timing/predet problem

[bushbasher]

-1988 Subaru GL SPFI wagon

 

Just went wheeling, and got back and turned off the motor, then about a 1/2hr later got back in to start it up, and it seems like it is sparking before the valves are closed, causing the flame to blow up into the intake. It barely starts, and backfires into the intake when you punch it, but then goes smooth at higher rpms. I also feel a hard pinging through the shifter. So I figure at high rpms it predets, and at low rpms it backfires into the intake. That seems like the timing is stuck all the way forward. The disty hasn't moved and I'm not getting trouble codes. It also was running hotter than normal before I parked it, even though I had the fan on constantly. It was at about 2/3 heat at the hottest point with the fan running. Whats going on???? My dad says predet also causes engines to run hotter, so that supports my diagnosis.

[Subi81]

maybe your t belt slipped, happened on my brothers 87 turbo, it would run but get hot. put new belts on it and ran just fine.

 

Good luck

[TomRhere]

Early ignition timing will cause the engine to run hotter.

 

Would check the T-belt timing, and then disty timing.

[bushbasher]

I got in today and it started up fine, and I drove it around, got it up to 1/2 heat, fairly spirited off-road driving, and it was working smoothly, though I could still feel a light pinging feeling in the shifter, though I couldnt hear it at all. I parked it, then 1/2hr later went out to try it just to test, and sure enough, the pretetonation was enough to stall the engine in its tracks while cranking, then once I got it running it backfired through the intake again. Exactly the same experience twice, same amount of time driving, same amount of time parked, same experience.

[Subi81]

Wierd?

[asavage]

Originally posted by bushbasher

1988 Subaru GL SPFI wagon . . . got back and turned off the motor, then about a 1/2hr later . . . barely starts, and backfires into the intake when you punch it, but then goes smooth at higher rpms. I also feel a hard pinging through the shifter.

 

Cap. Rotor. Coil wire. Coil -- in that order.

 

If you feel it in the shifter, it's not preignition nor detonation (which are different though related things). You are having one or more cylinders missfire.

 

If it runs fine now but runs bad later then runs fine still later, it's not a timing belt issue. Look for ignition secondary failure: Cap, rotor, coil wire, coil. Possibly one of the plug wires but that's less likely. Not a spark plug, don't bother looking. You are losing juice to the plug, one or more. Look hard at that cap & rotor.

[bushbasher]

This pinging feels like someone is tapping the shifter rods with a small hammer, a very metallic feel. In my experience missing feels like a quick lurch. The "electrodes" in the cap are fairly worn, so I will replace the cap. My conclusion is that a spark is jumping to the wrong cylinder, causing it to ignite way before the valve closes. Theres no way the timing could be adjusted to fire this quickly without preventing the engine running at all. It feels like there is just one cylinder creating the problem. And like you say it cant be mechanical if it is on and off like this. It is weird how heat affects it though, and how my car heats up with a recent rad and a fan on constantly. Anyways, Ill get a new cap and after that maybe mess with timing for the hell of it.