Ok, this is a saga, but I will make it short and sweet.

What the car is doing is running 180 degrees off so to speak. It wont' start and when it does it backfires and dies..its loading up on fuel so bad you could take a swim in the intake.

This is a classic symptom of a bad crank sensor, but that has been checked and is not the problem.

A snap-on scanner has shown that the car is throwing a code for low voltage from the cam sensor. Keep in mind I replaced every sensor in the motor(cam, crank, TPS, coolant) when the problem first started.

So I took the plug that goes to the cam sensor and put a multimeter on it..the multimeter stated that the plug was totally dead, recieving no power OR ground even throught the harness.

Traced the wires back to the PCM and checked with multimeter at origin, the wires were fine at the PCM. So I figured something got fubared in the harness somehow. So I cut the plug off, cut the wires at the pcm and "hot wired" the plug by connecting wires right from the pcm to the plug. Mulitmeter showed the plug now had power and ground.

What's messed up is that this didn't work. The car did the same crap and threw the same damn code. This is nuts.

I understand that the cam sensor is a magnetic sensor. My motor is freshly built forged internals shorblock that I just got back..this problem started with the old motor, causing me to find mechanical damage and have the motor re-done.

About it being magnetic, I'm wondering is it possible something is messed up with the magenet on the wheel that the sensor reads on the back of the cam? I've put alot of hours into this problem trying to find it..finally thought i had it when the cam sensor issue cam apparent, but now still nothing.

I guess I'm looking for some input..and any idea on how the crank sensor could still be playing a role in this despite checking out fine??

I pulled the harness out of the car last nite that goes to the crank sensor/starter area, and all came out fine.

The manuals don't give a way to test these sensors themselves..anyone know of a way to test the actual sensors and not just the wiring??

Any help would be very appreciated, this is getting beyond frustrating..

 

Maybe it needs a Crank Relearn? (not sure if this can cause the issues you're having, but seems like something easy to try w/a scan tool that supports it)

https://ls1tech.com/threads/showflat...rue#Post539356

https://ls1tech.com/threads/showflat...rue#Post733449


http://www.seattleautomotive.com/ckpdoc.htm

 

I saw that in the chiltons.

Only reason I disregarded it is that in the instructions for performing one it says start the car and then proceed.

so obviously the car should be able to start.

maybe i should try swapping my old crank sensor back in, it works far as I know. I just changed it to eliminate possiblities when the problem started.

 

Did you change the harness?

Maybe you pulled the wire and the wiring is bad.

Have you verified:
-cam is not messed up
-all 8 coils are firing
-running on 8 cylinders

 

The Cam Sensor has the magnet in it along with a hall effect switch. When metal, ie-when the cam trigger is near the magnet it will pull the signal line to ground. The signal should be at a positive level when the cam trigger is away from the sensor. There is a pull-up resistor for the signal line integrated into the cam sensor. You could test the sensor by removing it and applying +12V to the supply terminal, Ground, and then using a voltmeter the signal line should read a positive voltage with no metal(steel or iron) by the magnet. When you place a wrench or something metal in front of the magnet the signal line should go to within .5 volts of ground. One thing that is confusing here is that the LS1 should start even with no cam sensor signal present. The PCM will try to fire a cylinder and if it does not detect an change in the MAP sensor signal it will try 180 deg differance. Have you check the wiring for the crank sensor as well?


This is from a diagnostic manual for the LS1.

If there is no CMP signal present the system
attempts synchronisation and looks for an increase
in MAP signal indicating the engine started If the
PCM does not detect a MAF increase, the PCM
assumes it incorrectly synchronised to the exhaust
stroke and re-synchs to the opposite cam position
A slightly longer cranking time may be a symptom
of this condition.

 

I recall another problem like this about 15 months ago.

did you ever have the coil packs off?

Did this happen one sunny day all of a sudden before you pulled the motor?

check the coilpack orientation, and the wires from the harness to that.


Also, try swapping coil packs with someone else. Unplug the one white connector, and pull the bracket with all 4 on there. Sometimes people pull off the packs individually.

Give that a shot, and let me know.


I may be taking a trip to Chicago with in the next week or 2, and I would be glad to take a look at it for you.


Louis

 

I you sue the computer isn't going bad. maybe for ***** and gins see if you can borrow a computer and see if it fires. This sounds like my kind of luck.

 

Thanks for the replies everyone.

Tuff, I tried a different computer, a stock 98 M6 one..no change.

G2LS1, I'm going to p.m you about your offer to look at it, would be appreciated. Also, there is spark in all cylinders(did screw driver test with plug wires) and the coilpack harnesses are on there properly according to the numbers shown on them.

Thanks for the time on the phone last nite PSJ, that conversation on the timing of the backfiring made me think of a few things.

Technoman, I will try that testing procedure you have outlined tonite. And yes I have put the mulitmeter on the wiring that goes to the crank sensor, checked the plug and also checked continuity of the wires..also took the harness apart and visually inspected all the wiring that goes down there.

One other thing for Technoman..so the car should start? Well, it does for a split second then backfires and dies. This brings up and interesting idea. Let me tell you what I found. When I put the multimeter on the plug for the MAP sensor, it had the proper 5V reference, but it had TWO grounds coming up, instead of just one ground and one 12V+. That can't be right, both logic and the manual state that the MAP sensor should only have one ground. To me that meant the MAP sensor was grounding out somewhere, right?

So theoretically if the car was starting but then recieving no reference from the MAP sensor because its grounding out then you're saying it would try to go 180 degrees? That would cause what the car is doing, yes?

However, this still doesn't explain why the plug to the cam sensor was totally dead, no power or ground when I tested it. The other question is if this is somehow MAP sensor related, would it be possible to cause the car to throw a cam sensor low signal code and not a MAP code?? The cam code is the only one I'm getting.

 

Sean:

To go back over your timeline, you said you removed the intake to address a vacuum leak, and at that point you JB welded a spot on the intake and you replaced all of the injector o-rings.

Now, let's go back to my point that I made over the phone last night...

Our cars either run great, crappy, or not at all. Your car is in the "not at all" category. It can crank and start and then it shuts off almost immediately and then backfires out the exhaust. So like I said before, if you had a perfectly running car and disconneted half of the coil packs, the car will still run, on four cylinders. So you have a basic problem.

You also mentioned that you have all three grounds in back of the driver's side head on one bolt right?

Here is my theory.

You have an electrical problem, not a fuel or mechanical problem. if you had a mechanical problem it would be the pcm not seeing the cam wheel or crank wheel because they are not there or are damaged.

If you have a dying fuel pump or regulator the car will still run, next.

Now, your car shuts right off. I bet the pcm is shutting off the spark. I think it's doing that because it's detecting an anomalous condition, like the cam sensor or something does not work.

The backfire is a result. You lose spark, fuel just runs down the primaries and BOOM is ignited on hot exhaust surfaces.

I'd redo the grounds in the head first.

Then I would consider installing a new engine control harness.

 

Yeah, like we talked about last nite I'm going to be examining all grounds tonite as well.

What I still don't know is what exactly those grounds on the back of the head are for..maybe someone can shed some light on that one??

Is one of those grounds potentially for the MAP sensor..because a faulty ground there would possibly explain why in the MAP plug I had two grounds show up instead of one. Sounds to me from the info posted here that if that MAP sensor were not reading correctly the car would have problems.

 

You could try checking all fusable links in the harnass prob the wire and wigle and pull to see if you have a bad link just another opion. I wish i could take a look at your car this suff bugs me

 

https://ls1tech.com/threads/showflat...rue#Post478332


Dug this up, but his car ran did run,albeit, no well, but it still fired.

 

Ok, here's an update, I just told it all to G2 LS1 in a p.m but here goes again.

I believe I have figured out last nite exactly what the problem is, but can't find what is causing it.

The codes being thrown are low signal from Cam sensor and the MAP sensor. When I put the multimeter on teh plugs that go to these sensors I intitially get X amount of voltage(X depending on how long my Optima has been sitting on the charger that evening) and then it IMMEDIATELY starts dropping rapidily in fairly large increments down to zero, doesn't take long at all to hit zero, and the initial amount is never anywhere near 12 volts anyway to begin with..I think the most I saw was 7 or 8 volts last nite.

Obviously the car isn't maintaing power to those plugs for some damned reason. My theory is this is why the car will start on occasion, but that voltage sucks down right away and then the the CMP loses signal and the car doesn't know where to put spark, therefore screwing everything up.

I called my buddy Chris Sikora of SSRacing to confirm my diagnosis, and he agrees, but can't imagine what is causing that to happen either.

I guess the next logical step is to go into the wiring harness where those plugs run through and start snooping around.

Here is the very perplexing part though. We did hotwire that cam plug and it didn't change anything, which it should have. And if the power/ground problem was in the PCM itself, that should have been corrected when I tried a different PCM before, so I have no idea what the hell could be casuign this.

I went over all grounds last nite, and all are stable, including the one for the battery in the back of the car.

Tuff, lombard is not all that far from where I have the car in Glenview, you'd be more than welcome to come look at it if you want, I'll take all the different perspectives I can at this point..