fuel pump or....?

Discussion in 'Chevy C/K Truck Forum' started by dvharris, Nov 15, 2009.

  1. dvharris

    dvharris New Member

    1977 Chevy K10 400SB w/86K miles.

    Started up this morning with a couple pumps and then died after about 30 seconds. Won't start up again. Yesterday I was idling the truck in the driveway while it warmed up and it died on me. I was able to get it going again after a couple tries and drove to the store and back. That was the last time it ran until this morning.

    I checked the plugs and distributor, everything there is working. The engine cranks and cranks but will not fire. I had someone pump the pedal while i looked into the carb and saw no evidence of fuel pumping in. Pulled the fuel line and had someone crank the engine, no fuel came out. There is a full tank of fuel, btw.

    So, my thinking is fuel pump must have died. I'm on my way to purchase a new one now, but I wanted to put this up in case someone had an idea before i went through the work of replacing it. Thanks!
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Could be a plugged fuel filter but I think your first diagnosis is correct.
    Is it electronic or mechanical?
    You could plumb and wire in an electronic one in a few hours.
    I like electronic fuel pumps on older vehicles because they tend to suffer with fuel delivery issues at altitude and during hot weather.
  3. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    Another tip to diagnose fuel delivery issues is to use carb cleaner and spray it in the carb to see if it will run on carb cleaner.

    The best way is to test the fuel pressure if you have the proper tools.

    If you're changing the fuel pump, it would be a good idea to change the filter too.

    Let us know what you found.
  4. harrisdave164

    harrisdave164 New Member

    ok so i cant log in under my name anymore for some reason so i had to create an alt. reset the password twice and it still wont let me.

    so i have changed the fuel pump. no fuel running up the line to carb. took out the fuel pump to make sure i got the rod in the correct place, i did, reinstalled it. still no fuel running up the line. didn't test the pressure yet, i guess i'm going to purchase a pressure tester soon. I tested spark, and yes i have power to the distributor and spark at the plugs.

    thanks for the reminder unplugged, sprayed some of my carb cleaner in there and WHAM! fired right up. for as long as that lasted. still no fuel. the engine cranks and cranks but i'm not getting anything to burn. I have dual tanks and switched back and forth to see if it was a clog but that changed nothing. I dont think are sending units on these models, does anyone else know? My service manual doesnt say anything about it.

    So.... ideas please? I'm thinking a clogged line but how the heck did that happen?
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    This is a 1977 model truck, if it didnt have scale and rust in the tank I'd be surprised.
    Disconnect the fuel line at the tank (on both tanks) and at the fuel pump, blow compressed air into the fuel line at the pump end and have someone watch for disharge out of the lines, if somethings blocking it should come back out the way it came in.
    On older dual tank GM's they usually get blocked at the "T" where the two fuel tank lines connect to become one.
    It's also possible the switching mechanism has malfunctioned and is blocking both inlet lines.
    The blockage shouldnt have gotten past the fuel pump, but if it did you'll have to do the same thing to the fuel line between the pump and the carb.
    On pre FI trucks they usually didnt put an inline filter before the pump, if it had one it was usually an aftermarket filter placed between the pump and the carburator. On some older trucks I've seen a sock type filter over the end of the fuel pick-up line, I dont think this was factory as I've never seen two the same.
    If you do blow out any scale or trash it's probably time to have the tanks drained, de-scaled, and sealed.
  6. dvharris

    dvharris New Member

    ok, update:

    removed the feed mile from the tank selector switch to the pump and blew it out. Good airflow, a little debris, nothing more than specks and that's it. blew air through the line from pump to carb, good air flow. removed the feed lines from the tanks at the selector switch and blew through the slector, good air flow. and blew some low pressure air back up the lines into the tanks (not really the best idea but hey, i was there.) that resulted in return flow from the tanks to the selector switch, as the pressure in the tanks went up a little, it pushed the fuel back out.
    So I hooked everything back up, reconnected the battery, cranked the key for an extended period of time (figured I got to prime it now) and still nothing.

    So the last line on the fuel pump instructions sheet (didn't know there was one, lookey there!) says "if pump does not deliver sufficient fuel there is a strong possibility of engine cam wear. This should be checked."
    anyone got any ideas? I am not about to pull a cam and my local mechanic wants to charge me $85/hour to start where i started.
  7. dvharris

    dvharris New Member

    called around to a few local shops, one of the guys mentioned that I may have gotten a bad fuel pump. It was brand new but has that happened to anyone else?

    Mechanical fuel pump, not electric
  8. dvharris

    dvharris New Member

    Final Update: Start New Conversation?

    Finally got smart and began testing each segment: Got a can of gas and a 2' section of fuel hose then isolated each segment of the system starting from the pump. Pump drew fluid out of the can and fired engine. Next attached to the feed line ahead of the selector valve, pump drew fluid from there too. Attached to the back of selector valve from current tank, didn't appear to draw from there. So i disconnected the spark, unhooked at the carb, and had my son crank the engine for about 2 minutes. Basically, priming the pump and feed line. Oh yeah, that went dry!
    So then i got down to the selector valve and tapped on it with pliers while my son hit the switch in the cab a couple times. Went back to open piped cranking and it was drawing again. Hooked everything back up, without my external gas can, and it runs just fine.

    In conclusion, I think, the selector valve got hit two days ago when my daughter was in the truck with me. The other tank was completely empty. Now i saw the gauge drop E so I looked to the switch and switched it back. No problems from then until i shut down the engine and let it sit overnight. I'm thinking that the switch never fully closed one direction and allowed the empty tank to remove the vacuum in the line. OR, like tbplus10 said, something got caught in the selector valve and i knocked it loose while tapping on it.

    So here's where I am looking for expert opinion or at least your thoughts: Does this sound like an indication of the selector valve going bad? Was this just a chance happening and by keeping fuel in both tanks will I avoid this from happening again? Anyone else ever heard of the valves releasing an airlock?
  9. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    I've seen the selector valve cause something like vapor lock before.
    The selector valve on my 76 Dually sat low on the right side, during a summer trip from Calif. to Maine I kept getting vapor lock everytime I shut the truck off. After messing with the fuel line between the carb and the mech. fuel pump an old codger at a gas station in N.M. recomended icing down the fuel line at the switch for a few minutes before and after starting the truck, it worked.
    Another time I had the same symptoms but it was real cold out 22deg, I got under the truck to check the switch and found I had a leak that was causing the fuel pump to suck air instead of fuel.
    Those selector valves can get stickey at times, some of them were rebuildable, maybe this is the case with yours.

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