forester hesitation and mild stutter all models read this

[scoobydoobie]

hi i have been having a power loss hesitation issue on my forester 12/97 model ej20 sohc engine.

i have replaced coil pack as cyl 2 had a weak spark diagnosed by all the other spark plugs being burned like you would expect for their full service lifetime but number two looking new still (not rounded spark burned electrodes) this improved it but didn't fix the issue . I then tested fuel pressure and replaced all the injectors with a known good set and replaced the very old O2 sensor (350,000 kms ) with a new one again a small improvement but the issue still persisted some times working perfectly but most of the time hesitating on acceleration and lacking power and not maintaining a constant speed. I then checked valve clearances and compression the middle 4 valves on both  cylinder heads were were a little tight on the clearance but this is normal as they run slightly hotter than the outside valves again no change . The problem turned out to be the electronic relay driver box at the back rhs of the engine it has the two large plugs with all the engine wiring going through it and it contains the high currant driver electronics for the injectors and coil drivers turns out that one of the two capacitors that are part of the coil driver   circuit were getting to the end of their life and making an intermittently weak spark on cyls 1 and 2  i have heard many others report a similar problem that persists after changing all manner of other sensors, ignition components  and even the main ecu. I only found it by a process of elimination and knowing that older cars with points ignition often behave like this from a bad condenser, this sent me looking for the coil driver circuit . the spark was not weak on voltage but lacking heat form the blown capacitor. since replacing this driver box with a second hand one  the car now runs really smooth and goes up hills in fifth where it used to stutter up it in third and fuel consumption has improved from 9 km per l to around 14 km/l    I hope this helps others :-)

Edited August 23, 2014 by scoobydoobie

[Rooster2]

A good write-up for this forum. I have read others having similar problems. You may have given them the cure.

[johnceggleston]

 

The problem turned out to be the electronic relay driver box at the back

rhs of the engine it has the two large plugs with all the engine wiring

going through it and it contains the high currant driver electronics

for the injectors and coil drivers turns out that one of the two

capacitors that are part of the coil driver   circuit were getting to

the end of their life and making an intermittently weak spark on cyls 1

and 2

any chance you could post a pic of this relay box?

it would help me to know what it looks like.

 

thanks for the solution and the write up.

[scoobydoobie]

Sorry im a free user and cant post photos but if your standing at the front of the car looking at the engine bay go to the back of the cylinder head on your left ( cyls 1 and 3 right hand side if your in the drivers seat ) at the back of this cylinder head is an alloy box with two plugs protruding from the back side of it with a thick bundel of wires each, it looks like a simple junction box it is not. , It is above the o2 sensor and is about the size of a cigarett packet  and attaches to the top rear of the cylinderhead secured with 2 12 mm head bolts  , one loom going to the car body to the computer inside the passenger compartment and the other loom going to all the sensors, injectors and coil pack on the engine, this is the engine driver module ( dont know what else to call it i cant find other references to this part any where else on the forums ) if someone knows its proper name as called in factory manuals or parts books please correct me  but for now i will call it the engine driver box. Any way it comes apart with four screws and inside the  alloy box is highly integrated circuitree  in a transparent jelly goo dont touch th jelly it looks hard but is like semi liquid glue and will stick to your finger and stretch very far on this board is a lot of bare silicon chips of different sizes and many small surface mount devices .   The two largest components are little alloy can capacitors and they can only be the coil driver caps as if they were for the injector drivers there would have to be four of them  as they fire sequentialy not in pairs like the waste spark coil pack pairs. the bad board had a large and small bubble in the jellygoo under each of those caps and the good driver board from a smashed car had no bubbles under the caps so i would think that the bubbles under those capacitors is gas leaking out of fried capacitors but being of the possibly electrolytic type they can retain some capacitance and self heal internal shorts across their dielectric medium to a degree and still keep working with a reduced capacity and cause a weak spark that is variable in its amperage output. these two caps are small and not the type with a failure evident cap that pops up the top from internal pressure build up shoing a visual indication of failure but the gas bubbles probably came out of the dying capacitors.  

 

If one could remove this goo without damaging the board and all its tiny flywires and components then new caps of the same or slightly larger capacity could be soldered on  to repair it.  I think this problem may be getting many people and the computer said everything was fine and threw no fault codes while this problem persisted  one other poster said he had replaced all teh sensors and the computer and eventually the engine as well only to have a similar problem persist.

 

  good luck people