OK - I own up - I have not used as much petrol as I should over the years. Car is TF Sedan, running most of the time on gas. It started to run rough, so I got the injectors cleaned, replaced the fuel filter and WOW! - what a difference... Had a tankful of 98 OCtane and took it for a decent run. Put the foot down to overtake a truck and it died half way round....

Thereafter, every time I put the foot down (on petrol) it died - it was starving for fuel. It is OK on gas, so it is a petrol problem. I have run the fuel level down till the low fuel light is just coming on. I pulled the pump out of the tank and it was caked in dirt. More importantly, the pre-filter sock was full of 'mud'. I cleaned it out. It is fine for now...

Question - What would cause the 'mud' to build up inside the tank? It was just like regular garden soil. It scrapes off very easily. I was wondering if the 98 Octane fuel may have stirred up a lot of crap or has chemically mixed with the existing 91 fuel?

Question - What next? I have another filter, but presumably there is a lot of 'mud' still in the tank. I plan to use a few tankfuls of fuel to hopefully clean out the crap and then replace the fuel filter again.

I don't know where the "mud" came from, but I know it has to come out quick. I'd drain and remove the tank, then get a hose or high pressure cleaner in there to blast it out.

I would also use compressed air to blow out the fuel lines, starting at the fuel rail and working backwards.

Petrol won't shift it, it will just clog up your pump screens, filter and perhaps injectors again. You really don't want the stuff to dissolve and go through the engine, do you?

Thnx for your reply. I really don't want the crap going through the system, but if I get the petrol tank nearly empty (fuel light just coming on now) and then fill it and use that lot up fairly quickly, I hope it may go through in fine suspension. What gets through the filter will hopefully not cause further problems. I would like to know where the dirt came from.

The option of pulling the tank out is not an appealing one for me.

That garden dirt is just sludge. Australian fuel is very poor quality when comparing to other similar countries. As a result, a lot of sludge can form in the bottom of the tank over the years.

"That garden dirt is just sludge. Australian fuel is very poor quality when comparing to other similar countries. As a result, a lot of sludge can form in the bottom of the tank over the years. "

I think it is regular sludge from the petrol, but the filter sock was full of it, hence the starvation under load. When I say full, it was chocka, and it took a lot of effort and washing to get it out of the sock. I think I'll have to pull the pump again some time in the future and check it, but I am confident that it will be OK. I would like to remove teh tank and clean it properly, but that is nor really an option for me at this stage.

Is there a product which will dissolve sludge without dissolving the fuel lines, injectors etc?

You still want that gunk to move and go through the engine? OMG!!

I don't like the idea, but if I hadn't removed the pump, I would probably have driven the car and eventually sucked most of the dirt thru the filter (and replaced the filter) and not known the difference. It is the same as when you do a compression test. If it is all good, you feel great. If it is bad, you really worry. Do you do a compression test in the engine? I would estimate that when dried, the dirt layer was 0.5 mm thick, but what it is on the bottom of the tank, who knows?