Crank Angle Sensor

ariesdude · Post by **ariesdude** » July 16th, 2006, 4:08 pm

Philthy wrote:This a typical sine-wave when viewed on a lab-scope

No - that is an RC differentiated waveform - this is an actual sine wave

Philthy wrote:On our cars the "SGC" signal (in the distributor) will indicate a "square" when cylinders 1 and 4 are at tdc
the "SGT" signal (also in the distributor) represents crankshaft angle in 60 degree increments, one "square" for each

A good electrician/engineer would be able to verify that with just a multimeter.
IMO if a critical sensor was faulty it wont work with stock equipment either. If one pair of shoes fits me perfectly and comfortably and another one makes me cry out in pain - i would check out what's wrong with the shoes - not what's wrong with my foot.
My experience is that if someone sold me a faulty equipment (intentionally/inadvertently)- it would take a lot of effort on my part to convince them its faulty - that person is going to keep blaming every little thing they can think of rather than accepting the fault - its just human nature.

Philthy · Post by **Philthy** » July 17th, 2006, 11:58 am

A good electrician/engineer would be able to verify that with just a multimeter.

Thats just not true. Dwell, Duty, Frequency readings will miss the fact that intermittantly the driver can't pull the reference voltage down, or that the board is chopping off the top of the signal. Trust me, I've made a good career out of fixing electronic problems on cars. On the flip side I am not an electronics engineer! Just a good mechanic fixing cars.

Look at the example of a faulty square wave, the car will run. Often sensors don't fail completely. Sometimes the car runs great, sometimes it stutters, and sometimes the sensor fails completly. This is one way techs can find an intermittant problem by looking at the waveform. Also if you used a multimeter on the sensor shown in the square wave example you WOULD GET A GOOD READING! thereby missing a faulty sensor. There is a reason technicians (not the shop) spend thousands of dollars on labscopes.

No - that is an RC differentiated waveform - this is an actual sine wave

If you spin a magnetic pickup slowly it creates a sine-wave then as the shaft accelerates the "RC differential" is created
Sorry, in the automotive industry we incorrectly call the waveform a sinewave
Its funny how industries use some of the same concepts but twist the lingo a bit.
I bet ariesdude has some electronics background.

FlyVFR · Post by **FlyVFR** » July 23rd, 2006, 8:19 pm

With all due respect, you are both correct guys. I find that the easiest way to check such automotive sensors, is to take a resistance reading (if values are specified by manufacturer) and if it's not in spec then I consider it a faulty component. But I agree that a scope is a better tool. As it will display live data while the components are in operation.

Philthy · Post by **Philthy** » July 29th, 2006, 1:30 am

Iv'e never encountered a resistance spec for a position sensor that generates a square wave. Automotive sensors of course. Can any one give an example?

I need a new smiley. I need one for confounded. I try to to help in an area where I am COMPLETELY competant, and when I type that I mean the subject is so matter of fact, and material to what i've made a living on that there was no error in my previous postings!

PLEASE, how is a multimeter going to confirm a bad cam position sensor. I can just imagine the "engineer" using his multimeter stating " the meter reads 11.67 hertz but the engine was spinning 710 rpm, obviously a faulty sensor." BS, if your opinion is speculation and not hard fact then shut up and read. OK so you have a multimeter reading (hertz,duty,frequency,resistance...whatever) how do you condemn the position sensors in the distributor?
Are you going to trust your external sensors to the "T" i.e. 13.4 hertz here and 13.5 hertz means failure. Thats crap! But, the broken square waveform SAYS IT ALL.

This site has generated a lot of good info for me. When somebody makes a post that is BS it degrades the sites value. Come on guys!
If you got a question post it.
If you have something good to say, post it.
Otherwise read.

FlyVFR · Post by **FlyVFR** » July 29th, 2006, 3:31 am

All inductors have a resistance and impedance value. That sensor is an inductor, therefore it must have a resistance value in order for it to work.
Again, if the resistance value in out of it's normal range, then that component (in this case an inductor) will not generate the proper signal level. Basic Ohm's law. This is a fact Not BS.

BTW, a resistance check cannot be performed while the component is in the circuit nor if it has power applied.

ariesdude · Post by **ariesdude** » July 29th, 2006, 12:59 pm

FlyVFR - please dont deal with this guy philthy - its not worth it. He sent me a very nasty PM when i was trying to help jschrauwen.

FlyVFR · Post by **FlyVFR** » July 29th, 2006, 3:07 pm

Just stating the facts and trying to shed some light on the topic.

aries - I've been reading a lot of your posts and I am confident that you have theory knowledgeable in the electronics/electrical field and using it to help out here on the forum.

Now to bring thigs back in prospective

ninjajim4 wrote:is that the same as the crank angle sensor?

it checks out ok with an ohm meter, but i was wondering if anyone could tell me what sort of readings i should get from the 3 pin terminal on the harness that plugs into the sensor.

thanks

I would compare the reading to a known good sensor. Also if it was out of spec the ECU would generate a fault code.

Philthy · Post by **Philthy** » August 3rd, 2006, 9:59 pm

Sorry if i seem course, but i can't stand dung posted without thought. Especially if it is contradicting truthful/usefull info. When someone does that they are misleading the other members of the site. Again show me a resistance spec for a sensor that generates a squarewave. Let me say it simply for you flyvfr, a sensor that generates a squarewave not a magnetic pick up, not a reluctor wheel and coil. Read the post.

here is mazdas trouble tree for the three position sensors on their v6.

note no resistance spec for the two hall effect sensors in the distributor, and yes one for the reluctor on the crank.

I could give examples for chrysler,gm,toyota,... etc.etc.

FlyVFR · Post by **FlyVFR** » August 3rd, 2006, 10:29 pm

The schematic shows a coil type sensor with a shielded cable for Ne2. Step 4 outlines and states " Is resistance of crank angle sensor OK? Resistance 0.95 - 1.25K ohms A multimeter should be switched to resistance reading and should work for this procedure.

For Ne1 schematic shows a hall effect type sensor in which case a multimeter is switched to DC voltage and since voltages are specified you follow the procedure posted.

Now I got a question. Where is it stated that an oscilloscope is to be used and what waveforms are generated?

Philthy · Post by **Philthy** » August 3rd, 2006, 10:39 pm

Here are some real world waveforms on mazdas that had intermittant problems. They were professionly diagnosed and condemned with a lab scope. Replacing the faulty sensors as identified by the labscope cured both customers comkplaints of intermittant misfires and stalls.

note the top waveform, how the circuitry is faulty chopping off the top of the "square", the car runs even with the faulty signal. But the poor waveform indicates flawed circuitry. Where it goes flat is where the sensor failed completely, replacing the distributour cured the problem.

This customer had a miss intermittantly
by the way flyvfr no codes were set, which is not uncommon either.
Clearly the waveform is flawed, replacing the sensor generating that waveform cured the problem.

now i will ask my question again aries, what multimeter reading would that poor sensor generate and what would a good one generate.
If my pm was nasty sorry. After seeing your credentials I am dumbfounded by your statement that a good engineer could use a multimeter to catch a sloping/poor squarewave. Any engineer that knows his trade would know to use the labscope, especially for difficult (i.e intermittant) sensor failures.

Philthy · Post by **Philthy** » August 3rd, 2006, 11:03 pm

That tree assumes that a code is set.
Check the post above.
Customer is unhappy (car has a miss), no codes.
Obviously a labscope confirmed and fixed it.

Also, if i was in that situation that the tree is appropiate for. I would (without having to read that tree) pintest the sensor terminals with a lab scope. Looking at all the voltages. You guys out there should know you can have noise or glitches on the power and ground feeds causing driveability issues that won't show on a multimeter. So you could miss the problem. You could read an acceptable ground on your multimeter but a spike can cause a miss Check out the bad grounds below. If you used a multimeter versus a labscope while performing mazdas tree you would miss the bad ground. Checkout the waveform with the spike. The time scale is set set to 20 Microseconds per division. IF a multimeter could catch that you would never see it.

I am an ASE master tech, advanced engine performance certified.
Former fuel and electrical specialist in the marine corps. With those titles came much schooling.
Every automotive driveability school ive been to stresses the use of labscopes.
Tool manufacturers invest a lot in producing labscopes, And your average technician i.e. joelunchbox spends thousands in purchasing labscopes.
Diagnostic aids and libraries have stored waveform libraries for the unsure technician.
Why would techs pay thousands versus hundreds for a multimeter if it wasn't needed.

In short there isn't one element of this industry that doesn't recognize the importance of reading waveforms.

Ive worked flatrate most of my career, The quicker you diagnose it the more money you make. If your wrong you work for free. That makes a technician keen. Get it done fast and right.

Every shop iv'e worked for (including the dealer) iv'e been the electronic diagnostic guy.

Look at the info ive put up, where do you think thas comes from. Fixing cars. I don't spend days fixing driveability problems, 99% of the time I spend minutes.

If you want to discount a labscopes importance fine. If you made your living fixing cars you wouldn't.

Bad grounds not caught by a multimeter

FlyVFR · Post by **FlyVFR** » August 3rd, 2006, 11:45 pm

I've seen transistor based circuits perform in limbo and intermittently many times in the electronics field. As I've stated in my first post, I agree that a scope is a much beter tool for live data. Keep in mind that all MX-3 owners do not own a scope.

BTW- good job on your customer's Mazda Intermittent problem. I probably would have replaced the ECU as well since it did not store codes with such problems as stalling. But you are right, as I experienced it myself when my disty produced intermittent stalling (on the highway

) and no codes were stored.

Philthy · Post by **Philthy** » August 3rd, 2006, 11:58 pm

Those waveform examples where taken from a tech resource site, I have never taken the time to download my waveforms. I save mine on my scope and delete them after the repair is confirmed. But, those are classic examples of what iv'e done for over a decade, and classic examples of why there is more to diagnostics than what the engineers put in the books.

You are right vfr, who is going to have a labscope? most people won't.
My first post stated that most of the info in the post would be for the "geewhiz" file.

But, if someone suspected a bad sensor, at least they now have some info to use when interviewing a shop/tech for potential diag work.

FlyVFR · Post by **FlyVFR** » August 4th, 2006, 12:13 am

Philthy wrote:But, if someone suspected a bad sensor, at least they now have some info to use when interviewing a shop/tech for potential diag work.

Or they can replace it, insted of paying an auto mechanic to confirm it. Autozone has a lifetime warranty on our disty's.