ccrinc Posted August 19, 2010 Share Posted August 19, 2010 I found this Service Bulletin which may answer some of the questions regarding hesitation on acceleration. Number 11-53-98, dated 1/5/99 HESITATION ON ACCELERATION - 11-53-98 (2/99) Applicability: 97-98 Legacy, Impreza, and Forester Manual Transmission Vehicles with 2.5l and 2.2l engines. In the event you encounter a customer complaint of a slight engine hesitation between 1500-2500 rpm's when the engine is cold or hot, perform the following Eliminate all external influences, such as an incorrect or dirty air filter, loose or tracked intake duct, dirty fuel filter, low fuel pressure, PVC system, or low engine vacuum that would indicate an external leak or an internal engine component. If all external components are confirmed to be operating within vehicle specifications, the hesitation may be caused by the ignition control logic in the ECM. Under certain low rpm driving patterns, the ignition control system can pick up engine vibrations through the knock sensor and may retard the ignition timing. This ignition timing is learned by the ECM and placed in memory. NOTE: This area of memory can not be viewed by using the Select Monitor. When the vehicle is driven uinder these conditions, the timing may be retarded and could cause the engine to hesitate on acceleration. To confirm this condition, road test the vehicle while viewing the Knock Sensor Signal on the Select Monitor. If you duplicate the hesitation, and the reading on the monitor is around -10 degrees, you will need to change the ECM to correct the concern. [my note: this is an enhanced ECM, not a replacement with the same component. NOTE: Some vehicles (shown on the following two charts) were produced with different emission systems during the same model year. To identify which system you have, look at the Vehicle Identification Number. Refer to the chart to identify which system you have on the 98MY Forester and the 97MY Impreza vehicles and choose the correct part number from the following page. There are a couple of charts, but they are not complete. They also do not mention (in the charts) the Outback, just Legacy. Of course, in those years, the Outback was referred to as a Legacy Outback. The bulletin also does not specifically mention that god-awful CEL which so many of us have, including myself. But, given what the bulletin is saying, and the fact that Subaru has not addressed the CEL issue at all, I infer that using the enhanced system and ECM will correct both problems. Hope this helps. Emily http://www.ccrengines.com 1 Quote Link to comment Share on other sites More sharing options...
AWDfreak Posted August 19, 2010 Share Posted August 19, 2010 Wow, that explains A LOT! I'm assuming this is from http://techinfo.subaru.com/ right? Quote Link to comment Share on other sites More sharing options...
Olnick Posted August 19, 2010 Share Posted August 19, 2010 Good information--thanks for sharing, Emily. Just idle curiosity since it doesn't affect my car: Wonder if any later model ECU (after 2/99) would work? Or could the original ECU be "re-mapped"? Obviously a brand new ECU would be quite pricey. Quote Link to comment Share on other sites More sharing options...
ccrinc Posted August 19, 2010 Author Share Posted August 19, 2010 Wow, that explains A LOT! I'm assuming this is from http://techinfo.subaru.com/ right? It's actually a printed Service Bulletin we got from GO Subaru West. Quote Link to comment Share on other sites More sharing options...
forester2002s Posted August 19, 2010 Share Posted August 19, 2010 I'm not sure if this is related, but I experience hesitation on my 2002 Forester MT. The problem is hesitation/stumbling, particularly noticeable at low-speeds in 1st gear. I have previously posted my own fix for this problem: - when starting the engine, do NOT drive away immediately; - instead, let the engine idle for about 10-sec without touching any pedals or switches; - then drive away; there will be no hesitation. I'm assuming that the ECU 'learns' something during this 10-sec of idling. Anyway, it works! 1 Quote Link to comment Share on other sites More sharing options...
ccrinc Posted August 19, 2010 Author Share Posted August 19, 2010 I'm not sure if this is related, but I experience hesitation on my 2002 Forester MT. The problem is hesitation/stumbling, particularly noticeable at low-speeds in 1st gear. I have previously posted my own fix for this problem: - when starting the engine, do NOT drive away immediately; - instead, let the engine idle for about 10-sec without touching any pedals or switches; - then drive away; there will be no hesitation. I'm assuming that the ECU 'learns' something during this 10-sec of idling. Anyway, it works! That is the way any car should be driven anyway. 10 seconds is a very short time to spend to make sure all the juices are flowing in the right places and under the correct pressure. I know I've been guilty of start up and take off, but I got in the habit when my '01 Forester developed some piston slap. It's been beneficial to my '97 Outback with the hydraulic clutch which can be sluggish to respond on cold Colorado mornings too! Quote Link to comment Share on other sites More sharing options...
Grafton Posted August 20, 2010 Share Posted August 20, 2010 this might explain my odd "surge" of power @ 2500 rpms, it doesn't make any odd noises or anything, just seems like it has no power until 2500rpm and bam powa! i'm going to have to start monitoring my ignition advance more closely thanks Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted August 20, 2010 Share Posted August 20, 2010 Interesting. Does it say how to identify which ECMs are affected by this? Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted August 20, 2010 Share Posted August 20, 2010 I had similar problem that I fixed with a can of dry gas and high quality fuel injector cleaner. A bad tank of gas can cause the stumbling and hesitation at low speed as well. Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted August 21, 2010 Share Posted August 21, 2010 Hmmm interesting.. sometimes it feels like I have some heavy hesitation going on best felt when I'm rolling in neutral but then shift into first and apply throttle it's like a dead spot at 1500-2000 rpms my car is a 95 legacy 2.2 Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted August 21, 2010 Share Posted August 21, 2010 Hmmm interesting.. sometimes it feels like I have some heavy hesitation going on best felt when I'm rolling in neutral but then shift into first and apply throttle it's like a dead spot at 1500-2000 rpms my car is a 95 legacy 2.2 If it were me, I would start with a new fuel filter, and a bottle of dry gas added to a full tank of higher octane gas, such as 89 octane. Use up nearly the entire tank, if still feel the hesitation, add a good plastic bottle of injector cleaner. The good stuff that cost $6 or $7/plastic bottle to your next full tank of gas. The cheap stuff selling for $3 or $4 won't help. This cured the problem with my 99 with the 2.5 motor Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted August 21, 2010 Share Posted August 21, 2010 If it were me, I would start with a new fuel filter, and a bottle of dry gas added to a full tank of higher octane gas, such as 89 octane. Use up nearly the entire tank, if still feel the hesitation, add a good plastic bottle of injector cleaner. The good stuff that cost $6 or $7/plastic bottle to your next full tank of gas. The cheap stuff selling for $3 or $4 won't help. This cured the problem with my 99 with the 2.5 motor well the only thing left for me to try from what you listed is 89 octane. Quote Link to comment Share on other sites More sharing options...
slayersean87 Posted September 2, 2016 Share Posted September 2, 2016 My 98 OB is having the same problems when im at a dead stop and am in 1st gear. other than that she drives fine. Quote Link to comment Share on other sites More sharing options...
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