Reduced Power

[Dingo]

I have an ABY coupe and all was well, but its developed a small reduction in power, I would call it a hesitation, so I took it to my local Rolling Road where its been before and sure enough when they overlaid the graphs its lost about 25 - 30 hp, but didnt really help with a diagnosis as it was just a power run.
I've lived with this for a while but would like it resolved now, what I know is....
Homefried V stream running 1.5 bar
No boost leaks (tested)
No fault codes
New Bosch plugs
New N75
New recirc valve
car pulls strong then at about 4000rpm onwards hesitates (no missfires) to the red line
Someone suggested that it could be detecting false knock and retarding the timing (I only run it on Tescos 99 Ron)
My friend has VAG COM, we did some runs today but I dont Know how to interpret the info and it will not let me upload the file (Excel) but looking at the timing its down to 5 or 6 deg at the top of the revs, is this right ?
The other thing I noticed is the Atmos Pressure changes between 1016.4 and 1012 on a flat road, (is this relevant)
I can have another go on VAG COM but what should I be looking for.

Any advice welcomed

Thanks

[S2central.net]

Would be useful to try it with a borrowed set of fresh coilpacks to see if that produces different behaviour.

[Dingo]

That would be good if anyone nearby could help, but what about "the timing"
should it be that retarded at the top end ?

[Dingo]

Can anyone help ? is my ECU retarding the timing,
going to have another go on VAG COM, what approx figures sould I be seeing.

[Rusty]

What fuel are you running? I find the S2 can be quite sensitive (see Tesco 99 mentioned so that's fine).

What have you tested for boost leaks? You need to test the whole system, not just the IC.

Check the knock sensor bolt torque, this can be an issue. Also, try unplugging the sensors and see what happens, it will just run a safe map but if the problem still exists then it's more than likely a different sensor.

As per Paul's comments, some spare coil packs would be a good plan too.

Also, try a spare MAF if you can find one, they seem to be responsible for all sorts of crap on these cars, temp. senders too

That's a small change in atmospheric pressure, if it was dropping to 800 then you'd have an issue.

[Dingo]

Thanks Rusty, defo not a boost leak, I' ve tested it to death (the full system inc all the small lines) and just fitted samcos, it gets full boost all the time and the gauge needle never flutters, I'm looking for things that will reduce timing, I thought a Knock sens either worked or didnt,
Do you mean air temp sens, is that the one on the top of the IM,
am I barking up the wrong tree here, is it normal to only have 6 deg timing at high revs
Thanks

[prj]

Well, 6 degrees advance is definitely not normal.
You will only get 6 degrees advance in Motronic if you either get knock or your IAT is very high.

Check the IAT sensor, maybe it has gone bad?

[Dingo]

Thanks, at last I now know this isnt normal and it is retarding the timing, just dont know whats causing it.
Whats the IAT, is that air temp ?

[prj]

Intake Air Temperature.

[Rusty]

That's good, what it needs to be

IAT is on top of the intake manifold by the TB. Resistance vs. Temp curvo on SJM Auto. Same goes for the coolant temp sender at the back of the head. Not sure on MFTS.

Just going through what I know to see if anything pops out of the grey matter...

• Cam and crank sensors limit boost so guess they're not relevant.
• Altitude sensor also limits boost so "".
• Knock sensors retards timing initially then boost IIRC.
• IAT adjusts boost on ABY and timing in extreme cases.
• Temp sender may do the same (rear of head).
• N75 could be sticky / slow.
• DV might be leaking even if it's new (710N? Forge?)
• Small kink/blockage in MAP sensor hose. Try a length of spare hose routed where you can see it's not kinked.

[prj]

Knock sensors retards timing initially then boost IIRC.

No, knock sensors going off only retards timing. There are four main timing maps in the ECU (and one map for limp mode... but that is not happening here). Every time the ECU senses knock, it shifts to the next map "down", which has more conservative timing. After some time of not detecting knock, it shifts "up" to a map with more aggressive timing.
The only maps that have 6 degrees of timing under boost are the 3rd and 4th map... that would mean getting lots of knock...

IAT adjusts boost on ABY and timing in extreme cases.

Again, since the boost chip does not know anything about IAT boost is not affected here. Timing + fueling is always adjusted based on IAT, not only in extreme cases...

Temp sender may do the same (rear of head).

Head temp sensor adjusts timing, but only if that function is enabled. Most tuning software disables that function, I have no idea whether Paul's does that though... There is a certain 6x4 IATxHead Temp map for timing, but I think it's mostly to do with cat. converter heating.

N75 could be sticky / slow.
DV might be leaking even if it's new (710N? Forge?)
Small kink/blockage in MAP sensor hose. Try a length of spare hose routed where you can see it's not kinked.

All that would mean lower boost, but it doesn't seem that this is the issue here.

[Dingo]

Ok, I've just been out and measured the resistance across the IAT terminals and it was 499 ohms, engine was run a couple of hours ago, is this ok ?

[bigdan]

After checking the graph on s2central.net, 499 ohms would read about 25degC. Your best way of testing it is to remove the sensor and control it's temperature, then check its resistance. This way you know what it should read before you test it.

[prj]

If the car feels "dead" between 2000-4000 rpm, I would look into trying a different MAF and seeing whether the car gets more responsive.

[Dingo]

Ok, Thanks, will post in wanted section for a MAF, is there anything else that will cause the ECU to fully retard the timing ?