Connecting external and internal fuel pumps together?

[VCheng]

In addition to RacerF1's EXCELLENT posts above (BTW: WOW! ) allow me to add a few things that may be relevant:

Electric fuel pumps do not make much suction, but build up pressure on the output side very effectively. Therefore they need to be placed either IN the thank, or CLOSE to it.

The fuel supply circuit can be EXCESS flow type, where there is a great oversupply of fuel to the engine, and the un-needed excess is simply return via another line, or it can be EXACT flow type, where there is no return line and the fuel pumpt simply pressurizes the fuel input to the engine as needed and has an internal bypass.

The pressures needed depend on whether a carburetor (usually excess flow type) or injectors (usually exact flow type) are being used. Carburetors need around 10 psi whereas conventional manifold injectors need around 50 psi to work properly (specific pressures depend on the exact model and engine type).

Having said all that, I have no idea what the fuel system design is in the model of Cultus that is being discussed.

[Xulfiqar]

as I replied in your PM, get a low pressure fuel pump - your carb can only take 5 psi - the pump should be able to handle at least 10 psi for it to work efficiently. Leaving a thick pipe inside a tank for an external pump to suck it is like trying to sip coke from a 1 inch bore garden pipe (try that) - now try the same thing with a regular coke straw.

Its tough to find carb spec fuel pumps - but its not impossible. (or you can try an EFI pump with a resistor to slow it down) - old Mazda RX7s used this setup for off boost cruising - kicking it to full speed once it hit boost from its second turbo.

anyways back to the topic, get yourself a nice quality fuel pump - check the wiring (especially the ground) - you dont want your pump windings to act as a bridge to find ground. pour some good fuel injector and varnish cleaner - your tank would be filthy from not using petrol that often

[shqamar]

special thanks to xulfiqar, Racerf1,fasfas and vcheng to share there excellent technical and sound knowledge that made me understand this topic very clearly as for searching intank fuel pump i have been looking almost 20 shops in shershah and couples in shafiq mour but couldnt get any of the original ones that comes out in cultus , i had one spare one that is for cultus one but i am not sure if i will put this one or buy a new one also i am not sure that a new cultus intank pump which cost 4400 now is actually a original cultus intank one or just a remedy cultus version using so xulfiqar or any of u please suggest me what option i will go for now as i have decided after discussing this topic here to stick with the original setup for that i would be needed a good intank fuel pump which matches the actual pressure aswell so what would be the best option there for me
a) use a new one that cost 4400
b) use a original old one i have not sure how good that pump is
or lastly please advise me a brand or version of car that i need to search in shershah or old markets like mazda or what ever may be i would be lucky to get a good old one not cultus but a good matching one for my car .
thanks in advance and thanks every one for replying really appreciate that .

[Xulfiqar]

the low pressure pump would be smaller too, if you recall the old 660cc alto taxi - that also uses an intank low pressure pump

[Sharo53]

i think the intank pump of chevy joy would b enough..
the new one was around 3000 some time back..(from their showroom)
bt consult your mechanic first..

[Xulfiqar]

^^ all fuel injection cars nowadays use 40 psi fuel pressure, what we need is a pump that supplies fuel at 10 psi max

[shqamar]

i doubt it sharo53 all the new fuel pumps pressure is 40 to 50psi and i want a intank fuel pump that is low pressure around 10 psi max i think i need to go and look for the old taxi pumps as xulfiqar said or i will go on spare parts shop on monday and ask there opinion they might have a new low pressure intank pump or any one of u recommend any car or fuel pump brand that i go for in my intank cultus thanks in advance i prefer a new one though .

[Sharo53]

oh i see...
then its absolutly not for you..
yar the best thing would b the whole stock system..
get its its original pump

[shqamar]

i had a chat with the fuel pump guy and i was surprised how accurate and correct xulfiqar calculations were he told me the same thing that i need to search for a taxi intank fuel pump but they are very hard to find although he was convinced that the external inline setup i have now is better but i dont want to believe how a stock setup would replace and works better so i dont know i have to wait for other members to reply also can any one please tell me the new intank fuel pumps with low pressure ? and hats off to u xulfiqar u are a asset for pakwheels thanks all of u for replying .

[Xulfiqar]

I believe the GM TBI system (as in daewoo racer) uses a fuel pressure of 13 psi. now I dont know if the pump will be a weak version or its a full pressure pump but the fuel pressure regulator in the TBI stabilises it at 13 psi.

One thing that fascinated me was that it used a genuine made in Germany intank Bosch Fuel pump.

[shqamar]

i am gonna chat with quality autos water pump new spare part autos xulfiqar do u think we have any new intank fuel pump available with low pressure ?

as far as taxi intank fuel pump is concern he already mention daewo but he reckon they have larger pressure than 13 psi and not recommended in cultus otherwise they will over flow , i will look for old denso or bosch intank low pressure pumps if i may find one .

[shqamar]

update on my car that stops on petrol after few kms i change the following stuff change fuel filter , cleaning petrol tank , intank fuel change to inline fuel pump , all lines and pipes were checked throughly but surprisely the problem wouldnt go than service my carburator twice but problem still persist now just recently change the inline fuel pump to korean brand and interestingly the car is not doing that but it does give a jerk some time but starts after that i had a strongly belive it was a carburator fault the guy serviced the carburator hasnt done a fool proof job but now this is all confusing again because after changing 4 inline fuel pump which seems to be same brand anyways the car is not doing the same fault but it does take jerks some time again xulfiqar help me loads to rectify this problem but i guess now he will be confuse aswell that if its still fuel pump fault or still carburator is a culprit feel free to comment on it as i am still looking for the perfect solution of this problem .

[shqamar]

phew i think xulfiqar is the only one who knows a lot about fuel pumps or i guess every thing related to cars .

[Racerf1]

Wow, with so many changes still the problem presists. Then I think the problem lies elsewhere. Find out why are you blowing so many intank fuel pumps, is it coz of the quality of the pumps or the problem with electrical wiring to the pump from the factory?

The jerk you recieve is still fuel starvation but maybe this time the fault lies with the pipe not receiving any fuel at times.

We can try to help you but this is not an exact science and from behind computer there is not much we can do.

Time for trial and errors to isolate problem. Good Luck!

Ps. one more thing with the carb you do need a Rising rate fuel pressure regulator like the ones they have in the Daewoo racer.

[shqamar]

thanks racerf1 i do realise theres not much u guys can do but believe me xulfiqar and all experts like yourself doing a lot for others atleast users like us gather some idea where the problem lies so hats off to u all now about my problem well the carburator been service twice and the guy was so convinced that theres no problem in carburator before it was choked and i feel he was right because my car used to take a hitchi in 2nd gear and that fault has gone now , after changing 4 inline pump this one seems to do a 90 percent job atleast my car is not stopping every after few kms now the only culprit left is car jerks suddenly and than stops but after that it starts again i cannot think of any leak pipe which taking air because in this process i had service my fuel tank and mechanic check all pipes for leak but any how i will change the main line just to see if theres any effect after that and now i will look for daewo intank fuel pump because u and xulfiqar both recommend the same so wish me good luck last but not the least i ask this question before aswell dont u guys think of a new intank fuel pump other than cultus that will precisely suit cultus version ?

[Racerf1]

No need to thank me just remember me in your prayers

To be honest my experience with carbs is very limited hence could not be of much help but I will look around and let you know what would work.

Good Luck!

[Xulfiqar]

you can make a reserve tank for fuel (old twin carb Fiat 124) style and feed it fuel from the tank - the other end feeds the carb. this setup would ensure a good solid supply of fuel to the carb at all times.

The problem what I see is that you have increased the pipe diameter in the tank pickup - that shouldve been the same as original - 1/4 inch is more than enough. and the biggest culprit maybe the pipe itself flopping around - firstly its too large for the pump to suck on - secondly its floppy too.

I would also want to know the material of the pipe - is it too soft causing it to collapse under pump suction

[shqamar]

thanks xulfiqar and Racerf1 for replying well xulfiqar increasing length of the pipe is a basic need according to the mechanic reason being when u use a original setup it will use the intank fuel pump length because pipe fitted in intank fuel tank now when we take out the intank fuel pump we need to increase the length to the pipe will go 1/4 of the depth of the tank so it wont be too short to suck fuel i didnt buy a new pipe for that it was my old pipe which was italian made and good and no the pipe wasnt too soft because it was been used before so that was the theory behind my mechanic to do this inline fuel pump setup , now i have one cultus intank original pump spare with me i am thinking to install that one again and remove this inline fuel setup but than i think oh well i dont know if that start works or how quick that intank fuel pump die again so i rather wait for a good daewoo or a less pressure intank fuel pump search or my question is still there that am i able to use a new brand intank fuel pump other than cultus that suits cultus carb i mean is there any other car brand that will do the job for cultus intank fuel pump ?

[shqamar]

and Racerf1 dude theres no blowing fuel pump i had change 4 because all of them were acting differently so i keep guessing that they were not working and the guy kindly change for me when i complain so i dont think theres a electric issue involve in that now the recent inline fuel pump i install seems to run fine my car stops once now and it starts after stopping after jerks so i dont know it might be 50 percent chance of carburator , 50 percent fuel pump install or it might be any line taking air so it might be any thing , in past all the mechanics i been too they are unable to trace the problem .

[shqamar]

i will go to shershah today lets see if i can find a old daewo racer intank fuel pump :s