2 hours ago, cliffcoggin said:

No, such things mean nothing to me.

same 😅

For what it’s worth, I would be surprised if this was fuel filter associated.

1 hour ago, Magnet said:

For what it’s worth, I would be surprised if this was fuel filter associated.

You would be surprised....   or you wouldn't be surprised mate ?

Quite clearly written mate! 
 

3 hours ago, Magnet said:

Quite clearly written mate! 
 

ok i wasnt sure,  as i didnt see you quote anyone that had said it was the fuel filter, and ive often mis typed wouldnt & would,  or its changed automatically from 1 to the other,  so thought it best to ask to be sure, 

hi mark,i admire your persistence and hopefully you get it sorted cheaply,best of luck.Greg

23 hours ago, coupe4 said:

hi mark,i admire your persistence and hopefully you get it sorted cheaply,best of luck.Greg

Thanks mate, I got it code read yesterday, It showed the misfire on a few cylinders, But nothing else sinister on the codes,  And because i cant verify if the spark plugs have been done or not for sure,  i was advised to change them, Its only £50, Then its got all new coils and plugs and air mass and carbon cleaned,  

He advised if the plugs didnt solve it, He would pressure test the cylinders, and advised that if the cylinders had an issue, At that point he would advise me to walk away from it,  

So im changing the plugs tomorrow, I have everything crossed 😁

Best of luck,let us know how it goes

ok so i had the car looked at tonight by somebody, they read the codes again, the usual misfire codes were present from the cold starts in the mornings, also 2 other codes below in the picture,

He deleted the codes, we took it for a drive,  and then rescanned  for codes again. The same 2 codes above came back up.  He noticed at the front of the car above the fan, some wires were not connected. He said it looks like somebody has done a manifold delete, Google says the following on what this is....

A "manifold delete" typically refers to the removal of swirl flaps or runner flaps from an engine's intake manifold. These flaps, located within the intake runners, are designed to improve engine performance and emissions at different engine speeds and loads. However, they can also restrict airflow, particularly at higher engine speeds, and can be prone to failure or carbon buildup. Removing them, often with a kit, can improve airflow and potentially boost performance, especially in highly tuned engines

So he is unable to delete these codes, and is of the impression that the codes need to be deleted from the ECU, And that the engine etc could still be sending the signal to these flaps but obviously they are not connected. And this (might) be the reason for the misfire when cold as he thinks it might be all connected to the choke on cold start.

All of this means nothing to me...   I was curious if the codes above meant anything to anyone else. any help would be greatly appreciated.

The plan at the moment is for him to ask his coding guy if they can be deleted. and when i go back he will also do a smoke test/ vacuum test to check for leaks.

Meanwhile im sure iut will misfire again in the morning and register misfire codes again.

The thing is, after 3 or 4 mins of warming up, the car drives lovely and smooth, quiet, powerful etc. Like nothing is wrong. These issues are purely on cold start for 5 mins.

I will see what his guy says, meanwhile any imput on here from you guys would be appreciated.

Thanks

It seems the car has been modified, and therefore possibly also remapped, for better performance. That is going to make it infinitely harder to diagnose and fix the problem. I doubt anybody here will be able to help, but I'd be glad to be proven wrong.

10 hours ago, cliffcoggin said:

It seems the car has been modified, and therefore possibly also remapped, for better performance. That is going to make it infinitely harder to diagnose and fix the problem. I doubt anybody here will be able to help, but I'd be glad to be proven wrong.

Its going to be pressure tested on all 8 cylinders tomorrow morning.  Will see what the results are from that.  I still havnt paid for the car yet, as it was a fix it buy it deal. if i cant fix it i dont buy it.  This issue since looking seems to be very common on these cars. with various fixes in each case, it seems i just need to identify which 1 is my fix,  But it would be good to eliminate any cylinder issues for sure. 

Magnet earlier in this post mentioned some redex i think or i jnjection system cleaner, Im seeing this same advise elsewhere too for older cars. altho im not sure if this will be a quick fix as most people are saying to do it over a few full fuel tanks, well i wouldnt even use 1 fuel tank in the time im trying to solve this, But its cheap to do from looking so will probably try it anyway. I guess ill see what tomorrow brings, But either way i dont have unlimited time to fix this so i hope i find it soon, 

Good luck.

Keep us posted on how you get on 

Todays update....

Had the cylinders compression tested if thats what its called.

All 8 cylinders shows the same values, I think they were all 150 i heard the bloke saying.

So it appears that side of things is ok.

Google says : 

A healthy Audi S5 4.2 V8 engine should have compression readings above 130 PSI

Im unsure what to do next tbh.

It was mentioned today about getting the injectors checked, apparently they can be spray tested and measured, then cleaned etc and sent back to me from somebody called audi tec.

BUT....  Now i find out this model and engine, the injectors cannot be cleaned. Its new injectors if thats the issue.

My question now is...  How does somebody test injectors, Can this be done by reading the cars live data ?

Does it need to be taken apart and looked at. I personally have no idea.

Does anybody know how you tell if a injector is faulty or multiple injectors ?

Thanks guys

Edited August 6, 2025Aug 6 by AudidoThat
missing information

thats good news mark,hopefully its an easy fix now.it sounds like a nice car and youve been persistent with trying to fix it so i hope it pays off,best of luck,Greg

At least the compression is good. You could try buying second hand injectors as I appreciate new ones aren't cheap 

Found some info out today.....  

When we read the codes last, it came up with 2 codes it would NOT let us delete.

Code: P1655 & Code: P1658

Upon googling the codes, below is what it says for each 1.

For anyone reading this below, Bare in my fault only happens at cold start for 5 mins.

Once warm this dosnt happen, Which may or may not point to specific things more so than others

Maybe somebody more knowledgeable than me might know.

code P1655

Audi S5 4.2 V8 with engine code P1655 likely has an issue with the fuel system or oxygen sensors. 
This code typically indicates a problem with the fuel mixture being too rich or too lean, 
Often related to the oxygen sensors or fuel delivery system. 

Here's a more detailed breakdown:
P1655 Code:
This specific code points to a malfunction in the engine's fuel trim system, 
meaning the engine control unit (ECU) is having trouble maintaining the correct air-fuel mixture.
 

Possible Causes:
Oxygen Sensor Problems: 
Faulty oxygen sensors can send incorrect data to the ECU,
leading to improper fuel mixture adjustments. 

Fuel Delivery Issues: 
Problems with the fuel pump, fuel injectors, or fuel pressure regulator,
These could cause the engine to run too rich or too lean. 

Vacuum Leaks: 
Leaks in the intake manifold or vacuum lines can introduce extra air, 
This will cause a lean condition.

( Its been Cylinder pressure tested )

( which I am told would of shown leak problems, so not sure its this - But i dont know for sure ) 

Mass Airflow Sensor (MAF)
Problems: A faulty MAF sensor can also disrupt the fuel-air mixture. 

( Not sure it can be the MAF as i have fitted a new 1 )

The P1655 code might be accompanied by other relevant codes that can help pinpoint the problem. 

Check Oxygen Sensors: 
Inspect the oxygen sensors for signs of damage or contamination. 

Inspect Vacuum Lines: 
Check for any cracks or loose connections in the vacuum system. 

Test Fuel Pressure: 
Verify that the fuel pressure is within the manufacturer's specifications.

************************************************************************************

code P1658

The Audi S5 4.2 V8 engine code P1658 
typically indicates a problem with the fuel pressure regulator
or a related fuel system issue on cylinder bank 2. 
This often manifests as a lean running condition on that bank. 

Here's a more detailed breakdown: 

Code P1658 specifically points to a problem with the fuel system, 
likely a fuel pressure regulator or a related component, 
affecting cylinder bank 2 (the bank of cylinders on the passenger side of the engine)

Possible Causes:
Fuel Pressure Regulator: 
A faulty fuel pressure regulator can cause inconsistent fuel pressure, 
leading to a lean condition in the specified cylinder bank.

Fuel Injectors: 
Clogged or malfunctioning fuel injectors can also cause lean conditions, 
especially if they are not delivering the correct amount of fuel to the cylinders.

Vacuum Leaks: 
While less likely, a vacuum leak on cylinder bank 2 can also cause a lean condition,
potentially triggering this code.

 

( Its been Cylinder pressure tested )

( which I am told would of shown leak problems, so not sure its this - But i dont know for sure ) 

Fuel Pump: 
A weak or failing fuel pump could also be a factor, 
especially if it's not providing sufficient fuel pressure to the bank.

Fuel Filter:
A clogged fuel filter can restrict fuel flow and cause lean conditions,
although this is less specific to a single bank.

PCM Software: 
Outdated powertrain control module (PCM) software could also be a contributing factor,
though less common than the above.

Symptoms:
Expect rough idling, 
potential misfires,
loss of power,
and the check engine light illuminating.

Troubleshooting:

Fuel Pressure Test: 
Perform a fuel pressure test to verify the fuel pressure regulator is functioning correctly.

Fuel Injector Analysis: 
Check the spray pattern and flow rate of the fuel injectors on cylinder bank 2 
to identify any issues

Vacuum Leak Detection: 
Inspect for any vacuum leaks around the intake manifold and related components.

PCM Update: 
Check for available PCM software updates from Audi to rule out any software-related issues

Fuel Trim Readings: 
Monitor fuel trim values for cylinder bank 2 to assess the fuel delivery performance.

Repair:
Depending on the diagnosis, repairs might involve replacing the fuel pressure regulator, 
fuel injectors, or addressing any vacuum leaks.

 

So now the question remains, where to start, what to address 1st as a process of elimination the most cost effective way 🤔 😅

So today, Before i did anything else to the car, I took it into Audi for a diagnostics as i work next door to them.

I was hoping their software etc would show something more definitive.

In the afternoon i received a call from Audi saying they were unable to go any further, As The car has had the manifold delete done, and looks like its been remapped. And they didnt want to get involved in it.

I spoke to the guy at audi who told me the map could be knackered, or not done right to suit the manifold delete. The manifold delete could be a bodge job, and not done properly as they can see disconnected plugs that dont go anywhere by the manifold. So it might not have the kit on it thats used for the delete.

If this is the case, Then he told me more cabon can get inside and choke the engine on cold start. I spose this would make sense as the spark plugs i took out were black as hell. And the new 1s i replaced them with were also black when the pressure test was done a week or so after fitting the new plugs. Im assuming the sooty black stuff is the carbon ?

So these are the options to consider.

Get the manifold delete looked at, make sure it has the kit attached to it, or put it back to stock,

Price depending etc etc

Possibly put a new map on it that is done properly with the manifold delete sorted too, price depending.

This could be anywhere between £300 and £800 depending what gets done. And not a guarantee it is only that,

BUT THEN....

I spoke to a guy who does the Walnut Blasting and mapping etc.

The min i told him my issue, He said straight away the carbon clean i had done does nothing.

Especially on engines that are heavily caked in carbon ect,

He said he has done 50 odd carbon cleans of my engine, 

He seems to think that its misfiring on cold start due to the carbon, and when its warmed up things seal themselves and it runs fine hiding the issue, He is pretty confident it needs walnut blasting which should solve it.

He wants £1100 to do it though 😪.

I do not know what to do for the best if im honest, I think the carbon is an issue due to the state of both sets of plugs, so maybe thats the thing that should be done.

I dont know if the manifold and the map is the problem , as from what im reading online a manifold delete dosnt allow more carbon in, apparently its meant to improve it making it easier to clean etc.

 

If i could fix the car, i would keep it a fair while, For the last 10 years i have done 2000 miles a year every year.

So even at 84,000 miles on the S5, i could have it 8 years and only just hit 100,000. 

Does anyone have any thoughts ?

I sympathise, but as mentioned previously, the modifications make it almost impossible to advise. I fear you have bought a lemon.

On 13/08/2025 at 22:04, cliffcoggin said:

I sympathise, but as mentioned previously, the modifications make it almost impossible to advise. I fear you have bought a lemon.

Is it possible to have it put back to normal then, reverse the ECU map back to audi standard, And reverse the manifold delete, The issue might be that because audi wont touch it, will anyone else have a standard audi software.map for the S5 ?