Rough idle and rough running only when cold?
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Rough idle and rough running only when cold?
A buddy has an 03 7.3 truck with 80k miles. In cold weather the truck idles really rough and doesn't run smooth driving either till the temperature comes up some and then it runs perfect. Now that we've got warm summer weather it runs pretty good all the time but it's something he'd like to fix prior to winter. Any ideas where to start?
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Joined: Jun 2004
Posts: 9,293
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From: Parker, CO
To address the rough idle after a cold crank, check the GPR and also ohm out the glow plugs. More than likely a few plugs are burned out, so it's going to run rough until the temps start rising in those combustion chambers. Healthy glow plugs will run for up to 2 minutes after cranking the truck.
Next is the poor driveability when the engine is cold. The likelyhood is the exhaust backpressure valve staying closed. This is caused by the backpressure sensor tube being clogged with soot, so the PCM doesn't know that the valve needs to be opened to relieve that pressure when accelerating. With a closed off EBPV, the turbo can't spool up and you have an engine that is bogged down. The tube runs from the passenger's side manifold to the front of the engine under the idler pully. Remove the sensor that sits on top of it and clean out the tube with something long and thin enough to get in there.
Next is the poor driveability when the engine is cold. The likelyhood is the exhaust backpressure valve staying closed. This is caused by the backpressure sensor tube being clogged with soot, so the PCM doesn't know that the valve needs to be opened to relieve that pressure when accelerating. With a closed off EBPV, the turbo can't spool up and you have an engine that is bogged down. The tube runs from the passenger's side manifold to the front of the engine under the idler pully. Remove the sensor that sits on top of it and clean out the tube with something long and thin enough to get in there.
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