2005 Sierra Occasional crank/no start

rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
Hey folks,

My old but faithful 2wd workhorse (GMT800) has an unusual occurrence that has me pondering about how to approach a diagnosis. I thought I'd check with the brain trust to see if there is some existing experience to guide me.

For the past few years, when starting the engine, hot or cold, the engine will crank but not start. When I realize it's not starting, all I have to do to get it running is to turn the key off and try again, and it starts immediately. There are no codes nor other tell tales.

I'll mention that I recently replaced the ignition switch with a low mileage used one out of a GMT360, as they share the same part number. The replacement switch made no impact on the symptoms I just described, but it did improve the feel of the switch operation, providing a slightly better spring return from the start to the run position.

I'd like to hear your thoughts on how to approach a diagnosis. My initial assumption is to go look at and confirm the cam and crank signals and monitor their synchronization. But maybe I'm barking up the wrong tree. What say you?

Thank you,
Rick
 

gmcman

Guru
Dec 12, 2011
4,526
Do you have to turn the key off then back on when restarting to get it to start? What happens if you leave it on and only turn the key to the start position?

Not sure if yours has an oil pressure fail safe but if so it's someplace to check.

Also regarding the fuel, have you tried a new fuel pump relay?
 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
Do you have to turn the key off then back on when restarting to get it to start? What happens if you leave it on and only turn the key to the start position?
@gmcman I not tried seeing if it starts the second time without turning the key off first. That is an easy and sensible test to try that may provide further insight. The oil pressure fail-safe is a feature I had not thought of, due to the random and infrequent nature of the no start. I'll add that to my list of items to monitor when the scanner gets exercised, thanks.

@azswiss I have not checked fuel pressure. I can do that easily, and will confirm pressure soon. Currently I have the injector fuel rail off for installing a set of new (China!) injectors. I'll supposedly have them when the slow boat arrives on Wednesday!

@TJBaker57 I have not seen anything unusual with dash warning lights, and I lack experience with the Passlock security feature. Please describe what to look for for regarding possible telltales.

Regarding fuel delivery, and/or coil triggering, my thought is that the 'puter won't operate those system circuits without synchronization of the ckp and cmp signals. As of this moment, I'm assuming the fuel pressure is going to be there when I check it, and the issue is more in the Passlock security feature or some other condition (oil pressure!) that is not being met for commencing spark and fuel.

I appreciate the insight, and have a few new items to monitor.
Thanks to all,
Rick
 
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azswiss

Active Member
May 23, 2021
269
Tempe, AZ
@rchalmers3, you might also try swapping the fuel pump relay with a comparable relay from another circuit in the fuse box. As an example, on my '03 Suburban (GMT830, 5.3L) the fuel pump relay part # is also used for multiple features (horn, windshield washer, etc.).
 

TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
@TJBaker57 I have not seen anything unusual with dash warning lights, and I lack experience with the Passlock security feature. Please describe what to look for for regarding possible telltales


This is but one of a dozen or more entries from manuals covering my 05 Yukon.....

Screenshot_20211114-163324.png

I am uncertain whether or not there are conditions possible where cranking is enabled but fuel injectors are disabled.

The item that caught my attention was returning the key to off. The Passlock sensor activates at the turning of the key to CRANK. The sensor retains the activated state until the key is turned to OFF at which time the BCM removes the power feed to the Passlock sensor. I have read of instances where the Passlock sensor was not tripped by the magnet of the rotating lock cylinder due to wear or what have you. I have not personally seen such an instance though.
 

Reprise

Lifetime VIP Donor
Jul 22, 2015
2,450
My '03 Sierra has this issue; I've been working on it, but haven't resolved it, yet (to which you may think... "so, what good is the info you're giving, below?" LOL... that's fair.)
With mine, when it happens, it'll immediately start on the second crank attempt (no pedal).

(also, btw, I had replaced my crank / cam / oil pressure sensors earlier, as part of another project... no change / improvement). If you replace the crank sensor, btw, you're supposed to do a crank position relearn sequence as part of the replacement.

There's some differences between our two trucks; fuel filter & fuel pressure regulator were moved to the pump assembly on yours; also, the fuel system was made 'returnless' (you only have one fuel line at the intake manifold; I have a second that goes back to the tank).

The pump has a check valve, which prevents fuel pressure from bleeding off too low between starts, and it's in the pump assembly as well. As a test...
- From a cold start, turn the key to 'on' for 5 seconds. You should hear the pump activate (good idea to kill the radio / hvac fan while doing this). After 5 sec, it'll go quiet. Key off.
- Wait a couple of seconds, and repeat (key on, listen for pump activation). When the priming cycle stops, crank the engine and see if it starts on the first crank.

On yours, you can't test / replace the FPR without replacing the entire pump assembly. Same for the filter.

Hook up a fuel pressure gauge (you can rent them) to the test port (RH / passenger side of fuel rail). Run the engine, shut it down, and check the resting fuel pressure. It should generally be in the low 40lbs or higher; if it bleeds down into the 30s or lower (either immediately, or after a few minutes or longer, that's considered too low to reliably start the engine.) If you see this, it's a good indicator the check valve is bad (not uncommon).

Before replacing the fuel pump (lots of work), swap the fuel pump relay with one of the others in the underhood fuse box, and see if the problem lessens / goes away. It's a lot cheaper / easier to replace this relay, over the pump.
This relay is the same as a couple of others in the underhood box, so if you just decide to buy one / try it, and the existing ones were still good... you'll have a spare, and won't be stranded on the side of the road someplace).


Notes on replacing the pump...
(and there are videos a-plenty on doing this... Briansmobile on You Tube has a good one, using the 'bed tip' technique.)

First... relieve the fuel pressure. Start the truck, pull the fuel pump relay, and the engine will stumble to a stop about 5 seconds later. After the work is done, it's better on the starter / fuel pump if you prime the system to re-pressurize it, before cranking the engine (see above).

If you decide that the fuel pump is the culprit, you have the choice of tipping the bed on the driver's side, or dropping the tank. I've done both; I personally prefer the tank drop (with two floor jacks, it's not too bad.) Try and do it with 1/4 tank of fuel or lower. You do have two metal retaining straps to disconnect; the bolts can rust in place / break off. Replacements are available, if needed. If you live in the salt belt, put your penetrant of choice on those bolts at least a day before attempting to remove them. 15mm bolts, IIRC.

If you go to tip the bed, you have 4 bolts to remove on the driver's side, along with disconnecting the filler neck (and the ground strap!). On the passenger side, loosen the opposite side bolts almost all the way, but don't remove them. Once the bed is lifted, you have to be a bit of a contortionist to squeeze in between the bed and frame, while working on the pump retaining ring / connections. Oh, and get a new metal retaining ring. The old one will be rusted in place. There's also a plastic lock tab on it that needs to be pushed in, once you get the ring to start moving (counter-clockwise to loosen).

If you have an engine hoist or similar, definitely hook it up to the driver's side of the bed. Even so, you'll want to brace up that side with 2x4s, etc., to prevent it from falling. Because if it does fall with you in between, you'll be seriously hurt, or even killed.

If you have a friend or two, and room, you can just outright lift / slide the bed back (or off). This is by far the easiest option, but it's tough to do if you don't have help; the bed weighs a couple of hundred pounds. Again, you'll need to disconnect the fuel filler neck and ground strap... and you'll also want to disconnect the 4 plugs from the main harness connector at the back of the bed, on the driver's side. Removing the tailgate beforehand saves some weight, before lifting the bed.

If yours is the original fuel pump, you may have to rewire the connector (it's still 4-wire, but the old style is a 4-inline plug; GM went to a stacked 2-on-2 plug after '03). Most kits for trucks around that timeframe supply the new style plug / pigtail, to wire into the circuit. I think (?) the wire colors are the same, but check. You may be spared having to do this, since yours is an '05.

As far as pump brands... the Carter pumps are 'made in USA', but tend to fail.
The GM (AC Delco) and Bosch pumps are generally regarded as the most reliable. The AC Delco, especially, is pricey. Bosch used to supply the OEM pumps for GM, so if you can find one significantly cheaper, it's as if you replaced with an ACD, anyway.

Moving on from the pump, if the existing pump / relay test out good... prevailing wisdom next checks the EVAP valves / solenoids, along with the charcoal canister (next to the fuel tank). The purge valve is a green-shaded object on your intake manifold (my '03 has it at the front of the intake; yours is likely on the D/S of the manifold.) Your purge solenoid is near the charcoal canister, if you have one (my '03 doesn't, but I have the 6.0L; if you have the 5.3L, you'll likely have a solenoid.) What you're checking for here is a blockage; you can disconnect the plastic tubing at both the tank and manifold ends, and see if you can get air through it. With the charcoal canister, if you find that it's blocked, you can sometimes run compressed air through the inlet / outlet, and get it at least partially unblocked. (Note - If you've had problems filling the tank, with the gas nozzle / pump shutting off constantly, you may find this situation resolved / improved, as well).

In order to test the valves / solenoids, you'll need a high-end scanner to activate them (like a GM Tech2, or similar).
 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
Thread resurrection time. Happy New Year fellas, and thank each of you who have offered your ideas and suggestions. I appreciate having more eyes on the task!

I spent a few moments out in the cold the past few days, eliminating some of the potential culprits behind the occasional crank but no run issue I'm interested in solving.

The first test was confirming the CMP and CKP signals were present and correct. You folks were not aware of the complete history of the vehicle. This past summer I had the engine out for resealing and freshening. I left the long block assembled and repackaged it like it was a new engine! While it was out I replaced both CMP and CKP sensors due to traces of engine oil inside the connector cavities. I once again used the price attractive Chinese units bought off Amazon. While the issue was present previous to the sensor replacement, I nonetheless needed to put aside the notion that I had induced collateral problems while installing inferior parts. Here is a screen capture of the cam and crank sensors while cranking the engine and exhibiting the no starting:
IMG_0403.jpg
The peak voltages are a bit low due to the starter draw, but it's cranking normally and the peak voltage on both sensors goes up when it does run.

Next I confirmed the fuel injector rail does indeed build and hold 51psi. I could hear the pump run and was not concerned about this possibility due to the unusual and intermittent nature of the issue, but I wanted to cover all the bases you fellas have suggested.

Lastly I monitored a fuel injector duty cycle using a multi-meter. I also monitored for spark via an inductive timing light around a plug wire. I have confirmed that whatever is happening is inhibiting both spark and fuel injection. With spark and injection present, off we go!!!

@TJBaker57 I'm interested in exploring your postulate regarding the theft deterrent system. It seems to fit the situation better than anything else suggested thus far. This old beast has 370k on the clock, and it's had a rough life before I put it in my stable. What do you suggest I do to divide and conquer the Passlock system? Is there something in the FSM for me to utilize to perform checks on the components? Your thoughts and experience is appreciated.

Thanks again to all,
Rick
 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
Do you have to turn the key off then back on when restarting to get it to start? What happens if you leave it on and only turn the key to the start position?

Not sure if yours has an oil pressure fail safe but if so it's someplace to check.

Also regarding the fuel, have you tried a new fuel pump relay?
@gmcman I do not need to turn the key to off. I can return it to run, then try again to start it and it fires and runs immediately. Furthermore, during the past testing period, I learned that it will sometimes start after prolonged (6-8 seconds) cranking.

It's an old engine, so I can imagine that it does not build oil pressure like a fresh, younger engine would.
Please advise me on monitoring the fail-safe to see if that is a cause.

No need for swapping relays. The pressure is good. It is missing both spark and fuel during the condition.

Rick
 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
I just signed off this forum and went looking in Mitchell DIY at the Passlock system diagnosis.

I saw there that there is a method of investigating the Passlock system when it cranks but won't run. I am to follow the diagnosis path that is described in fault code B2958. I have to ignore some of the conditions and actions, as the diagnosis and repair procedure is predicated on the code being set. Since I'm not having a warning light illuminated nor a fault code, I'll investigate this issue through the diagnosis procedure as if I do have a code. I'll keep y'all informed of my findings.

Rick
 

TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
I do not need to turn the key to off. I can return it to run, then try again to start it and it fires and runs immediately

This bit of information would lead me away from thinking the Passlock system being a cause. The reason I say this is that the Passlock sensor circuitry 'latches' when activated by turning the key to CRANK and passing the magnet in close proximity to the sensor. Once latched the sensor remains in that state until power is removed from the sensor. Returning the key to RUN does not do this and thus the Passlock does not reset until the key is turned back from RUN. On my TrailBlazer the reset occurs at ACC as seen in this video. The video is a silent film as most of these I do simply to remind myself "how does this work again?!" There is a short summary of operation in the video description.

 
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TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
I must confess that even though I own an 05 Yukon it's wiring is unknown to me. On my 4.2 Vortec TrailBlazer I know the fuel injectors and coils share a common power source. If the Yukon/Sierra does the same could you be looking for something like a bad fuse socket in the fuseblock or similar such condition?
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
From what I remember, when Passlock is activated (locked), it won't even allow cranking. That I know for sure during the security relearn.

Sounds more like an intermittent electrical issue. Have you taken the fuse box apart and checked the copper traces and fuse connectors? Maybe a loose fuse could do this. Because of the nature of the intermittent failure, there's almost no way to determine if it's the coils or injectors that fail to fire. You would need to check on your first start attempt. Maybe noid lights on the injectors and coils could tell.
 
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MRRSM

Lifetime VIP Donor
Oct 22, 2015
5,714
Tampa Bay Area
This may be a solution with very nice simplicity if THIS turns out to be the source of the problem:


If not... Remembering your actions mentioned in the 1st Post... Occam's Razor might suggest replacing the Used OEM Ignition Switch with a Brand New ACDelco Unit:

One more suggestion involves checking the "Sweet Spot" on a slightly Mal-Adjusted Park Neutral Safety Switch ...which can occasionally jump up to bite us when out of alignment. :>(
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
One more suggestion involves checking the "Sweet Spot" on a slightly Mal-Adjusted Park Neutral Safety Switch ...which can occasionally jump up to bite us when out of alignment. :>(
According to his symptoms, I doubt it would be this as this would prevent it from cranking at all. His cranks but intermittently fails to start.
 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
....... Because of the nature of the intermittent failure, there's almost no way to determine if it's the coils or injectors that fail to fire. You would need to check on your first start attempt. Maybe noid lights on the injectors and coils could tell.
..... could you be looking for something like a bad fuse socket in the fuseblock or similar such condition?
Thanks fellas, I can easily probe the pink wires supplying power to the injectors and coils. I'd be very surprised and pleased to find the solution to be so basic. However I don't hold much hope for this being the case. I imagine there would be other driving symptoms relating to this idea.

@TJBaker57 I appreciate your study and postings on the Passlock circuit. I will continue to investigate this area further, as I don't currently have other alternatives to consider.

The engineers must have experienced some permutation of circumstances that will cause a crank/no start condition that is outside the programmed checks and measures. My proof of that is the missive I read at the end of the B2958 fault code description that recommends following the fault tree in the case where there is no lit indicator light nor codes.

I happen to have a spare GMT360 steering column laying about. Part of my investigation will be to feed some firewood into the basement stove for comfort, then have a good look at the pieces that comprise the Passlock system.

Thanks again to all,
Rick
 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
If not... Remembering your actions mentioned in the 1st Post... Occam's Razor might suggest replacing the Used OEM Ignition Switch with a Brand New ACDelco Unit:

One more suggestion involves checking the "Sweet Spot" on a slightly Mal-Adjusted Park Neutral Safety Switch ...which can occasionally jump up to bite us when out of alignment. :>(
Thanks @MRRSM I recently opened the wire harness, traced and repaired the G10x (can't remember the specific number, but it was on the rear of the passenger cylinder head) mentioned in the video after having the engine out for repairs. The ground was intact from the head to the ECM, but had a severed splice leading to the transmission.

Rick
 
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TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
then have a good look at the pieces that comprise the Passlock system


To save you any destructive testing maybe take a look here at this video where I show a Passlock sensor removed from the housing. Removing the sensor usually destroys the assembly. I have 3 or 4 of them taken from junkyard vehicles. I have even gone so far as to trace the circuitry of the sensor and identified
the specific resistor that varies from one vehicle to the next in order to produce that semi-unique signal to the BCM. Too much time on my hands I guess!!

IMG_20210310_185719~2.jpg




 
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rchalmers3

Original poster
Platinum Donor
Jul 11, 2020
166
Irmo, SC
To save you any destructive testing maybe take a look here at this video where I show a Passlock sensor removed from the housing. I have even gone so far as to trace the circuitry of the sensor and identified the specific resistor that varies from one vehicle to the next in order to produce that semi-unique signal to the BCM.
@TJBaker57 Thanks for sharing your explorations. I'll share with viewers these reference images, first of the Passlock sensor in-situ on the Key assembly:
IMG_0405.jpg
Next, with the key cylinder removed, you can see the Passlock sensor exposed in the lining of the lock cylinder cavity:
IMG_0406.jpg
Finally, a blurry close-up photo of the magnet embedded in the key lock cylinder:
IMG_0407.jpg
Given my current understanding of the Passlock system operations, I agree with you that I won't find a solution to my issue within the Passlock data communications back to the BCM. The body codes that relate to Passlock voltage and data errors seem to cover the potential issues it may experience. On the other hand, I do not have any other ideas to explore. If you have any other ideas that I can arrange to test for, I'm all ears.

EDIT: I have another observation to add to the symptoms: sometimes I hear what I think is a backfire through the intake when the engine does eventually start. This occurs about 20% of the time after it starts running.

Rick
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
I'm thinking it's still the ignition switch. What you could do is semi permanently install some lights to it that will correspond to each key position (aux, run and start) and watch them each time you start it for when it does the crank no start.

You could do the same for the ignition coil and injector power.
 

MRRSM

Lifetime VIP Donor
Oct 22, 2015
5,714
Tampa Bay Area
As a Follow On to your Investigation... You KNOW All of this Information already... But for other interested Readers using Oscilloscopes:

It is VERY nice to see your use of an Oscilloscope for making comparisons between the timing of your (CKP) Crankshaft Position Signal vs. the (CPS) Camshaft Position Signals. However, a small suggestion here would be to overlay them BOTH on screen within 720 Degrees in view on their Rising Slopes.

Then, after setting your Trigger Point on the Crankshaft Notch Break at TDC for Cylinder #1... ZOOM in close enough to be able to make an A/C Sine Wave Signal Count of the (CKP) ...just ahead of the Rising Slope at the start of the (CPS) Hall Effect Camshaft Square Wave Signal as depicted below:.

This is a different GM Motor involved here… but conceptually still accurate:

Known Good Wave Form of (CKP) RED Sine Wave versus (CPS)GREEN Square Wave Signal on the Scope:


GOODCRANKWAVEFORM.jpg

The Discovered BAD Wave Form of (CKP) RED Sine Wave versus (CPS) GREEN Square Wave Signal on the Scope:

BADCRANKWAVEFORM.jpg


It only takes a variance of 2-4 Degrees of Advance or Retard being off in their relationship to confuse the PCM and prohibit the Engine from Timing the EFIs and Ignition Spark close enough to prevent the Engine from either running very rough, poor idling or stalling.

I don't have a "Known Good Wave Form" of these two signals for the LS Motor in your Truck, but if you can find one online, it will save a lot of time in the decryption of those enough to pinpoint problems.

These Engine Stumbling Issues may manifest as having either excessive Crankshaft Main Bearing Wear causing the Reluctor Ring Teeth Points to Wobble in and out from the (CKP) Sensor showing on screen as Vertical Waves in the A/C Signal Peak and Valleys, or from a Loose Reluctor Ring, a Loose Crankshaft Bolt/Harmonic Balancer or a Stretched or worn Timing Chain and Gear Set that can plague High Mileage Engines.

Post #23 in THIS Thread delves into greater details on this subject:

 

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