Hesitation when driving, afraid this is gonna b expensive

[ryu_haneda]

Okay, so some of you already know the story behind my car: replaced engine, removed heatshields, replaced catalytic converter (twice), and replaced front and rear o2 sensors.

The replaced engine is a 2.5 liter longblock, same as the factory spec but with new headgaskets (to reduce the chance of getting the fatal "headgasket flaw").

Heatshields gone - more noise than my brain was comfortable hearing.

Current cat is a borla catalytic converter (OEM replacement) with bosch front and rear o2s.

Here's the breakdown:

February of 2008, I di scover I need to replace my catalytic converter. So instead of paying a Subaru dealer 900+ bucks for parts (not including labor) to replace my catalytic converter with a stock one, I ordered a cat online. Turned out to have a problem, but I was re-imbursed for it.

...then...

I got a replacement cat (Borla) and had it installed. By that point I had both the front and rear bosch o2 sensors.

After replacing the cat (twice) and the sensors, I got a code (PO1420 I think) about a knock sensor. Had that replaced along with a tuneup, plugs came with it.

Today, whenever I drive in the first 15 minutes to half hour, there is plenty of hesitation. With a warmup, things get slightly better.

Did I blow something up?

[Huffer]

How long has the hesitation been going on? Just today? A week? Since Feb 20008?

[ryu_haneda]

Additional story:

Got the cat replaced initially in March 2008. That converter had a defect, and was giving me random CELs, and was later replaced under warranty in July 2008. From July on, I started having hesitation problems.

What happened in July?

* New Bosal catalytic converter
* Bosch pre and post-cat O2 sensors
* replaced knock sensor

Then, in September/October, to attempt to remedy the hesitation, I opted for a tuneup. As it turns out, I hadn't tuned the car since I bought it. The sparkplugs were dirrrrty, and there was plenty of carbon from the exhaust service they performed. That helped a little bit, but eventually the hesitation returned.

I wonder what's up? Let me think about the bigger picture here:

* Remanufactured engine
* Main seals fixed
* Water pump replaced
* Starter replaced
* Ignition wires replaced
* Bosal catalytic converter with 2 Bosch O2 sensors
* Tune up; spark plugs replaced and fuel system cleaning service performed

The hesitation is the most prevalent on cold starts, and when gently pressing the accelerator from an idle (especially on a hill where it is easy to put a load on the transmission). I'm currently running with a CEL (most likely a PO420 code - I really, REALLY need to get it cleared). I'm wondering if I'm running too rich, or if the Bosal cat (which is an OEM replacement, not really a performance part) is hampering me more than helping.

I'm stumped. Maybe I should stop pouring 87 regular in my car?

[T_F_E]

Not sure if this is relavant but is your mileage been affected?

[ScaryFatKidGT]

87 is fine unless u have high compresion pistons or somthing

im gessing either tranny problem

or sence it started after replacing the cat it has something to do with the cat or o2 sensors are they in properly?

[Huffer]

The cat you have is flowing too much exhaust for the rear O2 to handle. You can avoid this by installing an O2 spacer to pull the rear O2 out of the exhaust stream by about 1-2".

I would check your spark plugs again - if "they" did this carbon cleanup on your engine with new plugs installed, it's probably accelerated the wear on the new plugs.

If it helps, I had/have the same hesitation in my car. Slight depress on the accel. and the car "hiccups". No issue if I push past that point. Hesitation on my car is usually at 8-900rpm. Above 1000 it's not an issue.

[ryu_haneda]

I had the catalytic converter installed by a local garage, same with o2 sensors. I think I'll go to the place where I'm currently getting service to have them checked. The tranny is probably still the original one, so getting a new one or getting it rebuilt may not be out of the question.

Huffer: you posted as I was writing this. In light of your info, I'm going to look into getting a spacer set-up. I'll also have my current garage check the spark plugs again. My hesitation kicks in between idle to 1200 or 1500rpms.

[Huffer]

You can either buy a spacer from Rallitek for $25 and some change for shipping, or go to a local Autozone, and get two "HELP!" sparkplug antifoulers that can be joined together:
http://forums.evolutionm.net/evo-how-re ... light.html (http://forums.evolutionm.net/evo-how-requests-questions-tips/114931-how-install-spark-plug-anti-foulers-remove-ses-cel-light.html)

I actually have both fixes, neither of them installed on my wagon. I never got around to installing them on my sedan.