Where/what sensor does the tach get it's signal from?

Thanks,

 

The tach is operated by the PCM, which receives data on engine timing and speed from the CPS.

 

If the CPS is starting to malfunction although there are no codes or outward signs, could the tach be getting a 'false' reading?



About 2 months ago out of the blue I noticed the truck running approx. 200 rpm higher in od than it had in the past. Determined that TC was getting weak via some troubleshooting with Brian at BTS. He wasn't totally convinced that that TC was causing the problem but that it still was getting weak. Replaced the TC with a factory new one and still have higher rpm's. Starting to suspect od cluch slippage with people opinions here on FTE.

Ran by a local tranny shop that was highly recommended to see if there was any advice or testing that could be done to determine slippage or not. The guy was very knowledgable about our trannies. He originally thought that the chip (Edge) that I HAD in it was causing the problem and screwing up the PCM till I explained to him that I had that in there for well over a year before it started. He explained to me that if the speed sensors at the front and rear of the tranny where reading any variations outside of the normal perameters, that it would throw codes and the od light would flash. I've had none of these happen. He wanted to know if mpg was any different, but I've not driven it enough on the highway lately to find out. He's suspecting something electrical like a sensor or something giving a false reading instead of actual parts failure.

I replaced my CPS over a year ago when my factory black one started giving out. Got the factory grey one from ford and thus far (as far as I know) have had no problem with it. Have a new spare grey Ford one still in the bag that I can switch it out with.

What do you guys think?

 

What happens if you set the truck back to stock? Since the RPM reading is coming from the PCM, maybe the edge has somehow affected this. Tire size still the same? Do you know anyone around you with an AE so you can monitor engine RPM on that too (should read the same as the tach) I don't remember if the AE can read TSS (input shaft on the tranny), but if it can, you can check the TSS speed compared to the RPM when the torque converter locks. I would think the tranny guy would be able to do that as well.

I'm not really up to speed on the autos, but in my mind, that should tell you if you have any slipping issues.

 

The truck is back to stock. Pulled all the programming off of it and sold them. Tires are exact same. Truck is identical to how it was before. There was no change after this either.

Don't know anyone with an AE but am going to check around. The one diesel performance place here said, "For $30 we can tell you anything and everything that is going on with it." They've got some 'high dollar' Genesis machine or something. The guy made it sound like it was created by God himself. I asked him how it'd test to see if there was slippage between the input and output shafts, he said that they could do it sitting still in the shop, because "the computer will tell us everything." I'm thinking HORSECHIT!! considering the shafts will have no movement in park! This coming from the guy that's got a 'souped up' Dodge Cummins that he 'drag races' with it's "secret" programming that they won't tell anybody about. Needless to say, I wasn't impressed.

Jeff at the tranny shop said that if there was enough slippage to cause a 200 rpm increase, that codes would be thrown, but there aren't any. No flashing od light, no ses light, nadda.

 

$30 isn't bad for a scan. You could always ask him why you have to pay if he can't find anything wrong.

I was thinking of slippage in the torque converter. What your tranny guy says sounds right. If there are clutches or parts slipping inside the tranny, the 2 sensors should catch it and throw a light.

 

No $30 isn't bad at all for a scan. It'd be 3 times that at the dealership.

I know there is no TC slippage because I replaced it with a new one and there's only about 100 miles or so on it. I'm going to do some mileage runs this weekend to see how they compare to before this issue arose. Might go ahead and swap out the CPS with the brand new one to see if there are any noticable differences. 10mm socket and it'd only take a sec.

Any other ideas, please throw them my way!