Can one of you fine knowledgeable folks tell me how to check the fuel pressure and what the pressure value should be. 1990 f250, 7.5l. I'm just wondering if my pinging problem could be due to low fuel pressure, running lean. What tools are needed? Where can I get them? Is this something a parts store loans/rents? I've seen something on the fuel rail that looks like a Schrader valve, is that the connection? Does disconnecting the vac line to the regulator change the reading?

All comments greatly appreciated.

 

You can buy a fuel pressure gauge at any parts store, Sears, etc. Don't know if they also rent them or not. I think I paid $30 for mine. You already discovered where to hook it up. Just screw the gauge on and start the truck. It should read between 35 and 40 psi. Be sure to check the pressure on the other tank now. With the truck still running, pull the vacuum line off the fuel pressure regulator. You shouldn't have any fuel at all in the line, if you do you need a new regulator. The pressure should jump up to about 60psi when you pull the line off. Now shut the truck off. Wait for two minutes, if the pressure drops more than a psi or two you have a leaky or stuck open injector or bad check valve in the tank. It should take several hours for all the pressure to bleed off, but there is a relief valve on the pressure gauge that you use to bleed off the excess fuel.

That about covers it... and don't be surprised if you don't get any pressure right away when you turn the key to on, it takes a bit for the pumps to build up pressure.

 

I just went through this drill with my '97 F-350 w/ 460. I borrowed a fuel pressure test kit from Autozone ($150 deposit). Stock pressure tested at 39psi. I installed headers and exhaust, intake, cam, ported intake, etc. and was pinging under load. I ended up installing an adjustable fuel pressure regulator set at 44psi WOT (46psi w/ vacuum unplugged). It was a night and day improvement for my engine. No bog or ping and my engine pulls strong.

 

The Pressure should be about 32-34 PSI at Idle and 40 PSI if you flip the throttle to WOT fast.
The pressure will jump to about 42-45 PSI when you pull the vacuum hose off of your engine, 60 PSI is for a 4.9L engine.

 

Yep, you're right. Brain slipped into neutral for a second.

 

Thanks Everyone for the great information. I now need to come up with the tester. I looked on the Autozone website and did not see a fuel pressure tester available as Dezertracer mentioned. I guess I'll actually have to stop in at the store to see as some items may be only available in specific areas.

Thanks again!

 

I bought mine from amazon.


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