hankosolder2 Posted November 19, 2009 Share Posted November 19, 2009 How about a compression test? If you have one cylinder down a bit, but not enough to misfire.... "removing a sparkplug wire" is a bad idea on a lost/wasted spark system like a Subaru. (the plugs fire in pairs) It can cause the coil pack to arc over. It can also cause 2 cylinders to miss which will not really help you narrow down your diagnosis. You can probably safely ground a plug out- you'd probably have to do it at the coil pack end due to the poor access on the plug end on the 2.5DOHC. It might be better to just disconnect one injector at a time. Good luck, Nathan Quote Link to comment Share on other sites More sharing options...
nipper Posted November 19, 2009 Share Posted November 19, 2009 Been doing that test for years on waste spark ignition systems, including subarus. Many people have done it here with no issues. People drive with broken spark plug wires with no issues on subarus (thankfully it is happening less and less). It is a valid test in diagnostics. Another thing would be to thorw a vac gauge on the engine and tell us exactly what it is doing. nipper Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted November 19, 2009 Share Posted November 19, 2009 It can also cause 2 cylinders to miss which will not really help you narrow down your diagnosis. Electricity takes the path of least resistance. Considering that the resistance of air is about 10k ohms per centimeter, I would think (actually know because I've done it) that the spark plug that is grounded to the engine will fire long before the spark is going to jump several inches or more of open air through the wire on the other side of the coil. Not saying that it's not gonna hurt if you hold the wire to close to the end of the boot. Use plug boot pliers if you have them. Quote Link to comment Share on other sites More sharing options...
wardssix Posted November 19, 2009 Author Share Posted November 19, 2009 Thanks for all the input. I've got a lot to check. Should happen hopefully Saturday morning. But I was thinking valves and had checked the vacuum at the brake hose: -20.5 steady as a rock then went to squat uopn stroking throttle then upon releasing it it went up to (or down to depending on your perspective) -25 then stabilized nicely back at -20.5 in a reasonable time. Not jerky or bouncy at all. As far as the timimg gears/pulleys don't know if they were changed - my guess no due to the belt being done at 80k at a dealer by PO - have reciept and it doesn't state that. i did the pcv valve the other day - no help. The 2 front axles were done in July. I was planning on grounding the pulled plug from the coilpack to the block; also can I disconnect the injector pulgs while running or should I stop/start engine for that? I don't have a compression test rig but I know a guy who does - what a *************** on this engine to do - 4th sooby in my life and the first and last ej25 dohc for me for certain. The 95 legacy I had for a couple years back then was a dream compared to this and so is my kids 98 Legacy he has now. The jury is still out on my wife's 05 Ltd Wagon, love the car but time will tell. bob :-\ Quote Link to comment Share on other sites More sharing options...
erik litchy Posted November 19, 2009 Share Posted November 19, 2009 i would doubt its compression if the vacuum guage is steady as you say. i would think its the mounts like everyone else said Quote Link to comment Share on other sites More sharing options...
nipper Posted November 19, 2009 Share Posted November 19, 2009 i would doubt its compression if the vacuum guage is steady as you say. i would think its the mounts like everyone else said I agree, rock solid vac gauge rules out everything in the engine. nipper Quote Link to comment Share on other sites More sharing options...
hankosolder2 Posted November 19, 2009 Share Posted November 19, 2009 Electricity takes the path of least resistance. Considering that the resistance of air is about 10k ohms per centimeter, I would think (actually know because I've done it) that the spark plug that is grounded to the engine will fire long before the spark is going to jump several inches or more of open air through the wire on the other side of the coil. Not saying that it's not gonna hurt if you hold the wire to close to the end of the boot. Use plug boot pliers if you have them. I won't deny that this procedure can work, but what you're failing to understand is that the two opposing coil terminals aren't in parallel. The secondary of the ignition coil's negative end goes to one plug terminal and the positive end of the ignition coil's secondary winding goes to the other. This is why the plugs in Subarus wear differently on the left side of the engine vs. the right side. When you're pulling a spark plug wire off, the remaining plug can't fire without an arc from the other side of the coil to ground. The secondary is completely floating from ground and it takes two plugs (or an arc) to complete the secondary circuit. That arc can also occur inside the coil and compromise the coil's insulation. I can probably find an internal schematic of the coil if that would help clarify things. Nathan Quote Link to comment Share on other sites More sharing options...
nipper Posted November 19, 2009 Share Posted November 19, 2009 Nathan i dont need a schematic, as i have one. Alos for test purposes this is a valid procedure. I am an automotive engineer by trade (with a degree to prove it), so I understand what you are saying. i'm not going to beat this to death anymore, so ill just reply to the OP only. nipper Quote Link to comment Share on other sites More sharing options...
hankosolder2 Posted November 20, 2009 Share Posted November 20, 2009 Nathan i dont need a schematic, as i have one. Alos for test purposes this is a valid procedure. I am an automotive engineer by trade (with a degree to prove it), so I understand what you are saying. i'm not going to beat this to death anymore, so ill just reply to the OP only. nipper Nipper, First, let me say that I do appreciate the assistance you provide for all on this board, and I agree with the vast majority of your advice. Secondly, I'll recognize that a lengthy off topic debate on this issue is not helping the OP solve his issue, so this will also be my final response to you. Frankly, if you didn't pull the "I'm an automotive engineer" [so I must be right] line I'd let it slide. Here's what the automotive engineers at Subaru say to this: Note:Care must be taken during cylinder power balance tests to prevent excessive fuel from entering the exhaust system. It is therefore mandatory that power balance tests be performed by disconnecting the appropriate fuel injector harness, not by shorting the secondary voltage to the cylinder. Should the latter method be used, fuel will enter the cylinder, and may fire on the exhaust stroke when ignition voltage is restored. This may cause severe damage to the exhaust system. Here's the original source of the quote http://www.subaru-faq.ru/pdf/electrical/ignition.pdf You will note that the (unfavored) alternative to pulling injector harnesses is SHORTING the secondary voltage to the cylinder, not pulling a wire off and opening the circuit. As I noted in my earlier post "it might just be better to disconnect one injector at a time." I stand by that. Quote Link to comment Share on other sites More sharing options...
nipper Posted November 20, 2009 Share Posted November 20, 2009 I'm down for the count, im being attacked by flying pigs. Send chicken soup. Quote Link to comment Share on other sites More sharing options...
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