engine hesitation and huge backfires - any ideas??

[Adam.p.s]

Hi all,



New to the forum and am requesting help diagnosing an issue with my K1.



Under light throttle, i.e normal driving, the car hesitates, some times bucking and always lets out a massive backfire (not a pop – a huge BANG backfire) with WOT it drives OK and while reasonably powerful a friend did comment saying the power is nowhere near stage 2…



I tried getting it remapped as I assumed it had a (really bad) pop and bang map, however this didn’t do anything.



I then investigated the hpfp follower and cam – the cam looked fine and the follower was also in good condition – however when I went to release the pressure by depressing the Schrader valve there was none (? is that usual?) im assuming the pump is ok as the problem is low throttle - surely if the pump was at fault it would get worse higher in the rev range?



I then replaced spark plugs, coil packs and a revision G diverter valve – ran slightly better as plugs were well worn but problem still persisted.



Right now I am trying out a new ECU/ECM as the engine codes cannot be read – again we assumed pointing towards a bad ECU/ECM



The car has previously had injectors replaced so ruling that out for now – any ideas? Don’t know what to try after ECM.. I’m also averaging 22.5 mpg which seems really low considering I’m not driving it quickly at all…

any help or advice as you can imagine is most appreciated - I've been scouring the site for a couple weeks now..

thanks

Adam

 

[Kenan]

When you got it remapped did the garage not look into the problem while you were there?

Mine was missfiring, new injectors and a walnut clean sorted it out.

Sent from my M2007J20CG using Tapatalk

 

[Adam.p.s]

When you got it remapped did the garage not look into the problem while you were there?

Mine was missfiring, new injectors and a walnut clean sorted it out.

Sent from my M2007J20CG using Tapatalk

no as i mentioned i said its got a pop bang map on and that i wanted it off thinking that was the problem. the mapper was a mobile one and he did say he also had trouble getting into the ECU..

when yours was misfiring di it also bog down under light throttle? ive ruled out injector for now as they were changed in 2018...

confused.com!

 

[Woody_72]

Have you had the timing checked?

 

[Adam.p.s]

Have you had the timing checked?

no but may be my next step - would that cause this? car still makes good power, surely if timing was off it would run terrible?? (i.e much worse..)

 

[Kenan]

no as i mentioned i said its got a pop bang map on and that i wanted it off thinking that was the problem. the mapper was a mobile one and he did say he also had trouble getting into the ECU..

when yours was misfiring di it also bog down under light throttle? ive ruled out injector for now as they were changed in 2018...

confused.com!

Mine was like it from when I got it, would be rough at idle untill warm and would feel like it was holding back a little. When it was plugged in the missfires were registering.

Sent from my M2007J20CG using Tapatalk

 

[Kenan]

Would be worth getting the codes read if there are any

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[Adam.p.s]

Would be worth getting the codes read if there are any

Sent from my M2007J20CG using Tapatalk

no codes and cant access the ECM

 

[R3k1355]

Sounds like you had some right cowboys map your car, any half decent tuner should refuse to map a car running like crap without understanding why.

Guessing at a previous bad map isn't good enough.

 

[Adam.p.s]

update on this:

fitted a new (de-immobilised) ECU - problem still present, however we can now read engine codes. the following were logged:

04759 - pressure drop between turbo and throttle valve (check D.V.!) P1297 lower limit reached.
04243 - Bank 1 fuel measuring system 2 malfunction P1093 not a plausible signal - intermittent.

from a quick look online I'm suspecting HPFP although as stated previously i checked cam and follower and look good - what / how else does the HPFP fail?

 

[Adam.p.s]

update#2 on this:

fitted a new HPFP - the shaft was extremely wobbly so was convinced this was the issue however it was not...

performed a boost leak check but before i could i noticed a section on a joiner that was not welded and could see oil coming out (massive hole) from it so i welded this up. again, convinced THIS was the issue but again no joy.

if all codes are cleared the car flies for one pull then goes into a limp mode, if this is cleared it works again for another pull, etc etc

will scan for codes in the week again, then look for other boost leaks.

any ideas if any sensors could be playing up? N75 valve problem?

thanks

Adam

 

[R3k1355]

How did you perform the boost leak check?

Have you had the throttle body off to inspect it? Could be the gasket for that.
What about the diverter valve, replaced it?

 

[Adam.p.s]

i haven't yet actually performed a boost leak as it was so apparent i had a massive one on that pipe!

not looked at throttle body - is that common?

diverter valve replaced yes

 

[R3k1355]

not looked at throttle body - is that common?

If someone's had it off before and not put it back on with a fresh gasket or forgotten it alltogether than yea it could leak.

You could find something else wrong with it when you have it off as well.

 

[Adam.p.s]

"You could find something else wrong with it when you have it off as well"

anything in particular? sounds like a comment from experience??

 

[R3k1355]

Not on a Leon but seen plenty on other stuff. Vaccum lines missing, or perished, or with a bolt rammed in the end of it. Even had the throttle stop/adjuster missing entirely.

Have you considered gunk on the inlet valves as well? Not sure if it was as much of a problem on this engine?

 

[Adam.p.s]

i have but have initially dismissed it as, 1. the engine was rebuilt so imagine it would of been done (although tbh not so sure now) and 2. it works fine until it has boosted then goes into limp.

i will continue with the boost leak check and report findings.

injectors and walnut clean are next step i guess but costly if not needed...

 

[R3k1355]

Cheap boroscope might be a better idea, shove it down the inlet manifold and look at the back of the valves.

Can get em on eBay for about a tenner

 

[Adam.p.s]

yes exactly - I'm still getting the same codes: P1297 and P1093 so as mentioned will perform boost leak check when i can..

previously i actually said "performed a boost leak check but before i could i noticed a section on a joiner that was not welded and could see oil coming out (massive hole) from it so i welded this up. again, convinced THIS was the issue but again no joy."

i thought the engine only used a MAF sensor? i thought MAP was generally used on older and jap stuff?

thanks for your help..

 

[R3k1355]

Nah MAF & MAP is pretty common.