Gti6 Major Hesitation Under Load

[James_K 6 1 Cars]

I have a lynx supercharged 205 gti6 that until recently ran perfectly. However, recently it has developed a major hesitation issue at low revs when under load.

It idles perfectly and I can drive off from my house (downhill) without any problems. As soon as I turn around and try to go back up the hill it loses power, then regains it in a very jerky way and sometimes misfires. It's almost undriveable. Over 3000rpm its ok again but its difficult to get to that point.

 

The problem started as a very occasional misfire and has got worse and worse.

So far I've changed the coils, lambda sensor and vss, all of which made no difference. I had a look at the spark plugs and they seem fine.

I've also hooked it up to Peugeot planet. There are no faults recorded and the throttle position sensor seems to be working fine.

 

I'm at a loss for what to do next, does anyone have any suggestions? I guess the fuel pump isnt at fault given that over 3000rpm its ok, but I don't know what else to test/swap.

Any suggestions would be welcome.

 

Thanks

[TAG 25 1 Cars]

A faulty VSS on the speedo drive will make a gti6 jerk like mad at about 1500 revs when pulling away I've found.

[dcc 855]

Have you swapped spark plugs yet James

[James_K 6 1 Cars]

Tom, vss was what I first suspected, but changing it made no difference.

 

Dan, no I haven't changed the plugs yet, just ordered some (not cheap for the sc). If it's not that, I'll be back to the drawing board.

 

Thanks both

[dcc 855]

if it isnt that then its compression check time, have you got a cat? and is your downpipe one with a split? have got you a boost reading? is the engine seeing proper boost levels? or even too much boost? have you noticed any increase in temp? is water boiling over at all? is oil nice and clean and no mayo/creamyness?

 

if all above is ok then start looking at what controls the spark and fuel. so coils breaking down, fuel pump relays, poor earth, etc... what voltage is your alternator charging at when it misfires? do you have e pas?

[James_K 6 1 Cars]

Good points there, thanks Dan. There's no cat and the oil looks good, I can't answer for the level of boost other than it pulls very well.

As you say a compression check is the next logical step.

 

what's the easiest way to disable spark and fuel for this?

[welshpug 1,657]

pull the double relay or crank sensor

[camgti 56]

What about O2 sensor?

[James_K 6 1 Cars]

So I did a compression test this morning and the results weren't good to say the least..

I warmed the car up, took out the plugs etc. and tested the cylinder nearest the cam belt, it read 50 psi!

I immediately thought I must be doing something wrong, so checked for any air leakage and went again, still no change.

The other 3 cylinders read 75psi consistently, I tested them more than once, and I dropped a capful of oil into one of them and did a retest where it achieved 125psi.

As these readings are so far off the mark, I guess the engine is scrap? Seems odd for all cylinders to be that low, but what do I know.

I'm a bit gutted, until very recently it was running fine, still starts and idles ok too, not that it helps.

[dcc 855]

It generally is just a gauge of how healthy the engine is, you'd want them to be withing about 5% of each other. But afaik a gti6 should show closer to 200. So, as these are compwrative figure first step is to check the timing is bang on. Fairly easy to do, if you need a hand drop me a text

[welshpug 1,657]

throttle not open I'd imagine with those numbers

 

closest to the timing belt is most common to leak the headgasket

[James_K 6 1 Cars]

WP - I thought at the time that the throttle might be restricted due to having to go through the supercharger, even though I had it open, so I just disconnected the inlet pipe going into the manifold to bypass the throttle and sc altogether. That should have been ok?

 

Cheers Dan, I'm close to giving up on this car, so any help is welcome

[welshpug 1,657]

ah so no throttle restriction but atill spinning a charger

[James_K 6 1 Cars]

Spinning the sc wouldnt account for 100+psi loss in the test though, would it?

[James_K 6 1 Cars]

This morning I checked the timing and all seemed fine, so as a last resort I changed the map sensor and the problem immediately disappeared!

 

So for anyone with similar symptoms (idle fine but massive hesitation and misfire at low revs under load) the map sensor 'might' be the cause..