gazfish

Hi,

Tested the fuel pressure regulators as per WSM and one of them has failed and is blocked, the PET version 928 110 198 01 is NLA. Can I use any Bosche 2.5 bar regulator as a substitute to replace both sides ?

Thanks,
Gary

Mrmerlin

Lets identify what your doing,

NOTE these locations are for a USA machine and locate the parts of the fuel system

the part in the CF center front of the engine is a fuel damper. Part 5 in PET 928 110 202 00

the part at the driver side rear is a LR fuel damper. Part 3 in PET 930 110 602 00

the part at the passenger side rear is a RR fuel regulator Part 4 in PET 928 110 198 01

The fuel regulator RR looks identical to the CF front damper except for the part number.

Important you only need one Fuel Pressure Regulator.

NOTE putting a regulator in place of a damper will cut off the fuel to the engine,
yes its happened a few times, so I am mentioning it

What test did you perform? please describe

gazfish

Thanks Stan,

Ran the pump by replacing the pump relay with a link, fuel pressure was 2.5 bar. Clamped the return line from the right hand regulator at the rear of the engine and pressure shot up to 3 bar. Repeated this on the left rear regulator and no change to pressure. No blockages in pipework so rear left has failed. I can hear all the fuel flowing back from rear right regulator only. Didn't do anything with the damper at the front.

Cheers,
Gary

P.S. Pet shows the same part number for right and left for my year.

DeWolf

So yours would be the 4.7?

jcorenman

Gary's sig says '86 Euro so yes, 4.7L M28.21/22. According to PET there are two regulators, one at the back of each fuel rail with the returns T'ed into the return line to the tank. I think that arrangement is peculiar to the 85-86 Euro's but I may be wrong on that.

So yes, it sounds like only one is working. Or someone swapped in a higher-pressure regulator on that one side?

Sunset shows that 928-110-198-01 is available but stupid expensive, 928 Int'l has them for $149 (or half that for used). They are also used on the USA 85-86 engines.

DeWolf

I have one I just removed from my car as I have chipped it and used an '87 FPR. If you need it let me know.

FredR

Gary,

What symptoms caused you to start looking for problems? You have one source of pressure [the fuel pump] and seemingly two regulators on your model year. When you "tested" the rear right by blocking the discharge hose the pressure went up- this tells me that the other leg is blocked either due to a regulator that has failed closed or a blockage in that leg- do you know which of those two possibilities is indeed the case? If you swap the regulators over and the symptoms reverse you know for sure where the problem lays.

A further snippet of info- when a centrifugal is operating at its design pressure and flow rate, when the pump is dead headed [no flow] the pressure typically rises to 121% of the design pressure at rated flow- thus pressure rising from 2.5 barg to 3 barg fits that profile nicely.

Mrmerlin

Based on your test report the RR unit has failed if you saw a rise in pressure after clamping the right side FPR.

Do you see any pressure changes by applying vacuum to either unit.

What are the running issues with the engine that caused you to do this testing?

Can you please post pictures of your engine and the rear FPRs and the hose routing

gazfish

Thanks for the responses, I'll try and take a picture later. The idle has never felt right since I got the car when in neutral or park when warm, it's at 750 rpm but hunts a little so I'm just going through everything. I did a top end refresh recently which didn't show up any issues or make any difference.
Since one of the regulators is working (pressure reduced with vacuum) then fixing the second may not have any impact but then again there must be a reason for two.

ROG100

I have 30 x 928 110 198 01 in stock and my price is $125 each.
2 x FPR used at the rear on all 84 to 86 S2 cars.

gazfish

This is my setup, didn't realize it was unusual ;-)

Thanks Roger I'll PM you.

Mrmerlin

FWIW I would suggest to replace both of them odds are good one failed the other cant be far behind also replace any old fuel lines .

gazfish

I will just in case Stan, the only reason I can think of for having two is maybe the response to changing vacuum levels is faster or has more effect then a single.

FredR

If you have one regulator that is working and it can control fuel pressure correctly at idle [minimum fuel consumption] then that tells me that two regulators are not needed from a system design perspective. Trying to control one variable with two identical back pressure self regulating controllers makes little sense given if there is the slightest difference in set point between the two items one will clamp shut and the other will try to control. If one clams shut long enough maybe it takes a permanent [i.e. seized] set and you get what you are experiencing. If your test data is correct then I doubt changing the duff unit out will make any difference to your idle.

This is indeed a strange system design wise as I am concerned and do not assume they knew what they were doing when they specified it. For sure it would be interesting to know what their design intent was. The only thing I can think of to justify it would be if the units fail in the closed position then it just may be that they used two units to facilitate a redundant back up to get one home in the event one failed. Given the S4 design is different and the functionality required is identical this leaves one to conclude that they realised this was a somewhat dumb or at best unnecessary design feature.

GregBBRD

......a fuel pressure regulator serves the exact same fuction as a damper, with the added ability to bleed off excess fuel. Worth noting, the flow dynamics of a regulator that is bleeding off fuel and a damper are slightly different....which can be an issue, especially with "batch" triggering of the injectors.

Double regulators are simply a "safety net" to ensure that fuel pressures never exceed the desired pressure......

There is also the added benefit of being absolutely sure that both fuel rails function exactly the same, if they have the same components on them.

Yes, they changed this, in the S3 and S4 models....but it should not be forgotten that the two separate sides of these engines ALWAYS have different CO, even with perfectly matched injectors.

....there's a clue in this informstion, for anyone building a high performance engine, where equal fuel delivery and the resulting burn is the same from one side if the engine to the other.