Fuel pump regulator question

[White Lincoln]

As you may know, or not, I have a 137/173 codes / bank 1 & 2 running rich (only 2 cats on a 94). I have no idiot lights, no rough idle and it runs great, but I noticed in my notes that I got the codes after replacing the regulator with a new from RockAuto last year. The regulator is spec'd for for 94-97 Ford, Lincoln and Mercury 3.8l and 4.6l. I cannot find the PSI specs on the regulator from any of the vendors the manufacture. I noticed that with several of the regulators' on RockAuto, they have various PSI ratings up to and over 50 psi, which I have learned is typical with RO parts. The current pressure running at idle is 38 and "giving it the onions" (strange phrase) it is around 40 psi.

Is there a way to test the regulator to see if the pressure spikes, drops or basically is part of the problem? Before I start part swapping, I wanted to see if there is a way to tell if the regulator is working correctly (using a pressure gauge or other means) and allowing more fuel than needed causing the rich codes. I have pulled vacuum the line several times when pulling the upper intake and never say gas from the regulator or vacuum line, so I don't think its leaking.

I read a few articles about bad regulators, but their issues where rough idle, idiot light was on, etc... I have none of those issues suggested.

 

[theterminator93]

The fuel system on these cars is designed to deliver 39 PSI between the rail and manifold vacuum. This is to ensure consistent fuel delivery rate from the injectors at various throttle positions.

Increased manifold vacuum decreases the absolute fuel pressure in the rails to maintain this balance. Without vacuum (or at WOT) there should be 39 PSI at the rail.

Fuel pressure at idle would equal your WOT/no vacuum FP reading less your manifold vacuum. Idle vacuum is about 20" Hg, or 10 PSI of negative vacuum, meaning fuel pressure of about 29 PSI on the FPR.

Based on your statement that you have 38-40 PSI at idle, it sounds like your FPR is designed to maintain about 50 PSI in the fuel system - or it's shot and it's not reducing fuel pressure with vacuum. "There's your problem".

It needs to be replaced, but you can determine if it's the wrong spec or just busted by checking to see if your pressure goes up ~10 PSI if you remove it from vacuum. If the pressure goes up, it's the wrong spec. If the pressure stays the same, it's just shot.

 

[White Lincoln]

Wow. Awesome answer. When I was reading up on fuel pressure for this year/ model, it seems that 38-40 as fine / normal. I will dig some more for specific specs, check the Town Car pressure and pull the vacuum on both cars to test drop (it uses the same regulator). And you are correct (of course) that the pressure should be constant and not fluctuate. It was really good to hear and explanation in the terms of the issue is the regulator.

The next thing I am wondering is if the fuel pump is delivering enough fuel, but that should not matter if there are no issues with acceleration, throttle rev, etc. The issue would still come back to what is regulating the fuel amount. Too much fuel (rich codes) would indicate the pump is fine, but the regulator is not doing its job.

 

[White Lincoln]

From, what few I could find, 94 Ford specs, including the fuel specs from my 1994 Service manual.

 

[theterminator93]

The Bosch EV1 and EV6 injectors found on these cars are flow tested at 39 PSI, which is what's in the tune, FWIW.

 

[racecougar]

Wow. Awesome answer. When I was reading up on fuel pressure for this year/ model, it seems that 38-40 as fine / normal. I will dig some more for specific specs, check the Town Car pressure and pull the vacuum on both cars to test drop (it uses the same regulator). And you are correct (of course) that the pressure should be constant and not fluctuate. It was really good to hear and explanation in the terms of the issue is the regulator.

I think you misunderstood Brandon's post above. The FPR maintains a 39.15 psi delta over manifold vacuum. You should see ~29 psi at the rail at idle (max manifold vacuum), not 38 psi. At WOT (no manifold vacuum), you'll see 39.15 psi at the rail. Rail pressure should absolutely fluctuate based upon manifold vacuum.

 

[White Lincoln]

I ran the car hard this morning, race hard. I performed very well, better than it has in years.

I ran some tests between both cars that share the same regulator. At the rail Schrader valve:
Town Car
33psi @ idle
40 psi @ rev (WOT)
No vacuum - 40psi idle and rev
Shut off - maintains 40psi

Cougar
33psi @ idle
40 psi @ rev (WOT)
No vacuum - 40psi idle and rev
Shut off - maintains 38psi

Cleared codes and ran KOER test and still have 137/173
Timing was off by 1, reset to 10btdc

Sprayed brake cleaner on the vacuum line fittings and lines and no change in idle. The idle is steady at 730-750 only dropping to 730 on occasion. I still have not tested the return line to the tank for the cannister and I need to test the return line from the fuel rail to tank as well.

The only variable after I got the codes was the regulator. I still have the old one that was on the rail. I did change the O2's after I got the codes, but that did not change anything. I have to wonder if it is going to take some time for the car to re-adjust to all the changes, but then I think that is BS and the code should clear if the problem is fixed. I will scratch my head at this for a while until I stumble on an article with a similar issue.