# Misfire under load and hard to start when cold



## ben5010 (Jan 2, 2015)

Hi all, I have a audi tt 225 apx

I've got a problem which I cannot seem to resolve,
first is I have a misfire under load, once the car warms up if you go full throttle it'll misfire, partial load is fine, also if I have low fuel level and start the car in the morning or after leaving it for an hour or so it'll struggle to start on the first attempt.

Once started it'll start again with no issues.

I have replaced the fuel pump, fuel filter, MAF, all vacuum lines, n75 valve, tried running with o2 sensor disconnected which didn't change the misfire, plugs are gapped to 0.28.

It's starting to become quite frustrating now so any advise would be awesome.


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## Myrddinemrys (Apr 15, 2015)

You don't mention coils?

My BAM engined 225 had a similar issue - turned out to be a tired injector. If you've got access to Vag-Com check engine misfire count to ID which cylinder is involved. Then move the injector, or coil, on that pot to see if the misfire goes with it.


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## Wak (May 6, 2002)

If the car has over 100k on the clock then Id say get a new set of coils.

The APX coils are very reliable so 100k should be good for them and over is borrowed time, not sure why you have problems starting but eliminate the coils first.

You don't have misfire diagnostics so you cant tell which cylinder is a problem on this model.

I'd have said fuel pump next but you have changed the pump, you could also renew the temperature sender if it old and the cold starts are a problem perhaps you have two issues..... coils first!


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## Hoggy (May 8, 2002)

Hi, Plug gap should be 0.032"/0.8mm.. 0.28 a typo perhaps. :wink: 
Hoggy.


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## Wak (May 6, 2002)

Hoggy said:


> Hi, Plug gap should be 0.032"/0.8mm.. 0.28 a typo perhaps. :wink:
> Hoggy.


I think he means 0.028"


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## rustyintegrale (Oct 1, 2006)

Wak said:


> Hoggy said:
> 
> 
> > Hi, Plug gap should be 0.032"/0.8mm.. 0.28 a typo perhaps. :wink:
> ...


Thank god you're about mate. I almost thought this was my problem. The car is annoying me now. :roll:


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## Wak (May 6, 2002)

rustyintegrale said:


> Thank god you're about mate. I almost thought this was my problem. The car is annoying me now. :roll:


Yours is a Fuel pump from the logs 95% certain, if you want 100% certainty then I can review and measure the fuel pressure, be about an hour to hook up the kit and do some runs to review fuel pump output.


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## ben5010 (Jan 2, 2015)

Hey,

I tried a set of coil packs from Euro car parts but the top of them split within a week of driving so sent them back, I replaced the CTS yesterday for the hard starting issue but remains the same.

I noticed some cracking on the coil pack wiring harness is this likely to cause the misfire issue? I wrapped the wires individually but they had a bit of green on the wires. Also when it misfires it seems to boost spike could if this is of any information?

and yes I did mean the 0.028 for the plugs gap 

I logged the car with VCDS and no faults come up for the misfire, i have also logged the car on a run but i cannot seem to decipher any real relevant information

I've uploaded the log if anyone can translate any useful information from it.

Thanks again!


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## Wak (May 6, 2002)

logs eratic and not complete, there is no consistency to review and not the best combination for useful input.

also you will never ever ever get misfires faults on an APX they don't have misfire diagnostics in that generation of ECU.

You need to go from around 1500 rpm to 6500 , foot on floor in 3rd gear, ( 4th if possible) be safe!

log these pairs only.
002-031
003-020
115-118

Harnesses can be the cause of misfires, but I'd still consider getting genuine hitachi coil packs rather than these aftermarket parts.


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## ben5010 (Jan 2, 2015)

Thanks I'll log them tomorrow and upload.

Hope we can get to the bottom of this eventually [smiley=bigcry.gif]


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## ben5010 (Jan 2, 2015)

Wak said:


> logs eratic and not complete, there is no consistency to review and not the best combination for useful input.
> 
> also you will never ever ever get misfires faults on an APX they don't have misfire diagnostics in that generation of ECU.
> 
> ...


Hey Wak

I managed to get out today and log these if you could take a look and tell me what ya think that would be awsome  btw when it misfires it seems to hold boost at like 1.5 bar on the boost guage but if you progressively boost it'll boost to around 1.2 and not misfire as hard.

Thanks!


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## Wak (May 6, 2002)

1.For the Level of boost you are making , the maf values seem low.

- I'd like to know the source, brand and part number of the MAF. 
- Have you tried testing the car with the maf disconnected. 
- Could you have an intake air leak, between the maf and turbo, could the TIP have a leak?
- Also What coolant temperature does this car run at?

2. There is some signs of lean running from the lambda but not from the injector duty 
It looks like a "more than stock" and "not as much as remapped" injector duty.
The misfires you are feeling could be down to that but this data is likely down to the maf values coming through hence point 1 is the biggest thing that stands out. 
If the maf reads low, the ecu may decide on less load and deliver less fuel while you are making good boost.

184 g/s at the top for example is about 230bhp and you are holding boost for about 250+ bhp

3. I'd still be happier with a known good set of genuine coil packs, but the maf discrepancy needs review.


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## longodds (May 8, 2014)

I know you've checked your plug gaps, but have you inspected them for any signs of tracking or cracks? That could/would cause the spark to be intermittent under load. Just a thought.


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## ben5010 (Jan 2, 2015)

Hey,

The MAF was a brand new bosch unit from euro car parts, I tried running without the MAF connected but it makes no difference, I had a drive behind whIle sone one else drove the car, I had what looked like unburnt fuel when on full throttle . Don't know if that is of any help.

I have a 82 degree thermostat in the car also and aroundtown it'll run circa 92 degrees.

BTW since I replaced the fuel pump,which was jut the pump and swirl pot, it's struggled to start first time even when warm,I think maybe the plastic piping which connects the pump to the top part has a small Crack maybe? I'm going to replace this piping with some submersible fuel hose as before I changed the pump it would only struggle to start when the fuel level was low.


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## ben5010 (Jan 2, 2015)

longodds said:


> I know you've checked your plug gaps, but have you inspected them for any signs of tracking or cracks? That could/would cause the spark to be intermittent under load. Just a thought.


There is no cracking in the percolin part of the spark plugs no If that's what you mean.


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## longodds (May 8, 2014)

Yes, I meant the porcelain part. Are there any blackened streaks on it as that would be an indication of the spark tracking down the outside of the insulator?


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## Wak (May 6, 2002)

That top to bottom fuel pump connection must be sound as its meant to hold about a bar of fuel pressure , if it leaks then it is a cause of poor starting.

If this leak is big enough you could be losing fuel pressure under load and perhaps this is a cause of your misfire

Can you give the maf part number as there are 2 for a 225 and you must get the right one.


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## ben5010 (Jan 2, 2015)

Hey, the MAF part number is 0 280218 084

I'm going to replace the pipes soon to see if that makes any difference.


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## ben5010 (Jan 2, 2015)

Hey, the MAF part number is 0 280218 084

I'm going to replace the pipes soon to see if that makes any difference.


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## Wak (May 6, 2002)

ben5010 said:


> Hey, the MAF part number is 0 280218 084


You know I have a reasonably good diagnostic handle on things when I say.....

0986 280 218 is a BAM MAF.

You need to get 
0986 280 211 for an APX. :?

and then do the logs again because it will have thrown out the load and maf values that the ECU is reacting too.

( but get that fuel pump pipe corrected too! ) 

One clue is the BAM maf tube will have a grill at both ends, the APX maf tube will only have a grill at the airbox end so make sure that's what you get with the correct part number.

Also insist on sealed boxes as they could get a return where the maf element is swapped out by unscrupulous mechanics who say they didn't need it.


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## ben5010 (Jan 2, 2015)

I just checked the box and the number on the MAF, which is a bosch number, this converts to the right part number for the apx, and it only has the mesh the one side.

I replaced the pipes in the fuel tank which solved my starting issue, PITA to do as they are a lot more rigid tHan the plastic stuff, misfire still there, I noticed slight ripping in the TIP, I've ordered a new sfs 3inch tip and will get some genuine coil packs in due course.


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## Wak (May 6, 2002)

ben5010 said:


> I just checked the box and the number on the MAF, which is a bosch number, this converts to the right part number for the apx, and it only has the mesh the one side.
> 
> I replaced the pipes in the fuel tank which solved my starting issue, PITA to do as they are a lot more rigid tHan the plastic stuff, misfire still there, I noticed slight ripping in the TIP, I've ordered a new sfs 3inch tip and will get some genuine coil packs in due course.


Ok, then if its got the single mesh I guess its ok, but don't understand the part number discrepancy , Ive been buying those two ending 218 for bam and 211 for APX for years but not many recently so catalogue numbers may well have have changed.

I'm thinking this is going to be coil packs if all else is done but lets see who you get on with the other bits, the low maf vs boost could be an intake leak in the tip but only if the rip is a hole big enough to allow air to be drawn in.

You'll get there eventually....


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## ben5010 (Jan 2, 2015)

Update:

Just to let you know that I replaced the coil loom today, fitted genuine coil packs and new plugs, Misfire now gone, drives perfect, the starting issue was down to the plastic flexi hoses coming from the new pump to the top connections in the tank, replaced these with some submersible fuel hose.

as you can see the coil harness was in pretty bad shape, new one installed with triple protection to help avoid this issue in the future, insulation wrapped then some exhaust heat wrap, then the original heat cover.

Glad this is sorted now, can enjoy the TT again.  thanks for your help.



Wak said:


> ben5010 said:
> 
> 
> > I just checked the box and the number on the MAF, which is a bosch number, this converts to the right part number for the apx, and it only has the mesh the one side.
> ...


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