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172k 5.7L, Long crank and rough idle

Discussion in 'The Garage' started by el bob, Jan 8, 2006.

  1. el bob

    el bob Registered Member

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    I've got a '94 C2500 Extended Cab with an original 172k mile 5.7L and it takes 1-2 full seconds of cranking to get my engine to "catch" and not die. The idle is also lumpy and rough until it gets it first rev past 1500 RPM. This is what happens in nice 60 degree Fahrenheit SoCal weather.

    I took the truck up to Bear Mountain at 7000 feet elevation and 30 degree Fahrenheit temperature and I couldn't get the truck to start with just turning the key and cranking. I used a trick I found online a while back. I floored the throttle first and then turned the keys and cranked the engine. This has always been a surefire means of getting the engine to start even after an successful attempt at normal cranking. At the mountain I did this and then revved the engine in Park at 1500 RPM for ten seconds or so because it tried to die at lower RPMs. The truck started fine after being driven a bit but would be hard to start again as soon as it sat for more then a couple of hours.

    I remember reading that flooring the throttle before turning the keys tells the engine computer to not inject but just spark and crank. This made some sense because I read that high mile 5.7L's get leaky injectors after some time and thus the need for a no-inject crank mode.

    Is there any truth to this? Can someone give me some facts to help in understanding this trick?

    Should my truck be hard to start with 172k and no rebuild?

    And one last question. When I step on the gas from a stop, the truck putters for a split second or two before rev'ing and moving forward. A friend of mine rode shotgun and told me my torquer converter is shot. Does this make sense to anyone?

    I'm trying to learn as much as possible about what's really going on in my Chevy truck. Help is appreciated. [​IMG]
     
  2. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    I'd be thinking more along the lines of timing!

    I didn't know what to think till you told me about it sputtering off the line :) Get a timing light, unhook the EST connector that is found behind that black cover up and to the left of the engine on the firewall (it is a single wire connector, the wire is brown, with a black stripe on it)

    After you unhook the EST, then set the timing to between 0 - 5 degrees BTDC, then re-connect the EST connector. Should idle up, and respond like a brand new engine again, assuming of course that the timing is the culprit!

    Sure, the TBI engines have electronic spark timing, but if it isn't set to the correct base, then the computer has no way to accurately set the timing :) I usually set mine 5 degrees before, becuase the timing in the prom is a bit conservative, and this is just a way of manually increasing the timing 5 degrees across the board. The ECM will run the timing that the prom tells it to, unless it detects pinging, at which point it will back the timing off. So by setting it 5 degrees before, it will give the engine a chance to use extra timing where it can, but if it doesn't need it, the ECM will take care of it, and retard the timing.
     
    Last edited: Jan 9, 2006
  3. el bob

    el bob Registered Member

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    Thanks SierraClassic. I don't have a timing light at the moment, but I will try to get a hold of one.

    Anyone else know what's going on?
     
  4. el bob

    el bob Registered Member

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    No takers?
     
  5. K5dreamer

    K5dreamer 1/2 ton status

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    with 172k miles and no rebuild, id say you need at least a new timing chain. my IROC had 150k miles on a pretty solid engine but was running rough, had a starting and low idle problem, barely passed emissions, and was getting poor gas mileage. after replacing several parts, i finally checked the timing chain for slack, and found 26 degrees of it. i was impressed it was still running at all. i replaced the chain and shes a whole new animal, fires right up and runs like a top.

    its pretty easy to check for slack. pop the hood, take off the distributor cap, pull the spark plugs, and get a big breaker bar with a socket to fit on the harmonic balancer bolt. now rig up a pointer to mark the position of the balancer, i used a length of coat hanger and rubber bands. now turn the engine over with the breaker bar in one direction until the timing mark is lined up with the coat hanger, now with someone watching the distributor rotor, start SLOWLY turning the engine back the opposite direction. as soon as the distriubor starts turning, stop turning the engine. now, measure the distance from the pointer to the timing mark on the balancer. use that distance to calculate the degrees of slack in the chain. 3-5 is ok, 10 and above definatly needs to be replaced.

    also, you say its a 94, it should have an OBDI system at least, OBDII if im not mistaken. have you tried running the vehicle for codes?
     
  6. Thunder

    Thunder 3/4 ton status

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    Before you do anything you should check for trouble codes.
    Here's how:GM trouble code Info
    Your data link is below the dash under the steering wheel shaft.
    The computer can tell you what may be wrong.
    Check for codes and post results.
    If you cant check the codes by the method shown in link. Take your truck to Autozone they will hook up a scanner and check the codes for free.
    I am guessing By your description. It sounds like the coolant temp sensor may be bad.
    Also how old is your fuel filter? It should be changed once a year on TBI.
     

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