HUGE flatspot at 3k revs....

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rossbrownlee

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Hi.
I have a 2000 APY with remap, not sure who/what map as it was on long before I had it.
Anyway, I am getting a problem whereby at 3000rpm when I am accelerating, there is a very noticable hesitation. This always seems to happen only at 3000rpm.
For example, I was on the road to Aberdeen last night, was doing about 70 and went to accelerate up a hill. I think it was in 5th or maybe 4th. Anyway got to the dreaded 3k mark and my face just about hit the steering wheel it was such a bad one. normally it is only noticable rather than as severe. It just seems odd that it is always at the same point in the rev range. obviously there will likely be something else happening at the same time to cause it.
Only mods are the map, sfs TIP, and forge recirc valve.

Anyone care to suggest what I should look for? I have access to vagcom so can log if required.
 
Yeah apologises ^^^

Just for ref thats all re: Ebay picture.




Joe
 
My car did exactly the same immediately after the remap and it turned out to be one of the coil packs. I had all 4 changed for piece of mind though. They're only about £30 each. Should make it alot smoother assuming it is this and not an issue with hoses leaking, collapsing at the point of max boost
 
ianysm said:
My car did exactly the same immediately after the remap and it turned out to be one of the coil packs.
Click to expand...

Exactly why I suggested the coils probly gone.

Common after a map so they say. (Whoever "they" are) lol



Joe
 
The noise of a misfire should be obvious though really. All of a sudden it should sound like a scooby. I agree, this is common with coil packs, especially about 3K as it is just starting to come on boost and requires a good spark to fire.

Does it clear after 3K or can you power through it? If so, how does it behave further up the rev band? If you can power through it and it continues to drive normally then coil pack is unlikely.

Check your fault codes on the COM of VAG and see if there is anything obvious there for starters. It should detect a misfire if that is indeed the case (although not always).
 
Welly said:
Does it clear after 3K or can you power through it? If so, how does it behave further up the rev band? If you can power through it and it continues to drive normally then coil pack is unlikely.

Check your fault codes on the COM of VAG and see if there is anything obvious there for starters. It should detect a misfire if that is indeed the case (although not always).
Click to expand...

No, I don't think coilpack. could be wrong but it is okay lower down and higher up the rev range.
When it hesitates it just coughs (last night was the biggest one so far although it is noticable some other times pulling more gently) but it seems to pick up okay powering through and carries on right up to as high up the range as I take it each time.

I have scanned a few times and have been getting an intermittent overboost, can't remember the code but it is upper limit exceeded.

Another possible symptom, there is a screech when the turbo is really kicking in. I thought this was a boost leak but i have been right through the charge air system, have replaced vac hoses where required and the bigger boost hoses appear not to be holed and the clamps are all tight, could this be the recirc valve passing (Forge 007)?

I am thinking:
1 - Recirc valve passing through/partially opening under boost condition due to being on weaker green spring
2 - Recirc valve passing through/partially opening under boost condition due to defective N112, although no fault codes for N112.
3 - Wastegate not opening ( i have checked the actuator mechanism by hand and seems okay. it is fairly tough to move and springs back to position so seems okay)
4 - Defective N75 (have checked this and N112 on VCDS and both 'click' however doesn;t mean they are not sticking/mechanically faulty)

What would be appropriate to log to help figure this out?
 
I'm getting this too occassionally (couple of times a week). Always at the same revs (about 3000) and it will just hover there for a couple of seconds before sorting itself out and launching off because I invariably have my foot planted at the time :(
 
I guess that 115 requested vs actual would be useful. But it sounds to me like there is something else going on there. Whats the spec of the engine? Mods etc. I can't see it being the 75 causing that sort me power loss, but possibly the over boost. If you are stage 1, a green spring will be fine.

Take it out and log 002, 115 and 118. The last one will show you the N75 duty cycle, meaning that you can see if the N75 is working correctly.
 
Welly said:
Whats the spec of the engine? Mods etc.
Take it out and log 002, 115 and 118. The last one will show you the N75 duty cycle, meaning that you can see if the N75 is working correctly.
Click to expand...

The mods are just: the mystery map, the sfs silicone TIP (which can't see causing anything like this), The Forge 007P.
I have done a fair bit of logging on the requested vs actual while hunting down leaks. It seemed to be okay other than the long lag which I believe is characteristic of the K04 anyway. once it was up there it held boost fairly well.

Unfortunately I am offshore just now so can't do any logging for a while.

It is doing my head in now. just can't think what is the cause.
 
Unfortunately I don't have access to VAGCOM (anyone around Cambridge/Norwich area...?). And as far as I know, my car is completely standard. I wasn't told that it had a map when I bought it, and I've never driven another A3 so I have nothing to compare it to!

Would love to have it logged and see what the issue was, so if anyone is near me and might have an hour or so free on a weekend or after work, please PM me or post below with location, availablity and favourite beer :icon_thumright:
 
I went through a nightmare trying to diagnose something similar when mine was mapped and not boosting on 3k at all. Would boost then come off, then on and never stay consistent. Ran fine before I mapped it. Changed the coil packs and nothing still coughed and hesitated on boost.

Hooked VAG-COM up and logged the misfire count thing, got my mate to start logging it when I was canning it. Sure enough misfire on every cylinder. Very confussed as I changed the coils and spark plugs and they seemed fine anyway. Dropped it off to APS in Brackely for them to solve.... It ended up being <drumrolls> ..my fuel pump! It wasn't feeding the cylinders enough fuel on boost hence the mis-fire! Worth going down that route and checking it, had no errors on VAG-COM and was fun as standard. Swapped and boom what a difference!

If you suspect your car is running to hot then it will be this as mine was running lean with my fuel pump failing and I did notice the engine bay hotter than normal after a run but wasn't sure why... Also had really bad corrosion on my exhaust tips because of it. APS pointed it out to me. Hope you track it down!
 
Last edited:
Right Welly et al, here are the logs from block 002, 115, 118. To my untrained eye looks like the airflow is decent, the boost looks to be spiking high at ~3280rpm but settling down and holding boost okay. This ties in with the intermittent over boost fault code i am throwing up now and again. I also found and fixed yet another boost leak from turbo pipe to recirc valve but that was before the run.

run1.jpg
 
****** hell, that is a big spike. 2550 - 1000 for atmospheric leaves you with 21.75 PSI.

2550 is nearly off the MAP sensor, the map sensor will only read up to 2550.

Line 9 is the interesting one - 2260 requested, 2480 delivered. I would imagine that is your overboost. N75 leading up to that point is at 95% or more meaning it is shut.

Have you tried another N75, I can't remember and can't look back at the post as in Advanced Mode. LOL
 
No mate haven't tried another N75 on.
So higher percentage load in 118 means N75 is shut? so take it that is the N75 shut so wastegate shut so more boost being produced = overboost.

Only thing is that that is looking at what the ecu is requesting the N75 to do not what the valve is actually doing. is it requesting too much boost or is the electro-mechanical parts too slow to react when the pressure is increasing?
 
Also, did some runs in higher gears 4th and 5th to slow things down and get a look at what's what. check these three logs out, on all of them at roundabout 3k rpm there is a big dip in the airflow. That proves what i can feel through my calibrated bumcheeks.
run3d.jpg


run4.jpg



run5.jpg
 
Again, my question has to be is it possible the car is starting to sh** its pants when it sees the spike and doing something to cause the hesitation and the airflow dip?
 
It's a possibility. I would try an N75 valve for openers. What sort is it on yours, have a look at the back and post the part number
 
It's dark and i'm scared of the dark, i'll post it up tomorrow but it's not been changed before i reckon, probably just the standard whatever that is.
 
other thing is, is the N75 adjustable? there appears to be a slot head on the top of it, wondering if it could be adjusted i.e. it has a minimum stop or something...
 
rossbrownlee said:
other thing is, is the N75 adjustable? there appears to be a slot head on the top of it, wondering if it could be adjusted i.e. it has a minimum stop or something...
Click to expand...

I believe it can be yes. BUT - adjusting in without proper measuring equipment is more likely to shaft it to be fair.

I tried it once on an old Vauxhall Bosch MAF. Just because it can be altered - doesn't mean it should be. I knackered the thing completely.
 
I presume you run the missfires block and there wasn't any? (060 or something if I can remember it correctly)
 
I also have the same problem it pauses at 3000rpm, so i unplugged the cable going to the MAF temporary and it cleared completely so im guessing i have a dead MAF, going to order a new one at the end of the month.
 
do poorly maf issues exacerbate themselves especially in the hot weather? feels slugish through the rev range
 
finesse said:
do poorly maf issues exacerbate themselves especially in the hot weather? feels slugish through the rev range
Click to expand...

Not normally I don't think. Never had experience with a dodgy MAF in hot weather though. Heat soak is most likely....
 
Know it may sound silly,but i have a 1999 APY,and had exactly the same problem... I changed my coil packs,gapped new plugs,3x MAFS,TIP,then full Forge boost hoses,new N75,EVERYTHING,and it still did it...

In the end (and i **** you not),what it was,was when i change gear i always hover my foot over the clutch peddle,and if a gnat were to of sneezed on it,it would of tiggerd the clutch switch!!! I tried a few runs completly removing my foot from the clutch,and the car has drove perfect ever since....

Pete...
 
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