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Old 04-03-2011, 07:39 PM
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98 chevy vortec 5.0 will not start cold

98 Chevy vortec 5.0 will not start cold unless fuel added in throttle body

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Old 04-03-2011, 07:49 PM
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A friend had this same problem with a TB Olds years ago . It turned out to be low battery voltage even though the engine seemed to be cranking fine. A new battery fixed it. Worth a try. BTW Even hooked up to jumper cables it didn't want to start.
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Old 04-03-2011, 08:02 PM
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Welcome to the site.


Cole
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Old 04-04-2011, 09:39 AM
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no start

when you turn on the ignition to run but don't crank the motor, does the fuel pump run for a couple secs and then shut off? it should. have a buddy help you so it can be heard over all the buzzers etc in the cab. close the cab door and get your head down by the tank and listen for a humming noise from the pump when your buddy turns the key to run (but not all the way to start).if no hum then the pump isn't getting power for some reason, or it's not getting a ground for some reason. could be a weak relay or a pump that just doesn't want to start up. sometimes a rap on the underside of the tank with a broom handle or the like will get them going. also, lots of those fuel pumps bleed off the static pressure overnight. try turning the key on (to let the pump cycle and try to pressure up the system) but don't try starting it until you do this a couple times. then if it starts up you know it's just bleeding off pressure and probably will need a new pump. if the pump starts and whirrs easily for a sec then changes pitch and seems to be working harder, that is a good sign that the pressure is bleeding off overnight. you could also try jumping power to the pump at the relay. I think there may be provisions there for a "fuel prime" at the relay. just check the wiring diagram if unsure, but I think there is a tan wire with a white stripe that goes to the pump. you would need to supply fused power to that wire. like I said, I "think" those are the colors, check first. sometimes the relay has a wiring diagram on it's side, if you know how to read them. there isn't a remote start on this truck is there? I have had lots of trouble with those things screwing people up.
let us know how it turns out
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Old 04-04-2011, 09:52 AM
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Now I may be totally off base on this, so anybody feel free to correct me. I was thinking that there is a provision in the TB to give a little shot of fuel when the key is first turned on. I am hurting my brain trying to remember for sure, so somebody please help me here . .....Allan
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Old 04-04-2011, 10:01 AM
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The Vortec needs at least 52+psi fuel pressure for the injectors to work properly. When battery voltage is low from running the starter, the fuel pressure can drop slightly and result in no start. A new fuel pump may be required, but try another battery first.
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Old 04-04-2011, 12:13 PM
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cold start

as far as I know there is no cold start injector on a vortec. the throttle body is just that, a throttle body. it has a throttle position sensor and a idle air control motor and that is it. the injectors are in the intake manifold near the head. first off, get the battery load tested somewhere that has the proper equipment. remember, they can't test it properly unless it is fully charged first, so if you have a charger use it. they should load test it at 1/2 of the cold cranking amp rating on the battery for 15 seconds and the voltage should not drop below 9.6 volts. if it does or comes really close, then the battery is toast. then, when the battery situation has been rectified and if there is still a problem,try the "listening for a fuel pump noise" approach. there should still be an audible buzz from the pump in the fuel tank for the first 2 seconds of "key on". if not, there may be a pump issue or a relay issue or a wiring issue. if you get an audible buzzing/whirring noise from the in tank pump, then you will have to do a fuel pressure test at the injector rail to see what you get there for pressure.
dsraven
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Old 04-04-2011, 05:15 PM
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new battery-new icm-new ign coil-new O2 sensors
new dist. sensor
fuel pump cycles
58 lbs. fuel pressure running or at rest

pour fuel in throttle body engine will start I let the engine run for ten minutes
and it will restart all day long if its warm. but engine falls apart at 1200 rpm
under load- no load 5000 rpm engine does not miss at all.
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Old 04-04-2011, 05:52 PM
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cold start

roughly what mileage are we talking on the engine here? have you done a compression test or does it warrant it? vacuum leak check (check the brake booster as well, the one way valve can leak and cause what seems to be a big vac leak at start up because it is trying to bring the vacuum in the brake booster down to what it should be). intake pipng system leak check after the mass air flow sensor (if equipped, can't remember. if so a leak can fool the ecm into thinking there isn't much air going in, so it gives only that proportionate amount of fuel to match how much air it thinks is going in). do the fuel injectors cycle when you try to start it (usually can hear them clicking with a stethoscope or maybe even feel them)? was that 58 psi pressure in the fuel rail when it is cold and won't start, or after you have had it started already and it would likely restart? got a pic of the underhood area? does it set a code (check engine light on?)
dennis
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Old 04-04-2011, 06:07 PM
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Quote:
Originally Posted by junkhouse
new battery-new icm-new ign coil-new O2 sensors
new dist. sensor
fuel pump cycles
58 lbs. fuel pressure running or at rest

pour fuel in throttle body engine will start I let the engine run for ten minutes
and it will restart all day long if its warm. but engine falls apart at 1200 rpm
under load- no load 5000 rpm engine does not miss at all.
Sounds like the fuel pump is weak. Also sounds like the fuel pump check valve is not holding, that is what is causing your hard start when cold.
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Old 04-04-2011, 06:33 PM
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fuel pump

did you try that thing where you listen to the pump before you start the engine for the first time of the day? did it go fast for a sec then slow down some? could be just like latech is saying, the check valve is letting the system bleed off overnight so the pump has to refuel the whole system when you want to start for the first time of the day, or when it has had time to cool off (and also time to bleed off the pressure). when it whirrs fast then it is easy pumping, like the system has no pressure in it.then it slows down because it is starting to build system pressure. did you try "hotwiring" the fuel pump at the relay to prime the system before you try starting when cold?
if you have a gage stick it on there and leave it on overnight so you can see what the pressure is before you start it. you could also see how long it takes to pressure up that way. maybe more than one cycle of the key is required to pressure up the system on cold starts. try it, key on for a couple secs-fuel pump runs then stops, key off for a couple secs, then key on again etc. a couple of those and then try starting.
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Old 04-04-2011, 06:51 PM
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The best way to tell if the check valve is a problem is to turn on the key in the morning and let the pump run its 2 second pulse. Then turn off the key .Dont crank the engine over. Then turn on the key and let it cycle again. then shut off the key. Do this 6 or 7 times and then just turn the key to start and if it starts right up, then your check is not holding.
What happens is when the check fails, engine heat pushes the fuel back into the tank and the line ends up empty. So in the morning several key cycles are required to refill the empty line before any pressure is developed.
That is why I cycle the key a bunch when I do a hard cold start diagnosis on a cold first start of the day, I let them set overnight to replicate the condition of course.
No load RPM and loss of rpm under load is a classic symptom of low volume/ pressure. Without volume you cant build pressure.Pressure can be OK untill a large volume of fuel is required and when the volume drops off the pressure drops.
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Old 04-04-2011, 06:53 PM
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woops ...yeah what raven said. X2
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