04 1.8T A4 project, P0202 and P0302

[1.8TFan]

Hey everyone, new member here with a "new to me" 2004 1.8T A4 project I picked up from a friend who had done some troubleshooting and basically given up on it after getting himself a Mk2 TT.

Anyway, here's the VIN:

WAULC68EX4A035147

The car has been taken care of pretty well except for a little body damage on the passenger side. I'll get that lined out in the near future. For now I'm trying to diagnose a misfire on Cylinder 2. I don't have a Rosstech yet but I do have an OBDII scanner and I am getting a Cylinder 2 Misfire and P0202 Cylinder 2 Fuel Injector Circuit Open codes.

Long story short I pulled the injector harness, stripped the harness insulation back to the #4 injector and found two bad spots on the wires. One was on Cylinder 1 and Cylinder 2 did have a knick in both wires insulation. Cylinder one had the insulation missing and the wires were twisted together and touching.

So I ordered 4 Bosch EV1 connector pigtails and last night I cut out the two bad spots in Cylinder 1 and 2 injector wires and replaced them with the new connector pigtails. I closely examined the harness all the way back to Cylinder 4, right before the harness drops in behind the engine block and other parts of the harness join together. Everything looks good to that point and I'm starting to get into a really tight area.

So before I get into cutting apart the harness any further I wanted to get some opinions on whether the Cylinder 2 injector itself could be the cause of the P0202 Open Circuit code? The injector terminals look good and the connector itself is new. I guess I could swap it to another Cylinder to see if the code moves to that circuit?

I'm planning on making a new injector harness. Using a 12 pin Molex Plug that will connect back just behind Cylinder 4 injector. I thought that was better than a big wad of butt splices/crimp connectors. I also want to try to adapt a plastic wiring conduit from a later model 1.8 or 2.0 for a little added heat protection.

I'll have to see what works? I plan to do the same thing to the coil pack harness. I plan to go through everything and get it back to solid running condition. This car has had the timing chain done and everything was properly maintenanced. I plan on rebuilding the turbo or possibly upgrading it. This car has the GBF transmission, I don't know what kind of power this transmission will handle?

I'm not trying to get crazy with it, but would like to be able to get ~225hp with a tune and rebuilt/upgraded turbo. I just have to get everything else rebuilt and tuned up first. I'm new to Audi's and VWAG cars in general. So I thought I would check with those more experienced and see if I can get some opinions on what I can do to this engine to make more power but not risk junking the GBF transmission.

Maybe down the road I'll swap in a manual transmission, swap the AMB head for an AEB head and build it. For now I just want to get it reliable and enjoy driving it while upgrading along the way. I love this car, I have built BMW's and a Scion TC this way and all those cars still run to this day.

I've really fallen for the Quattro and the 1.8T engine. I've driven this car in the past and helped my friend work on it here and there. Now that it's mine I want to give it some much needed attention.

Any advice on the codes or parts that should be serviced and/or upgraded is most welcome.

[1.8TFan]

Oh yeah, is it possible the Fuel Relay could be throwing a open circuit on just Cylinder 2? I meant to ask that but forgot earlier.

[1.8TFan]

Answered my own question, swapped #2 Cylinder fuel injector with #1 fuel injector and the P0202 code jumped to Cylinder #1.

Started building my harness, will post pics with progress. Still waiting on some stuff.

[1.8TFan]

Taking forever to get the replacement injectors in, hopefully they'll be in next week.

I spliced the new injector harness in, new cam position sensor is in. Now I'm trying to go through maintenance parts. I ordered a new 710N valve from ECS.

The car has ~170k miles. It has had all the major maintenance stuff done over that period of time. I've crawled all over the car trying to find anything that looks like it is in need of replacement.

Any advice on what I should be replacing? As soon as I can figure out how to post attachments I'll post some pics of the car. It's in excellent condition except for the passenger side doors being a little wrinkled.

I'll be replacing the door shells on the passenger side in the next few months. That will make the exterior perfect again. The interior is almost like new, rust free underneath. Should be a good candidate to restore.

[1.8TFan]

Hopefully these pics work:

IMG_20230108_165540.jpgIMG_20230108_165553.jpgIMG_20230108_165610.jpg

So this is my current project. Got the bad injector swapped out with a rebuilt one, went ahead and replaced all four. The car runs and drives great despite having 269k miles. Fortunately it was pampered and properly maintenanced during it's life. It runs and drives great.

Anyway, this car is in excellent condition considering the extremely high mileage. It's clean except for the passenger side body damage. I'll hopefully get that replaced and repaired coming up.

I'll keep updating as I get it back to it's former glory.

[Mike Tries]

I put a new diverter valve on my 187,000 mile 2003. I was getting fluttering from the turbo, so out with the old, in with the new. The old one was torn up and totally non-functional. You might want to replace that one too. Does it have 170,000 miles or 270,000?

[1.8TFan]

Yeah believe it or not that isn't a typo, 270k. But the original owner used to be an Audi Service Center owner back when this car turned 200k. All suspension is rebuilt, wheel bearings, etc. No rust, was gently driven and is the best condition 200k+ mile car I have ever seen.

The gold C5 A6 in the background is from the same original owner. It has ~140k and it runs/drives. But it slams into drive from a stop. I picked up a new filter, gasket and bolts to change the transmission fluid and see if it improves.

I have the 710N, plan to replace N75 valve at the same time. I would like to 6 speed swap this A4. It would be a blast, I may start hunting. I'm replacing the snub mount this week and I'm thinking about removing the boost reservoir. If it doesn't negatively affect performance I'm going to try running without it.

[1.8TFan]

Got a little time to work on "Red" today. I hooked up my new scan tool that I just got today, ANCEL VD700. Hooked it up to the OBDII port and cleared the old misfire codes from where I replaced the bad injector.

As soon as I did this and started the car it would run for about 3-5 seconds, start missing and die. Long story short I went through everything, immobilizer, electrical/battery connections, ecu reset via touching battery cables for 15min while removed from battery, etc.

Couldn't figure this out for several hours. No codes, nothing. I was finally looking everything over and to my surprise found my TIP pipe was disconnected from the MAF housing. It was loose and lying just in front of the MAF inlet. Is it possible the ECU somehow adapted to the leaking TIP? Because I've been driving this car for the past week and while I would sporadically get a stutter on acceleration, it ran and drove fine.

I also swapped the Autolite plugs the PO installed and put NGK BKR6E plugs in. I put them in thinking that the Autolites may be causing the issue? Didn't change anything because my TIP was not connected!

Once I corrected the loose TIP connection I took the car for a test drive, it's completely different. It had to be struggling before because now it runs so much better. Unfortunately I don't know how much of that to attribute to the new plugs? I gapped them to 0.32" per my research.

Anyway, it's running like a champ now. I have no codes other than P042000 - Catalytic System - Bank 1 Efficiency Below Threshold. I'm assuming this is either an O2 Sensor or Catalytic Converter issue. Talked to PO today while trying to figure out what could be killing the engine. He said he remembered having to take the Cat Pipe loose once and may have left the lower connection where the Cat Pipe meets the exhaust loose? Could throw the above code? The connection looks ok to me and I don't hear anything like an exhaust leak.

I also noticed the check valve up above the air box on passenger side of the engine bay was now clicking. I haven't noticed this before, bad check valve possibly?

[old guy]

Clicking is normal. That is your evap control valve.

A leak between the cat and down pipe could cause a P0420 cat efficiency code.

[1.8TFan]

Clicking is normal. That is your evap control valve.

A leak between the cat and down pipe could cause a P0420 cat efficiency code.

Got ya, thanks for that. I think the PO didn't get it tight enough possibly. I may go ahead and start looking for a high flow cat pipe. I test drive it again and I found a new error: P147900 Brake Vacuum System Mechanical Malfunction. So I'll have to dig into that next.

The car is so much powerful now, night and day difference. I will snug that exhaust connection up tomorrow and see if I can solve that P0420 error. I cleared it and it came right back, definitely something wrong there.

[old guy]

I assume you have an automatic transmission. Check the brake vacuum pump connections. May be something as simple a cracked vacuum hose between the vacuum pump and brake booster.

A DIY for reference: Clicky click®️

[1.8TFan]

I assume you have an automatic transmission. Check the brake vacuum pump connections. May be something as simple a cracked vacuum hose between the vacuum pump and brake booster.

A DIY for reference: Clicky click®️

Thanks for the link, yes it's the 5 speed TIP.

[1.8TFan]

Got the polyurethane snub mount installed. It does seem to transmit some vibration from the drivetrain. Hopefully it'll settle in with time:

IMG_20230121_195942.jpg

The original snub mount was completely disintegrated and missing. I know that it doesn't have as much affect on an automatic but it's there now anyway.

I checked the connection at the bottom of my catalytic converter and it appears to be tight. So I'm still trying to sort out the P0420 code. I'll have to go back and confirm, but when I scanned the data stream while the car was running I noticed one O2 sensor, don't know which at the moment, was running ~0.00mV. It would sometimes drop to -0.02mV but seems to steadily read 0.00mV most the time.

Does this indicate a bad 02 sensor? Or possibly incorrect voltage? I'm not sure if that sounds normal? I have a new 02 sensor on hand, but I wanted to ask if that's abnormal to see no mV? I'll scan the car again shortly and give the exact details on the error.

My heater core is definitely clogged or air locked. The bottom hose is noticeably hotter than the top hose under the hood going through the firewall. So I'm going to attempt to flush and bleed it this week. I'll try to make a post w/pics when I do it. It seems to be a pretty common problem.

I may have a lead on a set of S4 front calipers and slotted rotors. If it works out I'll be rebuilding/painting the calipers. Will have to wait until I get my new wheels before I can install anything bigger.