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.

Only one start a day (sometimes less)! HELP

Discussion in 'The Garage' started by ctanner, Sep 24, 2003.

  1. ctanner

    ctanner Registered Member

    Joined:
    Sep 23, 2003
    Posts:
    7
    Likes Received:
    0
    I have recently purchased a 1990 GMC Jimmy, 350, TBI all stock as far as I can tell. It runs great but does not start well after it has been started and run once in the day. Let’s see if I can explain better! The Jimmy was running well and starting well. A few months back it started having trouble starting after it had been running. The engine temperature does not seem to matter much as it will not start after several hours or seconds following the initial start and stop of the motor. When running it runs great.

    I can get it started right up by spraying carb cleaner in the TB and once it starts it runs great. I have looked at the injectors and noticed no fuel when trying to start and am suspecting that something is shutting off the fuel supply to the injectors even when the throttle is full open and engine cranking (ECM problem?). I cannot discover what would cause this or if there is a specific component (controlled by the ECM) that controls fuel flow for starting only. Any Ideas? There is no Service Engine soon light blinking when it runs so I doubt the ECM has any fault information stored on the problem. Is this assumption wrong?

    My first thoughts were to replace the cheap stuff (fuel filter) and check all fuel lines, cap, rotor, wires. All looks great or are new. I have no idea what electrical components would malfunction to prevent fuel flow to the injectors during starting but not malfunction once it is running. Again, I thought this may be heat related but if so it must have a very low heat threshold to malfunction due to having to give it 12 or more hours until it will start without carb cleaner spray. (No “vapor lock”)

    Thanks in advance for any advice. I can give more specific info if led by questioning.
    /forums/images/graemlins/1zhelp.gif
     
  2. 77Jimmy

    77Jimmy 1/2 ton status

    Joined:
    Sep 3, 2002
    Posts:
    661
    Likes Received:
    0
    Location:
    Atlanta, GA
    First off, welcome to CK5! /forums/images/graemlins/thumb.gif Great to see orange w/ low posts! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

    Sorry I can't help you w/ your problem, but at least this will get you back to the top so one of the guys-in-the-know can help you out! /forums/images/graemlins/thumb.gif
     
  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,681
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    Hey Charles!

    Welcome to CK5....someone here is going to help you solve this, I guarantee it! /forums/images/graemlins/thumb.gif

    Here are my quick suggestions:

    1. Fuel pump relay. It's on the firewall on toward the passenger side, up high...(easy to see, just looks like a small black box with a wiring harness going into the bottom) It's a cheap and easy swap to try. Usually, there's even a second spot to mount a "backup" relay right next to the first one...if it fails, just pull the wires and move them over! Could help...you won't see fuel from the injectors if this is bad, so I'd start with this.

    2. Ignition module - I had this problem on my '88. When the module goes bad it won't run. If it's STARTING to go bad, perhaps it acts more intermittent? Pull the cap and rotor, and the module is screwed into the base of the distributor....there should be a molex connector with 2 wires that disconnects, and the new module drops right in. The wiring connector only goes on one way, so it's pretty foolproof.

    Those things are probably less than $30 in parts, and even a novice could get them swapped out in around an hour.


    Hopefully that helps get you started. They're a couple of common failure points on K5's that are easy to check and fix.
     
  4. Thunder

    Thunder 3/4 ton status

    Joined:
    Jul 20, 2000
    Posts:
    8,946
    Likes Received:
    1
    Location:
    Northeast Nevada
    Yeah A bad Dist module will cause that problem. If the computer sees no spark siginal it will shut off the gas to keep it from flooding. They can be VERY heat senisitve when bad.
    Many parts stores will test them for free.
    Also there may be oil pressure switch that will shut down the engine if it sees no oil pressure.I cant rember if 1990 had them or not. But usually it will start up then die if that is the problem.
    It prolly would not hurt to check for trouble codes. The computer will set codes without lighting the CEL.
    If all you get is the normal code 12. It most likely is the dist module.
    You dont have to worry about vapor lock with TBI
     
  5. BowtieBlazer

    BowtieBlazer 1/2 ton status

    Joined:
    Jul 15, 2001
    Posts:
    2,462
    Likes Received:
    0
    Location:
    Baton Rouge, Louisiana
    Also has many symptoms that strike me with heat soak problems.... Try a remote selenoid...

    A previous wiring Tech post


    Also check that all your fuel lines are up and away or fairly well insulated to any major heat sources, I have bought one and seen numerous trucks with a vapor lock condition because of the fuel line routings near Hot aka. exhaust manifold places....

    Just some more thoughts
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,977
    Likes Received:
    189
    Location:
    Roy WA
    Get someone to hook up a scanner up to it. I'd at least check what the ECM is seeing for engine temperature.

    If it was the fuel pump relay, it *shouldn't* matter when you try to start it, if the relay is bad, it won't pressurize the system regardless of engine temperature. (of course, when dealing with faulty components, temperature can ALWAYS cause problems)

    Or, go ahead and start throwing parts at it. Hopefully before you reach the price at which you could have purchased a shop manual and a scanner you'll have it solved. Of course, you might as well replace one at a time, that way you can turn around and sell all the good components you mistakenly swapped.
     
  7. ctanner

    ctanner Registered Member

    Joined:
    Sep 23, 2003
    Posts:
    7
    Likes Received:
    0
    Thank you for all the advice /forums/images/graemlins/grin.gif. So far I have done the following:

    Replaced Fuel Pump Relay (FPR)
    Replaced Ignition Module (IM)

    Those were great suggestions but have not solved the problem /forums/images/graemlins/confused.gif. In fact, the engine has progressed to not starting regardless of heat unless I spray carb cleaner into the TB. I had not run it for two days and it would not start until the spray. After starting with the spray, I let it run for several minutes and shut it off. Tried to start immediately and again could not start without the spray.

    I do have a Haynes Manual. After looking at the electrical system schematic for the TBI control system I am now wondering about the Fuel Pump Primer. Anyone have any experience with this unit /forums/images/graemlins/ears.gif? It is switched via the FPR. Not sure where it is located? Not even sure it exists on my Jimmy. The reason I say this is that the RED wire coming from the FPR terminated at a female connector with no mate in site. According to the general schematic, this wire should go to the Fuel Pump Primer /forums/images/graemlins/thinking.gif.

    I checked the trouble codes on the ECM. Got code 22 (TPS problem). I am pretty sure I caused this by starting the engine a few days ago without the TPS connected. Still I would like to check the adjustment of the TPS as suggested in the manual. However the manual does not give info on how. Anyone check the TPS adjustment before /forums/images/graemlins/ears.gif?

    Thanks for more help!

    1990 GMC Jimmy, 179k miles, stock, 350, TBI.
     
  8. jeffro

    jeffro 1/2 ton status

    Joined:
    Jul 2, 2002
    Posts:
    406
    Likes Received:
    0
    Location:
    Scurry, TX
    Maybe your oil pressure switch is telling the ECM that you don't have any oil pressure. If I'm not mistaken TBI won't fire until the pressure comes up during cranking.
     
  9. ctanner

    ctanner Registered Member

    Joined:
    Sep 23, 2003
    Posts:
    7
    Likes Received:
    0
    Seems like I should have gotten a code 54 if the Oil Pressure Switch is problematic? /forums/images/graemlins/thinking.gif

    In any case, any idea where it is located?

    Opps... found it. Thanks anyway.

    Thanks,
     
  10. rick88blaze

    rick88blaze 1/2 ton status

    Joined:
    Jan 24, 2003
    Posts:
    2,342
    Likes Received:
    1
    Location:
    Knob Noster, Mo.
    try you coolant temp. sensor. if it's telling the computer that the engine is too hot, it won't start. it's right next to your thermostat housing.

    rick
     
  11. Confedneck

    Confedneck 3/4 ton status

    Joined:
    Nov 1, 2002
    Posts:
    5,236
    Likes Received:
    0
    Location:
    Lehigh Acres, Florida
    check the tps with a voltmeter, at idle, ie key on, engine off, it should read between .4 and .6 volts, and somewheres between 4.7 and 5.0 at wot...
     
  12. ctanner

    ctanner Registered Member

    Joined:
    Sep 23, 2003
    Posts:
    7
    Likes Received:
    0
    I appreciate the ideas but before I replace each switch and sensor on the Jimmy, I need to work out some of the logic here. /forums/images/graemlins/crazy.gif

    When the Jimmy is running both the Temperature and Oil Pressure gauges work fine. Is this not an indication of functionality of both these sensors/switches? If temp was sent to the ECM as high when starting, thus keeping TBI from firing, would this not also be reflected in the gauge? If the oil pressure switch had failed, thus keeping TBI from firing, would the pressure gauge read pressure as normal when running?

    Just trying to convince myself that replacing these components is going to do any good. They are cheap but time is not. /forums/images/graemlins/k5.gif

    Thanks,
     
  13. rick88blaze

    rick88blaze 1/2 ton status

    Joined:
    Jan 24, 2003
    Posts:
    2,342
    Likes Received:
    1
    Location:
    Knob Noster, Mo.
    there's a difference between your temp. sending unit and the coolant temp sensor. they are totally different parts. i'm pretty sure it's the same with the oil pressure switch. the sending units are on the side of the block, the coolant temp sensor is on the intake manifold next to the thermostat housing. /forums/images/graemlins/thumb.gif

    rick
     
  14. ctanner

    ctanner Registered Member

    Joined:
    Sep 23, 2003
    Posts:
    7
    Likes Received:
    0
    Re: Only one start a day (sometimes less)! HELP (Fixed!!)

    Ok, we have a fixed Jimmy. But it cost me! /forums/images/graemlins/deal.gif

    Turns out that it needed another ignition module, the one I installed was apparently defective. Go figure. I found this out by taking it to a mechanic and having them run the diagnostics. Anyway while doing that I decided to have the Dist Cap, Rotor, Stator assembly, Plug wires, and plugs replaced. Starts and runs like a champ now. /forums/images/graemlins/thumb.gif

    Thanks to those who replied originally. Had I though of replacing the ignition module a second time, I would have avoided significant cost at the shop.

    Anything else I should be checking on this 1990 Jimmy with 179k miles on stock motor and transmission?

    Again Thanks.
     

Share This Page