Need Detonation Diagnosis Help

[luket]

Hi All, posted a little while about this, still struggling. Also my backup vehicle is down so things are getting dire...

I had 'an event' a week ago where a previously minor and intermittent ping suddenly became very pronounced and the engine lost power, shortly after which (on the same drive) my heater core blew due to what i think was an overheat. I am not sure if the initial increase in ping and loss of power was during the overheat as the thermostat read 190.

The detonation is now pronounced and constant specifically uphill when shifting gears and accelerating.

Things I have tried

1. found a small leak in the intake manifold gasket, changed the gasket, idles smoother but same detonation.

2. Replaced the plugs and wires. Autolite AP63, medium heat, resistor type, gap set to spec, no better.

3. Burped the system a couple times to remove any air bubbles, no better.

4. Added octane booster, as much as i dared, no better.

5. Retarded the timing to 0 deg, ping is slightly less pronounced but still there and the thing is a dog.

Does anybody have an idea of where to go next. Was thinking about investing in a compression tester to see if the valves are doing there job. But wouldn't this just reduce the compression and if anything reduce the likelihood of a ping? Also, no signs as of yet of a bad head gasket. Maybe some cold plugs?

[seabeelt]

Have you tried a compression test. How about checking if all of your timing marks align to the proper position? May or may not help in your case, but eliminates other possibilities. You may have said, is it carbed or FI? Many moons ago I had this happen with a dodge colt (mitsubshi engine). The engine had basically slipped the timing belt and then subsuquenbt engine damage.

[luket]

Thanks for the reply. Just checked the can timing and all looks good.

Picked up a compression tester
Cylinder 1 - 103
Cylinder 2 - 112
Cylinder 3 - 89
Cylinder 4 - 88

Some oil on #4 plug but I've been idling it a lot lately...

Also did the manual's diagnostic check on the ignition system and it all pretty close.

Still scratching my head, any thoughts?.

[luket]

Should clarify above, point only happens under load, actually pretty smooth at idle

[luket]

going for top engine cleaner

[kilrwail]

Generally it's going to be too much timing advance or too lean a mixture. Double check the timing marks, as suggested, to ensure the belt hasn't jumped a cog. Check for air leaks, which would cause cause it to go lean, by spraying butane or propane around all suspect locations. The overheating problem is likely a symptom, not a cause, of the same problem.

[FiatMac]

Should clarify above, point only happens under load, actually pretty smooth at idle

Are you sure it is spark knock? You should not be getting spark knock with timing set at 0 degrees. It could be a rod bearing going bad.

[luket]

I'm in painful denial of that possibility. However, the fact that retarding the timing helps a bit makes me think its detonation.

Today's experiment with various snake oils didn't help. Did acdelco upper engine clean in the carb, then seafoam, then fresh syth oil and a full tank of high octane and its still doing it.....

[luket]

Think tomorrow check the egr, also might pull plug wires one by one and see if I can isolate a cylinder

[luket]

the EGR is broken and disconnected by the PO, i installed cooler spark plugs and set the timing to 0 and got it to stop pinging. thinking getting a working ERG will help the ping so i can re-advance the timing somwhat. still would like to figure out what changed to initiate the pinging problem though....

[So Cal Mark]

have you checked the timing advance? A broken spring can allow the weights to go to full advance at low rpm. You should also check the total advance

[luket]

have you checked the timing advance? A broken spring can allow the weights to go to full advance at low rpm. You should also check the total advance

Good idea, ill check it. I was wondering if my advance could be going too far. How far should it go when i rev the engine? i haven't seen a spec for this in my manual. I did however try driving it with the timing advance vaccum line pulled and plugged and it still pinged. After that i was shocked i could eliminate the ping by retarding the timing, cold plugs must have helped a lot.

Was also considering swapping out the fuel pump encase its lean, which would have also contributed to the initial overheating.

[So Cal Mark]

you want no more than 34 degrees total timing

[majicwrench]

Leave your fuel pump alone.
EGR helps control ping among other things, if valve in not funcioning will likely ping. Like Mark said, 34deg total WO vacuum advance hooked up. Measure balancer circumfrance (sp?), take 1/10 of that (36 deg) and mark it on balancer.
' Compression should be more than you have, that could just be gauge or how you did it.
' IN your first post you said you set timing at 0 and still pinged. Now you say you set timing to 0 and it doesn't ping??
' Keith

[luket]

I'll check the timing advance tonight, sounds like a likely cause. Before I had less ping at zero advance, but I just installed lower temp spark plugs which helped a bit and removed the ping all together at zero advance. I already picked up a new fuel pump and I doubt mine has ever been changed, will wait until I investigated the advance before messing with anything down there. Its been a challenge locating a working erg for the 79 but I'm going to keep trying. Realized yesterday that I can not be sure what the advance was set to before 'the event' as I hadn't had a light on it and didn't get a reading before fiddling, dumb of me.