Mystery Fuel up trend.

[APPLTrader]

Hey guys,

I have a question for you all, it's sort of a mystery that maybe you guys can help me figure out.

So I've owned the car for about 2 months now and when I first got it I filled it with 93 regular gas maybe 2 times before I was able to find a gas station nearby with 90 octane no ethanol pump.

Every single time I fuel up now the car behaves fantastic in the lower revs and responds so much better compared to when the tank is half way, which sometimes the car will hesitate when in the lower 1.5k to 2.5k rpm range.

Why the hell does the car behave so good with what I feel like faster revs off the lower rpms when the tank is full as compared to crappy hesitation when its half full?

If anyone can elaborate that would be great.

Thanks,

Julian

[HawgRyder]

Sounds like when you fuel up you make the gas in the tank swirl around and perhaps clean the in tank filter a little.
With better fuel flow...you have a better running engine.
I would take out the filter and check it.
Worst case...you need to flush the tank of crap...take it out and have it cleaned....even then...you need to clean the filter separately.
Bob

[techman1]

Here is another WAG: (Wild A$$ Guess)

Full tank, weight of the gas helps a steady flow past a sick fuel pump. As the level drops, less weight to help the flow.

[APPLTrader]

I'm starting to think it's the fuel pump as well.. I hear a sort of whine noise sometimes at cold start almost like in the new cars when your key is in the pre ignition stage. I can't really describe it but it happens maybe 1-2 times a week. I don't know what a bad fuel pump sounds like.. if it is the fuel pump then lucky me.. a $$$ fix.

[TheSt|G]

Since it is a new car to you, I would take care of all the basic interval items to get a baseline for future maintenance.

Change:
-Engine oil
-Trans/diff oil
-Brake fluid
-Fuel filter
-Air filter
-Spark plugs
-Dizzy rotor
-Dizzy cap
-Valve adjustment

And whatever else is slipping my mind.

[E Sully]

On top of the fuel filter in the engine compartment, one item to check is the in tank filter screen in the bottom of the fuel tank. The only way to do this though is with a near empty gas tank.
Another possible problem could be the vapor recovery and fuel tank venting hoses. If the lines to the charcoal cannister are not clear and connected properly, the vacuum created in the tank would prevent proper fuel flow.
Anything that restricts fuel flow could damage the fuel pump. It is cooled and lubricated by the gas flowing through it.

[93nav]

My first thought when I read your problem is same as E Sully. Next time this happens, could you try driving with the gas cap loose? Not sure if that would be considered safe, but it could eliminate one potential source of your problem.

[wayner]

On my new to me 73 911 and on my wife's old new to her hotrod pickup truck, I replaced the fuel filter AND fuel pump on each vehicle just because.

The way I see it, those parts are:
1) cheap to replace
2) major cause of vehicles not starting eventually.

I figure that if we plan to keep them 5 or 10 years those parts will need to be replaced eventually within our ownership period, so assuming the replacement is a quality component, I should be able to rule out the risk of unscheduled failure now (or at least assume the likelihood of failure has been reduced).

I'd did gas lines and oil lines and battery while I was at it.
Nothing like a fresh start to the maintenance schedule, and combined the total cost is still less than one good tow truck ride.

[APPLTrader]

Thank you all for your input, I also had the same idea..

I'm going to replace the Fuel filter,In Tank filter and Fuel pump. I also want to get the gas lines done while I'm at it..

I figured its worth it since I'm going to keep it and I know this stuff is approaching 30 years old.

Thanks all!

[Bob Kontak]

Originally Posted by APPLTrader

I'm going to replace the Fuel filter,In Tank filter and Fuel pump.

Filter in tank is a screen that can be cleaned. You need a horrendously huge hex driver to get the plug out. I had a big honkin' chisel in my tool box that fit nicely - five sided shank end - and I used a large crescent wrench.

Do not cheap out on the fuel pump. Get the correct one. It will cost circa $250. Alternatively, check the amp draw on the old pump. 6-7 amps is new. 8-10 is mid life. 10 and above is sunset.

[Mark Salvetti]

Here is a thread with a tip on getting the fuel tank filter out using a reversed spark plug socket:
Gas tank drain plug

Mark

[APPLTrader]

Originally Posted by Mark Salvetti

Here is a thread with a tip on getting the fuel tank filter out using a reversed spark plug socket:
Gas tank drain plug

Mark

Thank you, while doing my search I encountered that weird tool. I was wondering how that worked lol..