Fuel Pressure Regulator

I have a bank that continues to run too rich, and have addressed most of the common culprits (injectors, plugs, wires, position sensor, etc). I am now looking at the fuel pressure regulator. Anyone have:

1) ideas on how to test if it is improperly metering fuel

2) alternatives for replacements (Ricambi and others seem out of stock on it, and others are asking outrageous dinero for the part)

I have read through some posts but can’t seem to find any that address these two questions.


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FatBillyBob, I burned through the right side cat. Scoped it to confirm that it wasn’t a bad Cat ECU. Elements melted. Originally had a misfire as well, but that I attribute to crap wires, and have remedied. ODB Check does not show misfire anymore; only the Slow Down indicator remaining.


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Cribbj, I reset codes with ODBII reader, but admit have had troubles interacting with car. The Slow Down light was off for some time after remediation of misfires and the reset. But, given my shotty Autel’s inability to control beyond basic ODBII reads, there’s a possibility I failed to reset that properly.

Will pick up a fuel pressure gauge and test pressure out of the rail. Thanks for the suggestion!!!


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Franschman, I have an Autel DS808, but it has been unable to interact with the ECU beyond ODBII basic functions, even though it is advertised to be able to do so. It will read both ECUs, but before coming to the end of its read, fail with a communication error. I may have to fork over the dough to get to a local shop with a Leonardo (which I suspect will be confined to Miller Motorcars, and the consequent Ferrari law firm-like rates!).

If coolant temp is off, that would change the mix prescribed by the ECU. Would that be fairly quick, though? I would think that would take a bit of driving and warm up to come into play. I get the Slow Down light within seconds of turning over, well before the cats have heated up.

Will add it to my list to inspect. Thanks for the heads up, Franschman!


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Guzzo, I cleaned out the MAFs early in the troubleshooting, but you are right, a functionality check would be warranted here if the fuel pressure seems in line. Have a gauge coming in and will start with that first then walk over to the temp and MAFs next. Thanks for the pointer!!


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Measured fuel pressure, and all is good with the regulator. Spot on to 3.5psi. The regulator is set to 3.8 (how do I know, you ask? It’s stamped onto the regulator! Fun fact).

A couple of quick notes for the next shmuck needing to measure fuel pressure:

The connection is super easy to find, at the front of the fuel rail, covered by an easy-to-remove plastic cap.

My fuel pressure gauge could not activate the schrader valve. It wasn’t “deep” enough to press it. I could have Jerry-rigged something to push against it, but thought better of it, as I wanted accurate measurements. I opted to pull the schrader valve off with a schrader valve tool. You can get these from Amazon and all auto parts places. Release pressure by pressing on valve first, and twist her off; easy task. Tool is pictured below.

Connect your gauge and have your partner (in my case one patient and loving wife!!) turn the ignition. My measurements came quick and solid, and did not change through warm up cycle. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login

So, regulator is not the culprit. Will walk through other suggestions above and update as I go. I am still interested in knowing why the temp warning comes on almost immediately. It can’t be from a temp measurement, as the cats are not even starting to warm up. Something else is telling the system my cat is going to burn. That’s what i need to track down...


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Charlie, I had a few issues which I remedied, each of which would have contributed.

1) First, after changing fuel filters noticed quite a bit of black debris in there from tank. Cleaned out injectors and eventually replaced them, as a couple injectors seemed to have cracks in their base (in hindsight, I think this was excessive on my part; I should have tested them first).

2). I checked the flywheel sensors on bottom of the bell behind the engine block (pulled, tested, replaced). Also pulled and replaced Cat ECU with a good extra to confirm issue was still there.

3). Replaced the wires. This, I believe, was the ultimate culprit. They definitely were needing replacement.

4) after replacing wires I failed to seat one of the plug boots properly. This one was under throttle body. These need a real good push. I ended up using a wooden handle to get some leverage on it and ensure positive connection. Finding this problem actually was not easy, as I went through several other troubleshoots before getting back to checking that which I had just replaced! (Dumb me).

5). Had a related, but unrelated issue with a radiator fluid temperature sensor. Had to pull intake manifold off and replace that. That was definitely giving me some issues.

6). Finally, had an O2 error (showing as Cat performance) due to the temporary Cat I was using. I placed a spacer and cleared that up. I was using a cheap cat while working through this. Prospect of burning up $7,000 cats with the project was not desirable!

My ODBII tool could not read the Ferrari codes, even though it advertised that capability. This greatly complicated troubleshooting. I would have been able to track the specific misfire much quicker and ID’d the wires. There were a few other steps I took to troubleshoot which proved to be unrelated.

Really got to know this lovely engine, though! Some crazy qualities to it (like two separate engines essentially connected to a common crank!), but cool nonetheless.


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