1.8T 98 A4 issues. need some opinions

Shift518 Automotive
1

Here is the run down. 98 A4 1.8T. Cable throttlebody. Unitronic stage 1+, k04 replacment turbo.

So the guy said the car ran like crap ever since the tune. Thought it was the turbo, so he started taking the turbo out, couldnt get it all the way out and gave up, brought it to us. I put the K04 turbo he wanted in after removing the stock. (k04 is like 1-2mm larger, no big difference at all).

Start it up, run it down the road bad missfire as soon at you hit 10 psi. Neutral reving it wot missfires as it starts to rev up. Also has a MAF code signal low if I remember correctly. So I connect VAGCOM. Missfire counter goes through the roof on cyl 1 & 2. Maf shows G/ps flowing and responding. I swap coils from 1,2 over to 3,4… missfire follows. Get 2 new coils the next day. Put them on, run it and it fine. missfire gone, still has the maf code, still shows G/ps flowing on a log boosts to 15psi but surges abit. (requested boost is 16 psi) This thing has a decent size FMIC so I think this little turbo is having a hard time keeping all that volume full. Told him it still has the maf code, he says it is a brand new maf. (also told me it had new coils, but 3 looked original, one was different when I got it). If you are logging maf, and pull the clip of the sensor it STILL SHOWS READINGS??? Regardless, he comes the next day to pick it up.

Keep in mind, most of the times this thing starts, it needs a jump box… batterys smoked just about.

Following day we jump box it, he comes to get it and runs it down the road… runs like shit. Bad missfire/hesitation, actually over boosts 25+ psi under wot, only code is the maf. COLD. once it warms up it runs as smooth as it did the day i put the coils in, but still over boosts under wot. part throttle it runs fine, holds 5, 8, 10, 15, 20 psi even depending on foot position. So I get there that evening and start troubleshooting. Air pressure into the WG on the turbo, the shaft moves as it should. tripple checked the n75 valve, swapped it with another one, maf plugged in or out, no missfire counters, chalked it up to maybe a stuck flapper or something on the wastegate. Pull the turbo to check,nope just fine. I am baffled. Put it all back together. Think to myself, maybe the ecu is pissed from being behind a shitty battery so as we put the turbo back on we leave the neg terminal off and battery on a charger. put it back together, battery back on… hardly starts, touch the gas and it stalls… Now it has a throttlebody code. Following day we adapt the throttlebody and set readyness. Drive it out the driveway and it runs exactly like it did when I just swapped the new coils. Once warm. Cold-somewhat warm it overboosted slightly on a spike but settled back to 15 and surged a bit like it always did. Once warm, spike went away.

So now I am really questioning the battery and ecu. I am thinking its loosing enough juice to loose the throttlebody adaption, so I get a battery to put in it. Before I put the battery in it, I start it up the following day and take it for a ride to make sure it drives the same as it did the night before, then I was going to use jumpers to swap the battery as to not loose power to the ecu and loose adaption. Cold it missfires like its out of gas and stalls out, warm it is drivable like it was before, no missfires, but overboosts at wot, partial throttle controls boost fine and runs smooth. I think it lost adaption again, but I dont have the vag com to check it (I gave it back the night before). Somewhere along the lines in the last 2 days the maf stopped showing any signal and is stuck on 0 now. Also noticed the thermostat is stuck open and has a temp fluctuation which will mess with coolant temp and throw the tune off. Coolant cap is broken so it never seals to build pressure. Also has a JB welded oil return line that leaks, cv boots shot balljoints shot, abs kicks on when you hit the brakes in reverse backing up… its getting to the point that repairs are out weighing the effort. I think the tune killed the 2 coils, and he said the battery always sucked so I bet it kept loosing the tune or adaption or something like I am seeing here, ever since day one because the original turbo wasnt bad at all)

My last ditch effort/question to you guys. If the battery has just enough juice to start the car, most of the time, is it enough to toss throttlebody adaption and run like shit? The Maf has me too, I am suspecting wiring or ecu issue. (no signal now, and before it was showing reading, unpluged???). I know this is a book, but tech section is here for a reason.

2

hmmm id look into the thermostat to be honest if the car isent warming up its gonna be running like a bag of ass…

3

yeah I thought that too. cold it runs like shit. warm its not bad when it wants to work boost control wise. I just dont remember seeing the temp dip when I was troubleshooting it the first 2 days… but I was more focused on the missfire and boost issue so it probably was the whole time.

4

yea the engine not being up to running temp fucks up the fuel and air ratio ive seen t-stats do some funky shit

5

especially if the MAF circuit is fucked I assume its now running open loop and it might rely on the coolant temp for input?

6

Well, the coolant temp is generally what determines the transition from open loop to closed loop anyway. Where did this kid get the “tune” ? Is it possible that the injectors aren’t scaled correctly, or anything like that?

7

tune is from NA motorsports, its a run of the mill every day Unitronic Stage 1+ (+ is a gimic its for “aftermarket exhaust” so it probably does nothing more than raise the boost 1psi or something) tune. Stock turbo, stock injectors, etc. ONLY time I see a tune not be a flash and drive ordeal, is when the car has underlying problems. (like this one). The aggressive tune just makes them jump out more. Even well running 1.8T’s I have seen get flashed, and 100 miles later blow coil packs out of nowhere. Which I think this car also did in the beginning. 3 coils looked like OEM originals (green VW text and part numbers on top), and one was a black top no identification aftermarket replacement.

This is an all or nothing money pit I think. Either put $140 battery in it, $100 thermostat, $300 maf (labor included) then cross your fingers the wiring/ecu isnt fucked and sees the maf… or you spend all that money + labor/materials to troubleshoot the wiring, and/or replace the ecu and have to pay a dealer to sync the immobilizer to even make the car run which is $$$$… it runs ok once warmed up, put a MBC in parallel to the n75 valve to cap the boost spike and off load it.

8

Saab swap it. Done.

9

2.0 or 2.3?

10

It sounds like the MAF sensor readings are a shorted wire not the sensor if your getting a g/s reading with the MAF unplugged. Sounds like you might have an intermitent short from a chaffed wire. I doubt the battery is the cause of any drivabilty problem other than the idle learn being lost.

11

All or nothing money pit is exactly what i see this as. I spent a couple hours working on this with my full version vag com. The number of intermitent sensors and other parameters was endless. There were 3 main issues that i picked out as clear a day being a shot maf, bad thermostat and possibly coolant temp sensor, and intermitent signal to the n75 boost control valve. Each one of these problems could cause poor running conditions, let alone all of them put back together. Even as farmiliar as i am with 1.8ts and vag com diagnostics there is no way i could have proceded with anymore troubleshooting untill the above problems are repaired. That is not saying that fixing those problems will solve the issue. all the sensors on the car are my eyes and ears on what the car i doing, take a couple of those away and the scales on my computer might as well be an etch-a-sketch.