BlueCamaro

Hi.

I recently bought myself a 1984 Delta 88, with the original 307 and all the original emissions parts.

The car ran great the first week, until it suddenly one day just wouldn´t turn over. Now, this turned out to be a bad ground cable from the battery, I replaced the cable, and now the car turns and starts instantly.

And this is where my real problem start, because now the car will not idle when the engine is warmed up. It will start and run a few minutes, untill it gets warm and then it just dies and will not start again unless I push down on the throttle (must keep throttle down a bit to even keep it running at this point).

What I have done/found out so far:
If I disconnect the Mixture Control Solenoid on the carb, the car will run and be drivable (This turns on the check engine light). The car dies instantly if I try to reconnect (when warm that is).
Disconnecting the O2 sensor does nothing, does not even light up the check engine light (not sure if this is normal).
With the ignition on, engine not running, if I connect the MCS wire I hear a single click from the carb, not sure if I should hear several clicks or just one.
I have replaced the Engine Control Computer (reman. from Cardone, kept the old Prom). No changes.

Anyone have any idea what my problem could be?

Olds64

Connect the mixture control solenoid and with the engine cold put the key in the ON position. You should hear the MCS chatter (activate multiple times quickly, not just click once).

Sugar Bear

Check for trouble codes at the ALDL under the dash. Olds 64 is correct if you only hear one click then either the MC solenoid is bad, stuck or is not getting the proper signal.

With the car running connect a dwell meter on the SIX cylinder scale to the green diagnostic link at the front of the carb near the thermostat housing. Reading should be 30 degrees.

It's running with the solenoid disconnected as it is going to full rich. If you have had non-electronic Q-jets apart you can do this one also. Have read that the measuring tools are no longer available so try not to make any internal adjustments if you go inside the carb. count the turns if you do remove anything adjustable.

Confirm that the chassis ground is still good, sometimes they take a severe hit from the load while other grounds are going bad.

Good luck and keep us posted!!!

BlueCamaro

Thank you for your replies.

I have done some more testing:
If I "hardwire" the solenoid directly to the battery, I can cycle it as fast as I can with my hands. So I think the solenoid is ok.
Which leaves me wondering about the solenoid connector and the wiring harness.
I don't have a dwell meter, but I used my multimeter to measure the voltage on the connector to the solenoid (not the solenoid itself but the wiring), and I get a stable 12volts (or 14 with the engine running). If my understanding of this is correct, I should not get a stable reading on this connector if its cycling. Am I correct?

It seems to me that the solenoid is not cycling, because it has permanent ground. From what I have read, the computer is supposed to control the cycling, by controlling how many times a second it is grounded. Correct?

Are there any sensor malfunctions that would cause the computer to go full lean, or basicaly not cycle?

I will try tomorrow to get the trouble codes if any, but the check engine light is not lit if I keep everything connected. So not sure if there are any codes then.

Lastly, yes, there could be a bad ground somewhere else that could cause this type of problem I guess. However that would be extremely hard to find. Everything else electrical seems to work fine though.

joe_padavano

You MUST read the Chassis Service Manual. You MUST use a dwell meter on the green test connector in front of the carb to measure MCS duty cycle. A volt meter will NOT be able to see the pulses. An oscilloscope might be a better choice, but for $10 you can get a used tach/dwell meter.

Sugar Bear

Put the key in the run position and check for codes by jumping the two terminals on the top row on the right side of the ALDL connector with a paper clip. It should start with a code 12, all codes should repeat three times. When it returns to a code 12 it has returned to its starting point.

Check for shorting to ground in the wire to the green test connector and the o2 sensor wire. Unplug the o2 sensor to see if that changes anything. Try to move the connector at the MC solenoid, they do fail occasionally.

The terminal in the top right corner of the ALDL under the dash should be ground, confirm this.

It would help if you could get it scanned to see if the ECM is sending the signal to the MC solenoid to pulse. If it is then it sounds like a wiring problem, if not then it is in the ECM/PROM.

Does your VOM have duty cycle testing capability?

Sugar Bear

Try this, confirm the permanent ground at the MC solenoid. Disconnect the battery, then disconnect the plugs on the ECM one at a time to see if the permanent ground goes to an open circuit. If it remains, a wire is shorted to ground, if opens the ECM is telling it to ground.

shiftbyear

blue Camaro, the mixture control solenoid only controls the fuel during cruise, the idle circuit is totally separate from the cruise system, i'd be looking for a vacuum leak since it's idling when the choke is on then goes lean when it's warmed up. also check for fuel dripping out of the primary nozzles at idle. email cliff ruggles website in ohio for good advice, he's the best in the country for qjets. good luck


http://www.cliffshighperformance.com/

BlueCamaro

Update:

I have now replaced all the vacuum lines, and fixed two leaks. No difference what so ever.

I have replaced the O2 sensor and the temp sensor, they were cheap and actually in stock at my lokal parts store here in Norway.

Still no difference.

Engine codes:

I also checked the codes, they were at first; 12, 23 and 45.
Code 12: No distributor signal...(disregarding this code since it is supposed to be there)
Code 23: M/C solenoid circuit open or grounded
Code 45: Rich exhaust indication

I am probably getting these codes since I have been running the car with the solenoid disconnected.

So I reset the computer and drove the car a few minutes, then checked the codes again: 12. Only 12.

One thing though, when jumping the terminals at the ALDL connector and turning on the ignition, the solenoid is actually ticking, like it's supposed to.

I am starting to suspect the Prom.

joe_padavano

The PROM and ECU almost never go bad, yet are the most replaced parts.

Once again, have you rebuilt the car and adjusted it EXACTLY following the the process in the CSM. If not, you are wasting your time and money.

BlueCamaro

What is it that would or could go bad in the carburetor then, other than the solenoid, that would require a rebuild?

olds 307 and 403

Gaskčts could be leaking, throttle shafts worn out, causing a vacuum leak. The float could have gone bad with effects proper mixture throught driving. The accelerator pump can harden, the needle and seat can leak by or stick. Do I need to go on? That is why there are carb rebuild kits and service parts. Did you change the fuel filter? Simple and those filters are quite often ignored and plugged up.

83hurstguy

To add to what olds307and403 said, the idle circuits are mechanical and not affected by the computer. Some debris in the idle passages may not be allowing fuel through them.

The vacuum pulloffs for choke/secondary air valve could be bad, which causes a vacuum leak once the car warms up, those are very easy to test... another vacuum solenoid that opens with temperature could be leaking... the charcoal canister bag can break and throw carbon granules in through the canister purge system...

olds 307 and 403

Good call on the vacuum pull off's Luke. Our 81 Delta 88 non CCC Canadian 307, had a leaking front pull off. Didn't stall but idled rough, shook a lot at idle. New pull off and a smooth idle.