240sx starting issues

Up until couple weeks ago the car started up and ran fine but I haven't been able to start it since. There is no combustion when I crank the engine. I have checked the following items and they all seem to be working fine

1. fuel pump - it turns on and i disconnected the hose from the outlet of the fuel filter to check and make sure that the fuel is being pumped as expected - the pressure seems to fine though i hvnt checked with a gauge yet
2. injectors - i used the mechanics stethoscope to listen for injector operating clicking sound. I can hear the clicking on all 4 injectors. I still need to check to make sure the injectors are not clogged but the reason I haven't does this yet is because it seems unlikely that all 4 injectors will get clogged all of a sudden.
3. ignition spark - removed the spark plugs and cranked the engine to check for ignition sparks. no issues here.


I also tried spraying carb. cleaner directly into the throttle body and was able to start the car for as long as the carb. cleaner was being sprayed.


I suspect the issue might be with the fuel pressure regulator though I am not 100% sure. I disconnected the fuel return hose from the FPR outlet and turned on the fuel pump and noticed that no fuel comes out even after trying to crank the engine there is no sign of fuel coming out of the return outlet of FPR. I also tried to crank the engine after disconnecting the FPR vaccum hose and applying pressure to close the hose opening, this did not work either and still no fuel came out of the return outlet of FPR.

The question I have regarding this is, should there be fuel in the return line if you only turn on the fuel pump without starting the engine?

It looks to me like the next logical step is to replace the FPR and see what happens but I wanted to run it by more experienced folks on this forum before I go buy the new fuel pressure regulator.

Yes, there should be fuel in the return line.

Where is your FPR located? It should be on the return line. If your pump is running, the fuel rails should be getting fuel to the injectors. Have you put a fuel pressure gauge on it?

Yes, FPR is on the return line. I haven't check the fuel pressure with the gauge but when I disconnected the fuel filter outlet hose after i had turned on the fuel pump for little bit, I could tell that there was lot of pressure build up because the fuel sprayed out at a high velocity from the injector side of the fuel rail. Once the fuel filter outlet hose was disconnected I turned on the fuel pump again and the fuel gushes out of the fuel filter so I am pretty sure the desired pressure is there.

Given the spark is there and the injectors are firing as expected, shouldnt there be some combustion as long as fuel is reaching the injector even though there is no fuel in the return line past the FPR? I personally think there should be some combustion even if the FPR is blocked and not letting any fuel out to the return line, so i am a bit unclear as to what might be going on.

What do the plugs look like? If you were getting fuel into the cylinders then they'd be wet. Seems weird if you're getting spark and the injectors are operating that it doesn't run.

David

I think you have a fuel pump problem. when you disconnect return line you should have fuel returning. You should install pressure gauge on where fuel filter is and check pressure there. You should have about 45 pounds. It will run on about 20 pounds. Also make sure fuel pump continues to run in the start position. I have seen relay's go bad cause no start. If it runs on carb cleaner this tells me you fuel pressure issue.

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Originally Posted by hgrewal

Given the spark is there and the injectors are firing as expected, shouldnt there be some combustion as long as fuel is reaching the injector even though there is no fuel in the return line past the FPR? I personally think there should be some combustion even if the FPR is blocked and not letting any fuel out to the return line, so i am a bit unclear as to what might be going on.

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That makes sense, although I don't know that for a fact. Since the engine will run with the carb cleaner it must be getting spark, so the problem has to be in the fuel delivery. As you noted it also seems unlikely that all four injectors would go bad at the same time. My guesses would be FPR, fuel pump, or even some blockage in the fuel system - which would have to be in the fuel rail or the metal line running to it since you say you have fuel being pumped as far as the hose that attaches to the rail. The last one seem highly unlikely, but you never know.

Pull the spark plugs and crank the engine. If you are getting fuel (and proper fuel pressure) you will literally see it spraying out of the spark plug holes. Just make sure you don't have a spark plug wire arcing to anything too close by.

Thanks for all the replies. I went and got the fuel pressure gauge and hooked it up and looks like its a fuel pump issue. Even though the pump turns on just fine, its not creating the needed pressure (43.4 psi). I'll try replacing it and see what happens.

Since the car was built by someone else, I am not sure if the current fuel pump is stock or aftermarket. It'll be great if someone can suggest a fuel pump that works best in ITA prepped 240sx.

To add little bit more info...

The car is fitted with a RCI fuel cell and the fuel pump is on the outside.

the eary model rangers had a frame mounted fuel pump. I have used these on many street rods and Mustangs. I don't like aftermarket pumps though, I prefer Motorcraft pumps. They will stand up to the racing use as well.