I posted this on the internal engine section (Gen III), and it is long, but I will touch on the highlights: I had this car at Wheel to Wheel Powertrain in Michigan for 6 months, and they have told me that they think I should take it somewhere else and try to have a fresh set of eyes look at it!!!! That should say a lot about how complex/difficult this problem is!! After all was said and done, the car trips a "Crank Sensor Circuit Failure" as the coolant reaches about 180-186 degrees F. After trying to isolate the cars electrical system by using a Big Stuff 3 ECM with its own, separate 12 volt battery and wiring harness, it still did the same thing!!!!! W2W then hooked up an oscilliscope to the crank sensor and when the code tripped, the scope's waves were unchanged. HOWEVER, when they waited until the next day, letting the motor cool totally, they hooked the scope up to the cam position sensor. When the car hit 180 degrees on the coolant-BINGO-the oscilliscope went berserk. This told W2W that it was a mechanical problem somewhere in the cam, as they had already tried new/different sensors on the cam and crank, to no avail. They then pulled the cam and it did have one scored lobe-the first one back from the timing gear. The corresponding lifter, all the lifters, in fact, were fine. W2W doesn't believe that this is what is causing the problem, but admits that they don't know what the exact problem is, either!!!! The oil pan was pulled and the reluctor wheel checked-all was good. Crank thrust was also good.These guys are smart-and they are stumped!!!!. Help!! I want to add that my car ran fine for 30,000 miles-then this happened with NO PRIOR WARNING!!!! Now my car will not run and hasn't, for more than 10 minutes anyway, since last September!!!! I can't drive it and can't sell it, either. I am baffled, like everyone else is. I am hoping/praying that you guys can help me. It is tough seeing about 50 grand sit in your garage and not even be able to use/drive it!!!!!!! You guys are my last hope, as I have tried some of the finest minds in the business. Has anyone ever heard of anybody else having a similar problem, and what they did to rectify it? I talked to Tony Mamo from AFR today, and he suggested posting up here as a best shot scenario to getting an answer. Here's hoping you guys come through. It might be YOUR car someday, and we all could use this info in case any of the cars here would develop this confounding problem. I never thought this could happen to ANY car, much less my pride and joy C5. PLEASE HELP!!!!

 

I imagine you have replaced the crank sensor and made sure it is not contacting the reluctor wheel when the engine heats up. I have also had bad connections in the wire pins pluging into the crank sensor.

 

where are you located at?

 

Is the code completely dependant on temp? In other words....can you find out...or did you find out if the coolant temp of 185 sets off or brings in other sensors or functions. Such as turning the fans on or allowing the PCM to look for a parameter at or above 185?

Or is it more of a time thing....and changes. Sometimes at 175..sometimes at 190 etc? Things happen at certain temps. If you can correlate this code to a specific temp it may help you. Certain function or monitorings are activated at certain intervals...sometimes its temperature the computer looks for before it brings other sensors online.

Does the car exibit any secondary symptoms beside the code? Backfiring? Shuts down?Why cant you drive it? If its just getting a code? So it must be having secondary symptoms?

Why did you check the cam position signal if the code is for crank position signal?

Did you check and clean all grounds? Many times when a symptom or failure is associated with a specific temp...but not correlated to a computers function of that temp...it can be ground related. Increased temps will increase resisitance across a ground. Especially on grounds that are on the block or cylinder heads. As the engine warms...the grounds "move" and increase resistance.

I would take EVERY ground off that car...take them apart, clean the contacts and the mount surface and reattach.

I was going to say check the crank thrust bearing but you already did. I chased that one around for a month on one of my cars.

Some of these questions may seem out in left field...but its hard for you to include ALL the info thats pertinant. So if you can answer these questions...maybe others can help more.
Good luck!

 

This idea sounds more painful then it actually is... replace the engine harness. Clean the grounds while you're at it. It sure sounds a lot like a bad wire in there, that the heat is getting to. I've seen it before, though not quite exhibited how yours is.

Here's hoping you figure it out.

 

I agree with the two previous posts.

1) check to see what else happens at 185deg that can mess up a sensor. Does a cooling fan come on? Does a relay set??? If so, then....
2) look into the engine harness. There may likely be some damage to it that is messing with sensor outputs when other components become active.

Another thing. Was anything done to the car just before this problem started?

 

Did the cam and crank sensor wires get swiched when installing the BS3?

I'm confused as to why you are getting a crank sensor code for the cam sensor going nuts, unless the PCM is comparing the two and the bad cam sensor is what is setting the code.

Have you checked cam end play? I have seen this on GM diesels(not that they are the same, just as an example)

 

Theres a short in the harness when something is tripped. Id bet if you start wiggling wires , you might find the break. When extra current is drawn from something turning on like cooling fans, the extra resistance from a short or a wire grounding out in some sensor is pissing the PCM off enough to abort all functions.

 

Replace the wiring harness to start. there not that expensive . If you know anyone else with the same year and tranny type see if you could borrow theres. Id bet its in a connector or something .heat makes "hurt" curcuits worse. I once had a nick in my crank sensor conector on 1 wire it cut 3 of the 5 strands it would show good on a continuity test and would run/notrun speratic it finally stopped starting at the track one day.I started taking wire loom off and found the nic. i cut the bad section out and spliced a new section in and then no problems.

 

It definitely sounds like an electrical issue to me, and not a mechanical one. I don't have a camshaft position sensor handy (sitting in my cubicle pretending to work ) or a schematic for one, but if it operates anything like I'm familiar with it should go something like this:



In operation, the supply voltage powers the detector and supplies bias and a current source to the emitter of the transistor. The detector senses the position of the camshaft, and at the appropriate interval supplies a trigger pulse to the base of the transistor. When this happens it biases the transistor so that it opens (a transistor is basically just a small electronic switch), supplying the output signal. When the trigger pulse is absent, the transistor is closed and no current flows.

If the sensor itself has been replaced as you said, you can rule that out. This leaves us with the possibility of a problem with the supply voltage, the supply voltage line, the output signal line, or the PCM itself.

As was stated previously, the first thing to do is to check and clean all your grounds. Bad grounds can cause all kinds of crazy **** you wouldn't expect. If that doesn't help, beg/borrow/steal a PCM to swap with yours and see if that has any effect at all. Do these two steps first, as they are the easiest and quickest to accomplish. No sense in digging around in the wiring if you don't have to. If none of these resolve the issue, it's time to start proubleshooting the electronics.

First, put that O-scope on the supply voltage line to the CPS to see what happens to the supply voltage when the output signal takes a ****. Now, electronics is a two way street, so if you see the supply voltage do crazy stuff that doesn't necessarily mean there's a problem with it, as a problem on the output line can most certainly feed back through and effect the supply voltage. I don't know what kind of O-scope W2W is using, but if they have a decent 2-channel digital one that can do logs, you can hook one lead to the supply line and one to the output line. That way if there is some funkyness on the supply line when the output goes nuts, you can go back to the log, crank the Time/DIV on the scope way down, and possibly see which signal freaks out first.

You're also going to want to make some resistance checks with a multimeter, both cold and at temp where the problem is occuring, and compare the readings (so write them down). You'll want to measure from each individual line (supply and output) to ground, to any adjacent lines in the wiring loom, and to any adjacent pins on the connector to the PCM (you'll need a pin-out for this). All these measurements should be open, or a very high resistance value. A short or a low resistance value would indicate a problem, i.e. a short from line to ground or from line to another line in the loom. These values should not change from cold to hot.

Between all these steps, that should cover about 95% of the possible problems, if not more. Check the grounds and try a different PCM. Check the supply voltage. Take those resistance readings. Let me know the results, and I can guide you further.

If all else fails, I'd say just replace the wiring harness period. Any problems there should be identified using the outlined procedures, but better safe than sorry.

 

Okay, reading comprehension owns me once again. I missed the part about the BS3.

When you hooked the BS3 up, did it completely eliminate the the PCM and all associated wiring? Never had the opportunity to play with one, so you'll have to clue me in on that one.

 

the reason for checking the cam sensor is that the cam and crank sensor share a common circuit in the pcm.

 

O.K.-Thank you all for trying to help. I want to say up front one VERY IMPORTANT thing: The guys at Wheel to Wheel are the best people I have ever been associated with. Without their input/smarts/co-operation, this car may never run again. In my original post the other day, I may have inadvertantly implied that Kurt and the guys at W2W couldn't fix my car. I SHOULD have worded it more like-"They couldn't find the exact cause of the problem and I was running out of cash!!. I am certain that with more time-AND MONEY- they could rectify the situation. They honestly were as frustrated as anyone, including me, with this "nightmare" of a problem. At one point, Kurt thought that "maybe a fresh set of eyes could somehow find something we are overlooking". I really started worrying at that point, as I came right out and told Kurt "If you guys can't find it, thats like going to the Mayo clinic, and the Mayo clinic telling me I might want to have my local family Dr. do my check-up!!! In other words, if W2W couldn't figure it out at that point, there was no other choices to be made. Period. That is why I have NOT even thought of taking it anywhere else. But as far as I know, the BS3 was completely isolated from my cars electrical system. This does seem to be a MECHANICAL issue. I will update as soon as possible. Thanks.

 

Boy it sure sounds like a grounding issue. They can baffle the best minds in any industry. If the entire wiring harness was COMPLETELY replaced when the BS3 was installed you can rule that out.....UNLESS the same physical grounding points were used. I don't know anything about the BS3 or its wiring harness but I would bet it uses the same grounding points.

A bad ground can cause a seemingly unrelated circuit to backfeed another. Like when my stoplights illuminated my dashboard when I stepped on the brake in my C5. A bad ground in the rear of the car caused the stoplights to ground through the dashlights.

Check all grounding points, ground wires and GROUNDING STRAPS! A ground strap could also be missing! And in a C5 where so much is non-conductive that could lead to a floating ground.

One further tip is to realize that a circuit under no current load may show JUST FINE with a DVM resistence check. But could certainly still fault under a current load. GOOD LUCK!

 

pour water over the ignition coils and look for acring. erractic signal sounds like EMI.The way those factory sensors are designed they can act like Radio antenna given the correct voltages and amplitudes. the other possibility is coil flyback voltage not being clamped or being excessive at the PCM. If you have a fialing coil with A large flyback kick it will even screw with the BS3

 

Just a thought. You could have a spread socket in one of the connectors. When it's cold the metal contracts, and when you do a resistance check, it will read good. As things heat up the socket expands, and you get a poor connecton to the mating pin causing high resistance in that circuit. The point of the high resistance causes even more heat to build up making the problem even worse. When things cool off, everything works again. I've troubleshot those problems by using those canned air dusters they sell for cleaning dust out of electronics or optics. When you turn the can upside down, it acts as a refrigerant. When you hit the offending connector the problem will clear up momentarily. They probably sell circuit cooler or something specifically for that purpose, but it was what I had on hand at the time. It's worth a shot and doesn't cost much. Good luck.

 

First thing is to make sure your BS3 is completly on its own and doe's not have that adapter harness to make the gauges work because your tapping back into your pcm.Did you have this problem with a stock ecm and then switch to bigstuff and still have the same problem?Again is BS3 all on it's own if so were the sensers changed out.When did this problem start happening?

 

Just a thought you say 180 to 186 the motor acts up.Is that about when the fans kick on if so disconnect the fans maybe your getting a back feed from the fans (bad fan motor) or any other source that would trigger in that time frame or heat range.Just a thought

Mike

 

I am in the Lapeer area. I have been very busy lately and apologize for not getting back to any of you who have tried to help. Hell, I haven't even read all the posts yet, due to lack of time to get online. I have, however, found the problem, at least I am at least 90% certain I have. I am going to post up my discoveries on this most baffling AND heartbreaking, expensive problem, in hopes that it will help somebody on our forums, somewhere, someway. I think you will find this VERY interesting indeed!!!! Again, without the help of all of you guys, especially Kurt Urban and the guys at Wheel to Wheel, this discovery would probably never have been made. Thanks again to you all!