Results of the compression test - near enough spot-on 12 bar (170-175psi) across all cylinders :-)

I now have a spare AFM courtesy of h_gt which can be tried once I get it posted down...!

Made a video of the issue which I'll figure out how to upload shortly...!

Unfortunately the video was pretty poor and wasn't easy to see the prob.

Changed the AFM, no difference. Tomorrow the inlet and all associated bits come off! Hope to find the issue... perhaps a seeping inlet gasket or something.

New symptom is that for the first minute or so from -cold- start the problem isn't really there or is almost unnoticable. I'm thinking the extra fuel at this stage of the engine warm-up is helping. Would also make sense as disconnecting the blue temp sender has the same effect. I'm pretty sure though that the temp sender is ok.

Fitted new Bosch lambda - no change symptom still present. Removed swapped it back for the old one to stop any excess fuel from misfires killing it.

Now I really really really am out of ideas.

Vag-com doesn't connect to the car, will try with another laptop tonight.

Have only checked ~80% of the loom, but have checked the most of the connections from the engine sensors to the ECU connector. So need to check the remaining 20%.

ECU - this common to go wrong in this manor?

Fuel pressure - is it likely that a weak lift pump could do this? Is it likely for the lift pump to be weak?

Fuel filter clogged, even though it was changed 4 months ago?

My brain is convinced that it's mixture-related but may have 'tunnel vision' on the problem. But it appears that during the first minute from cold there is no issue (during the cold-start enrichment) and when the blue temp sendor is disconnected (diagnostic/limp home mode).

Shortly I'll either torch the b*stard or call out a mobile mechanic. It's about 50/50 at this point.

Any suggestions greatly appreciated chaps/chapesses.

Edited 3 June, 200917 yr by cheys03

bumpy wump

Could this be back-pressure related? I'm still running the normal SPI exhaust and manifold?

Took the car to the mechanic's garage on Saturday...

Seem to know his stuff, owns a Scirocco GTX (Bosch K-jet?) himself.

Confirmed that it is a low-load misfire. He doesn't think it's fueling-related.

Hooked up his bounce-proof VAG-com which showed realistic value for all sensors.

However the ignition timing was mad! Standard chip. It had a value of between -3 at idle and -215 degrees under throttle. Obviously -215* (is this retarded of advanced?) is impossible and will just max out at whatever it is actually capable of. Anyone with a GT know what the typical value are?

This would make sense as when the blue coolant sensor is unplugged (i.e. when ECU igniton timing timing is fixed) the issue seems to go away. What on earth could cause this? I will be stripping and double-checking the loom, especially where I have mated the GT engine loom and the other SPI engine bay (lighting and that other one?). Perhaps too low a cross-section wire could be delaying signals etc.

Could the ECU be faulty exhibiting this symptom?

I keep rolling the cam and dizzy timing around in my mind but I think it's fine.

The mechanic was also talking about checking the dizzy at TDC to see where the hall sender was in relation to the 'window' in the rotating wheel. Does anyone know what he could have been on about? It was a bit over my head at the time..!

Cheers

If you remove the dizzy CAP, so undo the two clips you will be able to see the rotor arm. If you look into the dizzy you will see a notch cut out, the arm should be central to this. I think thats what he means, sounds like he knows his stuff to me.

If you remove the dizzy CAP, so undo the two clips you will be able to see the rotor arm. If you look into the dizzy you will see a notch cut out, the arm should be central to this. I think thats what he means, sounds like he knows his stuff to me.

Thanks Carver, just to confirm...

At TDC the rotor arm should point to the middle of a window in the dizzy wheel?

Can anyone shed light on the weird ECU timing readings? Does -3 degrees on VAGCOM mean advanced 3 degrees or retarded 3 degrees?

I think from Hayesey's Vagcom FAQ on PoloG40, the ignition advance units is in degress BTDC (i.e. advance) so a 3 = advance and -3 = retarded?

How much can the ECU actually advance or retard the timing as a max?

Also confirmed today that with the blue temp sender removed the misfire is much much better, but not completely gone.

Am I using the right plugs?

NGK BUR6ET

NGK website says I am, as did the Helfrauds 'pick your spark plug' sheet, but I've seen Bosch W6DTC / NGK BP6ET's mentioned here too.

What affect would the wrong plugs have?

Thanks

Edit: have tried converting the Champion NGBYC that the Haynes manual lists without sucess. Also VW can only give me the VW part number for the plug, not the Bosch or NGK code.

Edited 11 June, 200917 yr by cheys03

Change the ECU and see if it still exists.

As a general rule - If it starts going pear shaped then put everything back to standard and go from there. So hard to diagnose an issue when you have a frankenstein engine.

EDIT - Your plugs are fine.

Edited 11 June, 200917 yr by GiorgioGT

Yeah, agreed. SPI is looming.

To change back though I require some fuel lines, coolant, SPI dizzy, so avoiding it for now....July 9th is the change-back date though!

Will check the loom carefully to make sure it won't damage the new ECU, then chuck on the new ECU.

Thanks for the info Georgio, do you know what the difference between the NGK BUR6ET and BP6ET plugs is? Is one three-prong and one single-pronged?

Cheers

If you remove the dizzy CAP, so undo the two clips you will be able to see the rotor arm. If you look into the dizzy you will see a notch cut out, the arm should be central to this. I think thats what he means, sounds like he knows his stuff to me.

Thanks Carver, just to confirm...

At TDC the rotor arm should point to the middle of a window in the dizzy wheel?

Can anyone shed light on the weird ECU timing readings? Does -3 degrees on VAGCOM mean advanced 3 degrees or retarded 3 degrees?

I think from Hayesey's Vagcom FAQ on PoloG40, the ignition advance units is in degress BTDC (i.e. advance) so a 3 = advance and -3 = retarded?

How much can the ECU actually advance or retard the timing as a max?

Also confirmed today that with the blue temp sender removed the misfire is much much better, but not completely gone.

Yeah if you take the cap off you will see what i mean, although i doubt thats your problem. I've had mine miles out once and it did 78 faultless miles until I did the timing

I would check the loom like you say, carn't remember if you said or not but have you done anything with the AFM? That can affect idle quite alot.

EDIT - When you un plug the blue temp sensor do the revs go up or down?

I have an afm you can buy if your wanting to try another, its still got the blue sticker over the adjustment so its not been tinkered with and worked perfectly on my GT when it was standard and my 1.6 (Havn't altered the settings myself btw)

Edited 11 June, 200917 yr by carver

Yeah I'm skeptical the dizzy timing could be causing the issue too...!

AFM has been replaced for another (used) unit with the bypass-screw untampered (at least it looks untampered). No difference

Loom comes out tonight! Yaaaaaaaaaaay (!)

When you un plug the blue temp sensor do the revs go up or down? I had an air leak after I put my recent 1.6 in and it was leaking between the ISV and manifold causing a type of hickup, also when unplugging the blue sensor the revs wen't down. They should go UP.

Eak! Quick post/edit getting in a muddle :-)

I think the revs go up with blue temp sendor disconnected, will confirm tonight. I've removed everything inlet port-back from the car are carefully examined for air leaks. Ran some more carb cleaner through the ISV at the same time.

Still don't understand the Vag-com ECU weird ignition timing of -215 degrees...!

I stripped out and very carefully and thoroughly checked the loom - all is well.

Re-did a couple of suspect solders.

Replaced loom with old ECU - still problem.

Repalced ECU - still problem.

ARGH!

Forgot to check the blue temp sendor unplugged revs up/down but am fairly certain they go up. Also as mentioned have had the whole setup off and carefully check for leaks with none found.

Really am out of ideas now.

The only thing I can think is the in-tank pump (it's the original) or the fuel lines are restrictive.

....heeeeeelllllp!

I again suspected an air leak after seeing Carver's post on this thread (http://www.clubpolo.co.uk/forum/index.php?showtopic=150797) about the engine dying if the idle control screw is all the way in.

If mine was all the way in the engine did run, but lumpily at ~700rpm.

Found that the small butteryfly on the throttle body was a whisker still open on idle...the linkage was hitting the adjustable stopper bolt a fraction too early.

This was corrected and indeed the engine does now die with the idle screw all the way in. I guess this proves there's no air leak.

However, it's not solved the misfire

Looked again at the spark plugs condition and got a second opinion. The thought is definately that the engine is running slightly weak. (The central white insulators are crisp white and not biscuity as the old AAV plugs were).

Running the car with the blue temp sender unplugged for a couple of miles leaves the plugs very black and sooty, but the misfire is for all intents and purposes gone. Also, adjusting the AFM-bypass bolt either way does not change the symptom on the old AFM.

Could weak fuel delivery from a poor in-tank pump or partially blocked filter cause misfires at low load? The car revs high easily and reaching 90mph is no problem - car doesn't complain as (with limited understanding) I would expect it to if there was insufficent fuel....

If you were closer I would come look at it for you, I carn't really think of anything else mate.

I wouldnt have thought weak fuel delivery would be the cause, when i got my GT the filter had xx.xx.92 stamped on it and it ran fine.

Carver, you are a generous man! Thanks for the thought :-) I may yet drive up to you with a boot of beer!

Given I have a FrankenGT, a few of things have occured...

1. Can be Throttle Position Sensor be mounted in more than one postition? Or is the shaft keyed to prevent this?

2. I have a spare standard AFM. Is it possible to play with this in order to indirectly adjust fueling?

3. If I reduced the voltage the lambda was sending to the ECU (i.e mixture weak) using a variable resistor, could this be an option the force the ECU to open the injectors for longer?

Cheers :-)

Edited 22 June, 200917 yr by cheys03

i doubt the fuel pumps are an issue, as you say with blue CTS removed the plug foul up with too much fuel, so the system can deliver enough fuel to foul the plugs with soot.

i have a similar issue, stutters under heavy loading, not high revs, but heavy loading. as yet not changed anything tho as its literally just started

Ha no worries, its how a club should be mate.

I wouldn't like to try option 3 if I'am honest, could really mess things up.

Just a thought but they are defo GT injectors on the rail arn't they?

Fairly certain they are. Also tried a second set from a GT too.

Mk2 Golf GTI injectors will be massive overkill I guess?

Yeah they are, I'm using them on my 1.6 GT and they are rich even on that.

Fuel regulator is okay isn't it? Vac pipe goes from there to the other side of the throttle body.

One on the front can be blocked off.

Edited 23 June, 200917 yr by carver

run a bottle of STP through it, fuel injector cleaner, generally if there's any miniscule crap in the lines, that'll clean it out.

the - means before tdc, so -3 is 3deg before, the spark event rarely happens after tdc. -200odd deg does sound nuts although vagcom does seem unable to properly decode some of the values from gt/g40 digifant one example is the inlet air temp on a g40 which is usually decoded as about -20deg c !! obviously not right.. Although for me, the ignition advance figures do seem sensible from logs I've done.

If you suspect the ignition timing is knackered then it could be down to the hall sender in the dizzy.