EA-81 engine predetonation

[Guest jistabout]

Hello all,

 

My 1986 GL hatchback (EA-81 engine) has developed a sudden case of pre-detonation on accel. I have tested and verified the following:

 

Ign. timing - 8deg. BTDC @700 RPM - normal.

 

EGR Valve - Vacuum tested - OK. Removed/cleaned/verified OK

 

Dist. Advance - Tested OK. Dist. was replaced with a new unit approx. 30k ago.

 

Carburator - Rebuilt approx. 10k ago. Verified ops OK.

 

All vacuum lies etc. - unable to find any leaks, using propane and an ultrasonic vacuum leak detector. Visual inspection shows nothing.

 

I've ruled out bad fuel because the vehicle has been filled at several different vendors with same results.

 

BTW - This car has 212k on the clock.

 

Problem suddenly appeared about 5 weeks ago, went away for about 2 days, then returned for good.

 

I'm a certified tech. and work on cars for a living but my own car has me stumped .

 

I posted this on the I.A.T.N (International Automotive Technicians' Network) awhile back, and of the 4 replies received there, 2 said to dump "Sea Foam" additive into it and then drive the heck out of it for awhile...

I'm not so sure about this..

 

Anyway, Thanks alot in advance, and if anyone here has experienced this and/or knows of a cure I'd sure appreciate any advice. I'm not driving it for now until this is resolved. Thanks again.

 

- Darrell

[Ross]

Bad/incorrect/dirty spark plugs?

engine running too hot/ localised coolant blockage in engine?

Hot air intake stuck on?

Excessive deposits on the heads/valves can cause detonation, but there would have to be something wrong to leave these in the first place.

[GLCraig]

Hmm interesting,

 

I spent a few years in Klamath Falls while attending Oregon Tech. This time of year with the cold weather and higher elevation, you shouldn't be having this problem, heck I managed to run my 84 GL at about 12degs BTC at idle without any problems.

 

When you checked out the EGR valve, did you check the tube that runs from the right cylinder head to the intake manifold for a blockage? Also there is a thermo vacuum switch that prevents the EGR vlave from opening when the engine is still cool, have you checked it yet.

 

You mentioned that you've had this problem for about 5 weeks, isn't that about the same time they start adding the anti-smog additive to the fuel down there? Maybe that's causeing you some problems. Also what octane level are you using? Maybe you just need to step up a grade.