4.2 petrol acceleration misfire problem
 

hi guys wondering if you could help.

when the car is idling its fine, when i gradually pick up speed its fine, but as soon as i put my foot down and accelerate rapidly/harsh the car starts to misfire and judder and the power is not there.

i have used some injector cleaner stuff where you put it into the fuel, it got better but when it finished it started again, now i cant keep putting injector fuel fuel in everything i need to use the car its expensive.

all the coil packs were replaced and spark plugs 6months ago just for your info.

so my brother decided we should start by cleaning the injectors manually and we will, however is there anything else i need to look at that is causing this problem...?

thanks in advance :)

Is the engine management light on and if so have you read the codes?

+1
 

as far as reading codes to avoid guessing. Given what has been replaced, included in those next guesses would be a possible bad MAF or a failing fuel pump.

You might change the fuel filter in any case. Easy to do and cheap, and it may improve the issue if it is fuel pressure or flow related. I change them a couple of times over the life of a fuel injected vehicle anyway, both to keep all running smooth and to try to extend fuel pump life by not having it work so hard.

yeh ill post them up later today

ok cool ill get the fuel filter ordered and changed in that case.

could you help me with the location and guide to remove thanks :)

Others w/ a 4.2 should respond
 

I have a W12 and the set up may be somewhat different. On mine, it's in the rear (U.S.) passenger side area under the floorpan. Basically, slightly in front of the right rear wheel and underneath. You have to remove some of the underbody plastic air covers to get at it. The fuel line clips at the filter are pretty intuitive if you proceed; someone has posted on it before IIRC. Some have had problems with the bolt/nut that tightens the basic clamp around the filter and holds it in place. Mine was fairly simple in that regard.

As always, do NOT do it in a garage or other location with an open flame like a water heater. Inevitably some gas will come out. I always have the new filter nearby to get the lines back closed ASAP. One of the lines I pulled (mine had three total; some have just two IIRC) had residual fuel pressure and so some sprayed out as I pulled it off. I had an oil pan ready to catch anything more significant.

I always change my fuel filters as preventative maintenance, always cheap and easy to do.

thanks mp4 i changed the filter and i can tell you and assume that it has probably never been changed due to the fact that the filter was pouring out black petrol.

i also removed the injectors and connected it up to a 9v battery and pressurized some carb cleaner through it.

and cleaned the MAF well i mean squirted some carb cleaner on the sensor bit.

and the result is my car is working again and not missing, but i have to warm the sucker up for about 15 20mins first thing, which is longer than my 5 mins warm up.

but yeh i think it may be the fuel filter with dirty nasty black fuel going through into the injectors at all times clogging it up.

you dont happen to know anything about injector spray pattern do you?

btw thanks for your help i found the filter quite easy and was removed easy as wel, i had a metal bracket with metal retaining nut so no plastic for me. and the fuel lines poped of with a flat edge screwdriver wedged in lol

thanks again :)

You need to scan that engine. When it is working properly no warm up is needed at all. It should work flawlessly from the first moment.

Not sure about your injector cleaning procedure. They are not simply clogged with some particles. It is a layer of petrified carbon inside them not that easy to be removed.

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Blast it with some Techron..
 

You mention you ran some stuff through the fuel system already, so that's good.

I would keep giving it some fuel treatment until you are satisfied w/ it. Cheap and easy. In the U.S. that would be something like Techron--sold in the bottle, not just what is added to a Tier 1 gas like a Chevron or Shell. An ounce per (U.S.) gallon, so I use two of the 12 oz. bottles for the D3 instead of one of the 20 oz'ers for the C5 4.2 with it's somewhat smaller tank. See bottle for how often you can use it--too much/too often and it can start to dilute the oil.

If still having warm up issues, I would scan it for any codes--after first clearing and running a while after your work. If still somewhat rough on start up, I would be looking at things like MAF and maybe O2 sensors. But again, just run some more gas cleaner through it for a while for the low hassle improvement.