Chasing down a miss (HEI)


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The other day while driving around, the engine started to miss. OK, no big deal, time for new plugs. That didn't fix it. So new wires...nope, still has a miss. Tried swapping the cap, rotor and coil with one from another car (all basically new). Still there.

Now what? Could is be something in the computer controlled distributor? The control module or the capacitor (or is it a condenser)?

The plugs were ACDelco R45TS gapped at 0.045". Book calls for 0.060", but I've run much tighter on my '83 without issues.


Fixer of crap..
I've had problems in the past with the pickup coil inside the distributor. I guess if the bushing starts to wear for the dist shaft, it can start contacting the tips of the pickup coil. Might be worth looking at if you haven't yet.



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Missing under load, probably ignition. Missing all the time, check compression or an intake cam lobe going away or injector if injected. Hei’s also had a problem with the pickup wires causing an open circuit when the vacuum advance moved if so equipped.


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Well it's not the ignition. I changed the complete distributor with no improvement. It's idles well, just feels like it has a miss in drive and it is low on power.

Using a scan tool, the sensors all seem to be OK. It evens cycles rich/lean while driving (with a fresh oxygen sensor). I believe I hear some knocking/pinging while driving, so I'm scratching my head. The Knock Senor (ESC) checks out at idle (bang on the block and the RPMs drop).


Fixer of crap..
You make any headway on this yet? Could you have wiped a cam lobe or something like that?

I have used an infrared thermometer in the past to shoot the exhaust tubes on a motorcycle to see which cylinder was missing. Exhaust wasn't "cold", but cooler than the others. May narrow down where to look anyway.


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I tried the IR thermometer, but couldn't pin point which was bad. Maybe it's not a cylinder miss, but just running crappy under load.

So I tried going another route to see if it's something other than ignition. Swapped oxygen sensors with the '83 (which runs well), but no change. Swapped carbs with no change. Capped off all emissions while looking for a vacuum leak. Found the EGR and the wastegate actuator (plenum side) were both leaking internally, so they are now both disconnected - but that didn't fix it.

The knocking under light throttle is still still there, so yesterday I compared the timing with a dial-back timing light.

With the 4-pin connector disconnected, both cars are set to 15°BTDC. Both jump to 25° at about 1500 rpm. (The jump is immediate. It goes from 15 to 25 without anything in between.)

With the 4-pin reconnected, the '83 has about 32° at idle and it gradually climbs with rpm to about 39°. The '82 has 35° at idle, 40° at 1300 rpm and if that's not bad enough, at about 1500, it jumps up 10 more degrees to 55°!


I'm guessing the timing it completely controlled through the ECM? I believe I may have a spare to try. Hopefully I haven't damaged the motor with all this timing/knocking.


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That's what I'm afraid of with all that timing.

This all started soon after removing the AC and smog pump. Alternator started flaking out when I re-clocked it for the new bracket, so I swapped it with a new one. I want verify it's output to make sure it won't damage another ECM or ESC module when I swap them.
I was also having timing issues.THE Turbo control unit was giving me false timing settings,it was bouncing around.Threw it on the shelf will never use a factory one again.Have several boxes and dizzy they are all junk in my opinion


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The alternator checks out OK. Pretty much the same on the '82 GN and '83 T Type. Battery was 12.5 volts and then 14.4 while running. Held steady at different RPMs.

My car doesn't use the stand alone ESC. It uses a ESC module through the ECM like the SFI cars. Tried swapping two other ECMs and another ESC module. No change. Timing stays about 42°, then pops up to 52+ at times.

It doesn't drift or climb up the 10 extra degree. It instantly jumps up. Just like when the 4 pin connector is disconnected. I think I'll look at the wiring next.


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Tried some more troubleshooting tonight. I discovered the MAP has something to do with this.

On the '83 T-Type, it seems to be insensitive to the MAP sensor. I get the same timing whether it's in place or I pull the hose off (and cap the vacuum leak).

But on the '82 GN, disconnecting the MAP retards timing by about 10° to about 32° at about 1200 rpm. And it doesn't do that jumping thing. Reconnect it and I get 42° which then jumps to 52° at ~1500 rpm. The 10° advance under vacuum might be OK. It's like the ECM is adding in a vacuum advance.

I did check the MAP sensors with the scan tool.
On the '83, engine off is 2.27 V, 18" vacuum is 0.56 V.
On the '82, engine off is 2.27 V, 18" vacuum is 0.74 V.
Close enough, IMO.