Need help, car suddenly running really rough.

[GregD]

Hello all, I'm having a bit of a problem with my car. I apologize for the length. 68 Camaro, 383, edelbrock 1406 carb, MSD RTR distributor. The car started running rough the other day and I'm trying to troubleshoot. I had let the gas tank get pretty empty so initially I thought I might be running out of gas. However, I have since filled the tank and I'm still having the issue. I then thought I might have sucked up some crud from the bottom of the tank. I checked the fuel filter and there was quite a bit of crud in there. I cleaned that out but am still having a problem. The problem is somewhat strange. At times, the car runs great for a few seconds then it feels and sounds like its losing a few cylinders. I lose power, it stutters a bit and occasionally backfires slightly. Then it will come back to full power as if someone just just flipped a switch. The best way to describe it is that its like someone is throwing a switch and the car runs great, then they throw the switch and it runs really poorly. Its really that pronounced. Would a fuel issue cause something like that? Because its such an on/off type of problem it leads me to question whether I have some sort of ignition problem rather than a fuel problem. I did find something strange. When I measured voltage at the coil, I'm only getting 11-11.2 volts while the car is running. With the car off, I'm getting 12.4 volts. This is without any electrical accessories running. Do you think this is a problem? Can I run a jumper wire directly from the alternator post as a test to see if that solves the issue? The wire is currently run up from the starter post. I measured voltage at that starter post while the car is running and it shows about 12.4 as well. I looked at the wiring and did not find any shorts or cracks. Any help is appreciated.



BTW, output at the alternator post is good at 13.7 volts.

[Hidro]

Check for vacuum leaks?

maybe someone else has a suggestion.

bump...

[Vegas69]

I would be suspect of your wire from the starter. Check your voltage at the starter terminal if thats ok then you can do a voltage drop check. You turn on the key and place your terminals on each end of the wire. It should be .2 volts or less. If that isn't it some of your debris could of passed through that filter. May need to clean the carb out. Also check the plugs to make sure you don't have a fouled plug. If none of this checks out let me know.

[GregD]

Well, I took the carb off and took it apart to clean it. It was so clean you could eat off of it. I blew some compressed air through it just in case. I'll be reinstalling the carb and putting on a fuel pressure guage to check that. If that looks good, I'll concentrate on the ignition wiring.