Fuel Pressure

[scottyjr]

Hello All. I've got a 98 I30 with a starting problem. The problem really started all of a sudden. Went to start it but it would crank but not start. Previous day it started instantly. Finally realized it would start but only after a very long crank. Ran good once it was started. After some additional education via the internet, I came to the conclusion that fuel pressure wasn't being held once the fuel pump was off. Fuel pressure gauge indicates that the fuel pump is providing 35psi at idle and throtlling up gives it another 6psi or so. With the ignition off the fuel pressure immediately slowly drops and after a couple of hours it's down to about 15psi. By the information I've read I concluded that it could be a check valve failure or an injector leaking. What I'm confused about is where the check valve is. I read that it is contained in the Fuel Pressure Regulator but I've also read that it's within the fuel pump. Anybody know where it is and are there any suggestions on a way to pinpoint the source of this problem? Thanks. - Scotty

[the converted]

I'm not sure if there is a check valve per say, but the fuel pump, injectors, and the regulator would all have a hand in holding pressure. The race cars that we run out of our shop drop down to 0psi in a few seconds of the pump being off, so I'm not really sure how much of an effect it would have on your starting. How is the condition of your spark plugs and MAF? Those would probably be more likely to cause slow starting.

[scottyjr]

Does the fact that it developed this starting problem quickly take the source of the problem away from the plugs and since it runs fine other after starting and there are no OBD codes also point to something other than the MAF? I still would like to know where the check valve is.- Scotty

[loystock]

As a 'patch' to your fuel pressure loss, turn Ignition to ON for @ 3-5 seconds then START. With Ignition ON, fuel pump runs for @ 5 seconds at 43 PSI and then shut down automatically. This will allow fuel pressure to build in the line minimizing hard starting problem.

You are correct in your search, Scotty. Loss of fuel pressure may be due to faulty check valve(in pump assembly) or Fuel Pressure Regulator-Fuel Injector. The suggestion above is just a patch but you need to fix the problem. You have to isolate where the leak-by is coming from - check valve or FPR-FI. You have a choice of running the engine (34 PSI) or just setting Ignition Switch to ON and let the pump run for 5 seconds (43 PSI). You save fuel with the engine off. Once the pump shuts down, fuel pressure should only gradually go down and then hold steady. To check if the problem is with the check valve, pinch the line downstream of the fuel pressure gauge (between fuel filter and fuel rail). If the pressure goes down immediately after pump shuts down, problem with check valve. If not problem is with FPR or FI.Pinch the return line from the FPR and if the pressure remains steady, it's the FPR; if pressure drops, you have a leaky injector. To confirm a leaky injector, pinch the line upstream of the fuel pressure gauge (between fuel filter and fuel pressure gauge) SIMULTANEOUSLY with the FPR return line and the pressure should drop to indicate one or more of the fuel injectors is leaking. To find out which injector is leaking, you have to pull out the spark plugs.

[scottyjr]

Thank you, Sir for that very informative response. The information you provided made it possible to narrow down the source of the problem and avoided a possible waste of time and money. Please give your thoughts on my opinion of the problem source.
Following your instructions, I turned the ignition on. The fuel pressure went up to about 38 PSI. I clamped closed the hose going to the fuel rail very tightly with needle nose vice grips and turned the ignition off. The pressure began to steadily decrease immediately and within 15 minutes the pressure was down to around 18 PSI. If I understand this test correctly, the point of the clamping isolates all components upstream of the clamping point (the regulator and fuel injectors) from the system under test, leaving only fuel pump assembly as the cause for the lack of maintaining fuel pressure.
Something that you suggested didn’t work and I’m wondering why it didn’t. I turned the ignition on for about 5 seconds before starting but it didn’t help. The crank was as long as when I’d leave it sit overnight and then tried to start it. I checked the pressure after turning the ignition on and it was 38 PSI prior to cranking it. I’m pretty confident the problem is the fuel pump.
Thanks very much for your help. - Scotty

[doomhammer1212]

Sorry to bring up this old thread, but I've been having the same issue and after considerable diagnosis I believe there the problem is in the fuel system but I can't pinpoint where it is on my '97 Maxima with 193k.

I T'ed in a fuel pressure gauge above the fuel filter. First issue, when I key ignition to ON I don't get 43 PSI (so initially I'm thinking fuel pump). I pinch the hose downstream of the gauge and key ON again. Now the pressure begins to build, but only 5-10 PSI. After 5 or 6 key ON's, it finally gets to 43 PSI and holds steady. Now I release the grips to un-pinch the line and the pressure drops fairly quickly, back to 0-2 PSI within a couple of minutes max. Now I'm not so sure about pump.

Start the car with nothing pinched and pressure holds at 34 PSI. Shut it off and pressure drops as before. Isn't some pressure supposed to be held for at least a few hours??? I pinch the return line and key ON multiple times. I can see a little movement on the gauge but it drops back down. I didn't pinch the return line with the car running, seems like if the pressure built up too high in the engine that wouldn't be good.

Now I start the car again with nothing pinched and pull the vacuum line on the FPR. The pressure jumps about 5 psi as expected and there is no fuel leaking out the vacuum line. Put the line back on and it drops 5 psi again.

Next I check the resistance on the ECTS while cold and check it against the chart in the service manual using the ambient temp outside. Looks good, maybe on the edge of the acceptable range. Drive for 20 minutes and check again. I can't check the coolant temp but the resistance has dropped considerable as expected.

Next I listened to each of the injectors putting a screwdriver to each and listening with ear against the other end. All sound the same to me, clicking away. I check for ghost codes and get cylinder one misfire (301) and knock sensor. So I decide to pull the injector from cylinder 1 expecting some kind of bad o-ring but everything looks fine. Relubed it and put it back. Oh and before I started all this pressure gauge business I dropped in a bottle of seafoam in the tank and filled with premium just for s*** and giggles, also replaced the fuel filter and fuel strainer. Also, when I saw this code last year I changed all the spark plugs but I guess it didn't work.

Any ideas what the problem is? I didn't pull all the injectors because it didn't seem to be worth taking off the intake manifold to get to them. Since I bought the car a couple years ago every once in a while it would crank for a long time before starting. The engine stalling out right away is new for this year and only in the cold. I believe the problem is in the fuel system, I just don't know where. I don't want to go swapping out parts if I don't know they are bad. I'd rather diagnose correctly and fix the one or two things causing this issue.