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Doesnt want to start: UPDATE Found Problem

Discussion in 'The Garage' started by 88Silverado, Feb 25, 2006.

  1. 88Silverado

    88Silverado 1/2 ton status

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    Hi all,

    A couple days ago the blazer started to have problems starting.

    It will spin over but doesnt want to start. After cranking it for a looooooong time it will sometimes fire up then run fine. Its especially bad when its cold but will sometimes do the same thing when its hot.

    Im going to get a new fuel filter and change it first but wanted some opinions on what it may be, Hopefully not the fuel pump. Its there any other sensors I shouldbe looking at?

    Thanks
     
    Last edited: Mar 1, 2006
  2. Rebel88

    Rebel88 1/2 ton status

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    If the fuel pump is starting to go it will have intermittent problems like that. Its happened on two different blazers ive owned.
     
  3. Rebel88

    Rebel88 1/2 ton status

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    Oh by the way, check your fuse under the dash and make sure its pushed in all the way. Ive had one trick me like that before too.
     
  4. readymix

    readymix 3/4 ton status

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    I take it's an 88? If so it could be a number of things. Is it getting spark? Fuel?

    Could be:
    Fuel pump
    Pick-up Coil
    Ignition Mudule
    Loose connectors
    Injectors
    Coil
    Fuel Filter
    ran out of gas...........
     
  5. 88Silverado

    88Silverado 1/2 ton status

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    Thanks,

    I checked for error codes and nothing found.
    I changed the filter and checked/re-seated all the fuses in the fuse block and its now starting up. Granted its now 70 degs outside and when I was having the problem it was in the 20's. I'll check it again in the morning.
    Im thinking the fuel pump could be getting weak of the internal filter sock is getting plugged.

    Thanks
     
  6. Leper

    Leper 1/2 ton status

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    sock problems usually start to show up under prolonged high use driving.
     
  7. 88Silverado

    88Silverado 1/2 ton status

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    Well that wasnt the problem :(
    Started right up and I took it out shopping with the wife. First stop, it didnt want to start again. If you crank the hell out of it for a long time it will start up. Interesting thing I notice is if I watch the oil pressure guage, when its cranking away the minute the pressure reaches ~ 30 psi it fires right up.

    Is there a oil pressure sending unit that will prevent it from starting?
    Once it starts, it runs great. No problems until I shut it off.

    Still thinking its the fuel pump How hard is that to R&R ?
     
  8. diesel4me

    diesel4me 1 ton status Premium Member

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    I'm no TBI expert,but I do think the oil pressure switch IS wired in with the fuel pump relay somehow,and kills the power to the fuel pump if it loses oil pressure...I've read in other posts here with similar symptoms as yours the oil pressure switch or relay can do what your describing..someone with more experience will likely chime in..
     
  9. 88Silverado

    88Silverado 1/2 ton status

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    Hum..from what I can find it appears the oil pressure switch bypasses the fuel pump relay and will turn on the pump when oil pressure is high enough.
    That would explain why it starts when the pressure comes up.
     
  10. readymix

    readymix 3/4 ton status

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    The sender that is right near the distro is the one that controls the fuel pump power.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Oil pressure switch SHOULD be quite low, about 5PSI.

    The oil pressure switch will NOT prevent the engine from starting. It will however, allow the engine to start if the fuel pump relay has failed. (given that both the relay AND the switch haven't failed of course)

    Procedures for testing the fuel pump relay have been posted on here numerous times.
     
  12. readymix

    readymix 3/4 ton status

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    Yeah, I probably should have made it a little clearer like you did Dorian
     
  13. 88Silverado

    88Silverado 1/2 ton status

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    Thanks!
    Since my oil pressure switch has had an oil leak that ive been meaning to fix I'll just get a new switch. I thought the switch should trigger at a low level but my guage has to hit the 30psi mark to start so i'll replace that.

    I'll look for the info on testing the fuel pump relay but since im getting a new oil sensor, Ill buy a new relay too as a backup.
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Sounds like your problem then...I'd bet it's bleeding off just enough pressure so that it activates a lot later than it should. Interested to hear the outcome if you swap JUST the switch first. Wait to replace the relay, (even if you bought one) see if the switch was "bad" due to the leak.
     
  15. 88Silverado

    88Silverado 1/2 ton status

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    I went to the local parts house yesterday and they had the relay but were out of stock on the oil pressure switch. I R&R the relay and that seemed to fix the problem.....at least for yesterday. It started up a good 10-15 times while sitting in the driveway and a short ride around the block said all was good. It fired right up this AM (I could actually hear the pump kick on for 2 seconds when the ignition is engaged) but leaving work for lunch, same problem. Happened several times after that. Have to crank the hell out of it til the oil pressure comes up.

    I picked up the oil switch at another parts house today and will swap it this eve. Im wondering if I have an intermittant electrical problem somewhere else. IF it was the fuel pump I would expect the engine to stop running when the pump shuts off but once she's running (via the oil pressure switch) it runs fine even on the freeway.

    Dorian, I will replace the oil switch and install the old pump relay and check that out. Any other suggestions?
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Don't forget spark...I don't think you've mentioned that it is getting spark, although it was asked. :) If it's consistent with starting at the same oil pressure reading, spark problem is pretty slim, but worth checking, and easy.

    You can always pull the air cleaner when it's playing hard to start and see if fuel is spraying as it's being cranked. If not, then check to see if the injectors are being pulsed. (noid light) If they are pulsing, but no fuel, you know that you've got a fuel pressure problem. (bad pump, bad wiring, etc)

    How did the wiring look for the pump relay? On the harness I got the wiring at the relay connector was in terrible condition, bare copper just outside of the connector. You'd probably have seen that though. If replacing the relay temporarily solved the problem, make sure all the pins in the relay connector are firmly in place (as in they are still locked into the connector) and clean. Disconnect the plug, gently pull on each wire and watch to make sure the terminal doesn't pull back more than a hair. Some play is normal, if the locking tab is messed up, either they can pull all the way out, or enough that they at least lose contact. BTDT

    I'd pull the oil pressure switch connector, start it, and start moving the relay wiring. Just wiggle any wiring you can reach, see if you can get the engine to die. Without the oil pressure switch as a backup, if it IS relay related the likelihood of it dying when you are in the right spot is pretty good.

    There are only going to be a couple of wires that will "kill" the fuel pump though, so if you can get it to die while it's running, you'll know you are definitely on the right path with the fuel pump circuit.
     
  17. 88Silverado

    88Silverado 1/2 ton status

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    Im 99% sure its getting spark but will check it anyways. I changed the wires, plugs, cap, rotor and coil last summer during a tuneup but you never know.

    Yes, its back to the guage reading ~28psi that it fires up. Now I just noticed last time I turned on the ignition key, I heard the pump run for 2 seconds but it wouldnt fire until the oil pressure came up again. Sometimes the pump comes on, sometimes it doesnt. I should probably check the fuel pressure at the TBI to see what its running.

    Ill remove the wire from the oil switch and see if I can get it to start then check the wires at the relay (which look real good). If the pump pressure is dropping off, that might be a problem but im still baffled why it doesnt show any signs of trouble once its running.

    BTW, I dont mind replacing non-faulty, old parts. As I get older reliability is more of a concern for me then it was 25 years ago. Especially since I occasionally make runs by myself into the eastern Mojave or Sierras and it can be a long walk back to the main roads!

    Thanks to everyone for your comments :)
     
  18. 88Silverado

    88Silverado 1/2 ton status

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    Had a chance to install the new oil pressure switch.
    Before I connected the wire, I tried to start the truck. The pump came on for 2 sec, then I had to crank the hell out of it but it finally started and ran fine. Didnt expect it to started without the oil pressure switch. While it was running I pulled on all the relay wires and nothing changed. All was well seated. I connected the oil switch wire and tried starting it again. Fires right up. Ill drive it some more and see what it does then probably pull the pump.
     
  19. 88Silverado

    88Silverado 1/2 ton status

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    Still thinking its an intermittant electrical problem I started chasing down the wiring. Then it suddenly occured to me I should check the connector plugs on the ECM unit since I replaced the heater core 3 months ago and was working in that area. To my suprise one of the ECM connectors had come loose and was barely in the socket. I re-seated the connector and it appears to be working fine now. Must have been the plug that controls the fuel pump.

    What I find interesting is no codes were set in the ECM (got the blinking #12 but nothing more). Also, I was able to start the vehicle last night with the oil pressure switch disconnected (maybe after many many rotations of the engine the crank sensor thinks the engine is running and sets the ECM in closed-loop engaging the fuel pump?)

    I dont know if only the fuel pump pins were making intermittent contact or if the vehicle will still function somewhat normal even with that ECM plug disconnected.

    Anyways thanks again for the help! Im still going to keep my fingers crossed.

    BTW, heres a link to a page that has lots of good info on GM TPI and some on TBI
    http://chevythunder.com/index.htm
     

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