[Mk2] [Turbo] Jerky revs overfuling back fire, faulty lambda??

[petemr2]

Right i have a rev 2 turbo rebuilt engine by me done 1500 superb miles no faults untill the other night drove fine for around ten mins went to give it some beans down duel carrageway boosted great then sounded like it was blowing the spark out.

pulled over every time i reved it, it was coughing an jerky as hell then when i tried to drive it was well jerky an everytime hit boost it would back fire. turned it off an was a b1tch to start seemed to flood it self.

instantly i thought knock sensor but no error code no boost leaks had all the pipes off an everything seemed fine.
It has new plugs when engine was built an leads rotor arm cap etc.
took home switched off for ten mins then went out again an it was perfect then when i left my mates after 10 mins driving it started to miss under boost again but only very slightly not half as bad as before.

Took it out the next night an it did not miss a beat an got a good pipe cleaner. lol!
The following night took it out an driving towards bp blew spark out im guessing as just died tottaly wouldnt start at all, although had mega spark off the coil but had
completely flooded it self got towed home an yeah you know it fired straight up lol!! but had a miss if u opened the throtle up rapidly on the spot.

gt rather annoyed left for two weeks an now got the enthusiasm to fix it again lol!!
ive changed the dizzy an before i did i checked ignition timing it was spot on.
it started fine but if u flick the throttle body wide open standing at the engine same as pushing the thottle straight to the floor it coughs once as it revs an produces some black smoke.

i pulled the air flow metre it stalled an threw an error code i pulled the knock sensor it threw a code all whilst running then i pulled the lambda sensor no change in engine behavior and no error code??
could this sensor cause it to behave this way?
Kinda running out of ideas..... what am i missing?

[sjm1984]

Dead lambda sensor i would of though

Stock managment right?

[petemr2]

yes mate stock managment.
and i thought this but as ive never had one go i was unsure of what problems to the engine they would give?
and why no error light?

[sjm1984]

have you popped the plugs out and looked at the condition? what plugs are they?

[petemr2]

they are grade 7s ngk coppers gt em off ebay prob a faulty batch no doubt.
i do need to pull them again but just when it started they were a tan colour

[JJ]

Hi Pete,

Couple of things to check... sounds like an ignition issue or and air flow meter issue.

Plugs > Pull the spark plug leads off, check that theres no residual of water built up in the plug well..

King lead > This is the lead that goes from the distributer to the coil pack... take it off at the coil end and heres the difficult bit, inspect the coil insert .. it often corrodes / tarnishes in there and causes an overall difficiency in the spark .. difficult to get to but worth a look in, clean up and WD40 it... ! ( likely cause = explain the problems you're having )

Faulty AFM > This is a ballache to diagnose.. I had one that was dieing once... never threw an error code, but would cause running problems... I'd be on the side of the road full throttling it just for it to idle... then after a few moments, would come back to life....

Randomly, check for split hoses too.. I know these are often obvious, but check where they're clamped .. if on boost, the demand for air is high, ( AFM wide open ) but its leaking somewhere.. then the fuel / air ratio is wrong, hence could be running too rich on boost... and bogging down / misfiring !

Couple of things to look at that shouldn't be painful to the pocket.

JJ

[petemr2]

Thanks for your input jj.
I will double check every clamp later I know it isnt A vac line as I double checked these yesterday.
I then took it out an Does seem to overfuel and black smoke when u feather the throttle on boost slighty mainly in high gears such as 4 th.

It doesn't do it everytime tho which is rather annoying lol!!
The coil is about 2 year old but I'll whip it off an clean it up.
I tested the lambda as by bgb an I fluctuates fine so I'm guessing it must be working even though it did not throw an error code which Is strange.

I had feeling it could be the airflow mete as when it first went and how jerky the car was an all the backfiring. An I remember someone else's going around Here an there car behaving similar.

Have see if someone has a spare I could buy or borrow??? to test it out as thats the one part I don't have two of typical

[Shmed]

I have an afm you can try before you buy if you want? It worked fine on my car (before I did the rev 3 conversion). If you cover the postage I'll send it you. If it works, you can have it for £30 if you want, if it isn't the problem, just send it back to me.

I'm sure you already know this as you built your engine, but the coil is a pita to get to.

[djpkins]

I had a very similar problem...it turned out to be fatigued IC hoses, they were full of tiny little cracks and when they got hot and boost was sufficient...they ballooned and leaked out air causing overfuelling, misfire on boost and bogging down...I replaced the last of them the other day with silicone hose...now I can't boost over 1 bar cos it leaks a bit, even though it seemed as tight as it could be, it's leaking under full boost...I will seal it on with high temp silicone later on today as this seems to work a treat with all the other joints...I have also sealed my king lead to the coil with silicone...to prevent possible moisture build up in the connector reccess

[petemr2]

Thanks for your input guys an yes I know the coil can be a pain but I've had alot worse lol!!
I'll definitely take you up on your airflow meter offer!! Thanks alot for that I'll pm you my address let me know how much for postage

The one other thing I will change is the coolant temp sender after everything else although tested an seemed to be wrking fine.

I was thinking of breaking the car but can't bring my self to do it lol!

[petemr2]

Right Sunday checked plugs outsides where bit sooty but other then that electrode was tanned so all good.
I changed a clamp on the throttle body ic hose an forgot to say it has all silicone hoses as gt a diff intercooler and whacked the air flow meter with an extension bar an believe it or not it went like a dream lol!!

I'm always against the "if in dout give it a clout" lol!! But seemed to have worked for now.

Just got back with my mrs an she has not been in the car since I ran it in an set the the hks evc up for a bar we went out burried the throttle in second and third an it shot her back in the seat an she screamed lmao!!
She took it for a blast an now can't keep her out of it she now wants one lol!

I have been kindly lent another airflow meter which I shall swap at the wkend to see if it makes a difference
I also machine buffed it over as been in a shed for two years and it's now deep red again an theres no more pink.
Glad I didn't break it now