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Ask Joe Prestia Your Own Question
Joe Prestia
Joe Prestia,
Category: Chevy
Satisfied Customers: 31
Experience:  Lead Automotive Tech at Belle Tire
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I have a 2009 chevy express 2500 6.0L vvt engine. Engine

Customer Question

hello I have a 2009 chevy express 2500 6.0L vvt engine. Engine cranks but does not start, I have compression spark injector pulse and fuel pressure, also no codes stored. But when I unplug the camshaft position sensor the van starts and runs fine. Plug the sensor back in and the truck does not start. I replaced the camshaft position sensor and it did not fix the problem I have gone through the entire harness and checked for open or shorts to ground and power every thing check out fine. opened the timing cover, engine is also in time so I am lost at the moment. Any ideas. I am also a licenced technician and this does not make sense.
Submitted: 9 months ago.
Category: Chevy
Expert:  Jared D replied 9 months ago.

How does the cam gear look? I've seen these shear off the keyway and let the cam gear rotate on the camshaft.

Customer: replied 9 months ago.
cam gear and locator pin on the cam itself is ok. valves open and close when I turn engine. if I unplug the cam sensor the van will run. if I plug the cam sensor back in the van does not start.
Expert:  Jared D replied 9 months ago.

Do you have any trouble codes?

Customer: replied 9 months ago.
no codes for anything
Expert:  Jared D replied 9 months ago.

Do you have a scope that you could use to check the signal from the Cam sensor and crank sensor? It's possible that the crank sensor could be the problem as well.

Customer: replied 9 months ago.
crank sensor is well within specs. I even gone as far as replacing and reprogramming the ecu and still I have the same problem. I hooked up a scope and it tells me the timing is out 180 degrees witch is not true the engine timing is dead on.
Expert:  Jared D replied 9 months ago.

Something has to have moved, the phaser, the reluctor ring, something.

Customer: replied 9 months ago.
I understand what you are saying I was also thinking the actuator itself, maybe stuck in advanced position and the cam sensor has a false reading but even when I stream live data cam and crank correlation is still ok. desired angle also is and actual cam angle is also ok.
Expert:  Jared D replied 9 months ago.

So if you unplug the sensor and start it and then plug it back in while running does it stall out?

Customer: replied 9 months ago.
it will. unplugged it runs, while running if i plug it back in truck dies after a couple seconds.
Expert:  Jared D replied 9 months ago.

I would probably pull that cam phaser and replace it. I would also pull the starter and look into the crank sensor orifice and see if there is any obvious damage to the reluctor ring with a good bore scope.

Customer: replied 9 months ago.
i have checked the reluctor wheel teeth, looks good. there is a tsb on this matter that does not make sense. it states a technician may encounter a no start but will have compression, spark and injector pulse. If engine starts with the cam sensor unplugged replace the engine. Absolutely does not make sense.
Expert:  Jared D replied 9 months ago.

I just found that also, but it doesn't say why it would need a new engine.

It just suggests checking for a powertrain warranty. What a bogus TSB.

Customer: replied 9 months ago.
all it indicates is that if the valvetrain doesn't move with the engine turning then the cam locator pin is sheared off, but in this case that's not the issue. i got the van apart right now and don't know where to go at this point. everything checks out ok.
Expert:  Jared D replied 9 months ago.

I would pull the cam phaser and just take a look.

Customer: replied 9 months ago.
that is what i was thinking.by cam phaser you do mean the cam gear itself right?
Expert:  Jared D replied 9 months ago.

Right.

Customer: replied 9 months ago.
now if everything looks good what would you do?
Expert:  Jared D replied 9 months ago.

I would pull the cam out and see if something has gone wrong. I'm not sure if that van is one where they press the cam journals and lobes onto the cam shaft. If that's the case, you could have a cam journal or lobe that has somehow spun on the shaft. Chevy did that on a couple of year models, but the express doesn't specify whether it has pressed cams in the manuals.

Customer: replied 9 months ago.
i understand what you are saying but the van runs fine, if it did spin a bearing the engine would seize up or something catastrophic would happen
Expert:  Jared D replied 9 months ago.

No, I don't think it spun a bearing, Chevy had a couple of CAM shaft designs where they pressed the cam lobes to the cam. If they weren't manufactured correctly the lobes could spin, thereby changing the valve timing.

Customer: replied 9 months ago.
if a cam lobe did spin wouldn't the engine not run or run very poorly when the sensor is unplugged
Customer: replied 9 months ago.
because when it is running there are no misfires also
Expert:  Jared D replied 9 months ago.

Yeah, that's the strange part. It would have at least a slight miss.

You are sure the cam sensor isn't faulty right?

Customer: replied 9 months ago.
yup its a brand new sensor.
Expert:  Jared D replied 9 months ago.

Not sure what else to suggest from here. I think the best bet will be to check out that cam.

Customer: replied 9 months ago.
ok thank you
Customer: replied 9 months ago.
camshaft is ok
Customer: replied 9 months ago.
Expert:  Jared D replied 9 months ago.

Sorry. Got pulled away here at the shop.

With all that you have done, I'm at a loss. I'll opt out and see if anyone else has any insights.

Customer: replied 9 months ago.
ok sounds good thank you for your help i will keep this page open if you want to send another message
Customer: replied 9 months ago.
have it all back together sensor is plugged in and the truck remains running now before it would die when i plug in the cam sensor. but still wont start unless its unplugged. when running i plug in cam sensor and no codes very weird and cmp actuator data is good too
Expert:  Joe Prestia replied 9 months ago.

Here's a thought. Try plugging in the cmp and unplug the alternator. I was told by one of my local dealers a while back that a handful of these vans got wrong alternators in them. If I correctly recall they were causing things like misdiagnosed throttle bodies or something. It's kind of a shot in the dark but I want to follow along on this if you guys don't mind.

Expert:  Jared D replied 9 months ago.

Now that it's somehow running...will your scan tool do a cam variation relearn?

Customer: replied 9 months ago.
when i watch cmp actuation through my scan tool everything looks good commanded angle versus desired is dead on and with 0 degrees variation.
Customer: replied 9 months ago.
with the cam plugged in it still wont start but it sounds like it wants to.
Customer: replied 9 months ago.
just spoke with the cutomer he said right before the van died on him the service trak light came on and went away. no codes in ebcm either
Customer: replied 9 months ago.
Expert:  Jared D replied 9 months ago.

I would probably replace the new cam sensor and then see if you can perform a cam variation relearn.

Customer: replied 9 months ago.
nothing wrong with the new cam sensor why would i replace it.
Expert:  Jared D replied 9 months ago.

It just seems to me that it can't be working right if the engine won't run with it plugged in and you have already fully tested the PCM. Unless there is a short to ground somewhere between the cam sensor and the pcm...

Customer: replied 9 months ago.
there is no open or short to anything have gone through the entire vehicle. very weird. i did put another sensor and its the same thing
Expert:  Jared D replied 9 months ago.

Still nothing with a new sensor? I have all of my Technicians pondering this one and we all come up puzzled.

Customer: replied 9 months ago.
when I figure t out ill let you know
Expert:  Jared D replied 9 months ago.

That sounds great.

Customer: replied 9 months ago.
I think somewhere in the harness there is rmf interference of some sort happening
Expert:  Jared D replied 9 months ago.

Maybe an aftermarket alarm or remote start?

Customer: replied 9 months ago.
I thought so to but that is not the case
Expert:  Joe Prestia replied 9 months ago.

I'm showing green with black tracer to the instrument panel and central junction box. Red to to battery junction block but turns orange at connector #3001. And a Black battery cable. Assuming this is 2.0 engine. If equipped with a 2.5 let me know and I'll check again

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