BUILD THREAD 84 Hurst Olds - TechG8

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That's a head scratcher fer shure.
 
I'm to the point I have to see O2, temp, TPS inputs.

Dwell just drops to open loop under heavy enough acceleration to open the secondaries. That appears to be working.

For some reason, in closed loop, the ECM thinks you are running WAY too rich and is continually trying to lean out the mixture.

Since this all started when you broke/swapped the O2 sensor, that is still where I think your problem is.

The troubleshooting steps 69Hurst provided above are imperative.
 
Did some more thinking and testing.

TPS resistance a:B 20500ohm
TPS resistance A:C 14000ohm

Temp sensor resistance
3000ohm cold (70deg?F)
190ohm HOT (190degF)

both of those look good by the manual.

The only issue I have found is at the O2sensor. When I ground the O2sensor ECM lead (full rich command), dwell drops waay down like it should. This tells me the ECM and system in general is functioning as it should.

So I checked the hot O2 sensor for voltage to ground. Manual says it should be .8V or more on a 2V scale. I read maybe .150V

Now, its a new AC O2 sensor. Lets for the time being assume its good.

Am I correct in thinking that the Voltage reading I get (assuming its a good reading) is an indication that the sensor is not getting hot enough? Or is too far out of the exhaust flow for a proper reading? I did not install the sensor bung in the pipe. Perhaps I need to take a look at it.
 
Consider converting to a heated O2 sensor. Just add key on power and a good ground. Then the sensor wire just can be attached to the factory connector.
 
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Its as if the sensor is not sending enough voltage and the system is not going into closed loop function as a result.

I checked the bung installation. It is an inch or two rearward of the header collecter, in the head of the exhaust pipe. I looked into the pipe and the sensor is not at all obstructed. I suppose I could have gotten a bad sensor. but twice? I doubt the headers can lose enough heat to make the sensor malfunction.

Is there a way to bench test an O2 sensor?
is there a part number for a heated O2 sensor that works in our cars?
 
(Disclaimer) OK I just turned 60 so brain damage is likely . . .

but your previous posts of MC solenoid dwell ~ 30 (normal) then going 47 “should” mean the ECM thinks the mixture is WAY rich. Grounding the O2 making the solenoid dwell go “down” is likely just going open loop. O2 sensor at only .15V should mean it is sensing nearly full rich hence the ECM sending 47 dwell.

So, is your car missing at all on that side? Dumping raw fuel into the exhaust will register full rich on the sensor even if the rest of the engine is running lean.

Otherwise, you should be seeing higher voltage at the sensor “if” the engine is actually leaning out per the high dwell.

High dwell means the ECM is trying to keep the rods down more ~ allowing less fuel to pass. Low dwell means the rods are up more ~ allowing more fuel to pass.

Other peeps monitoring this thread, enlighten me if my brain damage has reversed the above from what I remember? Combined with Kevin and I got my big block to run off the ECM (now) 14 years ago, I may be misfiring myself (??).
 
I would try something common like one for a GM TBI motor. It is a matter of making the connector work.
 
The thing here is, the dwell isn't varying like closed loop should. It sticks at a value like it's in open loop.

The dwell when hot does not respond to changes at the idle air bleed or mixture screws. Does not react to manually closing the choke flap.

This tells me it's likely in open loop which should be a preprogrammed value for dwell.

The question is what is preventing closed loop function? The only thing I can find wrong is the O2 voltage as described, reading taken w the test terminal and O2 ecm lead grounded, per the book. The book says replace the O2 sensor.
 
Stock exhaust or headers? I think you have headers, right? Stock exhaust goes in one place and that's that. On headers, you should put the bung about 5-7 inches past where the collector starts. If the bung is about an inch away from the collector flange, that would probably work. If the bung is too thick and the probe isn't actually in the exhaust stream, that would be a problem too. If you put it in the exhaust pipe, it may be too far away and start cooling down. That thing needs to keep hot exhaust on it. If it cools off too much, it won't generate a voltage and it will likely go into and stay in open loop.

Not saying this is your problem, but something to look into. Other than ruling out a wiring problem.
 
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