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help with 90 350TBI fuel system pls

Discussion in 'The Garage' started by rikk, Nov 14, 2003.

  1. rikk

    rikk Registered Member

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    <font color="black"> </font> :I was given a 90 Blazer, which had not been driven for about 3 years. It was started about once a month during that time. It's totally stock w/ 5.7L TBI. VIN # 1GNEV18K9LF166XXX. It was driven to our house and sat for 2 weeks. Then it would't start.
    What I know:
    1. The fuel pump relay doesn't come on when the ignition key is turned to "on". 12V applied directly to relay coil (relay out of truck) makes it pull in and shows 0 ohm connection between proper contacts.
    2. 12V connected to the "prime connector" on the fuel pump relay makes the pump run. Fuel comes out when the fuel filter connection is opened. I don't have access to a pressure guage but it does pump fuel.Sort of flows rather than gushes out?

    3. O2 sensor was replaced as it was broken off(rusted) and hanging by it's wire.

    4. Fuel filter replaced.

    5. A voltmeter across the pump relay coil connector(relay out of connector) shows 12V but only for like 1 second. Then 0V.

    6. Battery was bad and replaced.

    7. No trouble codes show up. Just flashes 12,12,12 and repeats.(Yes, I checked that only AFTER replacing the battery /forums/images/graemlins/mad.gif

    8. ECM fuses are good.

    I ordered the Helms factory repair manual (our local library had crap) but the weekend is here and the manual is not, so some questions:
    1. Where is the oil pressure switch that keeps the fuel pump running? Where is the fuel pressure regulator I've seen mentioned on here?

    2. Where is the brain thingy (ECM?)? And can it keep the pump from running?

    3. Any other ideas?

    Thanks in advance for any help. This is a graet site! Special thanks to the member that had the fuel system wiring diagram on his website!
     
  2. skratch

    skratch 1/2 ton status

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    1. The oil pressure switch should be the same one that is used for the gauge and thats on the back of the block by the distributor.
    The fuel pressure regulator is on the back of the TBI unit, you can pull out the factory piece and replace it with an adjustable unit.

    2. The ECM is under the dash on the passenger side, best bet is to pull the glove box out and you'll see it sitting in it's own shelf back there.

    3. Good luck getting it started.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    2. Where is the brain thingy (ECM?)? And can it keep the pump from running?

    [/ QUOTE ]

    99% of the time it's not faulty, so don't even think about it at this time.

    '90 may have had the fuel pressure switch and gauge sender in one piece, either way it will be either a two wire or three wire switch. Two wire if it has a seperate oil pressure gauge sender, three if they are all one. Not sure what year that changed.

    Are you saying the fuel pump relay "prime" wire doesn't get voltage when the key is turned to run? Not sure what governs the prime cycle (it's duration) but it should of course, come on when the key is turned to run.

    If the pump works, I wouldn't waste time on that until you can figure out why the relay isn't getting power with the key in run.
     
  4. rikk

    rikk Registered Member

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    Are you saying the fuel pump relay "prime" wire doesn't get voltage when the key is turned to run?

    The "prime"connector wire I mentioned is the short red wire on the fuel relay connector. My understanding is it is used to test the fuel pump. When I connect 12V direct from the battery to the red wire the pump runs (as it should) but this is only for test puposes. The red wire usually has nothing connected to it. My problem is that the fuel relay never energizes (pulls in)to run the pump. The relay itself is good.

    Thanks for the replys
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    The "prime"connector wire I mentioned is the short red wire on the fuel relay connector.

    [/ QUOTE ]

    OK, understand you know. Didn't realize you had a short wire. Mines on the ALDL connector now that I think about it. Had me confuzzled for a bit.

    In that case, whats not happening then, is that the relay is not being "told" when the key is in the run position, is that correct? (since you know the pump works and you can make the relay work)
     
  6. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    A voltmeter across the pump relay coil connector(relay out of connector) shows 12V but only for like 1 second. Then 0V.


    [/ QUOTE ]

    That sounds normal. When the key is switched to the "run" position, the fuel pump relay should kick on for about 2 seconds and then turn off. It will only stay "on" when the starter is engaged OR the engine is running. See if the relay stays "on" while cranking the starter. If so, then we can move on to other steps. /forums/images/graemlins/cool.gif
     
  7. rikk

    rikk Registered Member

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    That sounds normal. When the key is switched to the "run" position, the fuel pump relay should kick on for about 2 seconds and then turn off. It will only stay "on" when the starter is engaged OR the engine is running. See if the relay stays "on" while cranking the starter. If so, then we can move on to other steps. /forums/images/graemlins/cool.gif

    [/ QUOTE ]

    Thanks Skratch, Dyeager535 and HarryH3 for your helpful replies.

    So now we can move on. The fuel pump relay now closes when ignition is on and while cranking. I don't know what I did to make that work (if anything) but now its getting some fuel to the TBI inlet.I can actually hear the relay click on and off. Also at one point today some fuel actually squirted out of the injectors..... Once. Now there is nothing from the injectors but still fuel to TB inlet.
    What next?
     
  8. HarryH3

    HarryH3 1 ton status Author

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    Next thing is to check for spark. If the ignition module is dead, then the injectors won't fire. The computer sends the signal to fire the injectors based on receiving a signal from the distributor. If the computer doesn't get the spark input, then it won't turn on the injectors.
     
  9. rikk

    rikk Registered Member

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    [ QUOTE ]
    Next thing is to check for spark.
    edited 11/19

    Yes, we have spark, in fact the engine will fire up if fuel is squirted into the Throttle body. We hooked up a hose to the fuel filter outlet and fuel come out at like 1 pint in 50 seconds.
    Questions:
    can one of those vacuum/ fuel pump pressure guages be hooked up to the fuel line? It has a 10 lb. max on guage. I'm just not sure if fuel should be allowed to get into this this thing. I can easily stop the flow with a finger over the end of the hose. Does this seem normal?
    There is no fuel coming out of the injectors. Can a digital voltmeter across the injectors read whether they are being 'told' to open? Doesn't seem likely BOTH injectors would fail. Could something prevent fuel from getting from the TB inlet to the injectors? Is it a big deal to take the injectors out/ clean them out? Is it likely they could be clogged?

    Thanks for any help you can offer
    Rick
     
  10. rikk

    rikk Registered Member

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    I forgot to mention in the last post that I can hear like a gurgling noise in the tank when the fuel pump runs. I've been assuming this is fuel returning to the tank but now I wonder if the pump could be leaking internally causing crappy fuel pressure. I'm really not looking forward to dropping the tank as the skid plate bolts are super rusted.

    Thanks for any help with this.
    Rick
     
  11. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Thats probably the return fuel plunging back into the tank... I wouldn't worry about it...

    Have you had the ignition module tested? AutoZone will test it for free... or they'll sell ya a new one for something like $36.

    And YES, the ECM governs the injectors firing, and the fuel pump relay. But judging from the info you've provided, I wouldn't look there yet. But you could generally test the ECM by jumping the ALDL connector and checking for codes. If you get code 12, 99.9% of the time the ECM is fine.

    Hope this info helps.

    -Dan
     

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