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Author Topic: 02 8.1 crank sensor symptoms but no codes  (Read 173 times)

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baggednismo

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02 8.1 crank sensor symptoms but no codes
« on: January 15, 2020, 07:43:34 AM »

Hey All,

The problem I am having with this Avalanche is best described by every other thread detailing the crank/cam position sensor. It randomly shuts off, goes days without doing so and then once it starts it will do it all day at different intervals. Once it starts shutting off it never stays running more than 15 minutes at a time. Leave it til the next day and it will start and run fine. I can let it warm up 15+ minutes and then drive for 45min to work without incident. I can also start it after work without a warm up period and drive it home 45min without incident. I feel that if i am city driving i have a much higher chance of this happening but I have had it quite on the highway (only after it starting shutting off during city driving).

Once it shuts off I have to prime the fuel pump 5-6 times (seems to reset the sensor) and it will start. Its a rough start but it starts nevertheless. Wont stay running for long though. I replaced the fuel filter in hopes this would resolve it but that didnt help.

Could it still be a bad fuel pump? Sure, even though it sounds just like the sensor it could be the pump. definitely.

How can you be so uncertain when we have automagical electronic devices that read the codes from the ECM? Oh, well, it records absolutely no codes after it randomly shuts off...   :E: Both the dealer and a local shop say there are no codes. I brought it to both multiple times even went to a local parts store a day that it was happening and nothing.

My cheap $10 bluetooth reader and android phone however say otherwise. While I cant say I trust this thing I can get a code out of it after it shuts off but only immediately after. scan with this phone/device later and I receive no codes at all. Using Torque Pro I get P0336 and with Car Scanner I get P0011 both are crank position codes.

Assuming it were the pump and it was not electrical that could also not pop a code but I would still expect to see a cylinder misfire or something that makes sense. To have absolutely nothing for codes its really starting to peak my interest that maybe this isnt a crank sensor and fuel pump but rather an ECM issue.

I have it in the shop right now, they are replacing the crank position sensor based on my findings and research. They are not guaranteeing any work because they cannot find anything in the ECM to indicate that is the problem. The dealer wouldn't do the work at all unless they could prove that was the issue and without a code they are about as useful as a condom machine in the Vatican. Both shops dont know why its doing what its doing but I have a sneaking suspicion this might not resolve the problem.

Please advise.

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BainMan

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #1 on: January 15, 2020, 08:05:42 AM »

Fuel pressure test from the rail while it's acting up?
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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #2 on: January 15, 2020, 08:59:47 AM »

Fuel pressure test from the rail while it's acting up?

I would start with this.

For what it's worth, I have never had a code thrown on any of my GM trucks when a fuel pump went bad.

They either died with no warning or displayed some odd no or slow starting behaviour in a time period before they eventually died.

Manually check the fuel pressure with key on/engine off, engine running and also watch for pressure leak down after the engine is turned off.

This should give you a sense of the health of the fuel system.
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baggednismo

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #3 on: January 15, 2020, 09:32:08 AM »

I will need to get a guage to test this.

I appreciate the fast response guys. I will look into the tool and have it in the truck for the next round if the sensor doesnt fix it.
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2004Slickside

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #4 on: January 15, 2020, 09:54:15 AM »

I will need to get a guage to test this.

I appreciate the fast response guys. I will look into the tool and have it in the truck for the next round if the sensor doesnt fix it.
Get loaner from pretty much any local parts store like Auto Zone, Advance Auto Parts, O'Reileys - they all have loaner tools with deposit.  Just screw it onto the Schrader valve and be careful about leaks.

If you replace or even disturb the crankshaft sensor, you are supposed to have a crankshaft sensor relearn done.  Failing to do this won't cause an actual misfire, but can cause a SES light with false P030x (misfire) codes.
« Last Edit: January 15, 2020, 09:57:43 AM by 2004Slickside »
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2004Slickside

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #5 on: January 15, 2020, 10:00:21 AM »

Crank sensors are often replaced for no good reason and reported as a fix by those who are clueless.  They are very simple and are not prone to failure.

I'm betting on the fuel pump.  If so it will become apparent when you test. 
« Last Edit: January 15, 2020, 10:03:18 AM by 2004Slickside »
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baggednismo

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #6 on: January 15, 2020, 10:14:53 AM »

I have heard of this crank sensor relearn. Has to be done on a tech2 and only a tech2 from what i have seen.

Not that its a good guage but i can get a relatively cheap on from harbor freight or local auto parts store $50 or under which im going to do. That will give me what i need at least to figure out the issue.

what are the specs of the PSI priming/on/running etc?
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BainMan

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #7 on: January 15, 2020, 12:20:51 PM »

What model year you rocking baggednismo?
« Last Edit: January 16, 2020, 07:43:00 AM by BainMan »
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BainMan

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #8 on: January 16, 2020, 07:43:07 AM »

http://www.agcoauto.com/content/news/p2_articleid/280

The whole article is a worthwhile read. But to answer your question, i extracted the following two paragraphs from the article linked:

Around 2003, the system changed, and they specify fuel pressure as 55 to 62 PSI on the V-8 and six-cylinder.  Tests are with a cold engine, key on, engine off.  Acceleration will cause a slight increase in pressure.  This system is before the body style change, around 2007.

The fuel pressure specification for the non-Classic style, in 2007 is 50 to 60 PSI.  This again changes with the introduction of the fuel-pressure control-module, around the 2009 model.  Until 2013, the specification is 50 to 100 PSI.
« Last Edit: January 16, 2020, 07:46:28 AM by BainMan »
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2004Slickside

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #9 on: January 16, 2020, 09:32:04 AM »

I have heard of this crank sensor relearn. Has to be done on a tech2 and only a tech2 from what i have seen.

Not that its a good guage but i can get a relatively cheap on from harbor freight or local auto parts store $50 or under which im going to do. That will give me what i need at least to figure out the issue.

what are the specs of the PSI priming/on/running etc?
Assuming the 8.1 is the same as the 5.3, you should get about 60 psi on the first time key is turned on.  If it takes several key cycles to get the pressure up, then system is leaking down VERY badly or fuel pump is bad.  Once pressure is up and key is turned off, pressure should hold in the 50's for some time.  If doesn't hold, then gas is leaking past the regulator or coming out of an injector, or the check valve in the fuel pump is bad.  When engine starts, vacuum is applied to the regulator to lower the fuel pressure and from then it varies with engine load.

What is cheaper than a free loaner gauge?

Crank sensor relearn can be done with various scanners and softwares, but not with the cheapo stuff.  I have two (not Tech 2) that will do the crank sensor relearn.  HP Tuners VCM scanner (windows - $350) and the Vident Ilink400 (Definitely Chinese - $160) https://www.amazon.com/gp/product/B07FVMQ9TK/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1.  I would highly recommend the Vident to anyone that wants more than an Android Bluetooth scanner like Torque (Torque is also VERY handy to have).  The Vident does brake bleeding, ABS, air bags, etc, lots of stuff but first you have to update software via the Internet.  There is one Android Bluetooth Software that will display/clear codes for lots of systems on the data bus - even HVAC - Car Gauge Pro - but it really doesn't support past 2006 model year for GM Enhanced PIDs at all.  Also good Bluetooth/Android software is Dash Command - any years they claim, but you have to buy PIDs for each vehicle.  I like them ALL!!!  Which one I use depends on what I am trying to do.  If I could only have two I would want the Vident and the Car Gauge Pro.
« Last Edit: January 16, 2020, 09:43:40 AM by 2004Slickside »
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baggednismo

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #10 on: January 16, 2020, 17:02:58 PM »

Alright, so far I got the truck back from the shop and they had replaced the crank position sensor as well went through the relearn. It will take time to tell if it fixed it. I will update the thread if it didnt until the solution is found.

I already purchased the fuel pressure tester. Sure, I can borrow one but this truck went over 3 weeks without the issue. If this was happening every day or at least a few times a week I would just borrow one but i dont know if and when it will happen again. could be next month. could be tomorrow. Nevertheless Its in the truck and if it happens again I have one.

As of right now (without the truck acting up) fuel pressure looks good. The key is when its acting up.

@BainMan its an 02' 8.1 with the body cladding.
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2004Slickside

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Re: 02 8.1 crank sensor symptoms but no codes
« Reply #11 on: January 17, 2020, 21:15:30 PM »

Alright, so far I got the truck back from the shop and they had replaced the crank position sensor as well went through the relearn. It will take time to tell if it fixed it. I will update the thread if it didnt until the solution is found.

I already purchased the fuel pressure tester. Sure, I can borrow one but this truck went over 3 weeks without the issue. If this was happening every day or at least a few times a week I would just borrow one but i dont know if and when it will happen again. could be next month. could be tomorrow. Nevertheless Its in the truck and if it happens again I have one.

As of right now (without the truck acting up) fuel pressure looks good. The key is when its acting up.

@BainMan its an 02' 8.1 with the body cladding.
Now you know how the fuel pressure is supposed to be for future reference.

Please do let us know.  Alway interested in the cures.  Good luck and best wishes.
« Last Edit: January 17, 2020, 21:17:16 PM by 2004Slickside »
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