engine hesitation and huge backfires - any ideas??

Adam.p.s

Active Member
Jul 16, 2015
20
3
update on this:

performed boost leak test, heard hissing and took a while but eventually traced it back to the MAP sensor... took it out and found this:

20220204_143125.jpg
20220204_142849.jpg


the o ring wasn't sealing as it was the wrong size so it was PTFE taped - this was not sealing and leaking, also the actual sensor itself has been blown to bits - the crack at the front was like a flap lol.

replaced it and ran the car - heard the diverter valve for the 1st time... however still went into limp after a boosting fully.

getting closer - at least it doesn't backfire anymore..

friend suggested the car needed to be run for a while and right up to temperature before limp may go away but sceptical - is that a thing??

thanks

Adam
 

300bhpdaily

Active Member
May 26, 2020
1,250
571
Since you’ve owned the car has it ever actually been on the road and been driving without being in limp mode. The problem you have isn’t going to be solved by asking for help from others who haven’t seen the car unfortunately your going to have to spend your time to investigate what’s happened to it.
 

Adam.p.s

Active Member
Jul 16, 2015
20
3
I've been driving the car the whole time. i came here for advice from like minded people who may have advice or experience of the issues before and to help others if they experience what i have.

i have a friend who owns his own garage and have been there using his diagnostics and advice.

i clearly am spending my time investigating it.

do you have any helpful advice?

thanks

Adam
 
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300bhpdaily

Active Member
May 26, 2020
1,250
571
I've been driving the car the whole time. i came here for advice from like minded people who may have advice or experience of the issues before and to help others if they experience what i have.

i have a friend who owns his own garage and have been there using his diagnostics and advice.

i
I've been driving the car the whole time. i came here for advice from like minded people who may have advice or experience of the issues before and to help others if they experience what i have.

i have a friend who owns his own garage and have been there using his diagnostics and advice.

i clearly am spending my time investigating it.

do you have any helpful advice?

thanks

Adam
Yes check your boost pipes and joiners from the start to finish for leaks including intercooler,DV and pcv as you have a pressure drop like you’ve mentioned in your post. Remove and inspect every boost pipe for damage and check the intercooler hasn’t got a hole in it by leak testing the whole system again.
 

Adam.p.s

Active Member
Jul 16, 2015
20
3
unfortunately I'm based in oxford... thanks for the offer - I've pretty much changed all the expensive stuff now though lol :p

gave the car a good run yesterday and read codes, the original ones have gone and now i get:

"00564 boost pressure regulation limit exceeded (over boost condition) P0234 upper limit reached"

looking on ross tech:

Possible Causes​

  • Hoses incorrectly connected, disconnected, blocked or leaking
  • Boost Pressure Control Valve (N75) faulty
  • Boost Pressure Sensor (G31) faulty
  • Turbo Charger stuck/faulty

Possible Solutions​

  • Check Charge Pressure Control System
    • Perform Output Test (to check the Turbo Charger)
    • Perform Basic Setting (to check the Charge Pressure Control)
    • Perform Pressure Test to locate Leaks
  • Check/Replace Boost Pressure Control Valve (N75)
  • Check/Replace Boost Pressure Sensor (G31)
  • Check/Replace Turbo Charger

I've just replaced the MAP g31 sensor so ruling that out, the turbo is new (receipt and visually looks new) so think likely i have another smaller leak somewhere or a bad n75 valve.

getting closer!
 

R3k1355

Active Member
Oct 30, 2014
1,794
252
Yorkshire
The N75 on these, it's abit buried in the engine isn't it? If so I'd check the vac hoses that go to it first.

If a previous owner has done some dodgy work to the MAP then it's quite possible they've damaged other stuff too, and little vac lines are easy to split if yanked on too hard.
 

Adam.p.s

Active Member
Jul 16, 2015
20
3
Good morning all! update on this...

I've managed to boost leak check from post turbo onwards and now have no leaks and the system holds pressure. however pre turbo was not possible because of the oval air hose connecting the air box... so... i bought a ramair induction kit (as it was on the list anyway) that allowed me to pressurise PRE-turbo, now it wont hold pressure. i found a leak coming form the dip stick tube, i.e the crankcase is pressurising.

so my question now is how is the turbo pressuring the crankcase but connecting just after it doesn't?

is there another part of the PCV system that i cant see??

thanks

Adam
 

Adam.p.s

Active Member
Jul 16, 2015
20
3
another update:

removed and fitted a PCV blanking kit from X8R. - no change.
performed a compression check on all cylinders - 165,155,165,165psi so less than 10% variation across

inspected N75 valve hoses - no damage or cracks.

last action form ross tech list is to change the N75 valve, so wish me and my hands luck...
 

Adam.p.s

Active Member
Jul 16, 2015
20
3
final update.

ITS FINALLY FIXED!!!

it was indeed the N75 valve, totally transformed the car, even sounds different! so in summary, and what I have learned through this:

if you have any issue, even if it seemed like mine to be an ignition fault etc, do the simple (free) tests 1st! - boost leak check - this was 70% of the problem. i found two MAJOR leaks as previously described. (an incomplete weld on a boost pipe (still puzzles me) and a blown MAP sensor)

this cleared my P1297 and P1093 codes.

i was then left with the P0234 code and after another boost leak check and compression check (also free) ruled out boost leaks, this left the N75 as the only part not changed (apart from a new turbo..).

changing the N75 was time consuming and fiddly but not as bad as i was expecting. if it helps see following:

tools needed:
decent torch!
a 1/4 socket set with long reach extensions AN ABSOLUTE MUST HAVE FOR THIS!
torx bits for the N75 screws holding it on
small jubilee clips
tools to relax / break the original clips - THESE WERE THE HARDEST PART - i used a pair of welding wire cutters to mangle them off with various other screw drivers and a adjustable pipe wrench.

process:
jack up turbo side (drivers UK) and secure on axle stand (you need 70% access from under and 30% from above
remove turbo boost pipe and lower boost pipe from underneath
remove induction kit / air filer housing, MAF cable and pipe from coolant reservoir for clearer access
release the P.I.T.A clips as described and release all 3 small pipes from above and below for access
unscrew torx and remove N75

reverse for installation, use new jubilee clips to secure

thanks anyone who helped or gave advice.

cheers, Adam
 
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