Hard Starts Audi B6 1.8t (Can't figure out what's wrong.)

[KevinTheG]

I have replaced the ignition coils, the ignition coil wiring harness, the fuel injectors, the battery, and the starter, yet my 2004 Audi A4 B6 1.8t is still having issues. When I try to start it it just cranks until the battery is drained, unless I put my foot fully on the gas, put a jumper on the battery for extra power, and get lucky.

Here are the current codes:
https://ibb.co/SsV6t3S
https://ibb.co/hFRTV8j
https://ibb.co/ZRjsfBR
https://ibb.co/ZGqpcFr
https://ibb.co/pr8bQzs
https://ibb.co/X7tNyKS

[codemode]

Check your fuel pump.
Some of those codes are battery related.
Does it start immediately once on backup power?
How does it run afterwards?
Is the battery healthy, are you getting a continuous crank and not a slow dying one?

[EuroxS4]

Why note check the basics? Fuel supply at rail, Spark, and compression. If you have all 3 it will start. Simple shit.

[KevinTheG]

That's the thing.I know the compression is fine because I had it tested and it was okay, the spark plugs, ignition coils, and ignition harness are new, and the fuel injectors are new, as well as the battery.

[KevinTheG]

It doesn't start immediately, even with the jumper. It just starts more often. It then misfires a little bit but evens out and runs well. And the battery is new, so it's definitely good. It cranks at a normal power level for a long time and then if it takes too long it would kill the old battery, but I haven't seen it do that with this one yet. However, it still just cranks and doesn't start unless I put my foot on the gas.

[old guy]

Fuel pump going out.

[KevinTheG]

Could definitely be the issue. I'm not sure what else it could be at this point. I have also heard the coolant temperature sensor on the rear coolant flange could cause a problem starting if it's reading wrong but mine seems like it's reading accurately--not exactly the same as the one in the radiator, but I'm not sure if they're supposed to read the same or not.

[codemode]

AFAIK the CTS would only cause issues when cold because it would make the mixture too rich. I think you should find somebody with a fuel pressure gauge and hook it up at the rail.

[EuroxS4]

Does the tach move when cranking? If note It needs a Crank position sensor. If it moves, it would be a good idea to check fuel supply or camshaft position sensor. I have had them fail and never throw a code, just extended crank was present.

[KevinTheG]

The tach does change while is turn the engine over, yes, but thanks, I'll look into both of those.

- - - Updated - - -

Thanks for the recommendation.

[Protection]

I agree with [mention]old guy [/mention], most likely your fuel pump with the symptoms you describe. Why not throw a gauge on it and confirm? These cars are super easy to check as there is a Schrader valve on the fuel rail, IIRC.


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[q20v]

Went through similar issues with mine last summer. Hard start got progressively worse, until it wouldn't. Put a CTS (at the back of the head, in that plastic flange) in that I had lying around from another car and instantly solved.
I had the rail/injectors disconnected and verified fuel was injecting. Installed a fuel pressure gauge too, compression test, fuel pump... I tried everything. Hail Mary with the CTS and after 2 months of banging my head the car fired up like it never had any problems. No code was being thrown either, and I did not check the temp reading in VCDS, so no comment there. CTS is cheap and takes about 30 seconds to install, might as well give it a go.