Pre-HE Fuel Pressure Regulator

XJ-S
1

Not all that long ago, I spent some time re-plumbing my aftermarket fuel pump (the original was no longer functional) anyway, when I went to restart my 1977 XJ-S it just wouldn’t kick. It seemed as though pressure just wasn’t building( Fuel pump tone wasn’t changing among other things)

Long story short, I checked the fuel pressure regulators that appeared to be original (with the Lucas stickers and all) and the regulator on bank A was rattling as I handled it. I went to apply pressure to check the reading and found it wasn’t producing pressure at all. The regulator was shot.

Then, upon checking the bank B regulator, It appears to be holding 25 PSI.

So, I went to buy some new regulators and found that the Bosch 0 280 160 001 is no longer available. I even tried buying the Porsche P/N which was a relabel of the same part.

After some trouble (and comparing application vehicles) I came across the Delphi FP10545 which is shown as a replacement part for pretty much every vehicle using D- Jetronic EXCEPT for the Jaguars.

The pressure listed for the Delphi module is 29 PSI as opposed to the 31 PSI noted for the Bosch as noted here: Replacement fuel pressure regulator

Considering it seems the best option, I’ve ordered some to replace my faulty Bosch regulators.

Considering that every other vehicle with D-Jetronic uses these regulators, I’m hoping it’ll do the job. I’ll adjust them to 31.9 PSI if possible, though that 3.9 PSI difference most likely won’t be enough to matter, Considering one bank was running at 25 PSI (dangerously low)

Anyone have experience with these Delphi Fuel Pressure Regulators?

An interesting note:
A LOT of other cars share fuel injection components with the Pre-HE XJS. I checked out a friend’s 1971 Volvo P1800 today and found he has the same Fuel pressure regulator (the Bosch one), Fuel Pump and I suspect Injectors as my 1977 XJ-S.

Here’s some more information I came across-
https://oldtimer.tips/index.php/en/d-jetronic/102-jaguar

2

Might as well aim low. Lower pressure would presumably result in leaner running, and that’ll usually buy you a bit more pep. Too lean, of course, will burn pistons.

3

If OEM pressure is 29 psi, why would you think adjusting your new item to 31.9 is correct ? The 2.9 psi difference equates to appx 4.5 % increase in flow thru the injector. SD Faircloth

4

Yeah. The Burning pistons part is what scares me. Then again, I don’t know the tolerances acceptable in 1977 for a Fuel pressure regulator… It may not make much of a difference.

5

The listed pressure for the Delphi unit is 29 PSI. The listed pressure for the Bosch unit is 31.9 PSI (2.2 Bar). The Bosch units are OEM, the Delphi just seem like my only other reasonable option right now considering Bosch doesn’t make that unit anymore.

I’m working on the assumption that Delphi doesn’t list this unit as acceptable for the Jaguar V12 is because they’d have to adjust it to mimic the pressure of the original Bosch unit and wouldn’t sell enough to make it worthwhile.

Then again, Lucas may have readjusted the units before relabeling them. I just don’t know for sure-

I’d rather start with higher injection pressure and work down a bit.

6

The V12 OEM service manual indicates pressure between 28.5 to 30.8 psi for the D jetronic fuel system. If over or under, readjust the FPR. 29.65 psi is right in the middle. Since it is adjustable, I would aim for 29.5 or so. Either way, you will need to fit a gauge to measure. The easiest would probably use the fuel line for one of the cold start injectors. SD Faircloth www.jaguarfuelinjectorservice.com

7

Oh, that’s interesting, considering the Bosch factory pressure.

Thanks for the information on the pressure.

8

I have to thank you for this as I just bought two new Delphi regulators as per your post.

I finally have my 76 running after 15 months going through the engine bay and everything in it and it’s been running so rich it chokes plugs in minutes.

My fuel pressure was 50 psi (!). When I adjusted it down both regulators leaked fuel alarmingly so I had to shut it off.

Things were looking grim: like using a third party adjustable regulator which would have worked but looked really out of place.

Initial fuel pressure is 26 psi with the Delphis but I’m not starting the car until I have my replacement MAP (old one holds no vacuum), changed the plugs and changed the oil as I’m sure there lots of fuel in the oil now.

Thanks again. Malc

9

That’s great!
I’ve been running mine at about 29 since the original post. No more fuel issues!
NOTE: I did have to balance them as it’s a tolerance from factory, not an exact specification. Since we’ve two banks, I didn’t want one side fueling more than the other. Maybe you had better luck. Watch out for a lean mix.

Another note for those interested-
The 1971 P1800 Volvo did end up with a new Fuel pressure regulator as well, we used the same one and it fit perfectly.
As it’s also a D-Jetronic, many parts are much the same, with some slight calibration.

10

Manufacturers of the time typically fuelled a bit rich to avoid any possibility of a lean mix. Bywater once reported that some of the performance improvement from his modified ECU was simply reducing the overfuelling. This being the situation, perhaps dialling the pressure back a tad on these pre-H.E.'s would make the car go faster! It’d be nice if there were some indication of how far you could go without getting into trouble.

11

I’ve thought about that, but with so, so much sitting in traffic where I am, I’m a bit hesitant to tinker too much.

I suppose one could take a baseline EGT reading and then keep dialing back the pressure until the temperature started rising.
Think it’s worth a shot?

12

AFAIK, the issue with running too lean happens at WOT. If you run lean sitting in traffic, you just get a rough idle.