P80 Fuel Pressure Regulator Thread - Function Variations Sources DEC 2019

[abscate]

Placeholder to start a thread to document

What the FPR does

The different types used on Volvos

Volvo and Bosch Part numbers

Sources for parts - as of DEC 2019 at least some part numbers are discontinued.

[abscate]

My semi-educated musings on the FPR function - not all of this is confirmed. Pretty much a core dump of my understanding which is at the 3-4 Rivers level (non-expert)

My understanding is the FPR is needed as the early fuel injection systems do not have enough dynamic range of injection times to precisely meter the fuel required for the engine to keep stoichiometric air fuel ratio.

Injection quantity is open loop, in the sense that while oxygen content is monitored by the OXS, that can only tell the ECU to adjust subsequent fuel injection times, so under rapidly changing loads, air/fuel mixtures is not optimized.

The ECU has some number of bits, which get converted into an analogue injector pulse (technically, a closing of the injector ground in the ECU, since these cars get continuous 12V on the injector and are fired by grounding.)

The amount of fuel injected is assumed to be correct based on a certain working fuel pressure; small changes in the fuel pressure (5-10%?) will result in bad running, likewise if the pressure isn't stable, the system won't work well.

My conjecture is the early systems don't have a short enough rangel to control the injection amount at low fuel load.

Thus, the FPR.

At high manifold vacuum (low loads), the FPR reduces fuel pressure by sending pumped fuel back to the tank via a diaphragm control. Now the ECU can use the same longer pulse it uses as full flow, but meters less fuel to suit the load.

My deeper conjecture is that the FPR is a bimodal control - that is, it sets the incoming fuel pressure to one of two values - one for light load, one for full load. I might be wrong on this if the ECU is fast enough to use the OXS feedback to adjust the low pressure injection times - but that would sort of preclude the need for the FPR?

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More conjecture

In comes ME7 on the 1999 model in North America

Fuel pressure is now mechanically regulated to 50 psi +-

My guess is the new software has more bits and/or is faster and can control fuel injection metering across all engine loads at constant fuel pressure.

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And a post on function

My earlier understanding was that the FPR just senses manifold vacuum and adjust fuel pressure, so four hoses
One vacuum
One fuel feed from tank
One fuel feed to fuel rail
One fuel return line

Of course, this was exposed as wrong in this thread.

viewtopic.php?f=1&t=92321

On turbo cars, the vacuum is sensed between the manifold and snorkel

On 1997 cars, the FPR vacuum comes of the purge canister line, and is even more complicated

[abscate]

More conjecture

My thoughts above on the need for the FPR might be completely wrong

Another thing going on is the pressure differential on the injector will change from no load to load condition by about 10 psi, or 20 psi for a turbo.

Wi th a base fuel rail pressure of 50 psi or so, those are big changes.

[befarrer]

I haven't looked closely at the Volvo Pressure regulator on my 98, it's in a dumb spot. But the fuel pressure regulator usually keeps the same fuel pressure relative to manifold pressure, thus keeping the same injector flow rate. Usually most vehicles are at the 40PSI range with the pump running, and engine off. With the engine running, it's lower, usually 35 PSI or so. But there is less pressure in the intake, but there is still a 40 PSI difference from intake to fuel pressure. Under boost, say 5PSI, you should see 45PsI fuel pressure, but it's still 40PSI difference from the intake.

[abscate]

Thanks. That would argue that the FPR is continuously variable in absolute fuel pressure.

If that’s true , then on -1998 cars the fuel pressure setting is open loop as there is no fuel pressure sensor on these cars. Fuel is getting metered by injection time on faith that the FPR is keeping correct pressure differentials

I’ve scoured the web looking for more info on this and haven’t gotten deep insight into this yet.

[jimmy57]

Early D Jetronic on the cast iron OHV 4 and 6 cylinders were fixed fuel pressure if anyone cares. CI fuel injection is a whole 'nother matter. Through 98 on the bulk and through 2004 on the S40/V40 NEDCAR models: fuel pressure kept a constant value above intake pressure. MFI/ECM does not need to adjust injector opening time pulse for fuel pressure variation affecting flow since the force against outlet of injector will be kept constant. FPR on all these will have the hose on end of FPR going to intake manifold port. The intake manifold pressure effectively is another force added to the spring in the FPR. Some 95 through 97 non turbo 850 models get two speed fuel pump in order to reduce fuel heating by decreasing fuel volume recirculated from fuel rail mounted FPR. The ECM grounds one pin of pump relay that controls a switch coil delivering power to pump via a cowl mounted resistor below 3000 RPM. ECM grounds another pin for switch coil for direct power supply for full fuel pump speed above 3000 RPM. The new for 97 LPT and 98 HPT 5 cylinders get FPR reloacted off the fuel rail by mounting it on fuel line just behind engine on firewall. The intake manifold hose arrangement on these is strange. There is a 8 mm line for intake manifold pressure going to the T fitting on end of FPR with a small hose leading to a small metal pipe all the way over to inlet hose from MAF to turbo. If the pressure source did not have that orificed T fittting and the small vent line condensation could collect and freeze in cold temps.
99-2002 with 2002 through 2006 getting fewer engines through time with this version: FPR with no intake manifold hose. The fuel pressure is fixed. Generally 300 kPa(43.5 psi) for non turbo and 380 kPa(54 psi) for turbo. Starting with SULEV non turbo 5 cylinders the total non recirculated fuel supply systems with a fuel temp and pressure sensor and an ECM controlled transistor power stage for fuel pump current gets introduced. For 2004 some low pressure turbos get this and then more and more get this until the White Engine 6 cylinder Turbo reached EOP. For 2007 all get the variable fuel pump speed system. The system with variable fuel pump speed for fuel pressure regulation have FPR but it is a backup max pressure in cases where the regulation system has faults. These systems have some features that confuse pressure testing. The fuel pressure will be higher on restart after engine has run at full operating temp for a a period and also above a certain engine load. These conditions would mean more heat storage in engine. Once engine is started the pressure is higher by 100 kPa for about a minute to assure any vaporous fuel is condensed to liquid until cooler fuel flows into fuel rail.
Markets other than North America have differences in the time line for the changes and may not get some of these features due to varying emissions standards. Vapor leakage standards vary and the testing requirement for vapor leakage occurs a few years later in other markets.

[volvolugnut]

The different types used on Volvos

Volvo and Bosch Part numbers

Sources for parts - as of DEC 2019 at least some part numbers are discontinued.

Absacate, do you plan to include info on the early CI fuel injection systems? This is where I started with Volvos with a 1975 245. If you want to include info on the CI systems, I may be able to provide some help. It is not that I know a lot about them, but I have gathered several books about these type systems. They were also used on many other brands including Mercedes, VW, and Saab. I recently discovered there are now seal kits available for these fuel distributors.
volvolugnut