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1992 4.3 sierra wont start unless gas petal to the floor

Discussion in 'GM Powertrain' started by WorkTruck 4.3, Aug 4, 2011.

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  1. WorkTruck 4.3

    WorkTruck 4.3 New Member

    what could be my issue? it only starts when i have the gas petal all the way to the floor.
  2. stephan

    stephan New Member 1000 Posts 100 Posts

    Take the air cleaner off so you can see the injectors in the TBI. Have a helper crank the engine while you watch the injectors with a flashlight. Are they spraying fuel as soon as it starts cranking?
  3. silveradotrailblazer

    silveradotrailblazer New Member 1000 Posts 100 Posts

    Dirty fuel filter??
  4. WorkTruck 4.3

    WorkTruck 4.3 New Member

    i will have my wife turn the key as i watch when i get home... the fuel filter thats on now looks fresh out the box. but i did use star bright star tron the whole trip home so maybe it cleaned the fuel tank pretty good and clogged the fuel pump. on a side note... symptoms before it started jnot startingk where taking longer to start. hope its not the fuel pump, buy it maybe what you guys think?
  5. stephan

    stephan New Member 1000 Posts 100 Posts

    Since you made no mention of running problems after it starts, I'm assuming it runs fine after it starts, so I would give the fuel pump & filter a free pass for now. (It's much easier to look at the injectors at this point than to get a FP tester & check the fuel pressure (although this may be in your future) If the injectors aren't spraying fuel when first cranking, then the ECU is not grounding the injectors for the start. This is usually due to the ecm in the dist. not sending a strong enough pulse during cranking (slow speed) While you have the hood up, look at the wires coming from the distributor. Do you have the 4 wire plug?
  6. 2COR517

    2COR517 New Member 1000 Posts 100 Posts

    Almost definitely the coolant temp sensor. When they fail they tell the PCM the ambient temp is about 300 below zero. This causes the PCM to run a very rich mixture, usually to the point the engine won't start/run. When you put the pedal to the floor, it goes into flooded mode, and cuts fuel spray to almost zero. You need the sensor on the intake near the thermostat.
  7. WorkTruck 4.3

    WorkTruck 4.3 New Member

    Okay guys this is getting interesting... I went outside and wiggled the spark plug wire and the other wires that are connected to the dizzy. It starts every time now, but I did not drive it around to confirm... plus the temp cooled down from 110 that it normally has been to 100 degrees. Sure the outside temp has a bit to do with this but. I will drive it around here in a sec and report back.

    ---------- Post added at 07:35 PM ---------- Previous post was at 07:34 PM ----------

    Oh I had the wife turn the key and the injectors spray just like normal, but we shall see!

    ---------- Post added at 08:31 PM ---------- Previous post was at 07:35 PM ----------

    Well I took it for a drive and it runs a little smoother plus it starts every time. We will see if this continues tomorrow and so forth.
    Ok here's the run down of the truck it runs a little ruff, smokes white smoke, yet has good power like it should. The compression test results yeilded nothing lower than 179psi. after taking off the valve covers I saw some of the most buildup sludge I ever saw:( Never the less my dad put some gunk motor flush stuff in...... Why oh Why. The oil pump pick up clogged, so by the time I got to it I thought it was a fuel or trans issue. Pulled the oil pan and oil pump and knock out a hand full of sludge from the pick up screen:( I know that the valve seals need to be changed. I never had an engine that when you take off the valve cover about a quart of oil comes out??? I probed the cylinder head for drain holes and only found some closer to the intake( lookin at the engine head on the highest angle closest to the intake) Thus the reason I say the valve seal are bad.
  8. Ethan

    Ethan New Member 100 Posts

    Dang, sounds like you found your problem, sludge. That's never good. Sounds like you'll be doing a engine rebuild, or at least a header rebuild. I know the valve seals in these trucks are known to go bad if you don't take care of the oil on a regular basis.

    When you take the valve cover off, it soundn't drain any oil, it sounds like the oil ports are clogged with sludge, hence, needing a engine rebuild, or a very good cleaning.

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