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Guest Message by DevFuse

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EJ25D DOHC tuning Q's

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8 replies to this topic

#1 MilesFox


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Posted 23 July 2014 - 09:16 AM

As i have posted, i have a rescue 98 Legacy Outback Limited that survived a skipped timing belt. The car has 132,455 mi. Although i have messid with a few ej25d's, did head gaskets on one, this is the first one that i will be driving as my other example has ej22e heads on it (98 forester)


1. what is compression for 1998, and what octane fuel should i use. The car ran much better with octane boost until i could replace the knock sensor.


2. Does the car have 100,000 mi plugs from the factory? Are platinum plugs appropriate. I suspect the plugs have not been changed at all. NGK v power or copper for this one? Car runs great, but it seems like it should have a little more snap.


3. Even with the new knock sensor, the car does seem to hunt around for timing. I used a universal replacement with a universal pigtail from the NAPA Echlin brand. I could have ordered in ALTROM (oe supply paraut) but i needed the part right away to clear emissions.


4. Is there, or can there be an ECU flash update, as if there had been any TSB's or firmware updates since the time of manufacture?


Also considering a few other things with this engine:


I had changed the oil with Mobil1 0w40 'european formula'. I somewhat wish i had used mobil's 'turbo diesel' 5w40 in regards to the flat tappet cams, but the 0w40 does have good ZDDP content (1000 ppm phos, 1100 ppm zinc, whereas the 5w40 is i believe 1200) and is more than the 5w30 and 10w30 blends.


This engine has the 'football' air intake with a snorkus on it, and one near the MAF. I don't like it as it looks ugly and is in the way of poking around under the hood. Would there be any harm with retrofitting an ej22 intake without the football?


Everything else seems to be in good tune, with regard to a replace mentrear cat and catback exhaust pipe, no codes after clearing the knock sensor.


#2 grossgary


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Posted 23 July 2014 - 10:09 AM

1. octane doesn't matter, i believe 1996's "required" premium, though the ones i've seen run fine without it.

2. Subaru says 60k plug change intervals.  in general EJ engines do best with the OEM NGK plugs installed.



3. i doubt the knock sensor brand matters, but i'm sure one can get a bum knock sensor.  Subaru insists on installing it at a particular angle and torque value - did you follow that?  i've never seen that cause an issue though.


4. not that i've heard of, i would doubt that's the issue.


i'd see what kind of gas mileage you get the first couple of tanks, that may confirm poor running.


ideally you get a cable that allows you to monitor real time what's going on and you can inspect fuel trims, etc to decipher where it may be lacking.  but that requires some effort and training. buy the right cable and download some free software and it can be done on your laptop.  FREESSM i think is what most people use.


as long as it has a MAF you can do whatever you want to the intake.  i've seen people bolt a cone filter right to the throttle body before. LOL

#3 1 Lucky Texan

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Posted 23 July 2014 - 01:31 PM

 on the NA cars there isn't a lot you can do. lighter rims might free-up some power for acceleration. lightweight crank pulley too.

Edited by 1 Lucky Texan, 23 July 2014 - 01:39 PM.

#4 MilesFox


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Posted 23 July 2014 - 10:43 PM

Thanks for the advice. I just bolted on the knock sensor. I have read thatit can be relocated to the bellhousing if it is too sensitive. I am driving the car with its existing gas plus fill up on top of the existing fuel, and a con of octane booster. I have about 150 miles on the tank before changing the knock sensor, mostly highway. The rest will be mixed driving. Not bad for half a tank so far, i estimate the range to be between 275 and 325 as usual with subaru avg 20 mpg. Perhaps better than i expect having functioning cats and o2's.


Ok, i will consider the standard NGK v power plugs that i have always used.


Good to know with the MAF. I'll swap the intake with the one off my dead legacy. It just looks better.


I have a netbook if i can get reinstall an OS for it, i'll consider a tactrix cable to monitor. Can the ECU be reflashed?

#5 MilesFox


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Posted 05 August 2014 - 10:07 AM

I changed the spark plugs now. The original ones were well worn and largely gapped. The original ones were NGK iridium, and i replaced them with 'g power' platinum NGK's. The fuel economy has been averaging 21.8 mpg between the last 2 tanks of fuel with mixed urban driving and A/C use. This time, i am going for 24 mpg by exercising driving habits, new spark plugs. and refraining from A/C as it is 75 degrees in the middle of the dog days of summer here in WI. I drive 19-20 miles per day back and forth to work at 30-45 mph surface streets.


I may or may not change the ECTS as the car still seems to hunt for timing (not as bad) and the 2nd and 3rd gear upshifts seem to hang onto the TC lock, and then let go to gain RPM. I have treated the trans with sea foam brand 'trans tune' and anticipate a trans flush once i can afford it with synthetic ATF cam2 (ATF6)



#6 somick


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Posted 06 August 2014 - 11:20 AM

On my 2010 Forester they used iridium plugs with 30,000 miles change interval.


I have also had one ECU "update" from the dealer.  They do not tell you what they do there but that what I had.



#7 wtdash


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Posted 06 August 2014 - 03:10 PM


+1 on everything mr. 'grossgary' listed.


-AFAIK, nothing before about '99 had any ECU updates avl..  I was looking for tuning options on a '98 Forester (same as yours) and there was nothing.  87 unleaded is their drink of choice.


-If you've got a code reader/scanner/clearer I'd clear the codes after replacing the KS.


-I'd say your <22mpg is right in line w/the Subaru est. #'s. 


-The 'torque box' (football) you're replacing may actually affect your power and noise level.  I realize you're doing it for aesthetic reasons,  but it may shift the power band, which may or may not actually be better for drivability. It's kind like people putting on an aftermarket intake.


-I'd replace the CTS. They fail. 


- I wouldn't spend the $ on synthetic ATF; buy the good but regular stuff. I've not read where it makes a difference in the way the car shifts. If you've not read my posts about it (or others), I don't recommend getting the tranny chemically flushed or even a 'power-flush'. Jut drain/refill/repeat 3x to replace the old fluid. I would add an aux. tranny cooler. Heat seems to kill the Subaru 4EAT more than anything (other than neglected fluid).


1998 EJ25D specs:

Engine model EJ25D
Engine type Horizontally opposed, liquid cooled
4 cylinder, 4 stroke gasoline engine
Engine displacement 149.9 cu in. (2,457 cc)
Bore 3.92 in. (99.5 mm)
Stroke 3.11 in. (79.0 mm)
Compression ratio 9.7 : 1
Firing order 1 - 3 - 2 - 4




Edited by wtdash, 06 August 2014 - 03:11 PM.

#8 MilesFox


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Posted 06 August 2014 - 09:29 PM

I had cleared the knock sensor code and the car cleared emissions after servicing it.


I am considering synthetic ATF as i have access to it as i work at an oil change shop. For the price, i can perform the service at work for what it would cost to purchase 18 qts of ATF. We use a T-Tech machine, which is basically a reservoir that dispenses the new fluid, while collecting the old fluid thru the trans cooler lines. The work is done by the trans pump withthe engine at idle in park; nothing is being force fed or back flushed. The old fluid is pretty nasty annyway, and the front diff was too low when i had got the car. I already have mobil1 fluids in the front and rear diff (75w90)as well as the engine oil. (0w40)


I'll take into consideration the football on the intake as i have read the nasioc articles in regards to CAI and helmholz resonator with MAF.


Also with my consideration for syn ATF, the stuff we have meets merconV, LV, atf+4, dextron 6, and is backward compatible with dextron II/II, d, and e and all prior specs for dextron. I wager the fluid itself may lend to slight improvement in fuel economy, and what i am looking to gain in performace with shifting is it just doing a good job of cleaning out all the shift slolenoids and un-sticking them. 


Aside from routine fluid service, i wish to hack the TCU and manually override the tc lock, the duty c, and perhaps the shift solenoids if i am good enough. And tap into 'power mode' and retrofit a 1st gen shifter handle

#9 MilesFox


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Posted 10 August 2014 - 08:14 AM

I had serviced the car using professional methods the other day. I installed cam2 synthetic multi vehicle ATF. The machine is a reservoir that connects in line withthe trans cooler, and exchanges fluids while the trans is in park at idle. First, I had drained the pan and refilled it with about 4.8 qts before starting the machine. So far the driveability is much better, the shift delay is not as noticeable, and the torque converter seems to be more engaged with the engine. The car just seems to roll better as well, less duty c shudder in tight turns, and less hinting around for RPM. I also changed the 4th spark plug and the ECTS the day before i serviced the trans. At 144 miles, i calculated 21.6 mpg. Shooting for better than 22 towards 24 this time




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