Another stalling problem....

NavyGuy · September 13, 2005

I have a 2002 2500HD 4x4 with the 8.1L/Allison package. I've had the same stalling problems many others have had so I borrowed a friend's Mindreader 99 scan tool. Granted it's old, but it does give some good info.

When it does stall, I never get an SES light and I get no DTC's until after I crank it over several times and it doesn't start.....then I get P0335, sometimes A, sometimes B.....sometimes both. Is this a functioin of a bad sensor/connector or because It cranks so long without firing?

While trouble shooting, I noticed that the MAP sensor fluctuates between 30.2 to 30.4 inches of mercury with the engine off.....this is a perfect vacuum and not what I would expect. I unplugged the sensor, and the reading dropped to 2.92 inches and steady, but I did pick up P0107, which is expected. I plugged it back in and cleared the code and it hasn't come back. Once it finally does start, it drops down to 10 inches at idle and fluctuates as one would expect in response to throttle changes.

Is the MAP reading normal for the engine condition? Are the electronics biased so that a shutdown engine is supposed to give this "perfect vacuum" reading from the MAP? Could a failed MAP stall the engine without a DTC? Which should I replace first? The dealership is no help......

Thanks,

Sonny

Haulin' 8.1 · September 13, 2005

Your Crankshaft sensor is bad and the readings of your MAP are normal. It's a Manifold Air Pressure sensor, think of it as a Barometer reading in your intake.

If you need some help with the sensor do a search under my screen name with crank sensor and you'll find a good post.

By the way 335 is a crankshaft sensor code.

Vernon

NavyGuy · September 13, 2005

Thanks Vernon,

I was really confused about the MAP values until I read your post reply. The barometer comment you made got me thinking so I looked at one....low and behold....the light came on. In my line of work, inches Hg is used to measure the absence of pressure in steam turbine condensers....a barometer reports it the opposite way... and that is what the engine cares about. Thanks for the nudge in the right direction.

I read your posts about removal, crawled under the truck and found the crank sensor. Tight quarters, but doable....but before I dive in....

Does it matter that I don't get a 335 until after excessive cranking while trying to restart? I NEVER get an SES light when it stalls and no codes appear until cranking like mad for awhile.

I say this because I didn't think it important to mention on the original post. The first time I ever read codes the only one present was P1779 (Transmission Control Indicator Lamp Circuit - Out of Test Range) and I have picked it up several times since, but only after lots of cranking just like 335.....and the truck will not shift to 4 low.

Thanks for the help,

Sonny

Your Crankshaft sensor is bad and the readings of your MAP are normal. It's a Manifold Air Pressure sensor, think of it as a Barometer reading in your intake.

If you need some help with the sensor do a search under my screen name with crank sensor and you'll find a good post.

By the way 335 is a crankshaft sensor code.

Vernon

<{POST_SNAPBACK}>

Haulin' 8.1 · September 16, 2005

Vernon,

Below is a reply post the other day and you really seem to know your way around when it comes to this motor. I have a few more questions below....plus I keep reading about "relearn". Is it required after replacing the crank sensor to get the motor to start? Posting your answer in the Forum to all these questions is best....so that all can learn.

Thanks in advance,

Sonny

Thanks Vernon,

I was really confused about the MAP values until I read your post reply. The barometer comment you made got me thinking so I looked at one....low and behold....the light came on. In my line of work, inches Hg is used to measure the absence of pressure in steam turbine condensers....a barometer reports it the opposite way... and that is what the engine cares about. Thanks for the nudge in the right direction.

I read your posts about removal, crawled under the truck and found the crank sensor. Tight quarters, but doable....but before I dive in....

Does it matter that I don't get a 335 until after excessive cranking while trying to restart? I NEVER get an SES light when it stalls and no codes appear until cranking like mad for awhile.

I say this because I didn't think it important to mention on the original post. The first time I ever read codes the only one present was P1779 (Transmission Control Indicator Lamp Circuit - Out of Test Range) and I have picked it up several times since, but only after lots of cranking just like 335.....and the truck will not shift to 4 low.

Thanks for the help,

Sonny

Sorry I didn't check back sooner. You don't have to do a crankshaft variation relearn to use the truck but it will run better with it done. I've seen it cure rough idles. On my truck I didn't get a SES but there was a code stored in memory for the crank sensor. It will take a lot of cranking, 13 seconds continuous to be exact, to set any present code on a non starting GM OBDII engine. Take it from me you'll find your truck to run a lot better after a new sensor and CVR.

As for the 1779, that's a little out of my area. I'm an engine man, I send my transmission worrys to my transmission man. That being said I can tell you that you have misdiganosed that codes meaning. Those manufacturer specific codes mean different things on each make/model. I've got the Helms service manual for 2001 so I can look this stuff up. For the Allison this code is described (but not named, thanks for nothing Helms). If it had a name it would be something like "Thottle position signal at TCM out of range."

DTC P1779

Circuit Description

The Transmission Control Module (TCM) recieves input from the Engine Control Module (ECM) on Throttle Knockdown Signal Circuit connector J1 pin 9 for unmanaged engine torque (gross), and Delivered Torque Signal Circuit connector J1 pin 16 for managed engine torque (net). The TCM monitors and compares the engine input torque signals for proper torque requested values. The TCM sends a signal via Requested Torque Signal Circuit connector J1 pin 22 to the engine if a torque reduction is needed.

Conditions for setting the DTC

DTC P1779 is set if managed engine torque (net) signal is under 1.5 percent for 2 seconds or over 98.5 percent for 2 seconds.

Now I THINK this means one of the signal wires from your throttle to your TCM is dropping or pegging from time to time. But you can see why I let my transmission man work on my Allison. He has scanners that can monitor those signals and he knows what to look for. I set one of these code drag racing the truck once.

Good Luck,

Vernon

billcar9999 · September 16, 2005

I just did the crank sensor in my 2001. It took me about an hour and a half to do it. The problem was working the sensor out enough to pull it. The old sensor has O rings top and bottom of the sensor so you can't wiggle it much to unseat it. I tried a variety of tools to nudge it out. Because of the location you can't get any leverage to pull it. Be careful, you can break it off while trying to remove it. If you do break it, you'll have to pull the tranny to get enough room to remove it. I almost broke mine. When you hear the plastic breaking you may be very close to having a bad day.

Bill

NavyGuy · September 16, 2005

Bill/Vernon,

Thanks for all the info. Last night, I crawled under to clean up around that area and soak the fastner with some penetrant for my Saturday adventure in swapping the sensor out. After cleaning the grime away (and there wasn't that much) I used an small mirror and a flashlight to look around.....and I found a crack under the dog ear that secures it is place. Feels like it goes about 2/3 of the way around. There are two times that the truck always started and never stalled.....the first start of the morning and the other was if the engine and transmission were at normal temperature. Quite possibly a thermal expansion issue? Who knows, but I think there is a large possibility that I will turn that crack into a break....

As much as I would like to play and fix this myself, think I am going to have the dealership take care of it since it won't shift to 4LO as well and the P1779 I listed earlier is torque related.....besides it is still under warranty. I've been down this road with the dealer before, but talking to great people like you has armed me with enough knowledge to know what I need repaired. Thanks a bunch!

Sonny

I just did the crank sensor in my 2001. It took me about an hour and a half to do it. The problem was working the sensor out enough to pull it. The old sensor has O rings top and bottom of the sensor so you can't wiggle it much to unseat it. I tried a variety of tools to nudge it out. Because of the location you can't get any leverage to pull it. Be careful, you can break it off while trying to remove it. If you do break it, you'll have to pull the tranny to get enough room to remove it. I almost broke mine. When you hear the plastic breaking you may be very close to having a bad day.

Bill

<{POST_SNAPBACK}>