Swap dies while driving... ???
 

Hi All,

I'm hoping someone with far more LS expertise than myself can offer an opinion here...

https://lh6.googleusercontent.com/-m...o/SDC11609.JPG


https://lh6.googleusercontent.com/-v...o/SDC11605.JPG


I've got an '89 Camaro LS1/T56 with the entire and complete wiring harness from a 2000 Z28. I think I have somewhere around 4,000 miles on the setup, tuned with HP Tuners, and it's been running really well.

We took it out for a short drive last night, and it died pulling into the parking lot. All of the electrical stuff seemed to be working, but the engine just shut off. We went inside, socialized for a few hours, came back out to leave, and no joy.

The car would turn over, but no fire. I popped the hood, grabbed the harnesses on the passengers side of the engine bay, and then I could get it to fire.

So, we start the short trip home. It cutout after about a 1/4 mile.

Now, this may be of significance... I coasted for a few few feet, in gear, ignition on, and it made a loud boom. I think we used to call them "key bomb drops" or something stupid like that. When you turn the ignition off while rolling down the road, let the exhaust system fill unburnt fuel and air, then click the key back on and BOOM. (Saw quite a few people remove portions of their exhaust that way)

Anyways, I pulled over, wiggled the wires, and we were off again. A few hundred yards down the road, and the same cycle repeated itself; Drive, Stall, BOOM, Jostle Wires, Drive...

The tach works, all of the electrical systems seem to be working, it's definitely not lacking fuel when it dies. I'm stumped.

Any thoughts?

I thought it might have been the crank sensor. But that doesn't make sense, since the crank angle is used to fire the injectors... isn't it?

So, in theory, if I lost the crank signal, it would cut fuel as well.

I would start by checking the ground pins in the ecm, and the other end (where they ground to battery - or body). Ive had swaps do this after a period of time when everything has time to jiggle, move and shift. This is where I would start. BTW, beautiful, clean swap. Very nice. Hope this helps, Eric L

Thanks, Eric. When you say "ground pins in the ECM", do you mean in the big headers/connectors?

Now that you mention grounds, I remember a while back I tried to start it one day and when I turned the key to the start position it lost all electrical power. I thought for sure that it was bad ground or battery connection. I removed, cleaned, and re-installed the engine block to battery ground, and the problem hasn't shown up since. But, that was a total loss of electrical.

I'll poke around with the grounds and see what I see.

What I would do is unplug the two ECM connectors, pop them apart, and give a little TUG on each wire and make sure they are properly seated in the ECM plug. They are real easy to pop apart with a small flat screw driver. Just check over ALL your wiring. With the way it ran fine for 4000 miles than started messing up, I would turn my attention towards a loose connection from vibaration, etc. Eric L

If you're getting fuel to build up in the exh, then its not a fuel issue. You're losing all IGN

Check for codes in the PCM. Open circuit codes mean wire problems. No codes point to bad connection(s) on the power or ground

Alright, maybe I'm just not understanding the sequence here...

I inspected my ECM terminals -> All good

I checked the ECM grounds by checking resistance to ground on all four pins, and then removing the ground and checking continuity while moving the harness -> All good and stable

I managed to get the car started, and started prodding the harness -> This is where I start to get confused

I can push down on the harness behind the intake and the car will stumble and/or die. If I lift up on the harness, it will come back to life and run normally. If I leave it pushed down, it dies completely. I did this no less than a dozen times at differing intervals to rule out coincidence. The position of the harness definitely impacts the operation.

So, next up I went hand of hand on all of the wires. I did find one light green wire tha had been rubbing on the coil bracket. So, I relocated and repaired that, and tried moving the harness again with the same results; pushing the harness down resulted in stumbling and shut down, while pulling up returned it to normal operation.

Then I pulled the cam sensor connector. I did this more out of frustration than anything else. The wires looked like thy made a pretty sharp bend coming out of the plug. Nothing felt soft, or like it was losing continuity. So, I rotated the plug 360 degrees and plugged it back in.

I re-tested the impact of moving the harness on the operation of the engine, and operation is now unaffected by the harness position. So, I am fairly certain that the cam sensor plug is the culprit. But, I'm confused...

I thought the cam sensor was not used to fire the plugs? I thought the spark was calculated based on the crank sensor? So what does each sensor do? What is the crank sensor used for, and what is the cam sensor used for?

Thanks in advance for any knowledge you can share.

Sounds like messing with the cam connector was a coincidence

The cam sensors one job is to lets PCM know whether the engine is in intake or exhaust stroke when starting. After the engine is started, the cam sensor does absolutely nothing until the next startup

If you can change how the engine runs by messing with the harness, then there is a problem in it. I suggest removing it and ohming out every wire (takes 1-2hr). Removing it makes it easier and will identify a crappy ground ring if present. Ohming it will detect wire fractures internally and complete failures. Internal fractures like a sharply bent connector slowly wearing through will show up with high resistance, much like a crappy joint. Complete fractures will not have a connection and speed your troubleshooting

Has issues continued?
 

Have you had this same issue since you messed around with the cam sensor?

7-year old thread. You really think after this long you might get an answer?
Check post dates.... it REALLY matters.....

I know the thread is old, but it was the only one I could find on this subject anywhere and since I’m new, I couldn’t send a private message. Was hoping for a response and worth a shot. The worst that could happen is I run into someone telling me the thread is old haha.

You can always start your own thread, describe your problem, and await responses. A lot of guys will not even read through a thread once they realize it is old, and thus never get to your question.

He just might... since I still haven't fixed it myself and was just thinking about it the other day.

Yeah. I did manage to narrow it down to an intermittent open short (fractured wire or something?) in the harness across the firewall.

I'll try to get out there in the next day or two to trouble shoot it again. I really need a wiring diagram for a 2000 Z28 though...

you can find help on other sites.

https://www.the12volt.com/installbay...etail/490.html

I knew if I just waited 7 years, someone would point me in the right direction... :)

I'm actually in need of the wiring diagrams for the complete harness. They exist, but I always wind up down a path on a different project before I procure them. Oooh look, a squirrel...