fuel system problem

[scrowler]

hi,

1600cc efi ford laser 1987 ghia

car starts and idles roughly, you put your foot down on the accelerator and the engine splutters and backfires.

this leads me to think of 3 possible problem areas: fuel system, ignition system or air flow system.

when i completely clamp off the return fuel line after the pressure regulator, the pressure builds to around 70psi (way too high - will blow the fuel pump eventually) and the engine runs rich but well. this tends to make me think that there is not enough fuel pressure in the fuel system to run without having to clamp off the return; which is essentially ensuring there is always too much fuel for it to run at said rpm.

i believe this sympton rules out ignition problems (correct me if i'm wrong), and probably rules out air flow problems, because the engine revs and runs fine (but rich) with the clamp on the line, but it may just mean that the engine is flooded with fuel so the fuel to air ratio doesn't matter as much meaning the MAS could be slightly out and it wouldnt matter in that situation, but i'm fairly sure the problem lies in the fuel system. the clamp sympton also rules out bad valve timing problems aswell.

now before i go pulling everything apart and reconditioning it, my understanding of the fuel system is that the fuel pump pumps enough fuel through at a constant rate that the engine can run at maximum rpm. the fuel goes through the fuel filter, and into the fuel rail, where what's needed is sent to each fuel injector, then what's not used it sent through the fuel pressure regulator (which i suppose is like a dam, it builds up until the pressure is at the right level then starts releasing fuel back to the tank).

with that in mind, i am thinking the possible problems could be either a fuel filter which doesn't let enough fuel through for the engine to run without the clamp on (the clamp just floods the fuel rail so it doesnt matter how much fuel comes through the filter because there's always enough there), the fuel rail may have a blockage somewhere in it, but the most likely problem is the fuel pressure regulator letting too much fuel through at a lower pressure than its supposed to.

so my intentions are to replace the fuel pressure regulator first, and if that doesn't solve the problem then i'll replace the fuel filter as well.

before i do this, has anyone got any ideas about what might be causing this and can confirm/deny some of my understanding of what's happening here? has anyone had this problem before?

any help appreciated,
thanks,
robbie

[gouldie1903]

i'd start with changing the fuel filter, they're pretty cheap and can stop flow when really clogged.

[curtis73]

Agreed. Then I'd check ignition problems; bad wires, cap, rotor, plugs.

[scrowler]

hey,

i've replaced the fuel filter and pressure regulator and no changes, its the same problem. should i check the ignition? any ideas?

[UncleBob]

although I agree your symptoms sound like they could be linked to a lean issue, i don't agree with most of your assumptions. Blocking off the return line tells you nothing other than the fuel pump has some flow beyond what is needed for the engine to idle. Thats not much.

It could be ignition related. It could be a lot of things. Too many things to make a worthy suggestion. I'll have to suggest my usual: pay someone to diagnose it. It would have cost less than the parts you have into it so far.

[Ian Szgatti]

I agree with uncle bob about taking it for a diagnosis, but it isn't like you have to change a whole bunch of parts to rule out any problems here... checking your ignition for example is really easy, and I think you should do that.
On the one hand you said it sputters and backfires when you throttle down... then you say when you block off the return line it runs better... alright... you just need to check for good spark at each wire and plug, if your good there, replace your fuel pump.

[scrowler]

hi, i will check the ignition this weekend. the fuel pump has just been replaced (i had to replace it to get the car running in the beginning), is it really necessary to replace it again?

[UncleBob]

I'd personally check fuel pressure and fuel flow (and filter restriction), before replacing the pump.