This car is my hobby, and in the past and forseeable future I have/will always make time for hobbies (to help me stay sane).

You can't really test for a faulty primary O2 sensor other than replacing it, so yours should be fine considering that you recently replaced it. Though at one point I installed the wrong part # O2 sensor in my car because of a model year split... my old car is a 1998.5 and thus cannot use the sensor from a 1998.0 or earlier.

You can test the coolant temperature sensor's value with a VAG-COM or good OBDII reader. If it reports a coolant temp that's way off, then that could contribute to the engine running poorly.

 

ok, nice

i disconcted the temp sensor betwen engine and firewal and the only thing that happend besides that the acc tried to kill me and the temp gauge dident work was that the engine revs upp att start

my o2 sensor is for a 95 so it dident really fit my car, i had to use a saw, but the 02 sensor worked when the car was at vehicle inspection, and the car has been runing 4 months with the o2 sensor

but i will try with cag-com, thx

 

Good luck with it.

I just ordered the shims necessary to perform a 4:1 center differential, as seen here:
Audi A4 4:1 Center Diff Mod
Should be some of the best $55 I have spent I was planning to drain/refill the transmission fluid in the somewhat near future anyways so this should be a great addition!

 

Yesterday I had a chance to swap out the 2001 A4's rear brakes (which worked perfectly fine) with S4 rear brakes. It's a pretty straightforward swap, but in the midst of the bleeding them with my dad pumping the pedal, I let the reservoir go to low and air started coming out of the line... no bueno! Fortunately it seems they bled okay after that.
The pedal still feels a little soft so one of these days I'll go back in and bleed ALL of the brakes (maybe with a Motive Power Bleeder this time) and try to get a solid pedal.

I started swapping the rear suspension on the 1998 A4, but ran into a snag: the Bilstein sport struts use a different thread for the top nut than the OEM struts. Also I'll need shorter lower mounting bolts because the ones on the car were longer to accommodate the Neuspeed rear sway bar.

 

Today was somewhat eventful, for a day off work (while my wife worked).
Started out early changing by dad's 2005 V6 Camry front/rear brake pads and did an oil change. 4 hours (including 45mins wasted on a trip to Pep Boys) and $140 in my pocket I was finished.

Then I drove out to CX Racing's headquarters, less than 45mins away without traffic. Picked up their B5 A4 piping kit with intercooler mounting brackets for $240 flat I already have the same intercooler that came with the kit, but the painted black version, from my '98 A4. Started mocking that up today.

And my favorite news: just purchased the Motoza Hybrid K04 tune! Really looking forward to this... it's been rough driving around my car with FrankenTurbo kit/HFC/2.5" exhaust/upgraded brakes/coilovers/etc. on a stock tune.

 

Here's how the car looked on Monday:



Yesterday I spent a number of hours fitting the intercooler piping. Yikes, that was rough. I mean, it fits decently, but getting everything to line up in a suitable manner just took a while.

Wiping WD-40 on the inside of the silicone couplers allowed the pipes to move more freely, which made fitting everything easier, and WD-40 will evaporate. I would recommend this.

Today I made my way over to Harbor Freight with a 25% off coupon and bought their 3" cutoff tool. I knew there was no way my Dremel would cut into the bumper rebar.
It took a lot to cut the bumper to make it fit... more than I was anticipating. But it's on, thought could probably still use more trimming.
And I still need to start trimming the lower valence, but at least I have crash protection now (gotta go back to work tomorrow... 12 days off work FTW).

Here's how I finished tonight:

 

Had a bit of a scare yesterday on my way to my parents' house after work, making a right turn and getting on the throttle about 1.5 miles away from their house.
All of a sudden the car decelerated rapidly causing me to lurch forward, like the engine had a giant misfire.
After that the engine didn't want to stay running, requiring throttle input to avoid stalling.
I had to feather the clutch and keep the RPMs high to get the car to move at all. After a couple minutes the engine seemed to go into limp mode where it ran and would idle, but it ran kinda poorly. And there was no boost. But at least it moved under its own power.

Turns out an intercooler pipe popped out of its silicone coupler. This meant that all metered air was NOT entering the engine, so the ECU finally realized the MAF readings were wrong and went into limp mode. It was an easy enough fix after I drove back to my parents' house. You can bet I spent some extra time getting that T-bolt clamp nice-and-tight.

Coincidentally at the beginning of that same drive, the engine barely started after multiple attempts due to low battery voltage. So as you can imagine by the time the pipe blew off I wasn't feeling too hot about my car.
Then today I had a similar situation and enough was enough - went to Autozone and bought a new battery. Naturally though the battery their computer system called for didn't fit my A4's battery bracket!
I had a feeling this would happen so I drove the car to Autozone and changed the battery in the parking lot.
In the end I settled with a Duralast Gold 94R-DLG (3-year full warranty). This thing cost me $179 out the door after they took my old battery.

Oh and today I also retrofitted Morimoto Mini H1 6.0 bi-xenon projectors into my OEM Valeo xenon projectors
Easiest retrofit I've completed no doubt, and the second headlight took only 45mins to disassmble and reassemble with the Mini H1 projector (not including the time it took me to make the adapter bracket).
So now the car has excellent headlights and the high beams (from the bi-xenon projectors and high beam bulbs) are quite astonishing.

 

Had a chance last night to do some boost leak testing.
There were a few leaks, the worst being at the straight silicone coupler between the two metal pipes post-intercooler from the CX Racing kit. The two pipes just have a bit of misalignment that the straight coupler can't seem to account for very well. It's much better now (might not even be leaking anymore) but I ordered a 2.5" silicone hump hose coupler to replace the straight coupler for peace of mind.

Also my Motoza cable came in yesterday so last night I took an initial reading of my ECU and sent it off to them. Hoping to receive my first tune revision soon so I can start enjoying the benefits of all the bolt-ons on this car!

Yesterday I also received fabric to rewrap the 2001 A4's interior. The headliner sags, both A-pillars look poopy, the rear deck is fading, etc. So for the headliner/sunroof slide I have a flat knit foam-backed fabric in a similar color to stock (I think it's dark pearl/light gray), and for everything else I have a similar matching color in vinyl. Therefore I've been pulling apart the interior in preparation for new fabric. (it's also been apart for sound system installation/wiring)

And the inner trunk lid liner is off. I found a small backup camera which should fit nicely in the "cubby" to the left of the trunk lid button/lock and will need to remove that piece to drill holes into it. Looks like it should be fairly straightforward.

 

how does your car feel after the differential mod?

i thought you were selling your car, the 98?

my car will soon go to a scrapyard, it misfires constantly now even at idle, cant find whats wrong with it, and after many hours testing im tired of it

 

Haven't done that yet. Still need to buy new transmission/differential fluid (may as well do both while the car is up and level). Might do this in a month or so.

I will sell it, haven't really driven this car in a couple months. I'm still in-process of installing OEM rear suspension to the car so I can sell my Bilstein/Tein setup. The car has been sitting on jackstands in my parents' driveway for darn-near a month now and just last night I ordered a few pieces for the rear struts so it can finally be put back on its wheels.

Still will have some more work to do before it's ready for sale, too. And I need to have it smog-tested and registered before March!

That doesn't sound like fun :/ have you checked compression in each cylinder?


Friday night was a pretty productive night for me. I've had recurring problems of bad metal-on-metal rattling with the 2001 for the last couple weeks, after the engine/turbo have had time to get hot. It was the same rattling I got with the 1998 with the FrankenTurbo stuff installed, and I fixed it on that car by simply installing the 034 Motorsport K03/K04 locking tab to make sure the turbo mounting bolts couldn't/wouldn't back out.

Well, I used a K03/K04 locking tab on the 2001 from the start so I was surprised that the rattling started at all. Even re-torqued the turbo mounting bolts at one point which didn't help at all!
Then I tried a different approach. I've also always had problems with the turbo-to-manifold gaskets, and learned that Integrated Engineering offers a Cometic K03/K04 turbo-to-mani gasket. The price is steep at $15/each and it doesn't help that their cheapest shipping option is $10 (when you could ship the same things by USPS for less than $2...).

Anyways, I bought 2 of these gaskets and some other stuff to justify the shipping costs. Friday night I set out to replace the modified OE gasket with the Cometic gasket and also modify the stock turbo-to-block support brace (which I hadn't used with FrankenTurbo stuff since I first installed FT stuff 2.5 years ago). Ended up simply drilling a new 8mm hole at the bottom (block-side) of the brace that's about 3-4mm above the original hole, and also put a washer between the brace and the turbo.

Since the install of the new Cometic gasket and addition of turbo support brace, I haven't had any rattling! Think I might be getting a little better spool too as the modified OE gasket may have been leaking. But it's possible that's also just my mind justifying my use of time/money...