Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Fuel pump on but no fuel out injectors...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 89GMCSuburban, Nov 14, 2002.

  1. 89GMCSuburban

    89GMCSuburban 1/2 ton status

    Joined:
    Nov 15, 2001
    Posts:
    3,005
    Likes Received:
    0
    Location:
    Thornton, CO
    I have a no start problem that happens occasionaly. After being run, I turn the truck off and when I go back out to re-start it, it doesn't start. The fuel pump whirrs to prime the pressure, but when I crank the engine, no fuel comes out of the injectors. Anyway, this happened last night, I go out this morning, won't start. I get it towed to shop, they get in it to try and start it, starts right up. I replaced the distributor module a month ago, fuel filter is 3 months old, Fuel pump is an AC Delco replaced 3 months ago, new O2 sensor and knock sensor. Temp gauge never reads over 160 in the cab, but it's done that since I bought it a year ago. Oil pressure is at least 30-40 PSI. Maybe this will narrow it down. When I'm stopped at a light, my idle slowly starts dropping and after about 100 RPM, it turns off. I restart it and it runs fine. THis usually happens when I have the A/C on. What do you guys think it is? /forums/images/graemlins/angryfire.gif Thanks for the help!
     
  2. 89GMCSuburban

    89GMCSuburban 1/2 ton status

    Joined:
    Nov 15, 2001
    Posts:
    3,005
    Likes Received:
    0
    Location:
    Thornton, CO
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    I would be looking toward the IAC motor (idle air control). This is what controls your idle speed. When the A/C is turned on the computer senses a drop in engine speed due to the load added by the A/C compressor so it increases the idle VIA the IAC motor. When this motor fails you may have either a low idle speed or an erratic speed or even a high idle speed.
     
  4. 89GMCSuburban

    89GMCSuburban 1/2 ton status

    Joined:
    Nov 15, 2001
    Posts:
    3,005
    Likes Received:
    0
    Location:
    Thornton, CO
    I'll have to check that out, but any idea what the fuel pump thing is?
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    When the engine is cranking you should not be able to see any fuel coming from the injectors. The computer is what pulses the injectors to spray. I would start by checking to see if you have spark at the plug wires. If you do have spark at the wires then I would check for fuel pressure. If you have spark and fuel pressure then you need to find a NOID light to check that you have current at the injector wires when cranking. I hope this helps you out.
     
  6. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    </font><blockquote><font class="small">In reply to:</font><hr />
    When the engine is cranking you should not be able to see any fuel coming from the injectors.

    [/ QUOTE ] Say what? How would the engine start if no fuel was coming from the injectors? /forums/images/graemlins/shocked.gif
     
  7. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    I figured I would have someone respond to that comment. What I really meant to say was that you will not see a spray pattern as when the engine is actually running. Obviously you must have fuel for it to start, but when cranking the fuel coming from the injectors is not really in a spray pattern more of a drip, then a spray pattern once the engine has started.
     
  8. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    Watch the spray pattern with a timing light while someone is cranking the engine. You should be 2 nice cones of fuel spraying out of the injectors. It will be more constant at a higher RPM, but it should always spray when the engine is turning over.
     
  9. Depdog

    Depdog 1/2 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    1,657
    Likes Received:
    0
    Location:
    Georgia
    I have to disagree, when you are cranking it, it should spray, not drip. I have a Howell setup on mine and its basically a stock G.M. setup. I had this same problem. What mine ended up being was the tach signal was not strong enough. If I jumped mine off of another vehicle that was running, it would fire right up. The alternator on the running vehicle had enough juice to boost my electrical system which amplified the tach signal. Check your battey under load and see what it shows. According to Howell and the guys I talked with at G.M. you need to show 12 volts when cranking, if it has this, you may be having tach signal problems. Once it has run, it will fire right back up right, then you let it sit a few hours and it wont crank.

    What my fix ended up being was a tach amplifier module (I have a Crane aftermarket ignition, between the Crane tech and Howell, we figured it out and I got the module from Crane, works like a champ)

    To test if the injectors are getting power to them, get one of the little light moduels from AutoZone. I cant remember what they are called, but they are in the tool section, looke like a plastic fuel injectore (clear) it has a couple lights in them, you plug them in like a regualr injector and then when you crank the vehicle, it lights up when it gets signal (lights instead of the injector squirting) Only other thing I can think of it to make sure the fuel pump is pumping when the key is in the start position, I have seen them wired wrong and the fuel pump circuit looses power when in start, but has power in run.

    Good luck
    Depdog
     
  10. BiggerRigger

    BiggerRigger Registered Member

    Joined:
    Nov 3, 2002
    Posts:
    81
    Likes Received:
    0
    Location:
    C.D.A. Idaho
    have you checked all of your fueses under the dash as I have been down this road before and after two weeks of checking every thing twice and some things three times I finnaly looked at the fueses and thats what it was
    Hope this helps
    Aaron
     
  11. 89GMCSuburban

    89GMCSuburban 1/2 ton status

    Joined:
    Nov 15, 2001
    Posts:
    3,005
    Likes Received:
    0
    Location:
    Thornton, CO
    See, the weird thing is this happens occasionally. It'll start one day, but it won't the next...fuel pump is on when the key is on run, but I can't really hear it on start (when cranking). Fuses, I'd assume, would cause it not to start till I replace the fuse, but I'll check next time it happens. THe shop has it and they're trying to re-create the problem. No luck yet, starts every time. Keep it coming guys! I need the ideas!
     
  12. mattman

    mattman 1/2 ton status

    Joined:
    Feb 15, 2001
    Posts:
    152
    Likes Received:
    0
    Location:
    Austin, Texas
    Even though the pump pumps, is it pumping enough? I remember someone on here last year had a problem with crud in the gas tank causing momentary injector failure. The crud would plug the sock filter on the pump prevent the necessary pressure to run the motor and causing an intermittent failure.

    Or it could be a bad fuel pump ground. Temperature and humidity changes and corrosion will play havoc with a bad ground and cause an intermittent problem. Seen that enough in the wastewater field.

    Just some other thoughts.
     
  13. BurbinOR

    BurbinOR 3/4 ton status

    Joined:
    Feb 17, 2000
    Posts:
    5,829
    Likes Received:
    0
    Location:
    Oregon
    I'd check the fuel pump relay - not sure where they put them in a Burb but should be able to find it. Still sounds to me like that or the pump is failing - typical intermittent problems. My 89 S15 just did that for a couple of weeks, changed the pump, problem solved. Now, changing the pump sucked, but that's another story............. /forums/images/graemlins/frown.gif
     
  14. 502Burban

    502Burban 1/2 ton status

    Joined:
    Jun 8, 2001
    Posts:
    379
    Likes Received:
    0
    Location:
    Southern California
    I've run across this problem before (if it's what I think it is). Depdog is on the right track, I think.

    What I've found is that the injectors won't fire if there isn't enough voltage flowing while cranking. Pump will run, ignition will fire, but injectors won't. The way we found this the first time is by realizing that the injectors wouldn't fire when the electric fan was running. So, every time the engine had been running for a bit and the car was shut off for a moment (like in a gas station), when we would twist the key the fan would run, as the engine had a few minutes to heat soak, bringing the temp into the range where the fan would run. It would crank just fine, but no injectors clicking. Plug in the laptop, turn off the fan, engine would start right up.

    Once we got a clue on this, a voltmeter confirmed our suspicions. The fix ended up being a combination of installing a newer/better alternator and battery combination and placing a manual override switch inline for the fan so that it can be switched off when cranking.

    It sounds, from your description, as if your problem presents itself when you have heavy draw on the electrical system: A/C running, lights on. As Depdog suggested, I suspect that if you checked with a voltmeter, you will find that when it won't start, your cranking voltage is below 12V.

    Hope this helps a bit,
     
  15. 89GMCSuburban

    89GMCSuburban 1/2 ton status

    Joined:
    Nov 15, 2001
    Posts:
    3,005
    Likes Received:
    0
    Location:
    Thornton, CO
    Wow, thanks! I'll have to check that out!
     
  16. 502Burban

    502Burban 1/2 ton status

    Joined:
    Jun 8, 2001
    Posts:
    379
    Likes Received:
    0
    Location:
    Southern California
    Glad to help. Hope you find the problem.
     
  17. GOK5

    GOK5 Registered Member

    Joined:
    Aug 19, 2002
    Posts:
    23
    Likes Received:
    0
    Location:
    wandering aimlessly about
    Mattman, when you speak of this sock filter on fuel pump, do you need to remove the pump from tank to clean? I having a similar problem with hesitation at about 1 minute after startup from idle on up. This came after using injector cleaner.
     
  18. 88k5blaza

    88k5blaza Registered Member

    Joined:
    Oct 17, 2002
    Posts:
    70
    Likes Received:
    0
    Location:
    new hampshire
    my 88 has the same problem but it always starts if im at a light every once in a while it wants to drop teh idle way down to a stall but usually i 2 foot it and give it a lil gas sometimes by putin it in neutral and revin it a few times does it, there is a cam on the TBI that adjusts the idle and they get warn and actually pull out causing the butterflys in the throttle body to close and i think by reving it it allows that to go back in but thats just my theory on my rig but souns to me like you got the same problem!
     
  19. 88k5blaza

    88k5blaza Registered Member

    Joined:
    Oct 17, 2002
    Posts:
    70
    Likes Received:
    0
    Location:
    new hampshire
    oh yea one more thing and check the vacume to the MAP sensor and the wires for corrosion becuase mine did the same thing when the map sensor went! /forums/images/graemlins/thumb.gif
     

Share This Page