86 camaro. Q-jet with computer controlls.
i want to get away from the computer controls except for the use of an O2 sensor.
can the Q-jet be used with a vaccum advanced distributor? or am i wasting time?

 

No.

Yes.

 

Can it be done? Probably.

Are you wasting your time? Depends upon how much you value your time.

In order for the ECM to control the carb, it needs to get the engine speed signal that the stock distributor provides. That is a science project that I have yet to hear anyone tackle. Vader postulated an approach here a couple of years ago, I don't recall any details. If the factory had chosen to use the Tach terminal to do that, it would be fairly easy. But, they didn't, they used the module connection instead.

It makes more sense to try to get into the ECM's head than it does to try to curve a vacuum/mechanical advance distributor and tie it to the computer system.

 

I'm sorry for dredging this up from oblivion but I thought I might contribute with something.
First of all I don't understand what your prerequisites are, causing you to want to do what you say, it will probably involve more work and give poorer results than fixing what's wrong.
That being said, I'm sure the tach signal from a vacuum dist can be adapted and fed to an ECM, but it will already have an advance curve to it, whereas the ECM expects a fixed timing signal. It will surely confuse the ECM a bit but it might still be able to control the carb. and the converter lockup.
Controlling the CC carb is something you can do yourself manually. I'm running w/o the O2 sensor so I have built a variable pulse generator and connected it to the carb. instead of the ECM. Then I reprogrammed the EPROM so the ECM wouldn't set codes for the missing O2 sensor, mixture solenoid, and vap. can. solenoid. The car seem to work well with a lean 30% duty cycle setting for cruise, but it wants a 40% setting to give full power.

 

i want to run the vehicle this way b/c no matter what i do as far as adjustments i cant get the engine to run at a normal fuel/air mix

it is running way too rich. Ive tried new plugs, wires, distributor, aftermarket igniton, rebuilt carb, o2 sensors and no matter what i do it always runs rich.

second, im thinking that i can yeild more power like vehicles produced years before mine that were pre-ecm. But i want to use the non c/c carb because its very versatile and a good carb.

i want a good running car with great power. If i can id like not to hack up my car but i cant seems to find any other way.

will flashing the prom help this?

 

The O2 sensor tells the ECM what the MR is. The ECM tells the MCS how long to dwell to change it to the the desired MR. If the ECM and MCS don't do that, there is either something wrong with the O2 sensor or the MCS, or something wrong with the carb that keeps it from being able to do what the ECM is telling it. Reflashing the PROM will not help you here - it should be doing it with the current programming.

The prime culprits for the MCS not being able to control MR are: 1) a shot MCS; 2) float setting improper; and 3) main metering circuit well plugs on the bottom of the fuel bowl leaking (direct path from the fuel bowl to the intake manifold). This item isn't covered in the typical "rebuild".

Are you getting a SES light/trouble codes set?

When everything is working the way it was designed, this system will make the engine run better than those produced in years before. Just as good power and driveability, and much better economy.

 

Don't forget about exhaust leaks somewhere before the O2 sensor causing it to think it's too lean, thereby causing the ECM to command a richer mixture. Check gaskets and flanges. If the problem is caused by this and you have adjusted the carb., then you will have to get hold of a dwell meter to readjust the carb..

 

what if I mounted the o2 sensor on the passenger side instead of the driver side. i had to do this b/c there wasnt any room on the driver side.

will the swap to the other side through off the measurements and computer control.

 

It doesn't matter which bank it's on.

 

You say you don't want to hack up your car, but what have you been doing to it since there's no room for the O2 sensor in it's original location anymore?
Not that right or left matters, as long as it's approx equally far from the heads.

 

so the original distance from the heads to the mount on the exhaust manifolds should be the same on the headers?

Isnt that impossible? wouldnt i be putting the sensor in one of the primaries instead of the collector then?

 

Distance isn't that critical. People have been putting the O2 sensor in the collector of long tube headers for years. They often use a heated type when they do that, but it will still work.

Putting it in a primary would be about the worst possible choice. It's already a compromise to put it only on one bank so that the other bank could have an "issue" that is giving bad info to the ECM. Having one of 8 cylinders give the only information . . .

 

mixture too far out of range for good o2 readings will not allow ecm to rewrite blocks losing ability to control mixture

 

Ok, so finally we get to know there are headers (long tube) on the car..
How about leaks, might there be any? How far down is the sensor, and is it heated or not? Do you use the original ECM and PROM? Can you hear any clicking in the carb when it's running? Who rebuilt the carb?
naf: wouldn't that condition set the light and a code?
So many questions..

 

Not in my experience. The ecm will still control the mixture based on tps and vac sensor readings in a semi-open loop. It's thinking the o2 hasn't warmed up yet, essentially using its 'last known good' data. Keep in mind that the ecm only uses o2 data to rewrite its tps/vac:dwell blocks.

 

there are no leaks. NOt at all i am finatical with sounds that shouldnt be there.
brand new o2 sensor. NOt heated. origional ecm and prom.
yes the carb does make clicking sound.
the carb was rebuilt 3 years ago by a local carb shop. i dont think its the carb bc right after it was rebuilt my car was able to run; so i think its good.

what does all of this mean?

 

I have been down that road [this one never gets old, or does it?]. Was very certain that there were no vacuum leaks. Well, guess what? I WAS WRONG. Took only one year to figure out. Was an invisible crack in the vacuum reservoir, as well as a cracked tee right at the carburator. Never reinstalled the reservoir, as things work fine w/o it.

Before the weather turns, look more carefully. Doesn't take much of a leak to confuse the O2 sensor.

Seth

 

Thanks naf, a few things finally connected in my head there..!
Could this mean that if Z28 has a minute exhaust leak introducing O2 to the sensor, that the ECM has slowly rewritten the dwell table to give a richer mixture, and that the original tables will be restored if he removes power to the ECM for 10 seconds? If that helps then I guess a leak search is in order, both on vacuum and exhaust. Vacuum leaks can be traced with flammables I heard, but how are exhaust leaks found if they are so small they can't be heard? Could such a small leak still throw of the O2 sensor?

 

My guess would be vaccuum leak, I'd think an exhaust leak large enough to affect o2 readings would be noticed, but you should check all fittings from the head to the sensor anyway. Another possibility is that everything is in order and working correctly but mods to the engine have changed the mixture enough so that the o2 doesn't see a reading within its narrow range and isn't sending a signal to the ecm that it can adjust from. If this is the case, usually adjusting idle mixture screws (start around 3 turns out and add half a turn until you start seeing dwell ranging) will bring it in. A dwell meter can tell you which way to look.

Either: 1) He has a ranging dwell now and the o2 is adjusting the mixture (rewriting) and something is causing the o2 to read the mixture wrong (leaks, etc.)

Or: 2) The dwell is rock steady now and the o2 is not providing input to adjust the mixture. If this is the case I'd look at idle mixture screws first, although it could be as simple as the o2 not getting hot enough (or some other sensor prob).

 

u say to check all the connections from the head to the sensor, but this is a carb setup. what connections are you talking about? also where could a vaccum most likely occur?

 

What NAF means is to check everything.
Check the plastic tee at the carb, each and every vacuum hose [I found one rubbing against the back of the steering pump], the vacuum reservoir [the biggest leak on my car], the egr gasket, the carb gasket, the intake gaskets, the carb, the cruise cut-off switch on the brake pedal box, the hose to the maf sensor, to the air filter temp sensor, to the air pump valves, to the whatever else is there. The problem is right in front of you, and very simple. Go over EVERYTHING again. Today is warm.

Seth

 

thanks for the clarification. however that brings up a small situation.

ive removed the smog air pump, the stock air cleaner with the vaccum heat flaps (for cold weather i guess) ive tried just plugin all the loose vaccum lines but now that we've narrowed the problem to a potential vacccum leak; i wonder if i have everything hooked up correctly.

does anyone have a diagram for vaccum lines that deleted the stock air cleaner and the smog pump. i do have the egr valve still, and this big plastic canister at the front for the car.

any diagrams would help. also there is this sensor near the thermostat housing or might be in it ( cant remember) but there used to be two vaccum lines that went to that sensor but no longer are hooked up. can someone tell me what that sensor is and how i should connect it back in if i need it at all.

diagrams would help alot.

 

Disconnect every vaccuum line to carb & mani, icl. brake booster,
plug every port w/ a cap (don't drive like this). Run motor then reconnect each line checking for a change in idle quality. This works really well w/ a dwell meter as you can be sure the ecm is responding to changes in mixture.

 

The carb is SUPPOSED TO BE CLICKING. That's the MCS duty cyling. IF your carb does not emit a loud clicking with the engine running, or any time the key is in the run position, you have a problem

 

i always thought the clicking was the electric choke heating up lol

good to know

lol