2.7L Engine Pinging/Detonation

At 419k miles I had my cylinder head resurfaced 6/1000 after it overheated several times. Ran fine for a while on 87 octane, but started to get spark knock after a few thousand miles. Switching over to 91 octane helped with the pinging, but I'm now at 441k miles and it's gradually started detonating more & more. Still totally driveable, but if I'm at operating temperature I'll get a few solid knocks each time I accelerate hard under load. Avoidable if I leave my foot out of it, but pretty unavoidable if I need to accelerate up a hill.

I'm convinced this is happening because the milled cylinder head increased compression. However it's gradually gotten worse and since its now knocking on 91 octane it's high time to fix it.

Any suggestions? Would love to be able to run 87 again with these gas prices

 

I don’t know.
According to the website below, milling the head .006” would only increase the compression to about 9.75. Where the stock ratio is 9.6.

Are you sure they didn’t mill it .060”? Spoken as Sixty-Thousands
That would definitely bring the compression up.

I would maybe looking at getting tune and see where the timing is?

http://www.wallaceracing.com/millcalc.php

 

Have you tried running a fuel additive to clean out any carbon deposits in the combustion chambers? I had a high mileage car that would carbon up easily and part of my getting it to pass emissions routine was running some water through the carb to clean up the combustion chambers. Sounds crazy, but it works. In your case, maybe seafoam etc, in the tank will help out.

 

If the machining caused this issue the only real fix would be a thicker head gasket or a replacement head.

 

Make sure you don’t have an exhaust leak between the header and the midpipe. I have had a similar issue with detonation under high load only and it was caused by a leak there since it is before the primary O2 sensor and that throws off the readings

 

I went with a v-band because the stock donut gaskets suck. Worth the effort for sure. Also I can’t say for sure that it’s an exhaust leak, but I couldn’t hear mine yet it was enough to affect performance

 

Did you use Seafoam as an additive or something else like Techron?

 

Ive used both as an additive in the tank. I've only used water on a carb'd vehicle, so not sure how that would work on a fuel injected engine. Seafoam
did have a spray can version with a tube that slipped under the edge of the the air intake tube that worked well.

 

What is the status of your fuel pump/filter? Are they the original?

When is the last time the spark plugs were checked and/or gapped?

 

Thanks for the replies!

- Spark plugs were replaced ~2k ago.

- Fuel filter/pump haven't been replaced in my ownership, would these cause spark knock?

- There's no soot around any of the exhaust gaskets, also doesn't sound like there's any exhaust leaks. How do exhaust leaks lead to spark knock?

- I ran a can of lucas fuel cleaner through my tank about 9k miles ago. Didn't really do much, but I suppose these things take time. I can try a few more bottles over the next fillup cycles.

 

This many miles, if your fuel filter and pump are stock, they are well aged. The filter will be highly saturated with contaminants making fuel delivery a harder for the pump.