jeepfan93

998 keor

bluecar5556

Do you have 5 volts at VREF on TPS?

jeepfan93

Ok we replaced the TPS. That cleared the CEL. We now have battery voltage at the inertia switch. Still have 20 PSI at the test point. So going to replace the FPR. Remove the vacuum line and no change in fuel pressure. No fuel in vacuum line but could be running wide open and sending fuel back to tank. Will post results, Thanks for the feedback gang

bluecar5556

Pinch off the return line and see if the pressure increases then you will know for sure.

jeepfan93

Well, I did't pinch off the line, but I replaced the FPR. No change still 20 PSI. Maybe something about a check ball in the other tank?

vjsimone

I hate when the thread ends like this.......

bluecar5556

Many frown on reviving a 6 year old dead thread. I can't sleep so what can I help you with?

vjsimone

My regular answer is the truck is 32 years old, and any information back 32 years is relevant to me.

But, in this case, I was killing time waiting on my schrader valve tee to arrive so I can test a suspected low pressure scenario.

https://actron.com/content/dual-mani...der-connection

My, tis gett'in late....

bluecar5556

Why do you need a Schrader valve tee? At any rate, there are only a few tests to narrow down low fuel pressure.
1) Connect fp gauge and start engine.
2) Pinch off fuel return line at the regulator. If pressure increases, check vacuum line and if good vacuum, replace regulator. If pressure does not increase, proceed.
3) At this point, you either have low voltage or current at the pump selector switch, at least one of the one-way check valves in either pump has failed open 'allowing fuel to bypass.'
4) If low pressure is common across both pumps, I would check Voltage and amperage draw at the fuel pump selector switch first.

vjsimone

Unfortunately the 1985 F150 5.0L EFI Engine option did not come with a schrader valve. The engineers realized the error of their ways and added the valve to the standard 5.0L EFI fuel rail in 1986. So, I am adding this one so I can check the FP. The easiest spot is the rubber hose leading to the regulator.

Just put a new regulator on last week, there was no clear way to check FP at that point either, but did start the pump/s via the OBD test connector, and got what I thought was a weak squirt. (even by urologist standards). Frustrating not being able to test the pressure.

Even though I'm hard nose about checking the pressure, I suspect the in-tank pump is not pushing the fuel to the HP pump. I hate guessing on FP.

So, the next time crawl under, I want to disconnect the HP pump electrical so I can hear the in-tank pump a little clearer, not sure if it was running or not.

Also I need to remove the 32yo looking plastic Fuel Reservoir/Filter to clean or replace, if I can get it open, sprayed and tugged on with no joy. This will be an opportunity to check the pressure coming from the single tank, no selector switch.

I'm sure this will get down to electrical checks and tank pulling or bed removal before its all over. At this age, I'm sure there are a few corroded points of interest.

There has been a big sucking going on in my brain whilst attempting to absorb 35 years of past history in just 2 years. Trust me though, I have a plan, but I am always receptive to an easier, cheaper, faster way of approaching this project truck, and do appreciate all the knowledge documented here and provided by you members. Thanks for throwing stuff at me, keeps me honest and hopefully smarter than my smarter than me phone. Thanks.