I’m attempting to sort out an idle stumble/misfire (all the usual suspect components have been replaced - plugs/cap/rotor/wires/ICM/coil/pickup coil).

When checking timing, the mark on the balancer jumps around a fair bit. I can get it to 10°, but given the possibility of the balancer being incorrect due to slipping, and/or play in the timing chain, I wonder - is the Spark Advance value I see in the V6 Scantool (I can’t get WinALDL to display any values, though it shows that it’s connected) accurate? It reads around 30° for the most part, though eventually it’ll get down to 17.6° after letting temps get to around 200°F and blipping the throttle.

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1988 Formula, AT, world's longest restoration project

Time to change your timing chain and/or tensioner

I dont think ALDL can read at a fast enough rate to detect the changes.

[This message has been edited by Xenoblast (edited 10-21-2022).]

To set Timing, Jump ALDL A B.

Watch Timing thru a Scanner on these ECM is Pointless. Worse, activating a scanner will cause problems and affect timing because these old "OBD1" ECM and many later PCM are Not made to have "Multi-thread" operation. IOW your scanner Steals CPU time away for running the engine and why Desired Idle often is 1000RPM to all scans.

See my Cave, ECM Q&A & rest of section.
Other values are somewhat useless too because often a number changes way too fast to be useful.
Example: O2 Volts and Flag should "flip out" a lot in normal operation. If they "pegs" low or high isn't a problem unless finally trips a "Code" but even then often isn't a "Dead" O2 sensor.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

I’m definitely looking into doing the timing chain this winter.

For now, I’ve timed it per the FSM (at operating temp, in drive, terminals jumpered), and, accounting for the mark walking back and forth a bit, have it at about 10°, averaged between cylinders 1 & 4 (they were essentially identical).

Idles around 850 on the tach, hunts maybe 25 RPM or do occasionally. Idle is a bit coarse, and there seems to be a slight miss. I suspect I have at least one leaking injector, and will do a leak down test soon (it floods when warm - cranks forever before it’ll sputter to life, does better if I floor it when cranking to enter clear flood mode). Runs smooth and strong above idle though.

I guess what I’m wondering is: Even though the ECM can’t detect/provide values all that quickly, assuming you’re not making any adjustments, does it *ever* display the correct timing value? Just letting it sit there at idle, I’d think it would.

[This message has been edited by WhiteFormula (edited 10-23-2022).]

Not really... Even at idle the ECM can change Timing every scan output to you.
Is Why you jump ALDL AB trying to set Base Timing because ECM sets timing at it's whims.

ECM uses MAP, O2 and more to set timing and injector pulse to constantly keep Emissions low, prevent engine stalling, and so on.
Because most engine go into Close Loop operation as soon as O2 = Ready that can happen in seconds to a minute or 3 after the engine starts.
O2 = Ready as soon as Exhaust heats it > ~ 600-700°F and very often Doesn't give a crap about coolant or air intake temps.

V6 is a bit slower to heat the O2 because farther down the exhaust and after the Y. Duke have that inches from exhaust port right in the manifold and heat it very fast.

That's why you nearly never see O2 volts the same each scan even if stays lower or higher but often will see low then high the low again stay a bit low then high etc...
O2 Flag will flip each time crosses 500mV but you may see high or low more as scanner is slow to report.
O2 Cross Count is often more helpful because the count can jump numbers because ECM's CPU is counting not the scanner.

Most people saying Close Loop only happens when coolant temp above whatever and more nonsense have never looked at scanner at watch 1 value after starting cold that being Loop Status. If engine and more important O2 is very cold, status may bounce between open and close a bit until O2 is fully stable.

If you "hear" a missed cyl because of ignition or fuel problems... Then ECM will "See" that via O2 and set timing and fuel try to "fix" a lean or rich hit.
If have iffy air or coolant temp then can cause similar problem thinking temps are lower/higher then real numbers and screw up fuel map data. Example: 87-92 DIS Dukes (VIN R U and likely others.) can even set DTC 45 O2 High for iffy air temp sensor.

That's the only way old ECM/PCM know above missing. Not like OBD2 that can see a miss looking at ignition volts etc used by a cyl and tell just what cylinder missed.

Missing problems... See my Cave, HE Ignition & Ground "Myth" notes

Makes sense.

The data for MAP, O2 and certainly air temp all look reasonable, so I’m betting my miss and fluctuating timing indication on the balancer is a product of one or more suspected funky injectors. It’d also explain the hard start when warm, which appears to be flooding, as while it still cranks for a long time, putting the pedal to the floor when cranking (clear flood mode) causes it to start a bit more quickly.

Just for grins, I swapped out the MAP sensor with another, known-good one (mine was original). Runs a bit smoother at idle, but when cold started, it nearly dies when I put it in gear. I’ll be curious to see what the data is when I get a chance to test it.

Probably should do a timing chain just for good measure at 122,000 mi anyway. And sort out my valvetrain chatter, while it’s apart. But then, if it’s lifters, I should just replace them all, along with pushrods. And who doesn’t replace a cam when they replace flat tappet lifters?

Sigh.

Time to install that garage heater…

Before you start tearing into it, after your "hard starting while hot" issue, just unplug your cold start injector. It's the one on the end of the intake manifold, near the distributor.
It may be a bit harder to start when cold, but may help your hot start issue. (I'm thinking the cold start temperature switch may be failed or shorted. It's the one near the corner of the manifold where the thermostat housing is. It will have the two-wire connector with the rectangular plug. Or, you can just unplug that switch. Should have the same effect, for testing.)