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99 S-10 Blazer

Discussion in 'Chevy Trucks' started by EZSnow, Aug 26, 2003.

  1. EZSnow

    EZSnow Senior Member
    Messages: 205

    I need to get my wife's blazer running so I can get my truck back!

    It will run intermittently when the engine is HOT. Not full operating temp hot, more like heat-soaked hot. The cooling system is a touch weak, but if it is below 90 outside, it'll idle with the air on all day. If it gets over 90, it runs fine on the first trip, but either idling it with the air on or shutting it down hot and not giving it LOTS of time to cool will provoke this condition. Shutting it down for 15 min or so nets you about 230 degrees in heat soak as you re-start it. It'll come down real quick as you start to drive, but the engine will feel as though you shut the key off as while driving, then on-off-on....off-on... ugh- shock-loading the drive train to a degree I am not comfortable with. It can go off and on twice in three seconds, if not more.
    SOMETIMES, WOT will get'er to catch, but not always. Driving one gear lower (3rd on highway) seems to help a little, but not always.
    O2's are about a year old, and it doesn't throw any codes...
    Truck has 140k

    Here's what I know or have tried:
    TPS (a cheap guess)
    Fuel Filter
    Ignition Control Module $$
    Coolant is good (changed to green)
    Changed Thermostat to 180 to give it a head start on keeping cool
  2. wyldman

    wyldman Member
    Messages: 3,265

    Check the fuel pressure.The newer Vortec's are VERY sensitive to the correct fuel pressure.If it's off by even a few PSI it will act up.

    Is the ignition key very sensitive ?,or if you wiggle the lock cyl,will it act up ? I have seen a few with bad ignition swithces that will cause the same problem.

    Other than that,your going to have to pull codes,and see whats up.
  3. EZSnow

    EZSnow Senior Member
    Messages: 205

    No service codes. I haven't noticed a particularly sensitive ign switch... could that be tied to hot underhood temps?

    Could the fuel be vaporizing? I've heard that it's impossible in a modern fuel-injected engine where the engine is under 40-50psi at all times. My friends dad (old school) instructed me to pour a 5gal of ice water over the manifold next time it acts up... not on MY brand new $130 ingnition control module!!!

    I even had it hooked up to tracking software while it did it- NOTHING out of the ordinary... OBD II my eye... OBD poo
  4. wyldman

    wyldman Member
    Messages: 3,265

    Try a wiggle test,by yanking on the wiring harnesses,especially near the ign module and the ECM.You can also tap on components to see if they act up.

    I would still get the fuel pressure checked,and verified when the problem happens.Modern EFI systems do not vapor lock.
  5. EZSnow

    EZSnow Senior Member
    Messages: 205

    OK- I'll get on it with the wiggle and the fuel, but the fact that it is aggravated by heat really has me stumped!
  6. wyldman

    wyldman Member
    Messages: 3,265

    The fuel is also aggravated by heat.Next time your under the hood,try to hold on to a fuel line.Ouch !

    They use fuel to cool the injectors,and the fuel pump itself.It is constantly being pumped over a hot engine,and back into a hot tank,and through a hot fuel pump.High fuel temps are quite normal these days,and they lead to fuel pump failure.Also the hotter the fuel get,the harder it is to pump,as it loses it viscosity,and starts to vaporize.

    Keeping the fuel tank as full as possible will increase the time it takes for the fuel to heat up,and reduce the overall temperature.It also keeps the fuel pump submerged,so it gets cooled as well.It's a well known fact,people who drive around on empty all the time,are always replacing fuel pumps.

    CARDOCTOR PlowSite.com Addict
    Messages: 1,312

    have you check the fuel filter
    at 140k maybe its blocked
    which will kill the fuel pump
    back in the old school days they use to attach wooden clothes
    pins to steel lines to absorb heat

  8. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    You might try going to an electronics shop and buy a can of whatever spray they use to cool components. They do that on a device that craps out as it heats up, the stuff is some sort of refrigerant and cools whatever you spray it on. If you can get it to idle/stumble so you can get under the hood try spraying things and see if something happens when you cool it. Just a long shot but you might be able to isolate the bad component that way.
  9. EZSnow

    EZSnow Senior Member
    Messages: 205

    did the filter a year ago... nothing like laying in a pool of gasoline!
    It was suffering from this problem then, it did not help. By fall, I just let it go... "I'll deal with it in the spring" It's almost Sep- time to get a lid on this.

    I went and got a fuel pressure test gauge. It was not fussing tonight, but it read at high 50's... 58 or so with the key on engine off. With the engine running, the needle bounces with the tap of what sounds like an injector

    what is the minimum psi?
  10. wyldman

    wyldman Member
    Messages: 3,265

    Fuel pressure should be 54-58 running,and 64 or so KOEO.Your KOEO is a little low,maybe you didn't cycle the pump.What is the running pressure ?

    Take it for a ride,and watch the gauge to see if it drops off when the problem happens.Note the minimum pressure.
  11. Garagekeeper

    Garagekeeper Senior Member
    Messages: 459

    EZSnow, sounds like a CPI unit that may be going bad.
    I would of thought that you should be seeing some codes set.
    How does it run right after you get it started? Like it lost a cylinder?
    The other thing is the fuel supply lines that are under the plenum which are plastic, I have see them crack and open up when hot allowing fuel to be sprayed inside the top half of the motor.
    Some must be vaporized or pulled back into the intake by the pcv system.
    Haven't seen to much of it ending up in the crankcase.
    You almost need to have a fuel pressure gage set up while your driving to check everything out.
    You didn't say if the system held the pressure after doing the pressure test.
    It should hold pressure in the system after you shut the pump or engine down, and not bleed back to the tank or any where else.
    :rolleyes: John..........
  12. EZSnow

    EZSnow Senior Member
    Messages: 205

    I must confess,
    my fuel pressure test was done in haste... in the auto zone parking lot. Sorry- I know I let you all down:(
    I'll try to figure out how to read this gauge while I'm driving... could be interesting... or maybe it's an excuse for a cowl hood... nah.
    starts like a champ... warm or cold, but when it's HOT, (temp 225) it may stall on a re-start.
    ...inside the motor... IN the intake? IN the lifter valley? Help me out on that one

    KOEO ... is that engine ON or OFF? I forget. and what is the other proper designation?

    Alan- do you worry about cracking anything that's really hot using a super-cold spray?
  13. wyldman

    wyldman Member
    Messages: 3,265

    KOEO is Key on engine off
    KOER is Key on engine running

    Spraying an electronic component with a cooling spray will not hurt it,but it may show up an intermittent fault like a cold solder joint,broken circuit board,bas chip,etc.It won't hurt anything,but I find it doesn't work well on automotive electronics as they are very well sealed and potted,and they don't get cold enough.

    When the plastic supply lines crack,they dump fuel into the lifter valley.You can usually smell the fuel in the oil.When the CPI unit,or poppet valves go bad,they usually give you more of a miss,stumble,and will set a code instead of feeling like someone is turning the key on and off.Still wouldn't rule it out though.
  14. EZSnow

    EZSnow Senior Member
    Messages: 205

    I guess it might be described as a stumble, but a BAD stumble.

    Does poppet valve= regulator? or poppet valve= injectors? Maybe I don't thoroughly understand this CPI deal...

    Does pressure bleed-off mean ruptured regulator? Could it also mean sticky injector?
    So if the supply lines are cracked, is that a remove-the-intake kind of job??? ugh!
    Wait a minute... is the fuel pressure reg/cpi/whatever else ALL under the intake? no good
  15. wyldman

    wyldman Member
    Messages: 3,265

    Think of it kinda like an older diesel.The CPI unit distributes the correct amount of fuel,at the correct time,and that fuel pressure pops open the poppet valve,kinda like an injector.The poppet valves can get sticky sometimes.

    The fuel pressure regulators are known for going bad,but don't usually cause an intermittant stumble.They will leak down pressure when sitting for a while.About a 20 PSI drop when sitting over night is considered normal.
  16. EZSnow

    EZSnow Senior Member
    Messages: 205

    I'm a diesel rookie... 2 months now, so while I'm sure it is a wonderful analogy, it has been lost here... sorry
    Is a 20psi drop overnight a good normal or a failed pressure regulator normal?

    Anyway, while I enjoy learning the finer intricacies of my wife's engine,:eek: it seems the CPI and regulator might cause a less intermittent problem, no? What about the poppets- are they negatively affected by heat?
  17. wyldman

    wyldman Member
    Messages: 3,265

    20 PSI overnight is OK.Anything more would probably cause a hard start,and may indicate a leaking regulator.

    I would assume the poppets would be affected by heat,but most of the problems we see are poor\rough idle,and a definate engine miss.Doesn't usually cause a stumble.

    I think at this point you need to take it somewhere and have it properly diagnosed.A good repair shop should have the proper scanner to look at real time data,and a lab scope to trace out waveforms of suspect components.The long and short term fuel trims will give you a good idea of what's going on,and if it's rich or lean.Misfire data may also point you in the right direction.

    A good secondary ignition check wouldn't hurt either,as a bad coil,wire,or cap could also cause the bucking.
  18. EZSnow

    EZSnow Senior Member
    Messages: 205

    alright... I know this is your profession, but it hurts the pride to turn it over almost as much as it hurts the checkbook. I greatly appreciate all your free advice and time spent helping me chase this gobblin. I may throw a cap, rotor, plugs and wires, just cause it's probbly due... maybe I'll get lucky.
    Thanks Again, guys!
  19. wyldman

    wyldman Member
    Messages: 3,265

    If you think it's due for a cap,rotor and wires,it wouldn't hurt to do them.

    It doesn't matter at all to me how you proceed from here.I am always willing to answer questions and help you along.It may be at the stage though where it gets just to detailed or complicated to do so.You probably don't have all the right equipment either.Throwing parts at it can get expensive,sometimes more than would be spent on a proper diagnosis and repair.I would also hate to lead you off in the wrong direction if something is miscommunicated,or misread between us.

    Either way,keep me abreast of the situation,and how it works out.
  20. EZSnow

    EZSnow Senior Member
    Messages: 205

    I've had it on a laptop-based scantool while it acted up, I'll try to find the disk.... I know it's around here somewhere. Anyway, I'm no pro, but nothing seemed out of line as it acted up, and there are no DTCs stored except an anti-theft something or other... I don't THINK that would be related. If I misread something, it's my fault, not yours, and if I'm unclear, I'll ask for confirmation before I go any further with it. I'll check the psi overnight tonight and chase it with a regular tune-up and hope for the best.

    I'll keep ya on top!