for the love of god someone drop some knowledge on me PLEASE

[Audishiit]

Long post so bear with me haha

04 a4 1.8t
Couple months ago it started misfiring at highway speeds(75+) progressively got worse to misfiring I’m 2nd gear + started throwing P0172.

I replaced the coilpacks, bkr6e plugs (.032), coil pack harness, MAF, front 02 sensor
All in hopes to fix it.
Test drove it and was getting 18hg at idle and boosting @ 9psi
1. At idle it will sit at 18hg then hiccup to like 13-15hg and then normalize.
2. Was just driving and it was running good building boost @ 9psi then after 10min it wouldn’t boost past 5psi got to my destination thought maybe it’s heatsoak even though it was 60 degrees out and then heading back home it was boosting at 9psi until I hit the freeway and threw P0172 again. Plugged in a shitty reader and reset the code and started monitoring fuel trims.
Live data from scanner showed this:
At idle short term would be anywhere from -5%-15%
Long term was at 0 since I reset it Within 14 miles the long term slowly went to -21%

First step is in 3 Hours when I get home do a boost leak test and pray I find one.

From my knowledge negative fuel trim means air is escaping somewhere past my MAF causing the the AFR to be off thus running super rich.

Anything else this could be?

One thing to note is the fuel filter was replaced 20k miles ago, and I have a slight pump wine under 1/4 tank but haven’t addressed that issue because my thought process is: if it’s going out that would cause a lean issue.

[Audishiit]

Also The hiccup happens very rarely at idle

[EuroxS4]

Sounds like a failing SJP or a pcv valve. I would check all your vacuum hoses and connections. -21% fuel trim means the ecu is pulling fuel out of the equation. So Its either getting too much fuel or running lean at idle till pcv or sjp returns to normal operating and then it starts pulling fuel back out.Either way acceptable fuel trims are +/-5 or 10 tops IIRC. Anything above is out of spec.

The fact that your seeing a vacuum drop and only getting 18 in hg is suspect. I think they are normally between 20-25 in hg.

[FNK]

+1 for the boost leak

Depending on which line the leak is, you can either have a rough idle and good normal highway usage or the other way, like yours.

Additional test, have you done a fuel pressure test? I don't remember, but at idle, lets say fuel should read 10 bar, it should remain stable on woot. If it drop a lot, lets say 5 bars, your injectors will have to be opened longer until you reach the system limit of "fuel starvation/fuel cut". In that case fueling, thus boosting, will be significantly impacted.

[Audishiit]

I’ve only done a boost leak once before and it was my TIP that was cracked so forgive me if I sound dumb as hell, when I run the boost leak test tonight that will show me if I have a failing SJP or any cracked vacuum hoses under neath the intake Manifold.

[Audishiit]

Forgive my ignorance, but how would I even test my fuel pressure under wot? I’m assuming it’s as easy as hooking up a gauge to the fuel rail and then starting the car and then WOT= Having someone else Revv the engine to let’s say 3.5k rpms while check the gauge for any fluctuations.

[Audishiit]

Yeah the vacuum drop happens while at a red light and like I said hiccups then returns to normal after couple seconds and only happens 1 outta 15 times.
I have a questions, the fuel pressure regulator is in the fuel filter, is it possible that The fuel regulator malfunctioned causing it to be wide open aka causing too much fuel pressure to the rail that’s why I’m running rich?

[Audishiit]

1-Did the boost leak test but was cut short to it being 10pm, the barbed fitting that’s off the turbo the clamp was really lose.
2- deleted the SJP
3- pretty sure the pcv valve is not working correctly (don’t judge but i was covering holes and blowing and when I covered one side and blew it sounded like a duck call hahaha.

New one comes Thursday and going to finish the boost leak test tomorrow

[FNK]

Forgive my ignorance, but how would I even test my fuel pressure under wot? I’m assuming it’s as easy as hooking up a gauge to the fuel rail and then starting the car and then WOT= Having someone else Revv the engine to let’s say 3.5k rpms while check the gauge for any fluctuations.

No, use a fuel pressure gauge with a 2~3 feet hose extension and stick it onto your windshield. Have someone record a video to be on the safe side.
You will have idle fuel pressure, steady driving fuel pressure, then WOT fuel pressure. There are good videos on Youtube.

*On mine, in woot at redline, I was at half the pressure and seriously fuel starved. It explained the on-off boost behavior. A stock vemo or bosch fuel pump was the solution.

The fuel regulator malfunctioned causing it to be wide open aka causing too much fuel pressure to the rail that’s why I’m running rich?

Possible, but I would tend to think not really as fuel injectors are pulse modulated according to fuel need.
If pressure would be higher, then injector opening time, in milliseconds, would be decreased to keep fuel ratio, as per injection able.
*on a side note, double fuel pressure will not equal double flow rate. I've done an Excel file to calculate injector size according to fuel pressure, to size a fuel pump. I will send it your way later today. FYI, the Audi 1.8t 166hp fuel injector max out at 172~175hp with a good fuel pump, while the Golf 150hp use the same injectors as the 195hp version and are good to around 210hp, with a good fuel pump.
I've replaced the stock injectors with used 150hp from a junkyard and scaled back the injection table on Lemmiwink by 15%. Almost free performance mod that you can do yourself!

1-Did the boost leak test but was cut short to it being 10pm, the barbed fitting that’s off the turbo the clamp was really lose.
2- deleted the SJP
3- pretty sure the pcv valve is not working correctly (don’t judge but i was covering holes and blowing and when I covered one side and blew it sounded like a duck call hahaha.

New one comes Thursday and going to finish the boost leak test tomorrow

How are you doing the boost leak test?
It should be a round plug that you put in the TIP with 5~10 PSI, such as below;



It sound like you are doing it another way?

[FNK]

Here is the Excel file, look at tab "Injector evaluation".
The first injector "AMB" spec the Bosch injector and max capacity.
Second injector "Jetta/GTI", same thing, max hp, etc.

http://s000.tinyupload.com/?file_id=...49466768356908

*Our "Return less" fuel system is designed for 4 bars. If you system in WOT drop from 4 to 3 bars, there is a flow drop of 15%. Formulas are all there, enjoy

[Audishiit]

Yeah I made one years ago, so the check valve above the air box was leaking, and then 3 out of 4 injectors were leaking air.
I had a new check valve already but need to go pick up a set of o rings for my injectors
Then continue testing.
Something that’s weird is I have the oil cap off. And you can hear the engine oil pressurized and I have the hose that has the pancake valve blocked off, I even have the hose that goes to the pcv valve blocked off at the TIP( I have the pcv valve off right now waiting for a new one tomorrow)

But I ear almost like a very very faint dentist drill from wear the rear coolant flange is.
Although I have no idea what it is :(

[Audishiit]

All 4 of my fuel injector seats are cracked 😂😂
So I had
Check valve leaking
Turbo wastegate nipple leaking
4 injector seats leaking.

How the hell was I able to boost to 9psi?

[FNK]

Yeah I made one years ago, so the check valve above the air box was leaking, and then 3 out of 4 injectors were leaking air.
I had a new check valve already but need to go pick up a set of o rings for my injectors
Then continue testing.
Something that’s weird is I have the oil cap off. And you can hear the engine oil pressurized and I have the hose that has the pancake valve blocked off, I even have the hose that goes to the pcv valve blocked off at the TIP( I have the pcv valve off right now waiting for a new one tomorrow)

But I ear almost like a very very faint dentist drill from wear the rear coolant flange is.
Although I have no idea what it is :(

Ah! Had that problem also, it was the half moon seal of the valve cover.

[Audishiit]

Fixed everything
Start it and it idles at -12 short term
Figure I should reset ecu so un plug battery touch the terminals together to discharge system
Start it and go around the block and within 3 miles long term is -12.7
When I’m on the gas the short term goes to 0 but as soon as I let off it shoots to -15

I Pull in the garage and let it idle and short term slowly goes to 0

Going to give a break this weekend then Monday do another boost leak test.

[FNK]

You either still have an air leak or a fuelling issue.

If a boost leak at 10 PSI does not leak, even by the oil cap, then I would start looking the fuelling.

Do you have VAG COM? You can use the Lite version with a generic cable for this.

Start looking at the timing pull and ignition angle per cylinder. If one is off, then you might have a bad injector.
For example, if 1 injector is partially clogged and the spray pattern is not good, then fuel will not burn well.

When engine is loaded at highway speeds (3500rpm), piston speed is higher than idle, thus better atomization of fuel even from bad spray. (-12 fuel trim, ECU remove fuel as it mix better)

At idle, ECU has to add fuel to prevent knock. But it will do so for every injectors.

Yes there is the trick of cleaning the injectors, but at 5$ an injector at the junkyard, I would just replace all 4 or identify the bad one and replace that one. If the issue is the injector.

[Audishiit]

I do not have vag cam :.(
I feel stupid for not getting one after years of owning this car,
I have a code reader that can read live data & that’s how I’m getting the fuel trim info.

I’m convinced it’s a fueling issue for couple reasons.
1. I replaced all 4 with a remanufactured injector set and one was leaking terrible when I first installed them, so I’m running 3 reman & 1 original. Although when I first installed these injectors the problem still persisted. So just wrote off the injectors being a problem.
2. There’s a noticeable Audio from the passenger side of the car where if you know what your listening at it’s the fuel filter.

I’m honestly at my wits end with this issue :.(
I ordered new filter (coming tomorrow)
And gonna swing by the junkyard and grab injectors then run 1 more boost leak test and if problem persists I’m either trading it in or paying a euro shop to fix it

[FNK]

Don't give up, almost there!

Have you replaced the injectors with exactly the same part?
Because on my car, the AMB engine, the injectors are 271 cc/min, while the Jettta/Golf are 310 cc/min. They have +13% more flow at 4 bars.
AMB = 06B 133 551 M
GOLF = 06A 906 031 BM

If you do use the Golf injector, then yes your LTFT will be at -13.
Simply use a software such as Lemmiwink to lower channel 10, Primary fuel tweak, by -13%. Done LTFT will be around 0% and STFT will also swing in that range.

[Audishiit]

Thank you for the encouragement.
I’m about to head down to pic a part and grab some injectors & then swap my fuel filter also

I’ve been doing hours of reading other threads that my problem consists of and another thing I’m going to check today is my flex pipe for leaks.

When this problem first started I had a leak at the turbo to manifold flange so i pulled manifold & turbo and had it machined flat and confirmed no more exhaust leaks pre 02 sensor.

1.I’m going to double check for exhaust leaks,
2. Fuel filter
3. Injectors
4. Throttle body cleaning because it’s dirty as hell
(Has an oily layer on it.

[Audishiit]

I didn’t even get to swapping the fuel filter,
I was swapping injectors and I got a really bad misfire, let it run enough to pull a check engine light and I got P0203 and 204, I swapped some injectors and was left with P0203, I swapped #3 coilpack just for sanity sake, no change,

The wires to #3 are exposed, not metal exposed but the bottom end of the boot is off,
So it looks like I either got fuel in there when pulling injector or when I was popping off the injector the wires finally gave out,

I’m going to head back to pic a part and grab a connector and tie it into the fuel injector harness tomorrow

Here’s the good news, when the misfire triggered the check engine light i also has
P0141

So gonna grab a 02 sensor there tomorrow.

Also found out my code reading can test 02 sensors but i have to fix the misfire first.

[FNK]

I reread the thread.

Spark plug are new, have you gapped them to 0.032" or used the pregapped asumption? Have you tried to narrow it down to 0.028"? Since you have lot of oily residue, same here, it can be harder to light the A/F mixture. Especially under load, mixture is harder to light.

As for the P0141, secondary O2 sensor heater, from my understanding it should not affect fuelling, but I can be mistaken.

Wow you went all out with the machining of the flange flat! I just used the OEM gasket from VW/Audi.

[EuroxS4]

Rear o2 is only there to check catalyst efficiency nothing more. Front o2 determines fuel mix. Your fuel injector harness is shot. That is probably the source of all your issues. Coil pack harness and fuel injector harness are culprits on higher mileage a4's I know my avant has 512k on it.

[Audishiit]

@ FNK thank you for taking time out of your day to help me,

Wanted to run something by you.

Old guy said I should flow rate the injectors because there mismatched, by pulling the rail and weighing the glasses b4 and have someone crank it over then re weigh them,

So tomorrow I’m going to repair the final 2 fuel injector pigtails, then do the flow rate & boost leak test

But I was re reading you’re responses and it kinda clicked,
1. I’m at -25% Stft at idle but if I had a vacuum leak Wouldn’t I be running leaning instead of rich at idle and if I had a boost leak The STft would be fine but then when I’m in boost/under load the car would run rich.
2. Is it possible that I could be idling @ 4g/s but the wiring connector to MAF is old/cracked causing problems?

It just doesn’t make much sense that I’m that far out of spec where the computer can’t compensate so something is clearly not reading correctly.

This all started under heavy load(highway speeds in 6th) and slowly got worse.

Sorry for the rant, but anything else you could suggest I look into tomorrow?

[FNK]

Back to physics
Atmospheric pressure is 1 ATM or 14.7 PSI
So even if pressure is indicated at 0, it is in reality 14.7 PSIA
Vacuum in often measure in inch of mercury or inHg.
2 inHg is the equivalent of 1 PSI

Idle behavior
At idle, your engine is basically a vacuum pump and it should read 25~26 inHg (-12.5 PSI) for a LTFT & STFT of Zero.
If the engine has a "leak" then air will gush in to fill that vacuum.
Under normal condition, idle air metered should be at 2.6 g/s. If you do see 4.0 g/s, then there is an excess of air and ECU will have to enrich to keep burn condition at stochiometric to prevent detonation and pollute less.
A large leak will cause the fuel trim to be all the at -25 (Lean).

Highway low & constant load
At normal cruising speed with low load, the engine is not in vacuum and is not boosting either.
As such, the "leak" does not really impact the engine as there is no difference in pressure to either allow unmetered air into the engine or out of it.
If you reset the ECU fuel trims, then in such conditions the LTFT and STFT would be hover around the Zero compensation.

Boosting
If the engine does have a "leak", then at positive pressure (5-9-15-20 PSI) the pressurized air will escape from that hole.
So the MAF did meter X amount of air (g/s), fuelling will inject as such, but O2 sensor will not read the same amount. ECU will trip on the other side of the fuel trim, into the positive or "Rich".
Fuel trim will be reduced to compensate.
As pressure increase, it is harder to light the mixture, especially with a compensated one, so missfire will begin.


On my end, i've had leaks at;
-Back cover half moon seal,
-Puck valve (even a new one had a lead, I had to glue the top around the seal),
-Suction jet pump (even a new one had a lead, I had to glue the top around the seal),
-PCV coming out of the crankcase was brittle and broke to pieces, large leak.
-Check valve broken,
-T-connection broken,
-Brittle hoses,
-Loose clamps,
-Oil cap (had to double the seal, even after a new one, but I peak at 25 PSI)
-...

Our cars can take 20 PSI at the TIP for boost leak test.
At that pressure (15 PSI), you should not be able to ear any leak.


As to point #2, cracked wiring connector, if the wires would be cut, you would have a engine code or an intermittent code.
Testing the fuel injector is a good checklist item, but I maintain the "Leak" is somewhere.