Low fuel=Knock?

[SS/GN]

Will low fuel level cause knock.My sending unit would work and then not so I was leaving the level low towards the end of the summer,so I didn't have to lift a full tank out.On the last time out I got on it a little and the knock went to 7 and o2's were 720 on the recall.I just got the tank out pulled the pump and drained the tank.Their was 4 gallons left in the tank.Any opinions and I already know it wasn't a good idea

Kevin

 

[ttypewe4jim]

You better be careful!

there is my dumbass move..... popped it because it was low on gas

 

[fc227]

I blew the head gasket between 1 / 3 because I ran the fuel tank to low !


Lesson learned

 

[SS/GN]

How much is too low.Is 4 gallons too low or should I be looking for other things

Kevin

 

[pacecarta]

4 gallons is too low to go WOT

i try to run with at least 8-10 gallons (1/2 tank) at the track at all times , usually ill run with closer to 3/4 tank
besides the weight at the rear helps the traction more than it hurts performance


another thing to consider is with only 4 gallons the fuel pump is in air only so it doesnt run as cool as when submerge and..
with less fuel the fuel itself will be hotter which doesnt help when trying not to detonate

 

[87granny]

You better be careful!

there is my dumbass move..... popped it because it was low on gas

Holy chit if i didn't know you i wouldn't believe that that was from low on fuel full throttle

 

[poppy1440]

My guage was off and I went to the track and I thought I had five gallons left until I ran out of gas on the way home 20 miles from the track. Needless to say I discovered I had a blown the head gasket the next day.

Just for information.

I've blown my head gaskets three times. All at less than 20lbs of boost.

 

[ttypewe4jim]

Holy chit if i didn't know you i wouldn't believe that that was from low on fuel full throttle

And I have done it more then once :redface: First time the car got real sideways and out of shape popped a few times then boom smoke screen less then a week away from one of the point series races Second time going to a fire call lol (surprise surprise there I know lol.)

poppy1440, I totally agree! lol blown 4 gaskets over the years and every time was on pump gas like 17psi but I am known for beating the crap out of my cars LOL... Before I lost the cam in the fall with my car the boost was at 26psi on pump gas alky gt6776 turbo :biggrin: never really got it to the track before I had cam issues though In one summer I put 9k miles on the poor car and used more then 30 gallons of alky

 

[Razor]

Will low fuel level cause knock.My sending unit would work and then not so I was leaving the level low towards the end of the summer,so I didn't have to lift a full tank out.On the last time out I got on it a little and the knock went to 7 and o2's were 720 on the recall.I just got the tank out pulled the pump and drained the tank.Their was 4 gallons left in the tank.Any opinions and I already know it wasn't a good idea

Kevin

Easy.. fuel pump sucks air.. drops fuel pressure.. leans motor out.. boom goes the HG.

If your going to play hard.. have a full tank. Or you'll get real good with a torque wrench

 

[TR87386]

If you have an aftermarket replacement gas tank like me (without the TB specific baffels in the tank) it seems to make this issue worse. I am constantly topping off my tank just in case.I try not to run much less than half a tank.

 

[SS/GN]

Easy.. fuel pump sucks air.. drops fuel pressure.. leans motor out.. boom goes the HG.

If your going to play hard.. have a full tank. Or you'll get real good with a torque wrench

Ok thats funnyThanks for the input always appreciated Julio.I guess what I am try so say is,should I be looking at anything else while winter is here or is the 4 gallon level my knock problem.Don't get me wrong I will always have a min of 1/2 a tank in the future.The only reason I let it get that low was I knew I would be removing the tank soonThanks for the input

Kevin

 

[pacecarta]

unless your ecu is set up to correct the air fuel ratio cold weather requires you add fuel to correct the AF for the denser air , its 38deg right now and need to add about 8-10% over when its in the 70s
if its leaning below 15psi easy is if you're running a translator open the box and set WOT dial to +10 and see where the o2s are
if you have a tt chip you can add WOT fuel in the chip

old school would be if you have an adjustable regulator turn the fuel pressure up a little

or just wait till it warms up

 

[TRICKSIXPA]

Low fuel is not really your problem I drove my car down to fumes one day thank god I only had to make it 2 blocks but you will see a huge differance when your that low on fuel. if your running a new Walboro fuel pump and hotwire kit your good to go on that end. Lean I think the O2 would be lower? Lean is usually from a exhaust leak. After you put your tank back in start looking in that area.
Question when you said you go on the car how hard where you on it ie. Boost? RPM?

 

[pacecarta]

uh no

ruising and feeling the car stumble lean vs going leaning at WOT are two completely different scenarios
wot fuel sloshes back
lean cruising the car just looses power , lean WOT the car will melt pistons


and exhaust leak at WOT mean very little , at idle the leak has more effect due to the amount of air flowing and the scavenging of the exhaust pulses and it can cause lean condition and high blm which is why we usually as what the idle blms are
, at WOT the exhaust is pressurized to sometimes twice the boost pressure so exhaust leaks pre turbo dont lean the AFreadings

and even if they did it would lean the cylinder just the af reading if the af faslely shows lean from an exhaust leak as you say it will the cylinder would be happy and he wouldnt have knock .. but he does have knock

 

[87granny]

Yea what he said :biggrin:

 

[pacecarta]

and even if they did it wouldn't lean the cylinder just the af reading

correction should read "wouldn't lean the cylinder" .
, leaks though they indicate lean and drive the blm high it actually does the opposite because the o2sensor sees lean the ecm adjusts and is adding fuel , and that actually causes the cylinders to be richer
thing is stock ecm can only adjust for so much fueling needs and it needs drive time in those cells to adjust the blms for the temps , when its ballz cold out its just safer to add the fuel

read up
http://gnttype.org/techarea/faq/BLMINT.html

 

[meanchicken]

Also keep in mind that the Scan Master only records one blip in your entire run... you hope it will capture the worst point...but...it may not actually capture the lowest O2 or the highest KR...since they may fall outside the window that it actually records in...

Think of your SM as just ball park to let you know if you have an issue happening that you need to tune for...but don't tune based on SM read outs alone....or you'll still be into head gaskets, spun bearings, etc.

You won't see the real picture unless you data log entire WOT runs and this is the kind of visibility you need to really tune and really "discover" issues.

Oh...and WOT with Low Fuel = BAD

I fill up when I drop below 1/2 tank....and I drive my GN like I stole it on a daily basis...:biggrin: so trips to the pump are frequent...

 

[Razor]

Ok thats funnyThanks for the input always appreciated Julio.I guess what I am try so say is,should I be looking at anything else while winter is here or is the 4 gallon level my knock problem.Don't get me wrong I will always have a min of 1/2 a tank in the future.The only reason I let it get that low was I knew I would be removing the tank soonThanks for the input

Kevin

Kevin,
There are many reasons a car can lean out. The problem with guessing is just that. We are all guessing and relating to personal experiences. Easy solution is to fill up the tank and see if the condition goes away, if so.. you have your answer. If not.. then pull out the fuel pressure gauge, alky pressure gauge, and start watching pressures to see whats not keeping up.

Hard to tell, the faster the car is.. the higher the boost it runs.. the higher reliance on gasoline to make power. You cannot compare a guy with a race motor at high boost and 70 MM turbo to the guy with the stock turbo that runs 14's in the 1/4. The stock turbo car can run down to 1 gallon probably as it doesnt really pull any fuel. Other scenario.. better be more than half a tank.

I have a datalogger on my setup. And record air fuel, fuel pressure, alcohol pressure, oil pressure, egt, etc.. I want to know it all and not guess. That way I have data to support what I feel is happening.

No data.. its just a guess then. Full tank of gas eliminates a lot of guessing

Hope this helps.

 

[SS/GN]

Thanks

Thanks for all the input,:biggrin:I will put the car back together and check other basics again.Probably will put a fuel gauge on the window and have a be careful approach:wink:Still new to these cars and the learning curve is interesting.Thanks again

Kevin