Topic: Forester hesitating,surging.

[JohnnyCanuck]

In the last few days, my usually smooth as a kitten Forester has times where it hesitates/bucks and then it goes away. I know it has a new fuel filter/plugs/wires etc but I checked them anyways - all good. Also pulled the codes and didn't get any. I was suspecting bad fuel as odd as it sounds because I always fill up at either Shell (91) or Husky (94), today after work, it would barely stay running.  I had to keep one foot on the brake and put it in neutral at the lights and rev it up just to keep going, and I could smell stinky exhaust; I had 1/4 tank of fuel.  I pulled into the Esso on 50th and 23rd, filled up and never had an issue all the way home.  I'll go for a ride tomorrow but pretty sure it was bad gas, and I got it from the Shell at Beaumont.

[JohnnyCanuck]

I wanted to follow this thread up in case anyone else had similar issues and were trying to resolve them.  As stated above, I started experiencing surging/hesitation intermittently, one day it was fine, next day or later on same day surging. No cel, no codes so it was frustrating trying to pinpoint what it could be, especially with how intermittent it was; here's what I checked trying to find what it could be.

Tested upstream 02 sensor  - good
Tested knock sensor – tested good but had small crack - replaced
Checked MAF sensor, cleaned
Checked all vacuum lines – all good (broke BOV nipple; repaired)
Checked grounds – all good
Checked alternator/battery voltage
Checked air filter – good
Checked fuel filter – changed
Checked IC y-pipe - good
Checked Plugs & Wires – good
Checked TPS - good

It became personal, man vs machine  and I spent lots of time going over pages from different forums - including WSC - and came across this thread: http://www.westernsubaruclub.com/smf/index.php?topic=33084.0

Basically, the boards on the MAF sensor had an issue where the solder would pull away from the contacts, I pulled mine apart and found one contact that was not soldered tight and when I'd hit a bump on our lovely roads, it would cause the issue I was having.  I re-soldered it, put it back together and it is running back to it's reliable self again.  I'll wait another day before I can say 100%, but at this point it looks like the problem has been resolved.

[Blue_Subie]

Downstream Sensor in the Exhaust Pipe Post-Cat, maybe?

[Dr Beans]

I pretty much cleaned/changed everything on that list. Hopefully you didn't change the fuel filter again because I changed it as well.

My guess is you're right in thinking its the MAF and that solves it (or ittshay gas).

Also, how's the fuel pressure. Back when I was reading more on the forums about these cars there was quiet a few people have troubles with the fuel pump. If I kept the car that was something I was going to change.

I think I saw that you installed a wideband, have you noticed the A/F change at all when the car starts stuttering?

[Dr Beans]

Downstream Sensor in the Exhaust Pipe Post-Cat, maybe?

Secondary 02 only pulls A/F after cat and isn't responsible for closed loop. It will just thow a code but won't cause hesitation issues.

I don't even remember if this car is OBD2 or not.

[JohnnyCanuck]

Secondary 02 only pulls A/F after cat and isn't responsible for closed loop. It will just thow a code but won't cause hesitation issues.

I don't even remember if this car is OBD2 or not.

I pretty much cleaned/changed everything on that list. Hopefully you didn't change the fuel filter again because I changed it as well.

My guess is you're right in thinking its the MAF and that solves it (or ittshay gas).

Also, how's the fuel pressure. Back when I was reading more on the forums about these cars there was quiet a few people have troubles with the fuel pump. If I kept the car that was something I was going to change.

I think I saw that you installed a wideband, have you noticed the A/F change at all when the car starts stuttering?

These are still OBD1 so you have to use the plugs and read the CEL for codes.  I haven't checked the fuel pressure, I can't see it being fuel pressure.  It will run like a top for a day or two and then almost die/surge/buck and then back to smooth.  If it still isn't fixed I'll check the pressure, as for the wideband, I didn't change it.  I disconnected it one day to put it into open loop when it was running like a bag but it did nothing.  They don't always throw a code though so I pulled it and used a torch and mm and it was well within specs.  So far the drive to work and lunch have been back to purring like a kitten.  I didn't do a very good solder job on the MAF, my gun would barely melt the solder and It looks terrible I have better solder so I'm going to crack it open again and do it up properly. 

Here's what I was looking at last night:




the three pins that could cause a problem, pin two had no solder contacting anymore:

Downstream Sensor in the Exhaust Pipe Post-Cat, maybe?

From what I read, I was surprised to see that the downstream O2 sensor is responsible for up to 20% of the fuel calculations, I haven't checked it out though

**Edit** 5/26/16  no further issues, problem resolved by repairing solder connections on MAF board.