6.0 Fuel pressure question causing no start?

GRN250 · Nov 18, 2022

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 · Nov 18, 2022

GRN250 said:
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 · Nov 19, 2022

The oil pressure mentioned is high pressure and it is approximately 2000psi.

GRN250 · Nov 23, 2022

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 · Nov 23, 2022

GRN250 said:
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 · Nov 24, 2022

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.

GRN250 · Nov 25, 2022

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 · Nov 25, 2022

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.

GRN250 · Dec 14, 2022

The new crank sensor and ICP sensor (OEM) were installed and still no start. The ICP pressure builds in approximately 10 seconds to 1500-2000 psi. The truck is gray smoking as it is cranked and has a slight smell of fuel. The crank to cam sync still drops from 1 to 0 in a timed/cyclical basis. Is this normal for the crank/cam sync?

When removing the ICP sensor, there appeared to be trapped air pressure in the rail and no oil escaped when the sensor was removed. Not getting any error codes on my AutoEnginuity during the attempts to start the truck.

6.0 Tech · Dec 14, 2022

Do you still have egr on the truck?

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GRN250 · Dec 15, 2022

6.0 Tech said:
Do you still have egr on the truck?

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The EGR has been deleted.

bismic · Dec 15, 2022

When you replaced the cam sensor, Was there rust on the surface o the block where the sensor rests? Rust can push the cam sensor just far enough away where the Sync can come and go.

Do you have a steady rpm signal? If so, then I would begin chasing cam sensor wiring.

GRN250 · Dec 15, 2022

The mounting surface was clean where the cam sensor mounts and the rpm signal is constant. The cam sync signal to FICM is constant but the crank to cam sync signal cycles at a constant interval.

bismic · Dec 16, 2022

Since the rpm signal is clean, I don't believe your issue would be with the crank sensor or its wiring. That is why I asked about the cam sensor and suggested its wiring as a possibility. I have seen cam sensor issues result in no cam/crank sync while still having FICM sync.

GRN250 · Dec 16, 2022

bismic said:
Since the rpm signal is clean, I don't believe your issue would be with the crank sensor or its wiring. That is why I asked about the cam sensor and suggested its wiring as a possibility. I have seen cam sensor issues result in no cam/crank sync while still having FICM sync.

Thank you. I'll ohm out the wiring when home again. Haven't heard of many PCMs failing but wondering if it could be an issue as well.

Maryland dieselnick · Dec 18, 2022

What is pulse width on sncanner? It can tell you if CPS, ICP and VREF Voltage are linked.

Maryland dieselnick · Dec 18, 2022

Thanks bismic

.
Over the years, I have always viewed you as a fine tech.

I hope that you and yours have nice holidays.

GRN250 · Dec 19, 2022

bismic said:
Since the rpm signal is clean, I don't believe your issue would be with the crank sensor or its wiring. That is why I asked about the cam sensor and suggested its wiring as a possibility. I have seen cam sensor issues result in no cam/crank sync while still having FICM sync.

The wiring, including polarity, checked good from the sensor to the PCM. Checked the ICP voltage and it is 2.8-3.0 volts. After changing the crank sensor, I noticed a swing in the RPMs. The RPMS mostly stay around 250-280 but did dip to 177 for an instant.

6.0 Tech · Dec 19, 2022

GRN250 said:
The wiring, including polarity, checked good from the sensor to the PCM. Checked the ICP voltage and it is 2.8-3.0 volts. After changing the crank sensor, I noticed a swing in the RPMs. The RPMS mostly stay around 250-280 but did dip to 177 for an instant.

Ok, so this seems like it’s an odd one.

What is fuel pressure while cranking? You said it dropped off after letting it set, but the pump should turn back on while cranking.

Also, what is FICM voltage, all 3 voltages, 2 should be battery voltage and one should be 48ish.

We’ve got icp, and it seems it’s trying to fire from the smoke out of the tail pipe. Are the glow plugs good? Do all injectors click good on a buzz test, none that don’t click or have a muted/dull click? Try plugging the truck in to get some heat in it if the block heater cord is installed, and see if that helps any. Leave it plugged in for 12 hours or so so it’s got plenty of time to get some heat in it.

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Maryland dieselnick · Dec 19, 2022

You need to go back to basics.
Verify 5 volts at cps, ICP as a ref voltage. If they are not getting their 4.5 -5.0, it’s a no link and pulse width command becomes a no fire command. Don’t look at ICP in voltage for pressure. One can but. Look to that in pressure. If are ok in and about 48 in FICM and RPM, pressure is hinky but with no No start command in duty cycle, You gotta pull out the meter and look for those 5 volts and 12 IPR scanner show actual on FICM.
You have a gremlin. Fuel will be no start, weak or fade-out.
Be careful back at that IPR. It’s a skin stripper.