checking power at the tan/white wire and not the pink at C313?

Have you tried jumpering out the relay just to see if the pump is still good when it "fails"? I've had fuel pump relays give me problems in the past. Just remove the relay and jump the orange wire (E) to Tan/white wire (A). This will put power directly to the fuel pump and bypass any guessing.