engine not getting ENOUGH gas
 

hey guys i'm back, so i was having problems before as mentioned here:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/uh-oh-hot-dog-fuel-pump-problem-871749/

and now i'm still having problems...weird huh?

so basically i can tell what's happening is my engine is getting gas, but not enough. i just replaced the fuel filter and fuel pump. so i don't understand why this is happening. any ideas?

oh and btw, i know this because i can get the car to idle by pushing in the afm just a little bit (making the ecu think the engine needs more gas) and it will idle just fine forever if i held it there...as long as i start the engine with some starting fluid
maybe the afm is off? but that's weird

oh and also btw, its a 1990 n/a gtu.

thanks!

Check your TPS and adjust if needed

sweet i will do that. i'm not gonna go out there tonight it'll be too hard to get anything done, but tomorrow morning

any other suggestions?

check for vacuum leaks

could it possibly be exhaust blockage somewhere in the exhaust? i replaced tps haven't adjusted it but i think the car has to be running to adjust it, which it wont, so i dont think thats the prob. like i said the car idles fine when i press afm in just a bit and hold it there. seems like blockage somehwere

nevermind, the above idea was retarded. i bought a fuel pressure gauge and hooked it up. no pressure. but i just installed a new fuel pump, and I can definitely hear it pumping. so idk...fuel pressure regulator?

Are you jumping the fuel pump test connector (yellow plug on shock tower) and turning the ignition to 'ON'? With the gauge tee'd into the feed line, you should have ~40 psi with the engine off. At idle it should be around ~30 psi, but it will rise back towards 40 psi if you rev it and change the amount of vacuum.

yeah i'm jumping the test connector, and turning the ignition to on. i can hear the pump pumping. it's just not giving pressure....weird. and its not the gauge, because i unscrewed that one and put my other psi gauge from a compression tester and that one gave no pressure either.

stupid rx7. lol.

would it be the fuel pressure regulator? not quite sure what that does.

it restricts the line to produce a specific fuel pressure.

ok so that's more of restricting it if there's too much pressure?

so what could it be?

no...

a fuel pressure regulators job is to restrict flow so that the fuel injectors get a certain psi of fuel going to them. i dont know that if they fail they simply dont hold pressure and allow you to have none.

heres a test... put a vice grip on the hose and clamp it down just enough to barely allow any fuel to get past. or just clamp it down. then.... try and start the car.

clamp the line? won't that let less gas? and i need more? i'll try it though haha. clamp it where?

He means to clamp the return line to the gas tank. That way, there is no return to the gas tank, which raises the overall line pressure.

okay that's what i was thinking. i'll try that when i get home.

I'd start from the fuel pump since you just changed it. Maybe the fuel lines are switched? Pull 1 of the rubber fuel lines off the rail to the injector rail and see if you have any gas flowing.....

major vacuum leak
low voltage to fuel pump
someone screwed with your AFM

those are the 3 major causes that would come to mind, in that order.

this can all be solved with a damn gauge.

what would an EGT gauge do to help him?

Who said anything about an EGT gauge? ;)

I am assuming Cygnus is talking about a fuel pressure gauge, which would give you a very good indication of what is going on.

Wait, wait, wait... how did you hook up the gauge? Did you tee it in, or hook it up direct from the pump? Something else to try, is to get a bucket, open the line from the pump, jumper the connector, and see if you have flow. Don't burn yourself down though.

Another question... did you have this problem before you hooked up your new pump? Did you hook the polarity up correctly on the fuel pump? Maybe it is running backwards.

mm i tried that. everything is hooked up correctly. and i've pulled the line off and i have gas flowing.

i teed it in. but maybe i'll try going straight into it, haha, just to see if the pump is giving enough pressure to push the fuel through the lines...or if the gauge works. i tried it with two different gauges though.

and yeah i had the exact same problem before i installed the new pump. it was pumping but not enough to keep the engine at the idle.

and i know the pump is hooked up correctly. i hear it running, and like i said i pulled the fuel line off and gas flows out fine.

^fsho. i'm not sure how/where to check for vaccuum leak though. would it be obvious? like a loud sucking sound?


thanks for the help guys

a pump sounds the same in forward or in reverse, but we will trust that you are seeing fuel coming out. check for vacuum leaks with a can of carburetor cleaner, just don't spray around super hot exhaust or ignition breaks while it is running. ;)

Which side of the injectors is your gauge hooked into? If its the non pressurized after the regulator then you wouldn't see any pressure?

Fuel pump to fuel filter to fuel injectors to regulator back to fuel tank...

Gauge needs to be between the pump and injectors, not on the return line to the tank (free flowing back to tank, verry little pressure)... eh.

Your afm could be out of spec too. (dunno why?) Get a volt meter and check it.

Here's a diagram of how the gauge should be hooked up. If you've got the gauge on the return line, you'll see little to no pressure.

https://www.rx7club.com/attachment.p...1&d=1261167683

haha, the gauge is hooked up correctly guys I am sure of this. i am going to try clamping my return line to see if i get any pressure while priming with the return line clamped.

how do i do that?