I have noticed on my 308 that my fuel pressure drops off, i mean it takes about 1 hour to go from 6Psi to 0, but my last 308 had the exact same setup. IE guage and pump and quaddy and it didnt drop.
Its a new fuel pump, rebuilt quaddy, any ideas. how quick should it drop off it at all?
Cheers
JNR_ATE
FUEL PRESSURE DROP
Started by
_JNR_ATE_
, Jul 20 2006 01:08 AM
14 replies to this topic
#2
_devilsadvocate_
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Posted 20 July 2006 - 06:33 AM
Is the above after the motor is stopped/fuel pump switched off?
#3
_JNR_ATE_
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Posted 20 July 2006 - 08:21 PM
Yeah, engine is switched off.
I noticed that if i drive for a while get it hot then switch it off for 20 mins or so. i try to start it after and it cranks and cranks and wont fire, like its building the fuel pressure back up, or its just flooded because it splutters and i need to keep cranking till she fires properly,
Only mainly wen its hot or just been driven, if i park it then try to start 10 hours later after work in the cold night, bang straight away.
Im lost
Cheers
JNR_ATE
I noticed that if i drive for a while get it hot then switch it off for 20 mins or so. i try to start it after and it cranks and cranks and wont fire, like its building the fuel pressure back up, or its just flooded because it splutters and i need to keep cranking till she fires properly,
Only mainly wen its hot or just been driven, if i park it then try to start 10 hours later after work in the cold night, bang straight away.
Im lost
Cheers
JNR_ATE
#4
Tiny
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Posted 21 July 2006 - 01:02 PM
Sounds like vapor lock to me! the fuel in the fuel line is vaporising and not reaching the carby as liquid fuel. Try re-routing your fuel lines to keep them cooler or insulating them.
Is it a mechanical pump?
Is it a mechanical pump?
#5
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Posted 22 July 2006 - 12:47 AM
Yeah mechanical pump Tiny, the lines are insulated in some heat proof wrap i got off a truck at work which normally insulates air brake line, and they run approx 2 inches from the exhaust all day.
Current steel fuel lines are the standard and run neatly away from the extractors.
Cheers
JNR_ATE
Current steel fuel lines are the standard and run neatly away from the extractors.
Cheers
JNR_ATE
#6
Tiny
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Posted 22 July 2006 - 09:59 AM
Hrmmmm... Bugger! I had hoped that was going to be your easy solution heheh
It could still be heat soak.. I used to get this in my 202 torana cause i removed the heat shield from under teh carby and it used to heat soak and be a real bitch till the temps came right out of the carby itself! ( Ages!)...
maybe your insulation is working... it may be keeping the heat IN the fuel line rather than out of it? can you feel the carby area/fuel inlet line to see if its hot when this problem is occuring?
The only other thing i could think of is if the pump has some kind of fracture that opens up when hot releasing pressure.... have you got a relacement pump you could try?
Good luck mate!
It could still be heat soak.. I used to get this in my 202 torana cause i removed the heat shield from under teh carby and it used to heat soak and be a real bitch till the temps came right out of the carby itself! ( Ages!)...
maybe your insulation is working... it may be keeping the heat IN the fuel line rather than out of it? can you feel the carby area/fuel inlet line to see if its hot when this problem is occuring?
The only other thing i could think of is if the pump has some kind of fracture that opens up when hot releasing pressure.... have you got a relacement pump you could try?
Good luck mate!
#7
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Posted 22 July 2006 - 05:08 PM
Yeah thats what i thought, the heat shield might be holding it in aswell.
The fuel pressure guage is between pump and carby obviously and sits around 6 Psi when the problem occurs, there is fuel pressure according to the guage but seems to crank and crank and splutters when its trying to start.
But like you said with your 202, leave it 10hours between work and it starts first go, maybe a short plastic spreadbore carby spacer to suit performer to quaddy might help?
I dont have a new pump to try, maybe an electric one might be the go, lol
Whats the best option with Elec fuel pumps,?
Cheers
JNR_ATE
The fuel pressure guage is between pump and carby obviously and sits around 6 Psi when the problem occurs, there is fuel pressure according to the guage but seems to crank and crank and splutters when its trying to start.
But like you said with your 202, leave it 10hours between work and it starts first go, maybe a short plastic spreadbore carby spacer to suit performer to quaddy might help?
I dont have a new pump to try, maybe an electric one might be the go, lol
Whats the best option with Elec fuel pumps,?
Cheers
JNR_ATE
#8
_devilsadvocate_
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Posted 22 July 2006 - 07:38 PM
Dropping pressure: if it takes one hour to happen, doubt that it could be the cause of any driveability probs. How long should pressure be evident in the lines? ....Suspect the leakdown would be at the pump, but not sure about that one. You could find where the pressure leak is simply by just blocking the lines at different points, its all metal lines from pump to carby?
Your starting prob sounds does sound like vapor lock, to try and pinpoint the source-pour cold water on lines(they will be cooler inside the insulation).....if makes no difference try and rapidly cool area just around float bowel with fan or water spray.
Your starting prob sounds does sound like vapor lock, to try and pinpoint the source-pour cold water on lines(they will be cooler inside the insulation).....if makes no difference try and rapidly cool area just around float bowel with fan or water spray.
#9
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Posted 23 July 2006 - 02:12 AM
Devil, mine is metal out of the chassis rail, then fuel hoes about 12inches long into the pump, then approx 6 inches of the steel fuel line again where it goes from pump up toward the carby, then fuel hose with the guage in-line and to carby.
Sounds dodgy Steel hose, insulated fuel hose, fuel pump, steel hose, fuel hose with guage in-line then fuel hose into the carby.
Pictures might be better
I just cant see why it would be vapour lock if the guage reads 6 Psi, 6 inches before it enters the carby.
Cheers
JNR_ATE
Sounds dodgy Steel hose, insulated fuel hose, fuel pump, steel hose, fuel hose with guage in-line then fuel hose into the carby.
Pictures might be better
I just cant see why it would be vapour lock if the guage reads 6 Psi, 6 inches before it enters the carby.
Cheers
JNR_ATE
#10
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Posted 23 July 2006 - 02:47 AM
You can still have vapor at 6psi ......though its obviously easier for the fuel in the float bowl to vaporise at atmospheric press.
#11
makka
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Posted 23 July 2006 - 02:21 PM
my guess is that your needle and seet is stuffed and the petrol is actually leaking into the intake manifold, flooding your engine, after 10 hours or so allthis fuel has evaporated, making it easier to start.......
#12
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Posted 23 July 2006 - 08:02 PM
Now that you say that makka, i remember when i did my cam timing and had to remove my carby and manifold. it was wettish looking inside the manifold.
I would hope its not stuffed because the carby was rebuilt and jetted before the engine was started.
If the needle and seat were in trouble, could this cause bad fuel economy aswell?
Cheers
JNR_ATE
I would hope its not stuffed because the carby was rebuilt and jetted before the engine was started.
If the needle and seat were in trouble, could this cause bad fuel economy aswell?
Cheers
JNR_ATE
#13
_jimjet61_
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Posted 24 July 2006 - 11:57 AM
Is the carby an early model Rochester, as they sometimes had problems with the plugs under the main jets leaking, but that normally caused fuel to empty from the bowl over a longer period, (unless really bad),so didn't affect short term starting probs, mainly overnight, (fuel bowl empty) which in your case doesn't seem to be the case, the opposite in fact. Had the problem on mine and thought it was valve guide seals, as it would puff smoke on one side after decelerating or when sitting for a while and restarting. As someone suggested, you can still get vapourisation with pressure in the line, if the fuel gets hot enough then when it enters the float chamber and the pressure drops it flashes off (boils) this would be worse with city and summer driving one would think. From the symptons I would be looking at an over-rich mixture, or heat soak into the carby causing fuel to boil in the carby and spilling into the manifold while sitting. Normally get a strong fuel smell. Try starting with throttle wide open. You mention cam timing, did it happen prior to messing with it? Lastly, it may even be an electrical problem, as coils and other electrical components don't like heat much, and if they have any kind of fault thats when they'll play up. Just my two cents worth. Good Luck Jimjet
#14
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Posted 24 July 2006 - 01:25 PM
I would hope its not elec problems, the coil is neatly up under the dash on the passenger side as with the rest of the elec switches and relays, dizzy was re-curved and rebuilt about 2 months ago. I never drove the car much before the cam timing was re-done. i think the over rich-mixture might be a part and i will try insulating the lines from pump to carby.
Think i need it dyno tuned?
Yeah its an early model type rochy and my valve stem seal are fine,
Like i said, do they make spreadbore carby spacers to suit performer to quaddy that will eliminate the heat soak?
Cheers
JNR_ATE
Think i need it dyno tuned?
Yeah its an early model type rochy and my valve stem seal are fine,
Like i said, do they make spreadbore carby spacers to suit performer to quaddy that will eliminate the heat soak?
Cheers
JNR_ATE
#15
_jap-xu1_
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Posted 01 August 2006 - 09:36 PM
The fact that it has trouble starting when hot,but starts easily when cold makes me thing the fuel is leaking at the carby into the engine.
This would make for bad hot starts but when its cold it would love that extra fuel on startup
This would make for bad hot starts but when its cold it would love that extra fuel on startup
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