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98 Forester (5 speed)
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Discussion Starter #1 (Edited)
First off wanted to introduce myself, my names Tay, I own a 1st gen 1998 Forester EJ25D.

Ever since I first bought the car a few months ago I've had random misfires, low/sporadic idle jumps between 675-780. Far too low in my opinion and appears to be the source of misfires as it only pings the CEL when idling, not when cruising. I spent weeks trying to track down the issues, resurfaced heads + new gaskets, valve adjustment, new headers, new cats, new spark plugs + wires, new coil pack, new fuel filter, cleaned MAF and throttle body. I haven't changed the fuel pump or injectors yet, that was next on my list until today.

I bought new speakers to replace the busted factory ones, unplugged old speaker realized I didn't have shrink wrap on me. Went to drive home with my front speakers disconnected and I noticed the strangest thing right away. My engine idle speed for the first time was not rough or sporadic, I thought surely I'm just in open loop and this is just high idle until the O2 heats up and it gets to closed loop. Nope, double checked Creader and confirmed fuel system is in closed loop working with O2 sensor. Engine completely warmed up at this point. It drove exactly like it should, when rpms drop it hovered right at 1000 every single gear shift never once falling below 1000 rpm in any capacity. Previously, with speakers plugged in, every gear shift the rpms would drop to 400 sometimes as low as 375 and sputter back up to the 700s. I have since confirmed this by unplugging and plugging the speakers back in. Somehow this fixes my months long search to fix rough idle/low rpm??

Now I'm no electrician and wiring is not my forte, I don't have any meters or patience to go around testing every wire. My guess is I have a bad ground somewhere and by unplugging the speakers, it took enough electrical load off to put the system back where it should be? Please tell me what you think, I would preferably like to have front speakers if I can..
 

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2012 Forester 4 speed auto
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Seems like somebody installed your stereo speakers incorrectly. Take the car to an automobile stereo shop and have it wired correctly.
 

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98 Forester (5 speed)
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9 Posts
Discussion Starter #3
No please understand it can't be a bad "speaker wiring job" if it already ran light poop under factory default conditions BEFORE factory speakers were replaced. Imagine no wiring was done and all I did was unplug the factory front speakers. Car runs like poop with speakers plugged in, car runs like it should with speakers unplugged. Why?
 

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@taymo So the car, when it comes to the audio system, is stock except for the speakers?

I ask because the stock audio system just has left and right, according to the schematic I have. The left and right door speaker have tweeters connected in parallel to them. The rear have separate connections. All wires go back to the stereo so they may be grounded there or perhaps it is a class B amp of sorts.

So you have to unplug just one speaker or all speakers (door and tweeters) to make the car run normally? Is the radio on or off when this happens?
Not that I know the answer but just trying to understand what's going on.

Edit some more:
Maybe a ground is missing off the ECM and it somehow finds ground some way through the audio system. That connection may not be adequate so causes a drop in voltage to the ECM.
Get a ground cable (like a booster cable) and see what happens when you tie the black end (leave the red dangle) to a hard ground, like the battery negative terminal.
Then take the other end and find a good solid bare metal piece that the radio may physically be mounted to. If a ground connection is indeed missing, this black booster cable would bridge that missing connection and possibly buy you a clue, if it starts running normally (even with the speakers connected).
 

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98 Forester (5 speed)
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Discussion Starter #5 (Edited)
(edit) The car's audio system has an aftermarket radio with stock factory speakers. I only replaced the 6 -1/2" speakers on the bottom. I have L model which has no tweeters. Both front 6-1/2" speakers were unplugged with radio off when car ran normally for a a few runs.

Unfortunately it is back to rough idle/low rpm drops even with speakers unplugged. I put the new ones back in and everything is the same as before. RPM drops my idle falls to around 300 then bounces back up to 700ish. Occasional misfire code on every cylinder, happens one right after the other usually spaced several miles apart. Mostly happens to cylinders 2,3, & 4.

I did further inspection and found loads of dielectric grease on almost all electrical connections. Like heaps of this stuff oozing out, I guess previous owner put it on everything. Did a little research and found you aren't supposed to use dielectric grease on the metal connection parts, only spark plug boots. I'm going to see if I can get it off from my sensors with electrical cleaner. I'll post any results.

If cleaning doesn't work first I will trouble shoot for a bad ground. Is it possible the dielectric grease is just messing with my electrical system? :(
 

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98 Forester (5 speed)
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Discussion Starter #6
Also going to check/clean the ECM connections. Fingers crossed he didn't put there too!
 

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Also going to check/clean the ECM connections. Fingers crossed he didn't put there too!
Regarding dielectric grease, it depends on what type was used. It isn't conductive so if you already have a bad connection, it will not make it better. It is there to protect existing connections.
It does make me wonder why the PO thought it was necessary..

Hose connectors down with this stuff. DeoxIt is not cheap but is the absolute best.

Edit: sounds like unplugging the speakers was a red herring. It may have just happened to change idle when you fiddled with the connection. I wouldn't forget about it but don't put too much stock in that it may be speaker related.
It may very well be that the aftermarket radio install, dielectric grease monkeying around caused an issue. Maybe he thought the grease would make the connections better.
Definitely clean connections, spray it with that DioxIt, check for rub through on wires, etc. Stuff like this can be a bear on pogo stick to find.
 

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2007 Forester Sports XT 4EAT
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@taymo2 as to dielectric grease. I agree with @Remco.

Dielectric = electrically not conductive. The connection must be sound before dielectric grease is applied. The main purpose of dielectric grease is to prevent moisture (water) & air from contacting the sound... tight electrical connection. The connection has to be sound enough... tight enough so the mating surfaces make contact, displacing the dielectric grease. Once the mechanical electrical connection is made, the dielectric grease flows around the connection to keep air & water from compromising the connection.

As noted by @Remco, if the electrical connection is not sound... loose, dielectric grease will not make it better. It could make it worse, as it's a non conductive.

I prefer NO-OX-ID A for most of my electrical connections, as it's a heavier bodied grease. For higher temperature or when a lighter body grease works better, I turn to dielectric grease.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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98 Forester (5 speed)
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Discussion Starter #9 (Edited)
Thanks for the replies! So far these are the connection points that have dielectric grease in them:
MAF
IAC valve
Coil pack
Wiring harness

No grease on the ECM thank god

I also went to every ground point I could find, disconnected and cleaned them. If the ground had paint under it I sanded it down to bare metal and reconnected.

Results?

It runs a little better. I wish I had videos to compare the results.

The lowest rpm range is between 500 and 700 now when shifting out of gear into neutral.
Before it would drop to 300 and sputter back up to 700. It seems to idle stable though the more I try to fix it the more I notice the small quirks in the system. I specifically have a problem with the idle jumping up and down constantly. It's never going +100 or -100 rpm but still seems like it shouldn't fluctuate that much right? Every time it hiccups like that you can feel the car shake and then re-stabilize, shake re-stabilize over and over. Seems to match the rpm fluctuating at idle. No misfire codes yet, will keep an eye out if any pop up, I'm sure they will eventually.
 

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2007 Forester Sports XT 4EAT
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I also went to every ground point I could find, disconnected and cleaned them. If the ground had paint under it I sanded it down to bare metal and reconnected.
@taymo2 this is the perfect place to use NO-OX-ID A or dielectric grease. It would help maintain the connection, preventing corrosion.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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98 Forester (5 speed)
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Discussion Starter #11
@2.5x_sleeper Thanks for the advice! I'm going to take it to a shop soon to test the electrical side.

I forgot to mention it also backfires frequently and fuel has dripped out of the exhaust after high revs I don't know why I didn't think to diagnose for that too. Short term fuel trim is all over the place and can go down to -20 up to +10. Long term fuel trim is slightly more consistently between -7 and -15. I don't know much about what this means but I read that the fuel trim should average closer to 0 for both is that right?
 

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@taymo2 As far as fuel trim, combined long and short term fuel trim as close to zero is best but it can vary between +- 8 and be considered normal.

Fuel coming out of the exhaust? Are you sure that's fuel and not water?
If fuel, that really could do a lot of damage. It washes the oil off of the cylinder walls so would create a lot of wear. It finds its way to the O2 sensors and catalytic converter, causing them to faul. Do not drive that car, as is probably obvious, until you get that sorted.
I'd see if one of the injectors is stuck open, unless one cylinder is missing all together. Pull the plugs and wires, see which hole is wet with gas. It could be that there's absolutely no spark in that cylinder but you'd know it because that car would totally run like crap, stumble, etc. It would do more than just idle strangely, as it does now.
You could get a cheap spark tester, attach it to the engine block and crank it. You should see a spark.
If you indeed have a good spark, look at what the injector is doing by rigging it such that it is out of the engine and have it spray in a cup while briefly starting.

One more question - and don't take this the wrong way - but are you up for this?
We went from a speaker causing issues to bad connections and now gas coming out the tail pipe. I wouldn't want to steer you down rabbit holes you are not equipped for.
 

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98 Forester (5 speed)
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Discussion Starter #13
@Remco
Today's agenda is to check fuel pressure regulator for fuel in the vacuum line and replace fuel filter. I'll start with what's cheapest/easiest in the fuel system and work from there.

Ignition coil has been spark tested for each cylinder. It's brand new and appears to be working properly. Before I start pulling injectors though I want to see if I can't listen to them by ear first. I know it won't always tell me somethings wrong with the injector spray but if one is locked open I'll hear it for sure. Also going to change spark plugs and wires within the month. I originally bought cheap plugs from AutoZone, now I'm thinking it would be best to stick with OEM from Subaru instead.

Another thing that caught my attention is when I open the fuel cap I don't hear the tank depressurize like I normally do on other cars. This is my first Subaru, I know PSI on their fuel systems isn't as high as other cars I've owned so maybe I'm just used to hearing that depressurization everytime I open the gas tank. Thoughts?

I'm not not 100% certain it's gas out the exhaust. It had the texture/gritty feel of gas when I rubbed it between my fingers. If it was just water is that commonly okay if just a little drips out tailpipe on startup?

I'll admit there is no real method to my search, just checking things off the list as I go. I'm now inspired to solve this problem after the speaker mishap. I'm not sure what caused it to run like that and probably never will. The important thing is it runs and drives excellent outside of the small jumps at idle and occasional misfire code. It feels mechanically sound from my perspective. I'm probably not providing an accurate assessment of my situation making it sound worse or different than it actually is. I've owned many old cars from the 90s they all have their own ticks and quirks, just a matter of taking the time to learn them.

If my search this week ends dry I'll dive further down the rabbit hole but for now best to keep it simple for my sanities sake lol
 

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@taymo2 Water is a by-product of combustion so it may very well be water. If it were coolant, it would likely be pretty constant and smell sweet. Gas would stink --- and obviously burn.

If it runs much better: good. Likely cleaning those connections helped a great deal.
Seriously, get a can of that DeoxIT and spray it in suspect connections. Get that dielectric grease out, if you can. If really should not it.
Sounds like you are well on your way.
 

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98 Forester (5 speed)
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Discussion Starter #15 (Edited)
Thanks for all the help and reading my posts! I changed the fuel filter today, did a cheap little fuel quality test before and after with a plastic bottle. I wasn't originally concerned about the fuel quality I just wanted to see if I was getting fuel pressure to the lines. My phones being difficult with pictures right now but the before and after is impressive. It looked pretty dark and murky before filter change. After filter change it looks exactly like gas should, sure enough it not only runs better but sounds so much better at high rpm than it did before. It even smoothly drops to 1000 rpms between shifts and then gently lowers to 800 for idle. No more sputter, no more shakes. Just smooth happy engine.

I did spray a can of DeoxIT on my MAF, Coil pack, IAC, and ECM connections. I believe a combination everything suggested above helped track down the problems. So glad it's not the injectors or worse!

(edit) This Forester has 250k miles on it and likely has never had a fuel tank cleaning. Might do that sometime this year for good measure.
 

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98 Forester (5 speed)
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Discussion Starter #16
I'm wondering though, if my fuel quality was that bad, could some of it not ignite and escape out into the exhaust?

It's not dripping anymore from what I can tell.
 
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