# Misfire/ hesitation on boost



## scrappyloz (May 16, 2014)

I recently brough a 2002 tt 225 for my partner with two issues.

One was a roof problem which is now fixed but im struggling to solve the last one.

Around 3000-4000 rpm the car begins to hold back in power and hesitate.

I have replaced all coils and plugs with brand new oem items. I have also tested the n75 valve with a multimeter which all seems fine.

It does exactly the same thing with the maf disconnected.

It is showing no fault codes and i dont know where to look next.

The good news is it doesnt do it in 1st gear at all. It does not do it when the car is stone cold, and it idles and revs fine with no issues.


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## Lollypop86 (Oct 26, 2013)

could it be a misfire on a cylinder?

J
xx


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## Ayaz (Oct 17, 2013)

I had similar issues with mine and it turned out to be a dodgy coilpack, splits in the hoses under the inlet manifold and a leaking Forge 007 diverter valve :roll:


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## scrappyloz (May 16, 2014)

I have done a boost leak test and found no leaks.. I heard that if you remove the dump valve and push the pluger up and hold your finger over the vaccume port that if the pluger does not drop the seals are fine.

I have done this and it seems fine.

What hoses run under the inlet manifold?


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## anthony_839 (Apr 9, 2013)

try a new map


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## L33JSA (Jun 30, 2010)

You need to get some logs done with vagcom/vcds


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## Wak (May 6, 2002)

As Lee mentions Data logs next....

Could be a coil pack wiring loom issue or possibly weak fuel pump but some proper review and logging to isolate where to go next...


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## scrappyloz (May 16, 2014)

Right fuel pressure test done and all is good
Also I unrapped all the coil pack wiring and checked it all. All was good bar a small break in the insulation of the earth strap that bolts to the rocker cover. All re wrapped back up.

I ordered a replacement genuine bosch map and fitted it. Unfortunatly i had to break the old one off as the screws that hold it down were just spinning 

Because of this the spacer for the map sensor came of as well. I fitted the map sensor missing the spacer. The car runs a whole lot better but still hesitates. Is this spacer important? I have ordered a replacement pipe anyway but just wanted to know.


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## scrappyloz (May 16, 2014)

Btw a good friend of mine has vagcom but hes hungarian and i cant read that


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## Wak (May 6, 2002)

So what's the fuel pressure at around 6000 rpm under full load?

The most likely leaking map sensor port will not be helping.

Why did you buy a map sensor they are so reliable the part number continues onto mk2 tt's and I've never seen a failed one.


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## scrappyloz (May 16, 2014)

Wak said:


> So what's the fuel pressure at around 6000 rpm under full load?
> 
> The most likely leaking map sensor port will not be helping.
> 
> Why did you buy a map sensor they are so reliable the part number continues onto mk2 tt's and I've never seen a failed one.


Hi the map sensor port is not leaking as i fitted a rubber seal.

Its a good job i replaced the map sensor as the car now hesitates 50 percent less than it did before.

Fuel pressure was 2.5 bar at idle and 3 bar under load.


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## CapeTownTT (Apr 11, 2013)

have you got a boost gauge fitted?


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## acgtrider (Jan 12, 2014)

My map sensor failed and i lost all my boost. i having a similar issue to you if i boot it in higher gears it kind of struggles and whooshes. Could it be your N75?


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## scrappyloz (May 16, 2014)

Hi sorry i havent got a boost gauge fitted.

As i refuse to let my partner drive this until i have fixed the issue i decided to take the car for a 25 mile run and see what happened.

The car is almost perfect from cold with no hesitation.
As the car warms up there is a flat spot/ hesitation starting at 4000 rpm about 50 percent of the time at 100% throttle, 
After driving for about 10 minutes the car hesitates/flat spots from 3500rpm but clears after around 6000 rpm. this happens all the time at 60-100 percent throttle

These parts below have been replaced with oem or bosch parts and no codes have been thrown. No parts have made a difference apart from the map which has made the car seem much more torquey when not hesitating.

MAF
OEM Coils
Plugs
Map sensor


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## t'mill (Jul 31, 2012)

Maybe put your location up to see if there's anyone in your area who could kindly assist with VCDS. This way you can hopefully pinpoint something rather than changing parts on the off chance it'll fix it


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## fixitagaintomoz (Apr 26, 2013)

N75 wpuld be my next guess


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## Callum-TT (Jun 3, 2013)

Sadly there is quite a bit it could be.

N75
Fuel pump
The actual Map
Timing the list is endless

As said above the best thing you could do is look for someone with vcds or full Vagcom and get them to do some logs whist driving. That way someone could see where the flat spot is and potentially find the cause.

Sent from AutoGuide.com Free App


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## L33JSA (Jun 30, 2010)

fixitagaintomoz said:


> N75 wpuld be my next guess


Guessing costs money & time.

Doing some logging however costs nothing and gives you the information you need in order to diagnose the fault properly without guessing.


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## fixitagaintomoz (Apr 26, 2013)

N75 is free and easy to test the resistance


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## scrappyloz (May 16, 2014)

Dropped the car down on a reccommendation of a friend to an ex Audi Master tech with genuine vagcom.

Long story short he had it for two hours and couldnt find what is causing the issue. Didnt charge me though which is good.

Back to the drawing board it seems.


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## Wak (May 6, 2002)

scrappyloz said:


> Fuel pressure was 2.5 bar at idle and 3 bar under load.


So its not enough under load then! unless you are running 0 bar of boost!


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## scrappyloz (May 16, 2014)

Right new n75 valve fitted and the car is loads better. 06A906283E valve fitted (i have a bam engine)

When cold no issues at all.
When hot below 50 percent throttle and the car is perfect.
When hot and i floor it or use moire than 50 percent throttle it starts to boost and then it feels really flat. through the boost range.
The jerkiness which used to be there only very occasioanlly happens now.

I also removed the inlet pipe and all pipes undere the inlet manifold and no cracked or perished hoses have been found.


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## nelmanners (Feb 1, 2012)

Hi scrappyloz,

I had a problem like that with my apx TT and I litterally changed everything such as spark plugs, coil pack, n75, new pipe under manifold than was cracked, new maf, all new vacuum pipes, new clutch switch incase it was that, new temperature sensor, forged 008 and then even a new lamba sensor. After everything it was my valve cover that started to leak and when hot the oil around the spark plugs must have made a misfire and sometimes backfire. Im not saying it is that but is worth a shot. Hope it helps.

Cheers 
Werner


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## scrappyloz (May 16, 2014)

nelmanners said:


> Hi scrappyloz,
> 
> I had a problem like that with my apx TT and I litterally changed everything such as spark plugs, coil pack, n75, new pipe under manifold than was cracked, new maf, all new vacuum pipes, new clutch switch incase it was that, new temperature sensor, forged 008 and then even a new lamba sensor. After everything it was my valve cover that started to leak and when hot the oil around the spark plugs must have made a misfire and sometimes backfire. Im not saying it is that but is worth a shot. Hope it helps.
> 
> ...


 Hi Werner.
Do you mean oil was leaking into where the spark plugs were regards


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## scrappyloz (May 16, 2014)

Right entire inlet manifold removed and all pipes checked. I found a small split in one so I replaced all three with silicone replacements. Also changed every vacuum pipe I could find and put it all back together and its exactly the same [smiley=bomb.gif]

I decided to do a N249 bypass which seems to have made things worse.

I was finally able to hook up a professional fuel pressure gauge in the fuel line before the rail, as for some reason they do not have valves built in.

I have 2.5 at idle with the fpr vacuum line connected. This raises to 3 bar when driving but when coming on boost (3000rpm) it lowers to 2.7 bar.

without the vacuum line on the fpr i have 2.9 bar at idle and driving. When coming onto boost again (3000) it lowers to 2.7

could this be a weak fuel pump? i have no problems with idle or starting


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## Wak (May 6, 2002)

Wak said:


> scrappyloz said:
> 
> 
> > Fuel pressure was 2.5 bar at idle and 3 bar under load.
> ...


 did you miss my first comment! :roll:

Its a 4 bar fuel pump so on load it should be FPR plus boost capped at the pump rating so pretty close to 4 bar pressure on a stock 225 and pretty close to 4 bar on a remapped 225 come to think of it! :lol:

stock is around 0.9 bar so should see around 3.9 bar 
mapped if holding 1.1 bar should see 4 bar

give or take a little as nothing is absolutley perfect.


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## scrappyloz (May 16, 2014)

I know im an idiot 

Ive ordered a pump which will be here next weeks so fingers crossed all sorted.

I took the old pump out and at somepoint someone has removed part of the screen mesh. After removing the pump from the housing i found some pieces of metal  so i assume the pump has sucked up bits of rubbish which has damaged it.

Fail previous owner



Wak said:



> Wak said:
> 
> 
> > scrappyloz said:
> ...


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## John-H (Jul 13, 2005)

Info in Knowledge base regarding this issue with the pump. I expect full throttle logging would have revealed weak mixture drop outs on lambda too.


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## scrappyloz (May 16, 2014)

Fixed


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## John-H (Jul 13, 2005)

Good. So what was it?


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## scrappyloz (May 16, 2014)

John-H said:


> Good. So what was it?


Fuel pump.

At somepoint someone had cut the mesh off the bottom of the pump. This allowed it to suck all the rubish up from the tank and ruin the pump.

All sorted and driving well


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## Joe4000 (Sep 6, 2014)

I'm having a similar problem, no boost, no codes & hesitating/holding back, I replaced the N75 (did nothing) & the vac operated fuel pressure regulator on the end of the fuel rail... much smoother take up of power but still lacking, could be that your regulator is dud like mine was, not delivering the extra fuel & my pressure sensors dead? Will check it out & report back, thank you


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