600hplt1sm

Hello. Well i was driving the car today on the highway for the first time since my 383 build, and when im driving around town everything seems to be ok, but on the highway today i was cruising around 70mph and my fuel pressure started fluxuating alot at its lowest point it was in the 20's and my AF gauge was reading way lean. I have a new Aeromotive AFPR and I know it has been a source of frustation for alot of us but does that sound like a regulator issue.

What AFPR regulator is most reccomended. I need a boost sensative regulator. And i know the aeromotive is a direct replacement. What other parts would i need to convert it to a different regulator

I have one more question as well, My fuel pressure gauge is all over the place. I know it should go up slightly when your on the throttle, but holding at a steady 3000 rpm the fuel pressure gauge looks like a narrow band AF gauge. Its all over the place. I would think it should be a little more steady

Injuneer

The fuel pressure should hold rock steady with the throttle held in a constant position. Exactly how much is it fluctuating? What is the psi range under steady throttle conditions? Erratic intake manifold pressure/vacuum will cause fluctuations.

What fuel pressure gauge are you using?

Extremely low pressure (20psi) could be caused by a failing fuel pump.

600hplt1sm

while driving through town the psi moves between 38 to 46. all of my gauges are AEM gauges. I also have a boost / vaccumn gauge and it hovers around 15-22 inches of vaccumn. When i was on the highway i was crusing around 3700 rpm when the pressure was flucuating.

Injuneer

Was the fuel pressure moving in synch with the boost/vacuum gauge?

Are the AEM gauges digital?

600hplt1sm

all the gauges are digital, and as far as the gauges being in sync. I dont think so. the vaccum/boost gauge moves a little bit but its very slow moving. the FP gauge moves a ton faster. Like I said around town driving everything seems to be good, but highway driving after about 3 miles at a constant 3500 rpms the car started to misfire and stumble a little

Maybe i will try it on the highway again tomorrow and see if it does it again. I will pay close attention to the vaccum gauge in conjunction with the FP gauge

mrmint69

If you have one you can hook up to the schrader valve and take it for a run I would try that to rule out the gauge your using now.

600hplt1sm

well i had the car on the highway again, & it started acting up again @ 3000 rpm 60mph the Vaccum /boost gauge was holding steady around 18in of vaccum, and the fuel pressure gauge was flucuating between 31- 45 and the engine was sputtering and misfiring. As soon as i got off the highway and started through town it car drove normal,

600hplt1sm

I was checking the oil on the car today and noticed a spark plug boot was burned through. Its not touching the header but its close. Is there any chance that could be the cause of my highway issues when i get the rpms up a little bit , and would that cause the computer to adjust the fuel pressure on its own

Injuneer

Misfires cause fluttering intake manifold vacuum. The FPR is reading the intake manifold vacuum via the vacuum compensation line. That's why I asked if the boost/vacuum gauge was moving in synch with the fuel pressure gauge. Where is your boost/vacuum gauge located? It you have a very long, small diameter hose between the intake manifold and the boost/vacuum gauge, the response of the gauge is going to be "dampened" and will not move as much as the intake manifold pressure actually moves. You want that hose to be as short as possible.

600hplt1sm

my vaccum / boost gauge is actually a sensor that is screwed in a vaccum port on the intake, and then a electric harness that goes to the gauge. Im going to be under the car tomorrow, i might try changing the fuel filter. Im going to change that plug wire boot, I don't know where to start. there hasent been any codes thrown even when the car acts up on the highway the ses light doesnt come on.

600hplt1sm

well i changed my FPR today and went back to the factory unit. Started the car and the FP at idle was a constant 42. not flucuaiting at all. with the aeromotive unit even at idle the FP would range between 37-44. So im hoping that will cure the highway problems if been having

600hplt1sm

Ok. I had the car back out today on a long straight away cruising at around 3300 rpm and the Fp started flucuating againg and the AF gauge was reading really lean. The vaccum gauge is pretty solid its not moving around hardly at all. Once the Fp starts acting up if i let off the throttle and cruise at a rpm of 2500 the car acts normal. Im just wondering if the Fuel pump is going bad. It is a brand new pump

Injuneer

Do you have a lot of pressure in the fuel tank when you open the fill cap? Was the fuel tank level low when the erratic fuel pressure returned?

Excessively hot fuel might be vaporizing in the inlet to the pump, causing erratic discharge pressure.

600hplt1sm

As far as the fuel level it I had just put 15 gallons in it. & i dont remember alot of pressure in the tank. This was yesterday evening and the temp here was high 60's low 70's

600hplt1sm

I guess im going to get the racetronix kit and install it. Id like to get my fuel rails modified to have each rail with a feed line. I know i saw some threads on here with part numbers.