Power Issues

[Ereeves]

Finally took the car for a real drive last night. Everything was running fine after about 3mi. Pulled into a parking lot and swapped places with my son so he could drive. Not being use to the heavy clutch he stalled it. Who hasn't. It was after this that things just were not right. Pulling up to stops we would have to watch the rpms to keep it going, volts were going down then back up (has brand new battery) and even in the passenger seat I could feel it was running rough in the lower rpm range. It did die at one red light but fired right back up. The dash would also go out but car was still running. It would come back on when we would get the rpms back up. Brought it home and put it away.

I am confident its not serious but know chasing this could be elusive and tiresome. So has anyone been through this before and have an idea of where to start looking?

[secondchance]

I would check the MAP sensor hose between the intake plenum and bottom of the MAP sensor.

http://zr1.net/forum/showthread.php?t=15800&page=2

[Ereeves]

I will do that but wonder how that would affect the electrical system?

[secondchance]

Way too low rpm may be causing low voltage is my thought.

[gbrtng]

If the engine backfired on the restart, it probably blew the MAP hose off - a common problem. The service engine light will come on immediately - reconnect the hose and the
light will go out and all should be well again. Do not fasten the hose to its fitting because the next time the engine backfires, something else under the plenum might rupture. Think of the MAP hose as a safety valve ...

[Ereeves]

There was no backfire and I check the hose and it was still connected. Started the car and everything seemed fine. So I watched the volts. AC on at idle (with a new battery too) volts would drop down to high 11's and come back up to 13.4 whenever it would cycle on/off. I think that is pretty severe and I could have an alternator going bad. What a pain in the *** this thing looks to be getting it out to check it.

[secondchance]

Not too bad. Me and Jim replaced one at Carlisle for one of Net Registry member. Took about an hour. Figure on pulling the plenum or the air horn. Also, make sure you get correct alternator pulley for LT5. L98, I believe, uses same alternator but has smaller diameter pulley.

[gbrtng]

Not too bad. Me and Jim replaced one at Carlisle for one of Net Registry member. Took about an hour. Figure on pulling the plenum or the air horn. Also, make sure you get correct alternator pulley for LT5. L98, I believe, uses same alternator but has smaller diameter pulley.
Or have your original rebuilt - my preference given the pulley issue.

[secondchance]

Or have your original rebuilt - my preference given the pulley issue.

Rebuilt is good. Pulley can be changed over pretty easily too. Just need an impact wrench. Don't even try removing it manually. I tried...

[Demps]

All great advice.

One other thought...Following the KISS principle: are the battery terminal bolts correctly threaded and tightened? I had one that was stripped and appeared tight but wasn't.

Ted

[secondchance]

All great advice.

One other thought...Following the KISS principle: are the battery terminal bolts correctly threaded and tightened? I had one that was stripped and appeared tight but wasn't.

Ted

Great point! I had it happen to me twice.

[Hib Halverson]

If the idle speed is surging enough that the engine stalls, that could explain the charging output voltage changes. If the engine drops below the desired idle speed, the alternator cannot put out enough amperage and the voltage will drop from nominal charge voltage to battery voltage.

That said, if you are getting large fluctuations in charge output when the engine is idleing smoothly, then maybe there is a charge system problem.

When you say the dash would "go out" can you be more specific? Are you talking about the dash lights or the digital display in the center of the IP?

Before I'd spend money to start replacing charging components, I'd take a look at problems which would cause an unstable idle of which there are many.

The prime candidate is a vacuum leak although if the MAP hose if off, the MIL will be on.
Also possible are:
Faulty or fouled IAC
lazy O2 sensors
ECM ground(s) faulty
dirty throttle body
bad injector(s)
evap problems
...are just a few.

[Ereeves]

Hib,

Here is how it went down. Son stalled car in parking lot. Restarted everything fine. Got out on the road and came to red light. It died but could have been assisted by my son's lack of being familiar with it too. Restarted and continued on to next red light and noticed from the passenger seat that it felt rough. Asked him and he said it was. Turned onto another street and watched the dash go out (everything) and the DIC all light up. Told him to up the revs quickly which restored everything. Ran a little rough from there all the way home where she still sits.

Check the MAP hoses and it all checks out ok from the top and back of plenum. Started car and it runs and idles fine. I watched the volts and witnessed the variations noted. That is all I have to go on for now. Thanks!

[mike100]

C4's like to act possessed right before you lose a battery.

[rush91]

All great advice.

One other thought...Following the KISS principle: are the battery terminal bolts correctly threaded and tightened? I had one that was stripped and appeared tight but wasn't.

Ted

Great advice. I'd start there as well.....Make sure you don't have loose connections at the terminal. I would disconnect the battery for a minute, then tighten it down good. Did you hear the car backfire at all?