p38 4.6 bigas switch back to petrol runs rough, any ideas

Just been on a drive around town start stop. Stopped then went to start again on petrol, ran really lumpy, switch back to gas ran great. Got moving again and stopped filled with petrol because light had just come on.

Any ideas what has caused it to run rough, could it have pulled air into the fuel system or something. Has done this once before, haven't found anything common yet to justify it only doing it when petrol is low.

Cheers

afternoon

if you run the petrol tank really low, bearing in mind that your P38 is at least 10 years old, all the residue & other crap that settles in the very bottom of the tank will be drawn unto the fuel pump.

You will probably get away with just having to change the fuel filter (which is probably a bit blocked, causing your lumpy running on the go-juice).

On mine even tho' I run LPG I always keep the petrol tank 1/4 full in case

My 96 p38 4.6 is a bit rough on petrol when I switch back from gas, but it clears after a few miles, funnily it seems happier on ordinary unleaded rather than super, can't understand that. It seems that I need to run the rangie on petrol for a week or so (2-300miles) every now and then to keep it happy. I agree with Hawaii about c*** from the bottom of the tank, so change the filter now and at the right intervals. Hope this helps, Davef

The Petrol running through the injectors keeps them lubricated and clean....

If you don't run on petrol every few weeks, they can gunge up and fail to opening/close/inject properly.

Always give it a blast on petrol once in a while to keep them clean and lubricated....

cljcars said:

Just been on a drive around town start stop. Stopped then went to start again on petrol, ran really lumpy, switch back to gas ran great. Got moving again and stopped filled with petrol because light had just come on.

Any ideas what has caused it to run rough, could it have pulled air into the fuel system or something. Has done this once before, haven't found anything common yet to justify it only doing it when petrol is low.

Cheers

Click to expand...

Sounds like petrol injectors - not enough use, low fuel might have gunged them up. Select petrol only and go for a blast and see if they clear. If you have done a lot of miles then they may need a clean and re-furb.

Cheers chaps, done some switching whilst the petrol tank is 3/4 full and it seems better. I think you are right about the fuel tank being full off 16 years worth of Crap at the bottom. I think I may have disturbed a load of Crap on the tank, I have just filled it up twice this month since the engine rebuild with vpower petrol, I think this must have dislodged some Crap off the tank wall and pipes. Which must be going in when it gets low.

Way forward, bought a new fuel filter and some BG44k from kwik fit. Poured the 44k in the tank today to rip the rest of the Crap off the tank and hopefully clean the injectors as best it can. Once the tanks out of fuel I will change the filter and see whats in the old one.

Let's see what happens.

Ok just a reply to let people know what I found. Pulled the fuel filter off a couple of days ago because I was getting low on the petrol tank. Loads off Brown Crap came out of the filter, no solids, I cut it open to see if the was anything else left. Filter was dark brown/green even inside, really old. Hopefully this has solved the problem, not happened since. If it does I will reply on this post.