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Intermittent loss of ignition while driving

Tiny
BRAD97
  • MEMBER
  • 1999 CHEVROLET SUBURBAN
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 210,000 MILES
The engine/transmission/transfer case all have under 25,000 on them (full rebuilds of mechanical) but most electrical was reused from before rebuild.

Recently I have been experiencing a sudden loss of ignition while driving. I can be sitting at a stop light, lightly accelerating or on the interstate. Randomly it will lose power like someone turns the key off, then will go back to running like normal. The loss of power is always short, under 1 second then it runs fine. I am not losing any electrical in the cab when this happens. A/C blower, radio, gauges, lights all stay functioning. The only time I noticed a different scenario was the fuel gauge jumped from 3/4 to completely pointing down (due south) then right back to 3/4. I ran the codes and got one for crank sensor voltage outside of threshold. I replaced the crank sensor and the code disappeared but was replaced with the code for the CPS synch but nothing else.

I am still having the issue after replacing the CPS and do not want to just throw parts at it.

I should mention that cap, rotor, plugs, wires are new (under 2,000) AC Delco.
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Wednesday, September 22nd, 2021 AT 9:39 PM

11 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
At this point we can rule out an interference issue if all the ignition is new but let's start with what the actual code is that you have.

If you have a crank code and now a cam code then that will be related to what we are seeing.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Here is a guide that talks about this issue. Clearly the crank sensor is the likely issue but if that is replaced then it could be something related to the sensor like the PCM or voltage supply to the sensor.

https://www.2carpros.com/articles/engine-stalls

So this means we need more then likely monitor voltage on these sensors to find out why it is saying they are out of sync. However, let's start with the code and see what testing they have us run through and we can go from there.

Thanks
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Thursday, September 23rd, 2021 AT 8:47 AM
Tiny
BRAD97
  • MEMBER
  • 6 POSTS
So currently the only code reading is p1336 with a secondary p1336 archived.
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Thursday, September 23rd, 2021 AT 4:29 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Perfect.

If this is a new sensor then that means we need to do the learn procedure which most scan tools can do.

If it will not learn the CKP sensor then we could have an issue with the tone wheel on the crank.

So we need to chase this down because this make perfect sense as to what is happening so I am pretty sure this shutting off it related to the crank sensor.

See the info below on this.
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Thursday, September 23rd, 2021 AT 6:49 PM
Tiny
BRAD97
  • MEMBER
  • 6 POSTS
How do I do this? My scan tool is just a cheap $40.00 code reader and does not provide options for this.
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Thursday, September 23rd, 2021 AT 7:09 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Oh. Sorry. I misunderstood. I thought you had an actual scan tool that can perform different functions.

Code readers cannot do this as they just read codes.

I am attaching the specific steps but as you can see, it requires a scan tool that will force the PCM to learn the sensor.

If it is not able to then it is either the sensor or the tone wheel as the likely cause.

If you don't have a scan tool that can do this then unfortunately we are not going to be able to proceed because this code is pretty specific and needs to have this done.
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Thursday, September 23rd, 2021 AT 7:25 PM
Tiny
BRAD97
  • MEMBER
  • 6 POSTS
If my understanding is correct, the ignition/fuel is controlled by a variety of sensors that all send signals to the computer. If one of these multiple signals is interrupted it will cause the same issue. Similar to the A/C system, if high/low pressure switch or ambient air is faulty it will cause the clutch to disengage.

Could it be possible that any other sensors are the culprit, say throttle position/map/Idle Air?

The other scenario I have been throwing is that I know my cats are older and I have received codes for downstream O2 in the past. Could a momentary excessive back pressure cause this?

Sorry for the long winded response, I am just trying to reach all possible reasons.
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Thursday, September 23rd, 2021 AT 8:35 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Not exactly. You are correct that the various sensors supply a signal to the PCM and that calculates how much fuel to add to the engine to get the engine to run properly.

However the crank sensor is the only one that is going to cause the engine to suddenly just shut off like you turned the key off.

The other sensors, even if they just stop working, the engine will keep running but it will run poorly.

The crank sensor is what tells the PCM the position of the engine crankshaft so with out this it cannot correctly fire the plugs and injectors at the right time.

So if the signal is incorrect, or not there, the PCM cannot guess at that so it is programmed to just stop the injectors and coils. This causes the engine to just cut off like you turned the key off.

As for the exhaust, that is not going to happen intermittently. If the exhaust is restricted then it will be restricted all the time.

Given the fact that you have this code and the issue you are seeing, I think we need to chase that until the code is gone and this issue is still there but I suspect once that code is gone, the issue will be as well.
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Thursday, September 23rd, 2021 AT 8:44 PM
Tiny
BRAD97
  • MEMBER
  • 6 POSTS
Okay, I will see what I can do to get ahold of a proper scan tool to reprogram the CPS. Thank you so much for your time on this!
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Thursday, September 23rd, 2021 AT 9:10 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Sounds great. You are welcome. Please let us know how it turns out. Thanks for using 2CarPros.
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Friday, September 24th, 2021 AT 8:48 AM
Tiny
BRAD97
  • MEMBER
  • 6 POSTS
So, I hired a shop to do the relearn process for the CPS. They attempted the relearn 4 times, after each time the diag computer prompted "procedure successfully completed" but the code would not remove from the ECM.

I do not know where to go with this, they suggested maybe the dealer has a deeper access into the ECM with their software, but I am not sure that it would be any different than what professional mechanic shop has.
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Monday, October 11th, 2021 AT 6:14 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
So, if the procedure is saying that it is successful, but the code is still there then either the tool is not capable of running the learn procedure correctly or there is still an issue with the vehicle.

I am attaching the entire process. You will see towards the end that there are a number of things that can cause this like a chipped tone wheel or wiring issue, among others.

Let's run through this info and make sure we run through all this before we just have the process done again at a dealer.
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Tuesday, October 12th, 2021 AT 8:19 AM

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