Hi all,

Hoping someone can help — I’ve been chasing a non-start issue on my Hyundai (2.5 CRDi) and I’m at the point where I’d really value some experienced input.

Background / History

• Engine rebuilt Aug 2023 (head skim + rebore after blown head gasket)
• Ran well initially
• Mid-2024 started to get:
  • occasional loss of power
  • intermittent smoke
  • would recover and drive normally
• Nov 2024 (after bodywork repair):
  • car wouldn’t start properly
  • initially assumed flat battery
• AA attended:
  • got it to fire briefly on easy start
  • only after tapping around EGR/throttle area

Known issue found

• Found a bad earth (painted over after body repair)
• Cleaned it back to metal

After fixing:

• car started first time
• ran fine for ~20 minutes

Failure event

• Drove approx 20 metres
• As gearbox changed into 2nd → engine cut out
• Since then → won’t start

Work carried out since

• Replaced cam sensor + wiring previously
• Replaced crank sensor
• Replaced engine coolant temperature sensor (was reading ~600°C when cold)
• Battery fully charged / jump support used
• Fuel system primed and bled (manual primer goes rock hard and holds)

Live data while cranking

• ~190–204 rpm cranking

Rail pressure behaviour varies:

Sometimes:

• ~3000–4400 psi
• engine splutters / shudders
• smells like fuel (so injection happening)

Other times:

• very low pressure (~50–300 psi)
• no attempt to fire

Intake / EGR observations

• Located throttle body (flap confirmed open)
• Located EGR valve
• EGR feeds directly into intake near throttle body
• Some oil/carbon present in intake (not excessive)

EGR test

• Unplugged EGR:
  • rail pressure dropped to ~100 psi
  • no attempt to fire
• Plugged back in:
  • pressure returned (~2000–4000 psi)
  • engine splutters again

Unplugging EGR appears to affect rail pressure behaviour

Fault codes

• P0405 – EGR sensor low
• P0489 – EGR control circuit low
• P0532 – A/C pressure sensor low

(P0405/P0489 appear when EGR unplugged)

Additional note

• Previously had P0685 (ECM/PCM relay circuit)
• Removed and re-seated relays in fuse box
• Code has not returned since

Current symptoms

• Cranks strongly (~200 rpm)
• When pressure builds:
  • splutters / shakes / almost fires
• Will not start or run
• No sustained combustion

Current thinking

Trying to determine if this is one issue or two:

Possibility 1:

• EGR stuck open / leaking
  • would explain splutter / no combustion
  • matches earlier “tap and it fired” behaviour

Possibility 2:

• Fuel pressure instability
  • inconsistent rail pressure between cranks
  • possible air in system or pressure bleeding off

Possibility 3:

• Electrical / wiring interaction
  • EGR unplugging affects rail pressure behaviour

Next planned step

• Try to physically blank the EGR feed pipe (access is awkward on this layout)
• Continue working on stabilising fuel pressure

Questions

1. Could a stuck-open EGR realistically cause a complete non-start like this?
2. Has anyone seen EGR faults affect rail pressure behaviour?
3. Does the fluctuating rail pressure point more toward air in system vs regulator issue?
4. Anything obvious I’m missing before going down timing/compression route?

Appreciate any input — feels like I’m close, but not quite there yet