8.1l Stalling

Flash2004 · March 23, 2007

What are the chances that a new crank position sensor could be faulty? There are a few threads in here -including one of mine which detail the 8.1L unexpectedly stalling and all the symptoms seem the same. Others have replaced the sensor and their problem is cured. Mine's an 01 Sierra 2500HD SLE and the computer continually codes for the crankshaft position sensor.

We have replaced that sensor, but no change. It still stalls in exactly the same unpredictable way. We have checked the connection as carefully as possible since then but it is still the same.

Symptoms include stalling at any speed but usually in the same length of time since it started the engine on each trip - about 15 minutes - once we're past that point it can go for hours without stalling. It seems to be a time thing for sure since I can start it and leave it idling and it will still stall if its going to.

On other occasions - whether locked or not - it will simply fail to start when I get in it to drive somewhere. The surest cure so far is to disconnect the positive terminal of the battery for 4 hours at least and then the truck is good again, sometimes for up to a week then it will begin stalling again. Getting gradually worse and worse until I disconnect the battery again.

I wondered if it has anything to do with the security system? It seems like the immobiliser is getting out of sync with the various functions it performs. Soemtimes when it will not start, I can climb out, set the alarm with two presses of the Fob button, then unlock the door (with the key, leaving the alarm set?) and it will start normally?

This 3 year, thousands of dollars (failed repair costs) problem is really getting a worry now and any assistance will be gratefully accepted.

Flash2004 · March 23, 2007

I found my last thread about this: http://www.gm-trucks.com/forums/index.php?...mp;#entry434189 - the difficulty with diagnosis, oscilloscope or other device - is that the truck will not stall on demand. I've run outof technicians anyway, but I'm in the process of getting a new one interested in it. If there were a cam sensor, where would I find it?

ThorsHD · March 23, 2007

Mine did the same thing . I changed the crank position sensor. still did it. it was the cam position sensor that was bad.

runs great now

Flash2004 · March 23, 2007

Mine did the same thing . I changed the crank position sensor. still did it. it was the cam position sensor that was bad.

runs great now

Somehow I seem to remember the first ever time it was hooked to the diagnostic the tech said it came up as cam sensor, but changed to crank sensor and he never saw cam mentioned ever again. Any idea where the cam sensor is? I'll check the connection at least. thanks, Gordon

concours · March 24, 2007

Mine did the same thing . I changed the crank position sensor. still did it. it was the cam position sensor that was bad.

runs great now

Somehow I seem to remember the first ever time it was hooked to the diagnostic the tech said it came up as cam sensor, but changed to crank sensor and he never saw cam mentioned ever again. Any idea where the cam sensor is? I'll check the connection at least. thanks, Gordon

On the front, drivers side of the timing chain cover....

MEGA14 · March 25, 2007

Mine did the same thing . I changed the crank position sensor. still did it. it was the cam position sensor that was bad.

runs great now

Somehow I seem to remember the first ever time it was hooked to the diagnostic the tech said it came up as cam sensor, but changed to crank sensor and he never saw cam mentioned ever again. Any idea where the cam sensor is? I'll check the connection at least. thanks, Gordon

On the front, drivers side of the timing chain cover....

Have any of you with an 8.1 experienced the motor not stall but rough idle , especially when you came to a stop? Mine has 100k on it and has been doing it for 10k or so but has never stalled.

Flash2004 · March 26, 2007

Sorry, mine's only ever run brilliantly - or not at all. There's nothing in between.

ThorsHD · March 26, 2007

yep, check your plugs and wires

Flash2004 · March 29, 2007

Can you believe this? I went back and saw the Tech who was supposed to have replaced my Crankshaft position sensor and he now tells me he only replaced the camshaft position sensor? All this time and trouble and the answer is probably right there in every post on this issue. Sorry for the wasted time guys, I'm having a new CPS flown out here as fast as I possibly can. cheers, I know, I'm a mug.

spackelman · April 5, 2007

Flash, any updates - the stalling thing is happening to my 2002 8.1 - the dealer lists the part at $100.00. In stock.

I'm real close to changing the ckp, but I'm not totally convinced this is the problem.

Any feed back is appreciated.

Thanks

baborvik · April 21, 2007

I have an 2002 8.1 Suburban with exakt same problem as Flash2004. The only diffrense is that my car have never had something on the dia

gnostic, it says that everything is ok. My local GM dealer her in norway has changed parts in my car for approx. 1200$, they have also changed the security system and crankshaft sensor with no result, they have gave up the car last summer. It is 1000km to the next GM dealer (oslo) so i have some problem to get it fixt

Bjorn

Gonnagetem · April 24, 2007

Here's a bump to the top.

I have the same problem as mega14. Since 100K (107 on it now), when coming to a stop sign/lite, it acts like it want's to stall, yet comes back to idle, but hunts back and forth for a minute. Idle drops low enough for oil pressure light to come on. Doesn't stall though.

Its now a vaccum leak, have tried that. Cleaned the Mass Air Flow sensor (very carefully I might add), and that helped a touch, but still doing it. Could this be a crank or cam sensor?

chs249kid1 · April 26, 2007

Here's a bump to the top.

I have the same problem as mega14. Since 100K (107 on it now), when coming to a stop sign/lite, it acts like it want's to stall, yet comes back to idle, but hunts back and forth for a minute. Idle drops low enough for oil pressure light to come on. Doesn't stall though.

Its now a vaccum leak, have tried that. Cleaned the Mass Air Flow sensor (very carefully I might add), and that helped a touch, but still doing it. Could this be a crank or cam sensor?

Has anyone reported the crank position sensor to NHTSA

Flash2004 · April 28, 2007

Sorry I hadn't checked my thread for a while - I have been waiting for the new Crank sensor to arrive and it finally has. The truck has been undriveable in the meantime, stalling on every trip over 5 minutes.

Now I go to do the change and I can't imagine how it is to be done. From the underneath I can just see the top of the sensor and connector and can only just touch it. From the top, although I can squash my hand in there, I can't identify the sensor and even if I could I would not have any room to work on it.

Anyone have a step by step procedure for changing it? A crank relearn procedure would be good too, I've heard of this but have no idea how to do it.

Flash2004 · April 28, 2007

I have an 2002 8.1 Suburban with exakt same problem as Flash2004. The only diffrense is that my car have never had something on the dia
gnostic, it says that everything is ok. My local GM dealer her in norway has changed parts in my car for approx. 1200$, they have also changed the security system and crankshaft sensor with no result, they have gave up the car last summer. It is 1000km to the next GM dealer (oslo) so i have some problem to get it fixt

Bjorn

I really feel for you Bjorn. I know what its like to have an engine like that in a truck like that but to not be able to use it I'm hanging everything on the crank position sensor being the problem and can not afford to think any differently. If I still have the problem afterward I don't know what I'll or even can do. Maybe I'll donate it to George Bush and he can leave it where Osama Bin Laden might find it - sort of the ultimate US built secret weapon! OBL will die broke with frustration as the cause.