Problem with a DOHC 2.5L ....Rough Idle ??

[subaruVWnut]

I'm trying to diagnose a problem in a 98 DOHC 2.5L (in a Legacy Outback) I obtained recently that's running really rough at idle and wonder if there's some wisdom from the Group.

 

First...engine would barely start and run....and CHK ENG light was on. An OBD-2 code reader showed "Misfire" on cylinders 3 and 4 which we diagnosed to no spark on either cyl 3 or 4 plug wires. CAT would get red hot from raw fuel being dumped from the non firing cylinders.

 

We replaced the coil and ignitor with known good ones with no success....gradually traced the problem to a bad ECU. Obtained a replacement for the ECU and NOW have all cylinders firing on full throttle but idle is still really rough and lumpy.

 

But I'm not getting any trouble codes on the code reader....even though the engine still runs (idles) really crappy.

 

I suspected the timing might be off...perhaps due to incorrect belt installation before I got it. Can this be checked with a timing light without having to pull the belt covers?

 

I checked the timing at the crank with a light....Spec is 20 degress BTDC at correct idle rpm of 600-800rpm. At my rough idle...which seems a little too low.. maybe 400 rpm....timing was at 14 degrees. A slight increase in idle to about 800 rpm sends the timing mark to 22 degrees.....if I accelerate any faster, it climbs gradually to well over 30 degrees. Any clues here??

 

Carfax report showed it was a "gross polluter" by couple of CA smog inspections stations and the coil had been replaced in it's last days with the PO.....before I got it.

 

I could use some more diagnostic tips to get this engine running better..

 

Warren C.

[1 Lucky Texan]

I'm trying to diagnose a problem in a 98 DOHC 2.5L (in a Legacy Outback) I obtained recently that's running really rough at idle and wonder if there's some wisdom from the Group.

 

First...engine would barely start and run....and CHK ENG light was on. An OBD-2 code reader showed "Misfire" on cylinders 3 and 4 which we diagnosed to no spark on either cyl 3 or 4 plug wires. CAT would get red hot from raw fuel being dumped from the non firing cylinders.

 

We replaced the coil and ignitor with known good ones with no success....gradually traced the problem to a bad ECU. Obtained a replacement for the ECU and NOW have all cylinders firing on full throttle but idle is still really rough and lumpy.

 

But I'm not getting any trouble codes on the code reader....even though the engine still runs (idles) really crappy.

 

I suspected the timing might be off...perhaps due to incorrect belt installation before I got it. Can this be checked with a timing light without having to pull the belt covers?

 

I checked the timing at the crank with a light....Spec is 20 degress BTDC at correct idle rpm of 600-800rpm. At my rough idle...which seems a little too low.. maybe 400 rpm....timing was at 14 degrees. A slight increase in idle to about 800 rpm sends the timing mark to 22 degrees.....if I accelerate any faster, it climbs gradually to well over 30 degrees. Any clues here??

 

Carfax report showed it was a "gross polluter" by couple of CA smog inspections stations and the coil had been replaced in it's last days with the PO.....before I got it.

 

I could use some more diagnostic tips to get this engine running better..

 

Warren C.

 

Sometimes a slipped TB or stuck/broken valve might be indicated if a strip of paper held at the tail pipe is 'sucked in' when the engine is idling. Might not work for timing that's only off a tooth or so. If you slectively pull the plug wires individually, maybe you can pin down which cyliner is causing the problem. If you pull a wire and ther is NO change in the idle, that's the bad cylinder. Also, normal diagnostic stuff like compression tests might help too. I suppose, since you changed the ECU, the system was 'reset'? Does it ever warm up enough to run well/better? maybe the engine temp sensor is bad and the ECU keeps the 'choke' condition on. Are the plugs wet/carboned? Plugs wires in good shape?

 

just some stuff off the top of my head

 

Carl

[subaruVWnut]

Sometimes a slipped TB or stuck/broken valve might be indicated if a strip of paper held at the tail pipe is 'sucked in' when the engine is idling. Might not work for timing that's only off a tooth or so. If you slectively pull the plug wires individually, maybe you can pin down which cyliner is causing the problem. If you pull a wire and ther is NO change in the idle, that's the bad cylinder. Also, normal diagnostic stuff like compression tests might help too. I suppose, since you changed the ECU, the system was 'reset'? Does it ever warm up enough to run well/better? maybe the engine temp sensor is bad and the ECU keeps the 'choke' condition on. Are the plugs wet/carboned? Plugs wires in good shape?

 

just some stuff off the top of my head

 

Carl

 

One more "clue"....

 

There's a rather loud "whistle" that come from the exhuast on hard acceleration. Sounds like a turbo whistle.

 

I've warmed it up to the point where the radiator fan comes on with no change in the rough idle.

 

I'll try your individual cylinder check by pulling each plug wire.

 

I plan to do a compression check...but damn...these DOHC engines are a PITA to access the spark plug area. Guess Japanese engineers aren't perfect.....it seems like they designed this engine without test fitting it in the car. Maintenance was an afterthough. I ruined (separated) one spark plug wire just trying to get it off the plug....so at least one of the wires is NEW....the other three might be suspect.

 

Warren

[1 Lucky Texan]

One more "clue"....

 

There's a rather loud "whistle" that come from the exhuast on hard acceleration. Sounds like a turbo whistle.

 

I've warmed it up to the point where the radiator fan comes on with no change in the rough idle.

 

I'll try your individual cylinder check by pulling each plug wire.

 

I plan to do a compression check...but damn...these DOHC engines are a PITA to access the spark plug area. Guess Japanese engineers aren't perfect.....it seems like they designed this engine without test fitting it in the car. Maintenance was an afterthough. I ruined (separated) one spark plug wire just trying to get it off the plug....so at least one of the wires is NEW....the other three might be suspect.

 

Warren

 

Is the whistle in the engine compartment? could be a vacuum leak I guess.

 

good luck

 

Carl

[mwatt]

One more "clue"....

 

There's a rather loud "whistle" that come from the exhuast on hard acceleration. Sounds like a turbo whistle.

 

I've warmed it up to the point where the radiator fan comes on with no change in the rough idle.

 

I'll try your individual cylinder check by pulling each plug wire.

 

I plan to do a compression check...but damn...these DOHC engines are a PITA to access the spark plug area. Guess Japanese engineers aren't perfect.....it seems like they designed this engine without test fitting it in the car. Maintenance was an afterthough. I ruined (separated) one spark plug wire just trying to get it off the plug....so at least one of the wires is NEW....the other three might be suspect.

 

Warren

 

I'll bet that whistle noise from the exhaust system on hard acceleration is likely a plugged catalytic convertor. Chances are that the catalyst substrate (the "honeycomb" inside the convertor) melted down when it got so hot from the previous misfire condition.

[subaruVWnut]

I'll bet that whistle noise from the exhaust system on hard acceleration is likely a plugged catalytic convertor. Chances are that the catalyst substrate (the "honeycomb" inside the convertor) melted down when it got so hot from the previous misfire condition.

 

 

This is a good deduction.

 

Is is possible a "plugged" catalytic converter could also be contributing to my poor idle.....possibly causing too much back pressure.

 

Warren C.

[subaruVWnut]

Is the whistle in the engine compartment? could be a vacuum leak I guess.

 

good luck

 

Carl

 

Thanks,

 

I suspected vacuum leak also, which would contribute to my rough idle. But the "whistle" doesn't seem to be in the engine bay....it's loudest at the exhaust pipe.

 

Warren

[1 Lucky Texan]

Thanks,

 

I suspected vacuum leak also, which would contribute to my rough idle. But the "whistle" doesn't seem to be in the engine bay....it's loudest at the exhaust pipe.

 

Warren

 

I would say you now have 2-3 good reasons to suspect the cat converter - previously failed some kind of emissions, known fuel rich condition, and the whistle at the tailpipe. Curiously though, there seems to be no restriction at higher rpm and (I guess) no CEL pointing to it. I can't help wondering if a bent or chipped valve could cause a whistling sound?

 

Carl

[frag]

If you can put your hand on a vacuum gauge and connect it to the intake manifold (below the throttle plate) there is a simple test to know if the exhaust system is clogged (probably at the cat).

Register the vac at idle and then open the throttle and slowly rise the rpm to 3000 rpm. if the vac goes down significantly and progressively, there is a restriction somewhere.

Hope that helps.

[1 Lucky Texan]

If you can put your hand on a vacuum gauge and connect it to the intake manifold (below the throttle plate) there is a simple test to know if the exhaust system is clogged (probably at the cat).

Register the vac at idle and then open the throttle and slowly rise the rpm to 3000 rpm. if the vac goes down significantly and progressively, there is a restriction somewhere.

Hope that helps.

 

excellent! I also believe a jerky/pulsing vac gauge is diagnostic for valve problems too. (IIRC)

 

Carl

[subaruVWnut]

The good news is that we found out why.....even after a new computer gave us spark at all four cylinders.....the car still runs like crap!

 

The bad news.... the reason why........No compression on the #3 cylinder.

 

Engine rebuild (or replacement) time!

 

 

Warren C.

[Gnuman]

I would say you now have 2-3 good reasons to suspect the cat converter - previously failed some kind of emissions, known fuel rich condition, and the whistle at the tailpipe. Curiously though, there seems to be no restriction at higher rpm and (I guess) no CEL pointing to it. I can't help wondering if a bent or chipped valve could cause a whistling sound?

 

Carl

 

Well it would probably cause the #3 cyl to read 0PSI (you read that right: 0 ) on the compression test. . ..

the rest were between 125 and 130PSI. numbers 2 and 3 had black carbon built up on the plug, 1 and 4 looked good at the plug. Certainly looks like this engine is a candidate for rebuild (at least the right head. . .)

 

Edit: Damn! He beat me to it!!

[1 Lucky Texan]

Well it would probably cause the #3 cyl to read 0PSI (you read that right: 0 ) on the compression test. . ..

the rest were between 125 and 130PSI. numbers 2 and 3 had black carbon built up on the plug, 1 and 4 looked good at the plug. Certainly looks like this engine is a candidate for rebuild (at least the right head. . .)

 

Edit: Damn! He beat me to it!!

 

It's a shame that it's a problem so severe. I take no glory in making it one of my guesses. (BOO-yah!!! take THAT Gnuman! - oh ,wait - did I type that out loud or just think it?)

 

;^)

[Gnuman]

OK, update time. New exaust valve in #3, new head gaskets, new valve cover seals, timing belt, crank and cam seals (if you are going to take the damn engine apart, why go halfway?) and a new clutch later, the engine runs great. . for about 100 miles. After that time, the ECU kills #3 and #4 (guessing, the engine goes back to the stuttering condition that it had, and has no power). This is definitely pointing to the ECU killing the firing, as when I pull fuse #14 ("unit backup" which feeds the memory in the ECU) the car runs fine. I had been running for a while with a CEL thrown, and thought that was it. it was not. that CEL was the temp sensor (silly me for forgetting to plug it in ). Fixed that and cleared the codes (temp sensor, and IAC). Ran great for 100 miles, then CEL comes on, and no power (coupled with the rough idle, and a stuttering sound from the exaust). I can get sounds from the exaust both under normal ops, and with the CEL thrown. I'll be grabbing the codes tomorrow, and will post them. My question is this: is there any condition that would cause the ECU to cut power to #3 and #4? The car is not overheating at all (my first guess, because the temp sensors were unplugged), and the timing is good (or it would not run well at all. . .). Plugs are all new, the coilpack is good, the wires are good, and the ignitor is good. ECU is new, and I'll bet the old one does the exact same thing as the new one. The IAC code I got was "Idle control, aux inputs" which I took to mean the IAC valve. Any lights out there?

[a97obw]

I got the CEL today in my 97 OBW for the first time in more than 2 years and 30k+ miles. Plugged my code reader in and it was "misfire detected on cylinder #3". Funny, that is the same code it did more than 2 years ago, TWICE in about a month at very nearly the same spot on the interstate. Today I was within a mile of that spot going the other way when the CEL came on. I've had the "whistling" as well on the hard acceleration for a long time. I just clear the codes and keep on trucking (after throwing plugs, wires and coil pack at it the first time!). Every now and then I'll get the rough idle, but nothing ever below 900 RPM or the sorts. 90k miles now with timing belt and plugs done at 74k.

[1 Lucky Texan]

OK, update time. New exaust valve in #3, new head gaskets, new valve cover seals, timing belt, crank and cam seals (if you are going to take the damn engine apart, why go halfway?) and a new clutch later, the engine runs great. . for about 100 miles. After that time, the ECU kills #3 and #4 (guessing, the engine goes back to the stuttering condition that it had, and has no power). This is definitely pointing to the ECU killing the firing, as when I pull fuse #14 ("unit backup" which feeds the memory in the ECU) the car runs fine. I had been running for a while with a CEL thrown, and thought that was it. it was not. that CEL was the temp sensor (silly me for forgetting to plug it in ). Fixed that and cleared the codes (temp sensor, and IAC). Ran great for 100 miles, then CEL comes on, and no power (coupled with the rough idle, and a stuttering sound from the exaust). I can get sounds from the exaust both under normal ops, and with the CEL thrown. I'll be grabbing the codes tomorrow, and will post them. My question is this: is there any condition that would cause the ECU to cut power to #3 and #4? The car is not overheating at all (my first guess, because the temp sensors were unplugged), and the timing is good (or it would not run well at all. . .). Plugs are all new, the coilpack is good, the wires are good, and the ignitor is good. ECU is new, and I'll bet the old one does the exact same thing as the new one. The IAC code I got was "Idle control, aux inputs" which I took to mean the IAC valve. Any lights out there?

 

Do 3 and 4 share a coil? If so, might be worth trying to swap with the other coil just to confirm the problem doesn't travel with it to the other plugs. Could this be a fuel pump problem?

 

I dunno.

 

Carl

[ShawnW]

Timing Belt tensioner going bad taking out the valves on 3/4?