Possible fuel pump/main relay problem...help!

Ok, I have been slowly getting my car closer and closer to a point of actually driving it, but I am noticing some weird stuff with fueling, and I want to get it figured out.

First off here is my relevant setup:

- Its an 86 LX-i

- I have removed 'most' of the stuff from the little black box. (still have vaccum stablizer pump, cold advance, and map - and i think thats it)

- I am using a B16 AEBS manifold with AEM fuel rail and AEM adjustable fuel pressure regulator.

- I am using -6 AN fuel line from the fuel filter to my fuel input on the rail.

- All other fuel lines are stock.

- I have a fuel pressure gauge installed on the appropriate port of my fuel rail.

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I have recently started reading up on main relay issues, and how they can interfere with the car warm starting, and screw with fuel pump operation; I am not sure, but I have a suspicion that this might be coming into play in my situation.

When I turn the ignition ON, my relay clicks (not at my car, but I am 99.9% sure it has been clicking), my fuel pump primes (I can verify this on the gauge), and all is well. However, immediately after reaching adequete fuel pressure, it begins to bleed off at a rapid rate. In less than 1 minute I will have 0 fuel pressure.

Now my first instinct says its just a leak somewhere, but I have checked all the connections I can think of, and looked for puddles of fuel that might have caused such a rapid loss of pressure. There are no leaks to be found, and no puddles and no fuel around any of my fittings or connections.

The other thing I was thinking is that my fuel pump is either getting strang voltage or maybe the pump is failing. The strange voltage it sounds like 'could' be caused by a faulty main relay.

Another strange issue is that when the car is running, the fuel pressure gauge flutters aroung between 40 and 32psi ish.... it just sweeps back and forth REALLLY fast. the needle almost looks like a blur, its just an inconsistant pressure at the gauge (which is DIRECTLY before the regulator). When I rev the engine the fuel pressure drops to below 30, which I know to be incorrect (proper fuel pressure is 36psi +/- 3psi). I expect the fuel pressure to drop, but not normally that much, and when idling, I have usually noticed a constant fuel pressure in other cars I have seen.

What are some possible causes of this weird fuel pressure instability while the engine is running?


And what could keep my fuel system from holding pressure like it used to?
I seem to remember the gauge going up to 40psi - how the gauge comes shipped - and staying at a high pressure for quite some time. From my understanding your fuel system pretty much stays pressurized.

Perhaps the main relay needs to be soldered? Or perhaps there is a bad connection between the main relay and the fuel pump.

i don't think it is your main relay. it wouldn't hurt to resolder to get that off your mind.
I think your problem is pressure regulator. it is not holding the fuel. try putting stock one back and see what happens.


PS. are you getting any ECU codes?

its a brand new aem adjustable regulator, i suppose its possible that it is bad, but i just have a hard time accepting that. :)

and i dont think i can fit the stock regulator on the aem rail. :(

the only code i had was an Engine coolant temp sensor code (6 flashes) but that is probably beacuse my fan switch is unplugged and i have it jumped so my fans are switch controlled. :)

i do have a cosmo racing fuel pressure regulator i could try, but i would have to buy more fuel line cause it would need to be a temperary setup.

another thought i had is this: I am getting pretty low amounts of vaccum out of my manifold at idle. i am only seeing like 12-13 in/hg and stock is somewhere closer to 23 i believe. i could hook up a vaccum pump to my aem regulator, and simulate a solid 23 in/hg on it, and see what fuel pressure does....

though i am not sure how i would actually fix the problem, i don't have that many vaccum lines to begin with, so i guess i could check for leaks pretty easily. :D

i bet your intake manifold is not sealed properly against cylinder head. check that.
but even that shoudln't be your problem. if you are not getting enough vacuum, your car should run rich since pressure regulator would stay closed longer.

ok, small update:

i hose clamped a few of the vac lines going into my intake manifold, and secured my vaccum/boost gauge a little better. it didnt seem to affect anything, but at least i know they are not to blame for a vac leak.

also i advanced the timing back to where it was supposed to be (15 degrees warm, at idle) I had to switch the two lines on the dizzy, they had been put on backwards. after doing this i was able to pull about 19 in/hg so i am almost back to stock vaccum.

i took the car around the block since it was dark and i could see the A/F gauge clearly. :( at idle it just sits on rich (as opposed to bouncing between rich and lean) and when i start driving, when i apply throttle it jumps to lean and stays there until i let off the throttle.

so for one reason or another, i am not getting enough fuel...

I am tempted to buy a walbro 255 lph HP, because i will need one soon, but i don't know if the fuel pump is to blame.

in my manual it says when u turn the key on, if your pgmfi light stays on and doesnt shut off when the fuel pump is done priming, then your main relay could be bad. but my pgmfi light turns off after 2 seconds or whatever.

so at this point since i KNOW i am not getting enough fuel:

- fuel lines leaking somewhere (should be really obvious because of smell and gas on floor)
- fuel pump dying (dont know how to determine this)
- fuel pump not getting enough voltage (main relay problem)
- regulator is weird and messing stuff up (possible)
- gauge is weird and messing stuff up (is this possible? its a mechanical gauge lol)

any other possibilities?

the way i tested my fuel pump was to take off the gas line in the engine and put a guage on it...it should read around 30psi when you try to start it since the fuel pump has to work befor ignition. also did you change your fuel filters?

well i have a gauge on my rail, so i can always see my fuel pressure. i dont need to take off lines to test them.

i did change my fuel filter (efi cars only have the one in the engine bay). for an EFI car it is supposed to have 36psi +/- 3. but when i rev and presumably when i drive, the pressure drops way down, as if the pump cannot keep up with the demand.... but the pump primes to the proper pressure, it just fails to maintain that pressure. :(

so, when you take off your gauge is showing lean, but when you sit at idle your gauge is showing rich?
sounds like normal to me. that is what my gauge was showing when i had it on.
i still think it is your regulator. do you have anyother fuel pumps laying around?
if you don't you may as well get walbro one.
fix the fuel leak.
find out where it is.

thats the thing, if its a leak, there is no fumes and no puddles, and no visible leaks at all. maybe its getting through the injectors, thats the only thing i can think of, but that doesnt really make a lot of sense either... i guess i could pull off the rail and see what happens heheh...

i might as well get a walbro and see what happens...

hmmm....

Quote:

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Originally Posted by MessyHonda

the way i tested my fuel pump was to take off the gas line in the engine and put a guage on it...it should read around 30psi when you try to start it since the fuel pump has to work befor ignition. also did you change your fuel filters?

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The reason you would disconnect the line from the fuel rail would be to test the fuel pump for it's maximum output. Isn't your guage on your fuel rail reading regulated fuel pressure?

Edit

So inotherwords, if you take the regulator out of the equation and you have the correct maximum pump pressure then it's the fuel pressure regulator. If you have a funny reading for the max pump pressure, then it's the fuel pump or the wiring to the fuel pump (which you could test with a multimeter at the connector at the pump).

Ok I see what you guys are saying.

I will see about pulling the rail and removing the regulator, and replacing it with a 1/8 BSPT plug. Will a fuel pump actually build pressure without some form of regulation? Or will it just dump right on past the gauge without registering a high pressure?

I guess there are definetly some things I can check though, hopefully I will get a chance to work on it some today.

Thanks for your suggestions, I will keep you all posted as necessary. :)

did you find the problem?

i pulled the AEM regulator, and hooked up my cosmo racing regulator.

test indicate that the system is able to quickly build pressure easily up to 60psi. with the fuel return line being my driveway, I can see how much fuel dumps out, and also keep track of how fast the pressure drops. without that return hose, the pressure drops instantly.

i hooked the return line back up, and had my comso regulator/gauge, and my b&m gauge on the rail, both gauges read consistantly, and the pressure bled off soon after the engine primes, but it lasted longer, and dropped more slowly than before.

this indicates to me that somewhere behind the fuel pressure regulator return line, it cannot hold pressure. when i hooked all my stuff back up into the original configuration, i noticed that the gauge ready MORE solid than before, its still fluxuating, and dropping under load, but less than before.

i may just suck it up and build a -6AN line to the return hard line, so i am not worrying about hose connections.

so i guess i didnt fix it or solve it, but it is working better, and all i did was take it apart and put it back together. (maybe an o-ring is sealing better now?) the weird part is that there are no liquid leaks.

also i will be installing a walbro 255 hp this week sometime. this will probably make any leaky fittings MUCH more apparent, and maybe it will show me if my pump was just being lame.

i think i have ruled the regulator as being functional though. so that is a step in the right direction. the gauge is also functional. :D

yeah hope is just the pump....that sounds werid tho

Are Walbro Fuel Pumps strictly for high pressure applications like fuel injection? or do they have some for low pressure Carbureted setups?

Currently I'm running the stock carburetor but I'm interested since I may upgrade to a weber carb in the future and may need the higher flow but at low pressure.

Quote:

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Originally Posted by jackal

Are Walbro Fuel Pumps strictly for high pressure applications like fuel injection? or do they have some for low pressure Carbureted setups?
Currently I'm running the stock carburetor but I'm interested since I may upgrade to a weber carb in the future and may need the higher flow but at low pressure.

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first, yes the walbro pumps are high pressure pumps.
second, you should search and look at carb section.
You can get regular universal high flow fuel pump.