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Old 07-21-2013, 08:11 PM
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more troubles with the 350 in my silverado

truck was running perfectly fine drove to a friends shut it off , came back out a few hours later and it wouldnt start , my gas gauge has always been off so i thought just maybe it was out of gas but i thought to myself that cant be right when i looked down at my mileage.

anyways we put 5 gallons in it and it still wouldnt start, eventually after tons of cranking and playing with the throttle it started but ran really rough and really rich.

limped the truck back home took off the air cleaner and spacer from the tbi to check the injectors out , both tbi injectors have a nice pattern and dont seem to be spraying to much fuel.but the idle air motor is wide open

witht he truck idling if i rech in and press up on the bottom of the egr valve to open it the idle smooths out and the rpms come up to what they should be, unfortunatly the motor was to hot to do it for anything longer then 10-15 seconds., the iac also closed up when i did this

the ecm has no stored codes and no check engine light

now heres were it gets puzzling i decided to check out the map sensor by unplugging it from the harness since this will put the ecm in limp home mode

in limp home mode the truck idles great nice and smooth with no misfires, but the truck stalls while u drive it , had a spare known good map sensor laying around and installed that truck still ran the same

also swapped out the coolant temp sensor with one i had , no change
did the same witht he o2 sensor no change

i do not have access to a scan tool to check live data , so i have to rely on checking sensors against known good ones , and or checking voltages /resistances with a dvom

all sensors with a 5v ref feed have 5 volts on the feed wire , all sensor grounds also check out good

unfortunatly i have no easy way to check the fuel presure as the tbi does not have a test port


any ideas guys ?
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Old 07-21-2013, 08:49 PM
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Check your TPS with the meter.Closed throttle should read @ 0.Reading should rise steadily as throttle opens to 5 volts @ WOT with no spikes or flat spots.
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Old 07-22-2013, 04:40 AM
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Also,what you describe with the EGR'is exactly backwards of what should be happening.If you open EGR @ idle,it should run ruff,or,die out.The EGR should only open @ hwy speeds,higher RPM.Ck your PCV system also.Could be clogged ports in intake under TBI.Opening EGR could be compensating for the blockage.
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Old 07-22-2013, 06:10 AM
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Could be a leaky FPR.
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Old 07-22-2013, 09:38 AM
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Quote:
Originally Posted by jokerZ71 View Post
Also,what you describe with the EGR'is exactly backwards of what should be happening.If you open EGR @ idle,it should run ruff,or,die out.The EGR should only open @ hwy speeds,higher RPM.Ck your PCV system also.Could be clogged ports in intake under TBI.Opening EGR could be compensating for the blockage.

thats why i thought but guys on my local forum are insiting that the egr may have a piece of carbon stuck in it so im going to pull it off today and check it.
Everything else on the truck has checked out tps pcv system etc etc etc

only thing i have not checked is the fuel presure i have to go get a tee and some barbed fittings so i can screw a gauge in place of the fuel filter
, hopefully when i pop the egr off i will find a piece of carbon or something stuck in it cause this really has me scratching my head at this point
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Old 07-22-2013, 12:34 PM
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pulled the egr off and made a blockoff plate , no changes

so i grabed a can of starting fluid since its all i had laying around and sprayed it around the intake, looks like the manifold gaskets went out , spraying around the distributor area and the passenger between cyls 6 & 8 the truck idles perfectly

looks like i get to rip the intake off tomorow and replace all the gaskets
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