BFH results inside


Jun 22, 2001
It was finally warm enough to go through the testing. This is from a no start situation. I am getting 10, and 7 for the voltages on the module side of the cam and crank plugs with the key on. To make sure there wasnt a funky grounding problem, I plugged them back in and probed them and got the same voltage. However, when cranking, I only get .181 volts from the crank sensor. This shows that its probably that sensor but it was the first thing I replaced. Is there somethign that I could have done incorrectly during the install? bracket))ring) Thats the slot I have my ring in. Thanks for the help.
Ok, first off, are you using a digital or "needle" type voltmeter?

While cranking, the crank-trigger wheel will be travelling past the sensor fast enough that the voltage WILL be low. However, as you mentioned, IF you're in the wrong slot of the sensor, it won't start! And I believe both sensors return LOW voltage when they see "air", and HIGH voltage when they see "metal". (PS, because you've seen 2 different voltages on the sensor, I'd wager the crank sensor is fine!)

there's TWO slots on the sensor; the INSIDE slot has an aluminum wall on both sides, the OUTSIDE slot has the aluminum wall on the inside, and a black plastic tab on the outside...YOU WANT THE OUTSIDE SLOT! CLICK HERE to see a picture...

Check it out, and we'll go from here! :)
My post must have been a bit misleading. Im not really getting two different voltages at cranking speed, I am getting those two different voltages when the key is on and not cranking.

When cranking I am only getting .181 nothign else. However, I am using a digital meter, and Im not sure how fast it refreshes. If it is true that it shows high for metal, I would think that if it were to "stick" on a voltage it would be more likely to stick high as there is more metal than not correct?

Maybe I can find someone with an analog voltmeter tommorrow.

Thanks again. Ryan
Hope this helps out some. This is from some of the GM literature I have collected since '84.

"The crankshaft mounted Hall Effect is a pull-up design, while the cam sensor is a pull-down design. These terms refer to whether the ground or supply voltage is switched to trigger the appropriate device. Pull-up designs switch the voltage or "high" signal on and off, while a pull-down interrupts the "low" or ground side of the circuit. C3I uses a pull-up to indentify crankshaft position, while a pull-down is used for camshaft position."
Wish my car wasn't up on jacks with a bad crank! Then I could verify which is which...

Ryan, YOU can verify this yourself, which will also verify whether or not your sensor is working...

Grab your 1/2" ratchet, a short extension and the big socket that fits the bolt on the crank pulley (1-1/8"?)
--turn the crank and position the trigger wheel so the sensor sees the metal vane, turn on the key, and take a voltage reading.
--now turn the crank so the sensor sees the "air" between 2 vanes, and take a voltage reading...

You SHOULD have 7-10 volts in ONE position, and 0-2 volts in the OTHER position!

IF SO, your sensor is fine! And post the results of which is which so I won't forgit no more! ;)

IF NOT, then something's up with the sensor!

Your digital voltmeter reading a constant .181 does sound funny, it should vary SOME I would think, unless it's just trying to lock in an "average"...

With an analog meter, the needle will noticibly swing slightly while cranking as it reacts to the voltage changes, this is why it's preferable to a digital meter while testing the sensors)

(EDIT!!) Just thought of something, and this is off the top of my head, so someone else can correct me, but aren't both sensor plugs the same? Meaning (however unlikely) it could be possible the sensor plugs are reversed? (just a thought in the dark!)
Well, first off I sure hope they arent the same plugs because mine arent.

Ill be sure to test this out. (Its supposed to snow tonight so we will see if I get to do it tommorrow....)

Which wire should I be checking for this voltage? the middle or the outside one. (I know not to check the ground outside one)
Well, crawled around in two inches of snow for quite a while. Found out some bad things, and maybe a good thing (assuming you are an extreme optimist)

When the crank sensor is seeing air, the sensor registers at very near 0. When the sensor is seeing metal, it has about 7 volts to it. (there you go BFH) So, my crank sensor is good.

This leaves it down to two things then, Cam sensor and Module/coil. I did put a new module/coil on it, and it made no difference. It was, however, used so I don't know if it actually worked.

Does anyone know of any 99% surefire methods to test the cam sensor like BFH gave me for the crank sensor?

Once again, thanks for all your help guys.
Ryan! You can test the cam sensor the same way! (sorta)

Just follow these instructions for SETTING it! Click Here!

Not only will this test the cam sensor, you'll be sure it's set correctly! Just BE SURE the #1 cylinder is on the COMPRESSION stroke!

If you find you can't turn the sensor cap enough to change the voltage, then unscrew the cap and have a look underneath. Under the cap is a metal "dish" that spins, and there's a notch missing in the side of the dish. At TDC on the compression stroke, that notch should be very close to lining up with the small sensor tab in the cap when the cap is installed. If it's not close, you may have found the problem. Check the "dish" to make sure it's tight on the shaft, and doesn't "freewheel".

If the notch IS close to lining up to the sensor tab, and you're not getting voltage changes when turning the sensor housing during the setting procedure, changes are the cam sensor is bad...

(we'll figger this sucker out yet!)
All right, Im good on all of those directions except for the 25 degree rotation. Do I need something special to tell me where 25 degrees is? Why cant circles just be 100 degrees that would make this a lot easier.
here's how to figure the 25°...

cut a piece of masking tape just a teensy bit MORE than 1-7/16" long (it's supposed to be 1.45", and 1-7/16" is 1.437")

put the RIGHT EDGE of the tape at the TDC mark on the damper, so that as you turn the crank clockwise, you'll reach the other end of the tape with the pointer---that's where 25° is!
Well, I unfortunately have found part of the problem. Instead of resetting the cam sensor like instructed, I thought it would be a good idea to simply hand crank the engine to see if the sensor ever went to 0. This way I wouldnt damage my setting, and I wouldnt have to worry abuot causing more problems. I rotated the crank 360 degrees once and it never showed anything below 6.9 I figured that I wasnt turning it slow enough, so I repeated rotating very very slowly. Still the same result.

After this I was beginning to doubt my sensor. I pulled the cap off and started cranking the engine by hand. Guess what? No cam sensor spin at all. Right about now, you're probably thinking I should be happy that I found my problem. However, I now feel worse. From what I've read, after initial start up, you can unplug your cam sensor and nothing happens because it is no longer used. My car Died when in motion, so the cam sensor cant be the root of the problem. I tried to manually spin the disk myself like I saw mentioned in other posts. Its rock solid. With normal force I just cant spin it.

So, what am I looking at here? Timing chain? Cam?

Thanks again for everyone that is helping. Sounds like its a good thing I have a shop to work on the engine now. Guess ill have to put off the Intercooling project after all.
No cam sensor movement while cranking? Ouch...

Remove the plastic oil-filler tube from the valve cover, so you can see the rockers--have someone crank the engine and see if the visible rockers are moving...if not, you've definitely found the "root" of your problem--couple of reasons would be: broken timing chain, sheared woodruff key on the camshaft or the crank, or all the teeth stripped off the cam gear (if you still have the nylon gear)

HOWEVER, if the rockers DO move (hopefully!), then your problem lies with either the cam sensor drive gear (broken or really bad teeth) or the sensor shaft is somehow broken...

check the rockers for movement first!
Well, its a sure thing now. The rockers aren't moving.

Maybe you can still give me some hope though. I didn't hear anything when my car died, and I still dont hear any banging or knocking. Is it possible that I haven't hit a valve, or chipped a piston up? I hope I will just be able to fix the timing assembly and not have to worry about valves and pistons and such.

Ryan, I'm not sure if these are "interference" engines or not, I've heard it both ways. I'm thinking they're NOT, with stock cam lift I don't think the valves will hit the pistons (but, like I said, I'm not certain--ANYONE??)...I'm thinking you would've heard some clattering of some sort when the engine died, especially if A) the pistons and valves were hitting each other, and/or B) you broke a timing chain! I'm betting you'll find a bad woodruff key on the cam gear.

Good luck!
I must say that every single one I have fixed at work has hit valves. Intakes mostly. I have probably done at least 200 or so timing chains on n/a 3.8's and afterwards do a leakdown check. Every time they have bent intakes (very few exhaust) and run like crap. You might get lucky and the cam stopped in a place where none of the valves were open enough to hit. I have heard others also say that so there is a chance they might be ok.
OK, the 3.8's are interferance engines, but it is also possible with a stock lift cam to not hit any valves. Like mentioned already, if the cam stopped in the correct spot then no intake valves would be fully open and you probably dont have any bent valves. You could check by loosening all the rockers and performing a leakdown test. That will tell for sure.
I would also guess it is the woodruf key. While you are in it change the timing chain even if it is still good.

Good luck in your endevours, and keep us posted.
Got the car started and drove it home. Besides some minor troubles, (bucking, no power brakes) it appears to be in great condition mechanically. I am 99% sure that I did not hit any valves as the car drives just like I remember it. (With a bit more bucking and less braking power)

I would like to thank everyone that has given me aid and opinions. You guys really did help me to better understand my situation.

BFH, I should have done this earlier. I would like to specifically thank you for taking the time to aid me in my diagnoses. I honestly think that I now know no start situations well enough to write a guide on them.

Thank you very very much for your time.
Glad I could be of help Ryan! Maybe you were saved by the steel shim gaskets? ;)

When you get a few minutes, you may want to pull a valve cover and extract a couple of pushrods and roll 'em over a table to see if they're straight, just to be sure. If not, they'll just keep slowly bending...