Gti6 Power Loss Troubleshooting

[randomspeedfreak 4]

So had my gti6 conversion on the road for a 6 months or so now. Recently, I have a consistent problem with the car, please have a read and offer your 2p if you can

 

Around a month ago the car started to cut out on part throttle, it would loose power for consistently around 5 seconds, as if it was fuel starved, then abruptly come back to normal power. If you applied full throttle quickly this would clear up, if you were driving quickly it would be fine (aside from a slight loss of overall power and torque,,,but thats only seat of pants test no rolling road to confirm) it feels like the car is lean when running - if you are flat out, then back off ever so slightly, it seems to richen slightly and not decelerate for a second

 

 

In addition to this it will do this when its sitting on idle, it would go lumpy, then drop to 3 cylinders, then 2, then one then cut, all over the space of around 20 seconds, when it does this you can hear the ICV hissing more and more as it gets closer to cutting. if you quickly apply enough throttle it saves it and it returns to idle for around 30 secs, then does the same again. If you slowly and gradually apply throttle it still dies, even if you get to full throttle

 

It would only do this after it was warmish, after the second sector on the temp gauge, when cold behaves fine

 

what i have done:

Tested and replaced green sensor - both sensors passed test, also same behavior with either

 

Performed fuel pressure test - consistent 2.2 bar spiking to 3 bar as it should be i gather,

 

tested throttle position sensor - results came out as they should between 0.6v and 4.93v

 

changed throttle body (maf and throttle position sensor) - seems to have more power and torque across the rev range,

 

tested map sensor - seemed to perform correctly, the sensor spiked voltage when manifold pressure changed sharply however cannot confirm if it isnt slightly out

 

Changed icv - the spare icv i changed to was obviously stuck, engine sat at about 3 krpm when this one was fitted. cleaned and replaced the original one, it idled lower at first, then didnt stall for a while, then returned to bad behavior

 

Points of note:

Lambda sensor is one installed by previous owner - it is a non oem one, and has had the wires cut and soldered at some point - I was planning on changing this anyway

 

Wiring loom: my wiring loom is currently a mess. I had trouble converting my phase 1 205 loom to work with my already butchered phase 2 205 to gti6 loom. all connections are properly done by me - heat shrinked etc, but i cant rule out that some wires havent fallen apart on the inside when disturbed

 

Engine is a tapper, may have some effect?

 

 

Any advice or ideas welcome

 

Cheers,

Matt

 

[dcc 855]

Might be the split in the downpipe collapsed. Could be the fpr. Could be fuel pump. I think these are meant to run 3bar, so seems like a fuel issue. Its not unheard of that the fuel lines are restricting flow if theyre old too.

[welshpug 1,677]

2.2 bar fuel on idle sounds about right as they have the vacuum pipe to the plenum, should be 3bar on wot.

 

there is no maf, guess you meant I.a.t sender?

 

try it with the lambda unplugged.

[randomspeedfreak 4]

Thanks for your replies gents,

 

Might be the split in the downpipe collapsed. Could be the fpr. Could be fuel pump. I think these are meant to run 3bar, so seems like a fuel issue. Its not unheard of that the fuel lines are restricting flow if theyre old too.

Could you please explain the split in the downpipe part? did you mean inside a fuel line? I agree seems fuel pressure or fuel delivery related... however the fact it only happens on part throttle has led me to believe that it isnt a fuel line blockage? would have thought that at a higher throttle opening, the required fuel flow rate would be greater, and therefore the problem worse?

 

2.2 bar fuel on idle sounds about right as they have the vacuum pipe to the plenum, should be 3bar on wot.

there is no maf, guess you meant I.a.t sender?

try it with the lambda unplugged.

 

This is the result i got running a fuel pressure gauge in parallel to the line. I will repeat the test for clarity but im sure it was a pass.

 

yes my apologies, I ment the air temp sensor

 

When I unplugged lambda it idled correctly, fuel consumption increased as expected, it is clearly running richer. Although it no longer stalls, I couldnt confirm that this was the cause of the issue, just that it had enriched the mixture enough to avoid the symptoms. I now realize didnt actually drive it with it lambda unplugged. I will try this on the way home and see if it solves the power loss when driving issue...would your money be on that as the culprit then?

 

Thanks again for the help guys

Edited March 2, 2015 by randomspeedfreak

[welshpug 1,677]

its possible, the symptoms do point towards somethign altering the fuelling drastically after it warms up, the lambda is only used once the car reaches normal operating temperature.

 

It does appear that lambda wiring does not take to being soldered typically, cutting the joint out and adding some quality crimps might fix it, you need to pay an extra little bit to get a direct fit Lambda rather than one without a plug sometimes.

[randomspeedfreak 4]

ok ill get a new lambda to start with

 

This morning the car stuttered badly whilst cold! GRRRRR!

 

maybe this is a combination of multiple problems?

 

Will try with lambda disconnected now

 

Thanks again,

Matt

[jackherer 543]

 

It does appear that lambda wiring does not take to being soldered typically,

 

Lambda sensors need to draw fresh reference air via the wiring and soldering prevents that.

[camgti 56]

Exact symptoms of mine.

 

Replaced and tried all the things you have done.

 

Changes the lambda to an OEM one and its perfect.

 

Definitly change it. Or drive the car with it unplugged.

 

Unplug it, disconnect battery to reset the ecu and try that.

 

All pointing to Lambda.

 

Cam

Edited March 5, 2015 by camgti

[macaroni 17 1 Cars]

Another vote for lambda sensor, exact same symptoms as mine, cured by a new lambda.

[randomspeedfreak 4]

Ok thanks guys, bosch lambda arrived today, will fit tomorrow and report back - car has been behaving well (if a little thirsty!) with lambda unplugged so all signs point to that i have my hopes up

 

Cheers gents,

Matt

[randomspeedfreak 4]

Lambda fitted, problem solved! more power and torque across the rev range! no stalling! better fuel economy!

 

thanks a million for your help gents, cracking forum

 

Cheers,

Matt ​

[camgti 56]

Great news!