So I went for a drive in my '93 m6 Saturday night. I was getting off the interstate, and going though the exit some what fast (just over 50 mph on a 25 mph exit) when the car just shut off. Car was running beautifully for the near hour drive up to this point. Gauges were working, tach was showing RPMs when the clutch was engaged and car in gear, but it was like it was getting no gas. Push in the clutch, tach went to 0. Yes, I am fully aware of how these cars act in corners in relation to it's gas tank and the gas in it. Car should of had plenty of gas to not have this problem, around 3/4 of a tank. I got the car pulled on the side of the road, and at first it would not even try to start, just turned over. After letting it sit for about 5 minutes, I tried to start the car again. Now it would start, run very rough, and only get about 200-300 RPMs, only to stall out. Trying to give it gas would result in the car stalling out. Ended up getting towed home. Sitting on the side of the road for 2 hours with the hazards on, after trying multiple times to get the car to start killed the battery. Next day, I go out and hook the battery charger up and get the battery charged. After charging the battery, I tried to start the car, and the M'FER fired right up like the night before never happened. I'm really getting tired of this car leaving me stranded on the side of the road (3 times this year with over $500 in towing bills). Any thoughts on what may have happened?

 

You didn't mention it, so I assume there were not any engine codes. When the car is running, what does the charging system look like?

 

The biggest clue to me here is that your tach dropped to zero. This is the optical sensor. It is heat sensitive and this issue will get progressively worse until it will not restart at all. People will say do not jump the gun and think its the opti right away but, in this case--opti!

 

No codes, at least no flashing SYS light. Come to think of it, even when I was having ICM issues, the SYS light has never flashed in this car. Any chance this has been disabled? Is that possible? I'll go manually pull codes in a little bit. Kinda chilly outside right now.

Charging system is working fine. Battery died after about 30 minutes of trying to start the car and then +2 hours of the hazard lights flashing. I expected it to die because of that. It was almost dead (to the point of turning the engine over too slow to start it) from just me trying to get it to start for 30 minutes.


Tach only went to 0 when the engine was turning 0 RPMs (when I pushed in the clutch). When the clutch pedal was not pushed in, the tach showed the RPMs the engine was turning at. Car has a new ICM and coil, and a re-built Opti from the Opti Doctor (all installed last spring).

 

I always scan for codes. Even if there is no SYS light or SES light. If nothing, have a fuel pressure gauge hooked up. Get the car to act up, monitor fuel pressure. Running should be at least 36psi. Key on, 42 psi. Or if the car doesn't start or stalls, noid light test on a fuel injector connector. If no pulse while trying to start the car, bad opti.

 

As the OP noted below, the tach continued to function correctly. Therefore it's not the opti sensor. Probably also not the ECM. I'd be thinking about the coil and ICM, even though they were recently replaced. It sounds like one of them is failing when it gets hot. The way you describe the rough running and not taking any throttle once it sat for five minutes, I'd suspect the coil first. But the only way to know for sure is to drive into failure mode again and start testing.

First test would be to check for spark - when it dies and won't even start, is it getting any spark at the plugs? Is it nice and hot (white or blue spark), or weak (orange/yellow)? Then work backwards. Here's a good link to a diagnostic for the ignition system. The hard part is that you have to know it's fully in failure mode to diagnose it.

 

Well I may have found the issue. Like I said earlier, at least according to the gas gauge, I thought I had around 3/4 of a tank of gas. And that's about what it was saying when I got the car started yesterday. Well I went out and started the car this morning, and just left it running. Went back out about 20 minutes later, car wasn't running. Turned the key, car fired up and stalled out 2 seconds later. Turned key again, car wouldn't start. Looked at gas gauge, it says I'm into my reserve (over half a tank gone from reading the day before). I do know that I'm running out of gas before the gauge says the reserve is all gone. Luckily I was able to get the car to spit and sputter enough to get to a gas station when that happened. So I think what happened Saturday night is I lost gas at the fuel pump pickup because of the hard turn, and stopping the car in a incline. When I got it home, it was on (somewhat) level ground, so it was getting gas to the fuel pump again, which would explain why it started with no issue Sunday. Guess I need to go fill up the gas can and see what happens when I put some gas in it.

Thoughts?

 

That is definitely your first troubleshooting step!

 

I always reset the trip odometer to measure when to fill up even though my gauge works. I just do not trust it to always be correctly showing the actual fuel level. This is after having a similar experience (started a drive with the fuel gauge reading a half a tank and get 2 miles down the road and it goes on reserve). Fixed the fuel sending unit and it works well now but by monitoring the trip odometer I KNOW when I should be looking to fill it up. I try to never let it get below half a tank anyways so I am usually good to go. Seems like this is a common problem so now I just avoid it by keeping the tank full. I do not mind filling up even if it only takes a few gallons when I am close to a gas station. A full tank also means less potential issues with rust by not having exposed metal in a half full tank for an extended period of time.

 

Sell it, buy a C5

 

 

Easy though; when the car won't start or stay running, what's missing; spark or fuel?

 

Not 100% sure, but if I had to make a guess,going purely by the way it sounded when it died (I haven't done any actual trouble shooting past putting gas in the tank, btw, I do hear the fuel pump cycle , whether the car starts or not), spark