P38A Misfire over 1000RPM

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Nick O

Nick O

Member
Posts
12
Location
North London
Hi,

Slightly lost on this problem.

4.6 Gems

Starts with no problem but over 1000rpm serious misfire. So bad it can't be driven.

2 new fuel pumps were fitted and the fuel filter replaced, seems that the fuel pressure is ok and even checked the fuel rail for blockages.

Any advice would be a great help.

Many thanks
 
All my poor running problems on my THOR (not GEMS) P38 were knackered plug-leads and duff coil-packs.
Death by a 1,000 cuts as the garage repalced 1 at a time. I cut my losses and told them to just change both coil-packs and all HT leads. Sorted.
Probably totally different to GEMS. :(
 
Could be any of the usual suspects in typical order:
  • Coils, Plug Leads or Spark Plugs
  • MAF Sensor
  • Air Leaks anywhere from MAF to Plenum & Inlet ports.
  • Crank Sensor intermittent wiring (if it's failed engine would not start)
  • Cam Sensor (less likely as GEMS goes to fixed timing mode)
 
Thank you for your help.

This has been tried so far:
New fuel pump
Fuel lines
Fuel filter
Blown out fuel rail
Plugs & leads
Throttle position sensor
MAF

Probably only the coil pack and air leak to check.
 
  • Get diagnostic done & report results.
  • Check fuel pressure at tickover & when revving engine using a cheap tyre gauge (one you don't mind getting petrol in). There's a schrader port on the fuel rail.
  • Take each spark plug out one at a time & check how good the spark is. If a coil is bad, you will find two low sparks, because they fire in pairs.
  • Check the primary side connector on the end of the coil bracket. any corrosion or oil in there can affect sparks.
  • Buy some RTV sealant & then take the inlet pipes, throttle body & plenum off, and clean thoroughly with carb cleaner. Then reseal plenum & throttle with RTV.
 
Get a multi-meter lead, earth one end, then use the probe end to check leads / coil towers for tracking out. We had that on Otto, 2 duff leads, on different coils, so when they tracked they between them took out up to 4 cylinders.

This was me finding Otto's misfire. You should hear and see it tracking out.

 
Scotiawhiskers said:
Get a multi-meter lead, earth one end, then use the probe end to check leads / coil towers for tracking out. We had that on Otto, 2 duff leads, on different coils, so when they tracked they between them took out up to 4 cylinders.

This was me finding Otto's misfire. You should hear and see it tracking out.

Click to expand...


I was expecting to hear "arrrgghh, arrrrggh, f*ck that hurt" as it earthed through your fingers.
 
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