David. . .isnt the CPS also used in initial startup so the computer knows where the engine is in time???

 

never... buy the tool you need to get it done and do it yourself... there has to be one that will work. the speedo re-cal... well there's not much you can do there.

 

That is done with the crankshaft position sensor I believe...

CRANKSHAFT POSITION SENSOR (CKP) - ECM INPUT
The Crankshaft Position Sensor (CKP) is located on the lower left-rear side of the engine behind the starter motor.
Engine speed and crankshaft position are provided through the CKP. The sensor generates pulses that are the input sent to the Engine Control Module (ECM) The ECM interprets the sensor input to determine the crankshaft position. The ECM then uses this position, along with other inputs, to determine injector firing sequence and fuel timing. The sensor must be powered up by 5 volts to operate.
The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it.
The engine crankshaft is equipped with a bolt-on tone wheel. The tone wheel is equipped with 35 teeth and a gap where the 36th tooth should be placed. This missing tooth indicates to the ECM the relative position of cylinder #1 to the Top Dead Center (TDC) position. This does not mean that cylinder #1 is at TDC. When the CKP is aligned with the missing tooth, the missing tooth is 60 degrees away from cylinder #1 TDC position. The teeth cause pulses to be generated when they pass under the sensor. The pulses are the input to the ECM
.

 

When I had one go out in my ferd, it was $375 including the senser. So $180 isn't bad. I could see it, and I could touch it with my fingertip, but couldn't get a wrench on it. When it went bad the truck acted like a gasser with a plugged fuel filter. Cough, hack, and die. it would start up idle, add some pedal and die. An even sicker feeling is seeing your dually balancing precariously on a flat bed wrecker with the outside duals hanging over the edge!

 

I'm probably getting 2nd gen and 3rd gen lumped together here then. . .I know with the HPCR's, once the engine is running the cam sensor realy doesnt do much, it is the crank sensor that handles everything else with timeing.

 

I just went and bought a $180 gps unit and it tells me speed and altitude

 

Dave, I've gone to a couple of dealers, and so far this is the best rate I could find for a speedo recal. I had one dealer quote me $95.00 !! [:@]

I'm a little nervous though. They said they may not be able to do this. What they said was that there are various tires sizes pre-programed into the computer. If they don't have my exact size ( 285/70/17 ), they MAY be able to find something close. Do you know if that is right, or if that tire size is in there?

The reason for the recal is not for accurate speedo readings ( although this would be helpfull when figuring MPG's ) but for shift points in the trans. I don't want to eff my tranny up because it's shifting too early or late.


As far as the cam sensor goes, looking at your technical thing has me curious. I know when the tach dies, the truck DOES run a bit off. If that is the case, wouldn't the cam sensor be a little more than just something used for diagnostic stuff? Not arguing with you, just tryin to learn.

Thanks !!

 

Donnie, I do not have a 99 here but do have a 98. So I hooked up the DRB III to see about the calibration. They were only 2 tire sizes to recalibrate to. But they can also recalibrate it by tire revolutions per mile and this is the most accurate way. This is a very simple task but most techs have no clue as to how to do this. Will try and explain this as best as I can through typing..

Hook up DRB III
1st page--press "yes"
next "enter"
next "enter"
next "enter"
next #5 "anti-lock brakes
next #9 "miscelleneous"
next #4 "set pinion factor"
next "enter" to change
Next choose "dana axle" or " other"
if you chose "dana" the next page will be where you set revs per mlie. If you chose "other" you will need to chose "other" on the next page, then the page to change revs per mile will come up.

Now to figure out tire revs per mile. Take a piece of string and wrap around the tire (follow the tread). Make a mark where the string ends meet, now measure the legnth of string in inches. Write this number down in inches.
Since we know that there are 5280 feet in a mile, we multiply 5280 by 12 to get 63,360 inches in a mile. Now divide 63,360 by the legnth of the string that you just wrote down and this will give you how many times that the tire turns in a mile..This is the number to put in to recalibrate
Example using a 315/70/17.
a 315/70/17 is 108 inches around. we divide 63,360 inches in a mile by 108 inches around to get 586.6 revs per mile...
Hope this is a good explanation. If you have questions, call me...

 

THANKS for the info Dave !! If I printed out what you just wrote, do you think the mechanic will be able to figure it out? Do you think it'll **** him off?

I actually just got my revs per minute by useing this site ( a little easier than the string )

http://www.miata.net/garage/tirecalc.html

According to the site, with my 245/70/16's I was running 684.0 Revs/mile. Theywere 92.7" around.

My new tires 285/70/17's run 617.0 Revs/mile and are 102.8" around

It says that my speedo is reading 10.9% too slow. So if I'm driving 60mph, I'm actually driving 66.5mph. Checking with my Garmin this morning, I'd say that is pretty accurate.

Any more thoughts as to why my truck runs a little rouhg when the cam sensor starts acting hinkey?

Thanks !!

 

He SHOULD already know how to do this, but if he does not, he should appreciate learning something new that can make him some money. I am never pissed off when I learn something new...


I have an idea as to why this happens. I think it is because the cam position sensor is used to verify the position of the #1 cylinder during engine operation and sends a 5 volt reference signal to the ECM. If the Crank and cam sensors are sending a mixed message, I could see this confusing the computer or not sending the 5 volt signal at the right time...
Will do some more research into this and let you know what I find out....

But then again it may be just a Philly thing. Kinda like the Arizona divorce thing...LOL