Timing on '05 (sensor ?s)

[WOT]

I've been looking at the modified crank position sensor & ran across another thread on hard starts where the comment was made that the crank position is used for startup but then the cam position sensor is used after it starts. Is this really the case? If so, then I can't see how the modified crank position sensor would do diddly.



Thanks,

WOT

 

[betterthanstock]

In a 4 stroke engine two pistons are up at the same time, but the cam opens the valves. So it's actually backwards from what you heard.

 

[WOT]

Interesting. I don't quite follow with the 2 pistons up at a time, but from a controls perspective I suppose either one could be use since position can be calculated based on the duration between pulses. However the cam turns 2x the crank & controls the opening of the valve, so you would have to use it to figure out the which cycle is the injection cycle.

 

[rbattelle]

In a 4 stroke engine two pistons are up at the same time, but the cam opens the valves. So it's actually backwards from what you heard.

My lawnmower must be really confused, then, since it's a 4-stroke but it only has 1 piston. :-laf



And what does "the cam opens the valves" have to do with which sensor the ECM uses to determine engine orientation? Doesn't the cam open the valves on every engine with a camshaft?



Or are you trying to note that knowing the cam position at any moment allows you to back out the valve positions (and hence determine which cylinder(s) are about to start the power stroke)? This is true, of course, but I don't see why you can't determine it from the crank position sensor alone, since there's a constant direct relationship between crank position and cam position (via the cam geartrain).



I'm obviously very confused here...



-Ryan

 

[WOT]

I screwed up my previous post - the crank turns 2 times per 1 turn of the cam.

 

[Sled Dog]

I've been looking at the modified crank position sensor & ran across another thread on hard starts where the comment was made that the crank position is used for startup but then the cam position sensor is used after it starts. Is this really the case? If so, then I can't see how the modified crank position sensor would do diddly.



Thanks,

WOT

Just buy the sensor, and don't worry about someone(who does not know and has an opinion) If hard starting was the case then all 04's would be hard to start. Got it on my 05 and it will pay for itself in increased mpg's in 6 tanks. JMHO

 

[Bob4x4]

In the 2nd gen trucks,,,,,,,,,they have to have the crank sensor to start,but they will run off the cam sensor if the crank sensor fails. I haven't played with the 3rd gens enough to see if it still holds true. Maybe some day when I am really bored.



Bob

 

[betterthanstock]

All right, in more boring detail: The crank does not know which of the 2 cylinders in the up position (ok don't write me about flat or vee engines, or lawnmowers, which by the way have a wasted spark on the exhaust stroke if the magneto runs off the crank

instead of the cam)

we are talking 4 stroke even number cylinder engines (no VW 5 cylinders)



SO it has to know which of the two cylinders is on exhaust/intake cycle, and which is on compression stroke. You don't want fuel injected into the wrong cylinder. The cam sensor is the only one that knows.

Now, if your crank sensor fails, it will take a while to start because the computer recognizes something wrong, but it will strart OK but run kinda rough, because it does not have anywhere near the accuracy of the crank sensor, one because of the slower speed, two because of the gear backlash, three because of the smaller diameter of the cam gear.

Now if your cam sensor fails, it will have a 50-50 chance of starting (just like a coin toss) because it has to guess which cylinder is the correct one to inject fuel into.



Once started however it will run flawlessly, except with the check engine light and the appropriate codes.

 

[WOT]

Seems like everyone here likes boring details

Thanks!

 

[rbattelle]

Thanks for clarifying, betterthanstock. I understand what you were getting at now.



-Ryan

 

[fyrescott]

OK who sells this crank sensor? Improved MPG gets my full attention. Anything to squeeze another few MPG. Is this thing easy to replace?

 

[Sarge]

All I know is that I put in a new sensor before I left on a 4700 mile trip last month. I am home tomorrow, and will figure out what the total fuel/dollar savings was. I was towing 95% of those miles, and saw a consistent 1 MPG increase pulling the 12K fiver. I am pleased with the results... ... ... Sarge

 

[Sled Dog]

OK who sells this crank sensor? Improved MPG gets my full attention. Anything to squeeze another few MPG. Is this thing easy to replace?

www.rokktech.com

 

[fyrescott]

Thanks Sled Dog... . Ordered one last night.

 

[TFucili]

Rokk install

I got my CPS from Rokk last night(very speedy service I might add).



Install was very easy, EXCEPT the plug was all doped up with paint or sealer of some sort, which made it a heck of a job to slide the red locking tab . I thought sure I was going to wreck the plug in the process. Once past that obstacle the install was exactly as described in the instructions.



I have only put a few miles on so I can't judge economy, but the engine certainly sounds happier, with less pingy rattle, and is snappier off the bottom. An easy and inexpensive mod

 

[drandre]

TFucili, keep us posted on your experiences with the modified timing device. Does your engine idle faster? Please describe in detail.



Thanks. -Andre.

 

[Bob4x4]

I've been looking at the modified crank position sensor & ran across another thread on hard starts where the comment was made that the crank position is used for startup but then the cam position sensor is used after it starts. Is this really the case? If so, then I can't see how the modified crank position sensor would do diddly.



Thanks,

WOT

The crank sensor is used all the time... ... ..... but it is 100%necessary for the truck to start. The computer can make it continue running if the crank sensor drops out while it is running.



Bob

 

[Matt400]

From the Shop manual-



The CMP (Camshaft Position Sensor) is used primarily at engine start up and once the engine is running is used as a back up for engine speed to the CKP (Crankshaft Position Sensor).



The CKP is the primary engine speed indicator after start up.



Timing calculations are not mentioned in the Manual, however it would also make since that the CKP is the one used to calculate timing. I am sure that the ECM will set a code if the relationship between the 2 sensors becomes too far and is the reason boxes that change timing connect to both sensors so they can alter both signals.

 

[TFucili]

TFucili, keep us posted on your experiences with the modified timing device. Does your engine idle faster? Please describe in detail.



Thanks. -Andre.

It'll take me a while to accumulate enough miles to make a fair judgement on MPG. It's funny you mention the idle speed, as when I pulled into the garage yesterday I stared at the tach a while thinking it did seem to be idling a touch faster, but I think it is more a case of being smoother and less raspy sounding. The engine is IMHO much happier with the advance. I will update as I learn more.

 

[Sarge]

I just did some quick caculations after getting back from a 4700 mile month long vacation. 4700 miles, average of 9 MPG towing the fiver (conservative mpg estimate) would be just over 522 gallons of diesel. I used to average 8 MPG towing the fiver. That would have required just over 587 gallons of fuel. My MPG increased, just while towing, 1 to 1. 5 MPG. Using the lower figure for an estimate, I used 65 gallons less fuel. At an average of $2. 85 a gallon, (low estimate) I saved about $185. 00 in fuel costs. So the sensor paid for itself over twice on this trip. I am also pulling using an EZ set on the lowest position, so I am putting in a bit more fuel than stock, but the power to climb grades is nice.



Also as a reference, I generally pull at about 65 MPH, and set the cruise when possible. I crank up for impending grades of any significance, and usually pull them easily in 6th gear. The really long ones may require a down shift to 5th gear. The camping weight of the truck is over 9000 pounds (I carry fire wood, and a spare fuel can and leveling blocks among other misc items in the bed) and the fiver is about 12,000 pounds.



These estimates were all consertive, and I towed about 90% of those miles. For a low cost mod, the results have been consistent and satisfying. I don't drive the truck much empty now as do to the cost of fuel and a new job location I take the train to work now days, so I can't say what the increase in MPG might be without towing. So all in all, I can recommend this one for MPG increase, and a touch more low end torque. There has been no noticible change in idle speed. Can't say as to weather the engine idles smoother or not, as mine has always run smooth. Sarge