99Hawk120

And I only changed one part... the distributor. I swapped the computer controlled distributor out for a non-computer HEI. Within 10 minutes I got the timing settled in (hey, I had to wait for the motor to come off the choke). Nice smooth idle at 800rpm in neutral. I'm still running the ECM controlled qjet because I haven't finished the replacement carb. Fortunately these cars run a lot better this way than they do with a holley and the computer distributor.

I do have a random miss on the #1 cyl. The two on either side (#8 and I forget the other) on the distributor ar fine. Probably a plug wire or plug problem. It still idles smooth even with the miss which is something the computer setup NEVER managed since it would not leave the timing alone. And now that the computer can't screw with the timing, the carb seems to work fine--I'm confident at this point it was the computer all along

Next stop, non computerized carb. I could get to like this whole "knuckles scraping the floor" schtick.

five7kid

iTrader: (14)

I've drafted several responses to this in my head, all of them come out sounding like what I don't like to see people say on these boards. I'll try to keep it civil.

For years, problems have been blamed on carbs that were caused by ignition. You appear to have a secondary ignition problem that you're blaming on the computer.

Some things never change, they just take on different forms.

My computer controlled SBC idles smoother with more cam duration at a lower RPM than my non-CC BBC ever has. Saying that may not prove anything, but at least I can say that it is possible for a CC system to produce acceptable results. Other than "normal" tune up items (cap, rotor, wires, plugs), all it's had changed are coil & module. I've never had to adjust or replace anything directly associated with the computer controls.

Well, I probably didn't achieve my objective, so I'll just go ahead and say I think you're way off base; your current combo can't even come close to running right; changing the carb and distributor won't make things right if you've got secondary ignition problems; etc., etc., etc.

Jester

biting...tounge....not gonna....say it.....

99Hawk120

:shrug:

No offense taken, 5-7. Frankly, it's a case of me simply being tired of dealing with the ECM controlled system. It never responds the way I think it ought to. Maybe it's responding exactly the way GM intended it to, but I don't think having the timing jump is a proper way to deal with a misfire. More importantly, I was never able to diagnose the misfire with the computer controlled system as the ECM did its best to "mask" the actual problem by messing with timing, fuel, etc, making it very difficult to figure out exactly what the problem is. I'm just tired of trying understand what's going in its silicon little brain. It's easier to simply eliminate the computer from the equation so I can fix real problems.

More importantly, this about the 6th or 7th set of wires I've been through on this car. Several of them burnt on the headers right near the boots, so I finally bought a set of fiberglass sleeves for them. It's not ever idled right with any of the wires I put on it; perhaps I've always had at least one wire with a slight miss.

I still stand by my opinion that the programming of the ECM is pretty poorly done. Some of the behaviors are indicative of nothing more than bad programming; for example, on my Oldsmobile, the computer goes into a fixed dwell above a certain RPM in park/neutral. For a while, I had the problem of the "fixed" dwell being richer than the dwell it was using when correcting via the O2 sensor; hence it got into weird oscillations with the RPM going above the set point, getting rich from the fixed dwell, which dropped the RPM below the set point, which caused the computer to lean the mixture, which sent it above the set point... a patently absurd situation that never should happen, and wouldn't, if the ECM wasn't coded to revert to a fixed dwell under that condition.

It's not necessarily a case of "blaming" all the problems on the computer, but it's making my life more difficult than it needs to be, so it goes. It's possible that after I fix the ignition problem the comptuer might allow the car to idle properly; it's also possible that it might come up with some other bizarre behavior which causes me to tear out my hair while trying to troubleshoot it.

99Hawk120

Misfire appears to have been a loose connection at the distributor cap. Probably just didn't get put back on all the way when I changed the distributor.

99Hawk120

Well, I put the new carb on. Car is much less rich; I'm reading 730 steady on the O2 sensor, 18" of stable vacuum at a 900rpm idle.

Time to start tuning. Guess the 41 rods / 71 jets are slightly on the rich side.