6.0 Fuel pressure question causing no start?

GRN250

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Still working with a no-start issue. The fuel pressure builds to approximately 45psi when the key is cycled but quickly drops back to zero if the truck isn't started. I am thinking this has something to do with my truck not starting so I am questioning if this quick drop in pressure is normal. I am building oil pressure after 15-20 seconds, have ficm sync and 48v, crank/cam sync is present and the batteries check good. Thanks for your help.
 

6.0 Tech

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Still working with a no-start issue. The fuel pressure builds to approximately 45psi when the key is cycled but quickly drops back to zero if the truck isn't started. I am thinking this has something to do with my truck not starting so I am questioning if this quick drop in pressure is normal. I am building oil pressure after 15-20 seconds, have ficm sync and 48v, crank/cam sync is present and the batteries check good. Thanks for your help.

It is normal for that. The fuel pump only runs for about 30 sec, unless it sees rpm, then it’s commanded on constantly.

When you say building oil pressure, is that high or low pressure? And what is the psi if it’s hi pressure?


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GRN250

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Attempted to start the truck again after installing a 6.4 starter, 6.0 starter failed. The engine RPM was at 288, ICP peaked at 2255 psi then dropped to 1545psi, ICPR started at 14% then jumped to 85% then dropped to 48% once pressure developed. The FICM sync was steady but the crank and cam sync was coming and going. A new cam position sensor has been installed but not a crank sensor. Shouldn't the crank and cam sync be steady when cranking?
 

6.0 Tech

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Attempted to start the truck again after installing a 6.4 starter, 6.0 starter failed. The engine RPM was at 288, ICP peaked at 2255 psi then dropped to 1545psi, ICPR started at 14% then jumped to 85% then dropped to 48% once pressure developed. The FICM sync was steady but the crank and cam sync was coming and going. A new cam position sensor has been installed but not a crank sensor. Shouldn't the crank and cam sync be steady when cranking?

Yeah it should be steady. You’re probably gonna have to chase wires. Seen a bunch where the wires were damaged right at the back of the connector. Another common point is where the harness loops down under the air cleaner. You could also possibly have a bent crank tone wheel or one that came loose on the crank. Pull the crank sensor, and get a screw driver or something up in the hole and try to move the tone wheel. If it moves at all, that’s not good. If it doesn’t, feed a borescope up in the hole and crank it over and make sure there is no walk to the tone wheel


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bismic

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In addition to the above advice, you really can not depend on the reported ICP pressure. Sometimes that is an "inferred" value. You MUST watch the ICP sensor volts. If the PCM thinks that there is something wrong with the ICP sensor, then it will ignore the sensor output. This can happen even when the ICP sensor is working fine. Watch the ICP sensor volts when cranking.
 

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GRN250

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I'll check ICP voltage later today if possible. Forgot to mention earlier that the truck is not throwing any codes when trying to start. The crank sync is "pulsing" on and off but not throwing a code. Currently trying to remove the crank sensor and it is fighting the whole way! Thanks for the advice/help.
 

GRN250

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It took a while to remove the crank sensor but it looked good and the tone ring didn't move when I pushed on it with a screwdriver. I don't have anyone to work with me to spin the motor while watching the tone ring so that test is out for now. Ordered a new OEM crank sensor and waiting for it to arrive before progressing to check the ICP voltage. Thanks for your help.
 

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