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View Full Version : 2009 V8 4.2 Hesitation / Missfire / Flat Spot



the_big_1
08-22-2014, 01:54 AM
Hi Guys,

I have a 2009 V8 4.2 Manual S5. When I put my foot down, any gear, I notice that around 2600 rpm, there is a hesitation, flatspot etc for a spit second then all is good. Its like a flat sport, like the car missfires etc. I know its not carbon build up, I cleaned all the inlet recently.
Its been like this since I bought the car a few weeks ago.
I dont have any CEL lights etc.


any ideas?

MisterQuattro
08-22-2014, 07:53 AM
Im new to this forum as I just purchased an S5, but do you think it could be that you need a carbon cleaning?

How many miles?

- Rizzo

the_big_1
08-22-2014, 08:11 AM
Hi ya,

Thanks for that but I have cleaned all the inlet.

GateS5
08-22-2014, 02:31 PM
Obviously the first initial thought to what you are describing would be the dreaded carbon build up issue. If you are 110% sure that it's not that, then my next step would be to stress test the ignition coils for possible failure. When an ignition coil begins to fail they can exhibit a myriad of symptoms, from heavy consistent misfires/flat spots, to intermittent drops or hesitations in power when accelerating with varying degrees of severity. Also, when an ignition coil fails, it may or may not trigger a check engine light, just to make things interesting. Unfortunately, you probably will not be unable to stress test the ignition coils properly without proper Audi testing equipment, so a trip to the dealer may be in order. Luckily though, ignition coils tend to be rather cheap amazingly for Audi's. Check out www.ecstuning.com. They can help you out, and keep us posted. Good luck.

the_big_1
08-22-2014, 02:49 PM
Yeah 100% not carbon build up as I cleaned all the inlet valves, and yes they where bad, have all the pictures. Yeah could be coils, being an OEM engineer I can see why. Might be worth buying one and swapping out one at a time. I can not seeing it being more than one as it isn't that bad a flat spot. Could also be in need of a remap

GateS5
08-22-2014, 04:11 PM
If you can, check to see if there are any codes being stored in the ECU. I have seen vehicles record fault codes without illuminating the check engine light. Worth a shot, even if it is a long one.

JamesRS5
08-22-2014, 09:38 PM
Have you done any other checks, pulled the spark plugs out and checked their condition/gaps, run a bottle of injector cleaner through it, etc. simple things to eliminate before paying Audi to work on it.

JimmyBones
08-22-2014, 10:42 PM
Have you done any other checks, pulled the spark plugs out and checked their condition/gaps, run a bottle of injector cleaner through it, etc. simple things to eliminate before paying Audi to work on it.

This.

Also how many miles do you have? I would check your engine air filter to see how dirty it is. Audi's V8s have always been temperamental with their intakes.

the_big_1
08-23-2014, 04:15 PM
Hi guys,

I put new plugs in and a new air filter when I did the inlet valves as the air filter was horrid. I fitted Bosch plugs, the ones with 4 tips.
Does injector cleaner actually work???

JamesRS5
08-23-2014, 08:31 PM
Are the Bosch plugs ok for the engine type? I never did like them as you can't set the gaps and it seemed a bit of a con, only one electrode will ever fire out of those 4.
Injector cleaner can work if your injector isn't completely beyond the ability of the cleaner to do anything and for what it costs for a bottle of cleaner it's certainly worth a go.

the_big_1
08-24-2014, 01:53 AM
I got them from Euro Car Parts but never checked the part number. They looked exactly the same so never thought. Is there a good injector cleaner??

JamesRS5
08-24-2014, 07:16 AM
The wrong plugs really can cause all kinds of issues, misfire being the main culprit. It's definitely worth checking the part number or seeing what Audi fit and buying those (obviously from somewhere cheaper than Audi).

As for injector cleaner, I'm not sure which would be good or bad, maybe a trusted name such as Redex would work ok? If I'm honest, I'm not one for mechanics in a bottle treatments but for what it will cost you compared to removing the injectors and having them ultrasonically cleaned, it's worth a few $€.

the_big_1
08-24-2014, 07:23 AM
I will take a plug out when I can and get the part number off it. Then try find out if they are correct.

the_big_1
10-06-2014, 12:44 AM
Hi All,

Update, change for NGK plugs but the problem is still there, a definate hesitation when under load at about 2500 rpm. My next guess is injectors?

JamesRS5
10-07-2014, 01:35 AM
There is a thread elsewhere which points towards engine mounts. I wouldn't have believed this either but apparently the V8 engine uses an engine mount containing electrics, if these are on their way out, it can cause hesitation without putting on an engine warning light. Maybe worth checking out.

the_big_1
10-07-2014, 05:19 AM
Hi Ya,

I had found the same thing. Looked at them and they looked fine, noe error codes either. The solenoid in them is to remove vibrations at differnt RPM so only thing I would think that would cauze mountings to cauze flat spot would be engine knock?

JamesRS5
10-07-2014, 05:48 AM
I think it's to do with the solenoid being in the ECU circuit, a failing solenoid causes issues with the ECU that can retard the ignition and give the flat spot. Worth having someone check them out, you've almost eliminated everything else.

the_big_1
10-09-2014, 12:26 AM
Hi,

there are no faults showing in VCDS and I know that if the solenoid shorts out or goes open circuit then it shows in VCDS. Like you I think if they fail it will retard the ignition but I would they fail enough to retard the ignition but not enough to show a fault code ???

tofast2belast
03-27-2015, 02:13 PM
Yeah 100% not carbon build up as I cleaned all the inlet valves, and yes they where bad, have all the pictures. Yeah could be coils, being an OEM engineer I can see why. Might be worth buying one and swapping out one at a time. I can not seeing it being more than one as it isn't that bad a flat spot. Could also be in need of a remap


i know this thread is fairly old but i wanted to point out that it is adviseable to swap all coils out at same time. doing 1 at a time caun cause ecu to falsy determine misfire recognition due to variation in resistance. <-this is how it determines cylinder specific misfire

LINDW4LL
03-27-2015, 02:19 PM
New coils are only $17 each or so. Replace all.