VP 5.8 fcpncs. Vacuum and fuel pressure

[kodyman84]

Ran across something interesting while running tests to figure out my idle and power loss issue.

i have a fuel pressure gauge hooked up to the rail and a vacuum pressure gauge/gun hooked up through a T to my fuel pressure regulator. When I rev the engine the vacuum pressure increases and fuel pressure decreases. While vacuum pressure and fuel pressure are supposed to work inversely to each other this is wrong. When you rev the engine your vacuum should go down and fuel pressure should go up. This certainly seems like it could cause my idle and power issues. But what is causing this backwards function of my vacuum and fuel pressure?

 

[kodyman84]

Worth noting, my vacuum at idle is 17 in hg. I’ve checked for vacuum leaks with a propane torch. Nothing. I’ve also checked for fuel pressure leaking and again nothing.

 

[kodyman84]

Things that it isn’t:

iac valve ok
timing is correct
eec and fuel pump relays ok
cap rotor wires plugs all ok
no codes stored on eec light blinked an 11
ignition coil ok


have new fuel pumps and pressure regulator coming.

still trying to figure out why vacuum raises when throttle is opened and fuel pressure drops.

 

[kodyman84]

Got the new regulator in. And as I expected no difference.

Its got to be one of these fuel pumps, I’ll know by tomorrow. If all else fails I may pull that vac line from the pressure regulator and go take it out. Seems to run the best when that is disconnected, which gives me higher fuel pressure. Maybe something is blocked partially somewhere.

 

[Lou C]

Did you check the anti siphon valve on the gas tank to make sure it is not sticking/corroded inside? This is a spring loaded valve that prevents fuel from siphoning out of the tank if the hose from the tank to the fuel pump leaks. This was a problem on my boat when I first got it. The engine would not plane out the boat but would start and run fine in neutral. The mechanic who fixed it explained that the boat builders use cheap ones sometimes and he replaced it with a higher quality Evinrude/OMC one. Still good 16 years later.

Also where are you taking you vacuum readings? It has to be below the level of the throttle plates for a valid reading.

 

[kodyman84]

The anti-siphon valve is located in the gas tank? If so I think I’ve already eliminated that as a possibility. I connected an auxiliary gas tank and it ran with the exact same symptoms.

I’m taking my vacuum readings from the hose that I remove from the pressure regulator. When you say the reading needs to be taken below the throttle plate, are you referring to the height of the port in relation to the throttle plate? Or do you mean that the vacuum gun/gauge needs to be held below the throttle plate?

Coming off of the plenum there is four vacuum lines. The one for the pcv valve is highest. The other three, pressure regulator, map sensor, and one that runs to the fuel reservoir are equal with each other and at the same elevation as the throttle plate itself.

 

[Lou C]

Ok that sounds right then as far as the vacuum test, and your 17" of Hg is good. And if you are running it on a remote tank then yes you can eliminate the anti siphon. Its mounted right were the fuel line to the pump connects to the tank, the barbed fitting.

Are your fuel pump pressure readings in spec?

 

[kodyman84]

At idle the vacuum seems normal. Do you know why it would go up though when I open the throttle? Pretty certain it should go down when the throttle opens.

The reading for the low pressure pump was 4, I believe spec is 4-8.5 psi. The high pressure pump was 39 psi spec is 36-42. These were both with key on engine off. With the engine running the high pressure was 32 psi. I didn’t test the low side with engine running.

 

[kodyman84]

58fcpncs still funny idle and weird plugs

Continue on a previous post for the 96 horizon 200.

pulled the brand new plugs tonight to run a leak down test. Which turned out pretty much perfect. Everything was under 10%.

but the brand new plugs looked like some kind of funky. Check it out. This is two of them but they all look the same.

 

[Bondo]

Ayuh,..... I merged yer threads, otherwise, nobody has a clue as to what yer workin' on, nor what yer talkin' about,......

Keep postin' in this thread, not startin' new threads,......

Other than the poor picture lighting, what do you see wrong with the spark plugs,..??

 

[Lou C]

Plugs look a bit rich, is that the concern? If you’re idling it may be normal due to the engine not getting hot enough to burn off deposits.