grinder11

iTrader: (1)

O.K. guys, I think I found it. I checked and re-checked every thing I could on my old Futral cam and compared it to my new Comp Cam, side by side. Bingo!!!! There were several issues with the old cam, like the bearing diameters being very close to the low limit as far as the factory service manual goes. Even where they were not worn, a slight "land" area at each journal edge, they were only a half thousandth over the low limit!! The new Comp Cam measures a full .0025-.003 larger here than the Futral. And my cam bearings in the block are at the high limit, or oversize. All this added together equals too much slop in the cam to cam bearing-in-block clearances. BUT... as I was comparing them side by side, I saw something unusual.... it appeared that the Futral cam's "reluctor wheel", for lack of a better term, was MUCH smaller than the new Comp. I checked this diameter on a surface plate at work with an indicator and gauge blocks. It came in almost .035 smaller in diameter than the Comp!!!! I called Kurt Urban right away, as he told me that he and the crew at W2W were closing in on a "lost signal" theory when I took the car back home, and he wanted me to keep him informed as to what, if anything, I did find. We all have pretty much come to the conclusion that: A: The Futral cam had excessive cam journal to cam bearing-in-block clearance, even when new. B: Kurt had pretty much proven that this was a "thermal expansion" issue-i.e. the PCM was losing it's signal from the cam position sensor when the coolant reached around 180 degrees (And the block swelled the bearing diameters in the block, due to the thermal expansion). C: When I installed each cam in my motor, first the Futral, then the new Comp, I used a depth micrometer to check the distance the sensor might "see" from the top of the block down to this "reluctor ring" on the cam. D: The Futral cam measured a full .020 farther away than the Comp Cam did!! E: When magnets, like the cam sensor, get hot, the laws of physics say they lose some of their magnetic properties. In closing, Kurt and I believe that my set-up ran-and ran damn good, I might add-for 30,000 miles, but it was running on the edge of several "service limits" when it was "fresh". When it aged a little, and cam bearing clearances became larger with some wear, the sensor simply was too far away from this reluctor wheel pickup to read it any longer, especially given that this ring diameter was way undersize, also. I might add this VERY important fact: In talking to Kurt, I told him I was unable to find any spec on the diameter of this cam reluctor wheel anywhere in the G.M. service manual. He agreed, saying he too has tried to locate this info, to no avail. So W2W has attempted to measure this distance on their own, in their shop, and to the best of his knowledge, it is in the .022-.028 clearance range, from the sensor to the cam ring. But how much is too much?? No one seems to know for sure. In my case, Kurt and I agree that I am in the .045-.050 range when fully warmed up-which is obviously too much. Hope this may help someone out there. I damn near died in this car due to the exhaust pipes turning cherry red, actually melting my exhaust hangers, and melting thru the fuel line!!!!! It will be a good while yet before my beloved C5 is on the road again. But thanks to all of you, I am finally headed in the right direction. Thanks to all of you, and especially the W2W gang and Kurt Urban, my days are hopefully behind me!!!

DanO

yup.. thats what happens with aftermarket parts!! no real attension to tolerances.. costs too much to scrap out of tolerance parts..

Glad to hear you figured it out.

Tainted

iTrader: (9)

holy hell thats a novel! cliff notes plz

SScott236

If you need cliff notes...you probably shouldnt be in the advanced section.

joecar

Would you say this could've been found looking at the cam sensor using a scopemeter...?

(...assuming you had access to a good signal to compare against, and to know to hook up to the cam signal...).

qqwqeqwrqwqtq

Yeah, the tolerance on the cam reluctor doesn't seem to be held too tightly. We had a comp grind that needed .100 taken off of the reluctor in order for it to even fit in the block.

edcmat-l1

iTrader: (10)

With an oscilloscope? Yes, you could have seen it. The signal would have decreased in amplitude, but not frequency.