I'll post all the info I can think of for you guys. I have not had this car just die on me before. I took it on a 2,000 mile road trip to California and back in June with no problems. It's been my daily driver since the weather dried up. Three weeks ago I had just driven 80 miles on the freeway and was waiting in a left turn lane when the engine started to idle rough. It sounded like it was almost dying then catching itself but finally died. I tried to start it about 4 times and it would fire up then die, even if I gave it gas. When it finally started I got onto a side road and drove at 20 mph at about 2,000 rpm in 2nd gear. There were a few times it tried to die even then. Looking at my scanmaster, I noticed the O2 millivolts on both sides would drop to nothing when the engine almost died. Once in my driveway, I was letting it idle and started to cycle through the sensors on my scanmaster when it died again.

The next morning I ran some errands with it and it ran fine.

So it acted up again today. This time I got some trouble codes that I hope will shed some light on the issue.

18 - injector circuit
42 - ignition control circuit (shorted or grounded)
51 - eeprom programming error

I was running errands and drove about 35 miles around town with the AC running. My scanmaster showed coolant temp reached 214 degrees as I was heading home when I felt the throttle first become unresponsive, as if I was out of gas. I turned off the AC and drove a few more miles and the temp dropped to 193 degrees before it died at an intersection. I got it to some shade and let it cool for about 10 minutes. After that, even though coolant temp was at about 185 degrees, I could only drive it a half mile at a time before it died. It died four times like this the rest of the way home. I would have to wait a few minutes before it would start. While driving or idling it would start to die and be barely hanging on, lots of shaking. If I ever gave it gas at this point, it would die instantly and smelled strongly of gas.

I looked at as many scanmaster readings as I could through all this.

O2 millivolts were down around 7 like last time.
LBL/ RBL were up at 160.
Lin/rin were up at 194.
EGR kept quickly bouncing from 0 to 12 and back.

I checked the connections at the injectors, ICM and PCM and they were tight. The PCM was piping hot to the touch though. I did the ICM cooling mod mentioned on shoebox's site and it wasn't as hot as the PCM.

That's all the info I can think of right now. Could the PCM just be getting heat soaked on these hot days?

 

First of all, the temps you mentioned are in the normal range. The first fan should come on at 226*F and the second fan at 235*F.

I think your entire problem is from either the battery or the alternator. I feel that it is getting into a sort of 'brown out" condition. From a cold start, while the engine is idling with no accy on, measure the voltage across the battery.

Then check it again once it's completely hot and a fan comes on. Then once more with every accy you can think of turned on. You should not read below 13 volts. And actually you should be over 14.

 

Check your fuel pressure.

 

I have a 95 Z28 LT1 Auto.

I am having the same problems as the OP. My voltage at cold start up is normal. I am noticing low voltage, as you describe, after it has gotten hot. It even has low voltage when cruising at highway speeds. My voltage will drop as low as 8, at a stop-in drive. I was thinking that the rough running was causing the drop in voltage, not the low voltage causing the rough running.

I am going to check all of my connections. If everything is good there, wouldn't it have to be the alternator and not the battery?

 

Currently I am having an issue with low idle, hot engine and low voltage. You can tell this by bringing up the engine speed with the throttle. Watch and see the voltage go up.

There are 3 things that will bring the charging system down to a point that is not charging correctly.

A bad battery. Seems they go bad at the 2 extremes cold and hot. In case you wondering why the battery in your car may have been wrapped with foam from the manufacturer. It was to insulate it from the extreme under hood temperatures. The battery can boil the electrolyte and that destroys the ability to charge. A bad battery can suck everything you throw at it and still won't take the charge. Therefore the alternator has to supply everything the accy demand.

A bad alternator. Could be it's not putting out enough current. It could also be leaking AC onto what should only be DC. If this happens it can drive the PCM nuts. You get all kinds of random codes.

Too low an idle. This causes the alternator to not produce enough. If the voltage goes too low, just like an alternator that is leaking AC, it can cause the PCM to throw several unrelated codes.

This is what I think the OP was experiencing. Now it could be from too low an idle. And that could be from the fuel pump crapping out too. But you have to find out if the idle is causing too low a voltage. That would explain the weird codes.

 

My voltage according to the scanmaster has always been around 13.3 +/- .2 volts. I have an Optima red top that is 7 months old and my alternator is a re-manufactured Delco unit I bought 2 years ago. While I was limping the car home yesterday, I noticed the voltage was at 12.6. I'm about to go run some errands and I'll pay attention to the voltage throughout the whole trip. I'll also keep my fuel pressure gauge in the car so I can read the fuel pressure if I experience this again.

 

12.6 is not charging at all. A battery is normally at 12.6 If it's lower than 14 without loads on it while running, generally that is a problem.

 

This time was about 6 miles round trip. Volts started at 13.1 and were at 13.0/12.9 by the time I got to the store. That's with nothing on, just engine. When I gave it half throttle to full throttle, volts would drop to 12.5 then rebound when I took my foot off the pedal. On the way back, volts steadily dropped to 12.6. I turned on the radio and saw no change. I turned on the AC and saw an immediate drop of .5 volts. Giving it more than half throttle at this point dropped the volts to 12.0/11.9 then would rebound to 12.6 again. Car ran perfect otherwise.

 

Got a new surprise today. On the highway I had my cruise set at 80 mph and within about 15 minutes of starting the drive it began running rough. I noticed the LBL was at 108, RBL was at 160. I remember rin was at 196, and right injector pulse width was up near 10. Left O2 wasn't moving outside of 400-500 millivolts. Right O2 was bouncing from 0-999 like normal. Then I get a code 63 for Right O2 open circuit. It smelled strongly of gas for the next 10 minutes or so when I noticed fuel trims were returning to normal and everything else was go back to normal. For the next 15 miles or so, the sensors would intermittently go wacky then level off. After that for the next 60 miles it ran perfectly. After all this weird behavior, could my PCM be going bad? I'm also pretty suspicious about the PCM because of the eeprom error combined with the injector circuit error. The battery voltage was between 12.5 and 13.2 throughout the drive. So far it seems like if I start looking where the dtc's and sensors are telling me to start, I'd be checking every component in the engine management system.

 

damm i am having the same problem i though it was a bad opti replaced it had the same problems after ...

the only difference is that the car will run fine for about 20 min or until about 220 and if i shut it of it will not restart for about an hour

So I am pulling my hair out at this point and have pulled the opti 3 times (i thought it was bad and sent it back)

my codes are
51 - EEPROM program error
48 - MAF sensor circuit
16 - OptiSpark low resolution pulse not found
18 - Injector circuits
50 System voltage low (not sure if i am getting this becasue of repeat cranking )
42 Ignition Control (IC) circuit (shorted or grounded circuit)


have have gone through the wiring harness with a fine tooth comb to make sure there is nothing wrong with the connections helppppppp

 

Sure sounds like you have a problem with the left O2. I would replace it and see how it does after that. You might have more problems, but it would be smart to fix one at a time and maybe they all go away if it was related.

 

If my O2's act weird again today, I'm gonna swap sides and see if the symptoms follow the O2's.

 

That is a great idea. That way you can inspect them for damage also.

 

Since it seems that your alternator may be a problem, why don't you check for AC leaking onto the DC voltage line? Only takes a voltmeter to check it.

 

Ok speedy, I have a voltmeter and would certainly like to check that. Is it as simple as setting it to AC and probing the alternator wire? Engine running?