Thread: fuel pressure issue

when I try to start my car, most of the time it wont start unless I turn the key and let the fuel pump prime first. I know it could be a fuel pump, but it could also be the fuel pressure regulator. how do I isolate between each potential fault? the other thing I have noticed is that under increased engine load my O2 readings from the narrowband sensor lean out in PE mode, and sometimes there is kr other times there isn't. My fuel pump might not be able to keep up with the demand. just want to make sure before I start spending money on parts I dont need.

Xp cam, ported L32 heads, full size intercooler, 42 lb injectors, north star maf and tb, fuel pump rewire, ported gen 3 and a machined lim.

Check fuel pressure. Since you also have a regulator you can, while the engine is running unplug the regulator vacuum line and see that the pressure rises. Check the specs for that. Also when you shut the car off monitor how long it takes for the fuel pressure to drop. It should take a few hours.

Jeff

if the fuel pressure drops is it more likely to be the regulator? we checked the pressure, and it would check out at the pressure it was supposed to be, but then drop off a bit

ok, I will look into those things

What is a good fuel pump rewire to get? I have a 00 GTP that does the same thing as OP but have changed the regulator twice because I thought the first one I changed was faulty to begin with. I have a drop in fuel pump assembly coming in the mail now and figured I would try a rewire as well at the same time.
Thanks in advance,
Tate

the rewire increases the voltage the fuel pump receives. the oem fuel pump loses voltage because of the design/materials of the harness. any aftermarket fuel pump is going to need a rewire so it gets the voltage it needs.

^^^ that is good cheap advice. I would also measure amp draw before and after, that will tell you how clogged the filter was.

Jeff

Hopefully installing the fuel pump tonight, any tips or tricks to this?
Tate

Did you ever ch check fuel pressure or are you just going to throw parts at it?

Jeff

I did check fuel pressure, but I've never checked pressure, and the guy I was with didn't really know what he was doing either. we looked up the specs and the pressure would check out fine, but then bleed off. the problem is getting worse, so sooner than later the car probably wont start at all. to get it started now I have hold the accelerator down almost all the way.

this afternoon I plan on checking the pressure with someone that know's what's going on.

Well what where the pressures? It's supposed to be like I said about 39 and 45 with the hose disconnected. Was it close?

Originally Posted by J57ltr

Well what where the pressures? It's supposed to be like I said about 39 and 45 with the hose disconnected. Was it close?

38 to 51 with the engine running and 48 to 54 with ignition on. With the engine running it measured at 52 and was at like 50 with ignition on. I don't think the gauge was connected good the first time I measured. Current theory is a leakyour faulty injector is causing the problem

Possible, but you should have a plume of gaseous smelling cloud when you start. Did you just leave the gauge connected to see how long it took to drop?

Seemed like it dropped pretty quick on the first test but the second test it didn't drop