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98 Subaru Outback cranking but not firing

I had posted earlier about replacing the harness or at the very least the plug that broke off of the cam shaft sensor on our 98 Subaru Outback. Well, I replaced the plug, and the cam and crank shaft sensors as well and it is still cranking but not firing. Anyone have any ideas?

How do you know you don’t have spark
and the wrong tree is hearing you bark?

(Answering in rhyme is difficult but fun. We should all try it at least once)

I guess I should rephrase and say that its cranking but not catching and turning over.

All that is needed for cranking is the battery and starter motor to work. That part is done. For the car to run, it has to have two things: gas being injected into the cylinders, and a spark at the spark plug. B/c you’ve been working on gadgets which affect the spark (i.e. the ignition system), that’s the first thing to test. During cranking, do you have a spark reaching the spark plug? There are inexpesive gadgets available which can help you determine this. Or if you don’t know how to test for spark, ask here, and somebody will explain.

Remove one plug wire. Insert a screwdriver (rubber handled one) into the end of the wire and hold it close to the engine block. Have someone turn the key. If you have spark you’ll see it jump the gap between the screwdriver and the engine.

Mike

I asked about spark because the parts you’ve been replacing would all cause you not to have spark.
You can check easily with one of these things:

Plug it in series with any spark plug and observe it. If it flashes, you have spark.

So we finally broke down and had it towed to a shop and they can’t seem to figure out what is wrong either. They say its got spark, fuel, and has somewhat low compression. They suggest us towing it to a Subaru dealership. Any ideas what it could be or if anyone has had something similar happen?

Is the spark timing correct? If it’s not, that could be the problem. It needs to be firing at or near the top of the compression stroke. The top of the exhaust stroke, or most other incorrect places, won;t start the engine.

One other point that I believe is important; did they check for spark or just voltage? Voltage is necessary for spark, but it does not create it. It’s the interruption of the voltage and collapse of the magnetic gield into the coil core that creates the voltage spike sufficient to jump the sparkplug gap. If they checked for spark on an oscilloscope, the voltage, ramp time, etc will be visable, but of they only checked for voltage at the primary, that may not have disclosed the cause of the problem. The primary can have voltage but if it’s never interrupted you’ll get no spark.