GLE V6 new rad fitted...next challenge misfire - opinions?

[russwinchester]

Following a decent MOT with few very concerning advisories, the poor old girl blew a hose after the test, luckily was only a hole in the top hose, which I duly replaced. Upon removing the old hose (this was following a reverse flush not so long ago) I was greeted by sludge which reminded me of nappy changing on a bad day

Long story short, I managed to source seemingly the last B280E radiator in Europe and now it's fitted, and we no longer have brown coolant! Gearbox flushed and ready to go.

So now it's time to get to the bottom of a misfire. Not a subtle one but a proper power lost firing on no more than three-cylinders blip.

Just for background I've replaced most stuff now on this car, both fuel pumps, fuel filter, injectors cleaned, spark plugs changed (at correct gaps), dizzy cap, CPS, thermostat, rad, alternator, and probably some other stuff.

The misfire only happens when warm, either under load or not, it's pretty extreme, car won't rev, power lost, under load or at idle no difference. Stopping and restarting car can "fix" it.

I've swapped over the radio suppression relay with the adjacent one and no difference so that's eliminated that one (unless both are faulty of course).

So I'm thinking - power stage amp or fuel pump relay...

Would be great to hear any other hypotheses!

[Laird Scooby]

Originally Posted by russwinchester

Following a decent MOT with few very concerning advisories, the poor old girl blew a hose after the test, luckily was only a hole in the top hose, which I duly replaced. Upon removing the old hose (this was following a reverse flush not so long ago) I was greeted by sludge which reminded me of nappy changing on a bad day

Long story short, I managed to source seemingly the last B280E radiator in Europe and now it's fitted, and we no longer have brown coolant! Gearbox flushed and ready to go.

So now it's time to get to the bottom of a misfire. Not a subtle one but a proper power lost firing on no more than three-cylinders blip.

Just for background I've replaced most stuff now on this car, both fuel pumps, fuel filter, injectors cleaned, spark plugs changed (at correct gaps), dizzy cap, CPS, thermostat, rad, alternator, and probably some other stuff.

The misfire only happens when warm, either under load or not, it's pretty extreme, car won't rev, power lost, under load or at idle no difference. Stopping and restarting car can "fix" it.

I've swapped over the radio suppression relay with the adjacent one and no difference so that's eliminated that one (unless both are faulty of course).

So I'm thinking - power stage amp or fuel pump relay...

Would be great to hear any other hypotheses!

Pull and refit the fuel pump fuses Russ. Mine does this once in a while, basically it's dirt on the fuse blades causing resistance and after a while of running, the resistance causes heat to build up which in turn increases the resistance and stops the fuel pumps. Once stopped they're not drawing current so the misfire disappears soon after and normal service is resumed.

Could be the ignition amp module as you suggest, have you removed it, cleaned the back and refitted with fresh heatsink compund? If so it shouldn't be that unless it was already on the ay out before you even got the car.

Doubtful it's the fuel pump relay, it's full group injection or "batch fire" so all injectors fire at the same time and losing all power to the fuel pumps because of the relay would cause complete cutting out. Losing partial power like with the fuses causes misfiring (it can cause a total cut out as well) because the pump is still trying to run.

Also check your new HT leads haven't settled and "popped off" the top of the plugs, i've had this a few times with new HT leads!

[russwinchester]

Allow me to take a public walk of shame...the car was low on fuel

When I got the car the fuel gauge read empty, but since I fitted the slave pump and removed / refitted the sender the fuel gauge has just read full. Which is nice, until it runs out, obviously.

Could this be an easy quick fix or am I better off leaving it alone?

[Laird Scooby]

Originally Posted by russwinchester

Allow me to take a public walk of shame...the car was low on fuel

When I got the car the fuel gauge read empty, but since I fitted the slave pump and removed / refitted the sender the fuel gauge has just read full. Which is nice, until it runs out, obviously.

Could this be an easy quick fix or am I better off leaving it alone?

I think we all have that particular T-shirt Russ if we've owned a 7/9xx for any length of time!

Best way i've found (until i fixed my guage) was to carry a can full of fuel in case and meanwhile, zero the trip (while stationary!!!) when adding fuel, work out how much i've put in in gallons then multiply by 20 as a starting point (20mpg) and make sure i add more fuel before i expect it to run out. If it runs out before i expect it to, the can is there and i adjust the multiplication factor (mpg) downwards to something a bit lower than what it did when it ran out unexpectedly. Keep wprking on that figure until you suddenly discover a full tank then zero the trip and do a brim to brim and zero the trip again and work out the consumption. Then keep an eye on what it does as that can give early indication of impending doom!

You may find that once you've had a few tankfuls through it, the guage starts working as it sounds like a sticky sender float. I@d leave the float alone until you've got more miles on it and experience of what it's doing to the gallon.

Besides, you'll already have had a public walk of shame - to the filling station and back with a fuel can!