My 1991 745 Turbo has sat for about 15 months, and had about 5/8 to 3/4 of a tank of gas when I parked it in the garage, in late June last year. Still has the same amount of gas in it now.

Finally went to try to start it up, after the longest head replacement job in history. It turned over but would not start. After pulling one of the spark plugs, and then the fuel return hose (from the pressure regulator) and finding both bone dry, I conclude that she is not getting any gas to the engine.

Both pumps are running just fine.

I guess that the problem is old fuel that has varnished up everything. What do I have to do to clean it out? Change the main filter, under the frame for sure. Do I have to pull out the in-tank pump too and check the filter sock, or if I drain out all or most of the old gas and refill with about a half a tank (about 8 gal.) of fresh fuel, will that dissolve any varnish in the in-tank filter sock? Would adding some Redline SI or STP Fuel System Cleaner, or the BMW stuff, or whatever help to clean out the sock? I really, really don't want to have to pull the in tank pump/sender unit out. Is there anything else that I need to clean out?
--
1955 Human, Scott; 1991 745 Turbo, Thunderbolt; 1990 745GL, Posideon

Fifteen months is a long time to store today’s fuels with out a stabilizer. Any air in contact with gasoline causes it to break down by making the molecules oxidize. That is why it is a volatile substance that is “burned” it in our engines, just at a faster rate.

Gas tanks on cars are not good for long-term storage because of built in air spaces for expansion even if it was full. Being 5/8 to3/4 full made it only slightly faster. With even more air space, you could have gotten a gummy paste and then there is varnish when it is all gone!

You may have balls of gelatin in there, not varnish. The gel is heavier and sinks. Gelatin can be like moss over the surface of a rock. This would limit capacity to the main pump and it would be louder than normal from cavitations. If you find gelatin then the filters will have to be changed. I hope that the main filter will stop any gel from getting all the way to the injectors. It is a good chance the injectors will clean themselves with the fresh detergents from the fresh fuel.


Sound is not a sure fire way of know if fuel is moving or can flow correctly around the fuel pressure regulator and back to the tank.

As a suggestion, you could disconnect the main pump inlet hose to check the flow from the in-tank pump. The in-tank pump might have a clogged sock since you said the pump was new.
It might be easier, if you do not feel like getting under the car, to disconnect the fuel rail and verify that it is getting fuel from the pumps altogether then fall back to the main pump disconnect idea.

You can jump a system relay; run a larger hose to a gas can, as this will allow you to check the flow and condition of the fuel in either case. You can pump the tank almost dry and filter the fuel at the same time. You can mix back in the old filtered gas with the fresh gas in small amounts after all is well.

I surmise it will dilute the remaining untouched molecules in the liquid. Should it not, you can have some large autumn leaf fires!
Phil

Hi,


If both fuel pumps are running, then it is likely that there is a problem with the intake fuel pump hose.


Goatman

That makes sense Goatman. But on the other hand, it does not make sense: The entire in-tank unit, including the little hose, is only a few years old. I replaced the whole unit recently. Thus it is not the original hose that is 20 years old.
--
1955 Human, Scott; 1991 745 Turbo, Thunderbolt; 1990 745GL, Posideon