While installing a new battery on the positive side my open end wrench inadvertently hit the interface unit to the trip computer and saw a small spark which doesn’t make sense because the unit is all plastic exterior with no metal showing ! However, now she won’t start! turns over quickly, fuel pump running but not catching at all. sprayed a little ether in the left side butterfly and she caught till it was gone so not a spark problem. Didn’t think the interface unit did anything but tell the trip computer whats going on…Am i wrong?
sorry bout your issue, one thing I know for sure it is always best to install the negative terminal last…sounds as though you are not firing the injectors now. Kirby should know this one posssibly…did you download " The Book "…many issues are fixed by reading it…free download somewhere here…Art…604 465 7244…
Hi Art: I’ve had his book for years great resource. What is strange is;
I have pressure from the fuel pump at the filter but I have no pressure
at the fuel rail! Don’t know how that could be possible. There isn’t any
check valve that would have clogged up between the filter and the fuel
rail…Dennis
Hi Dennis,
Must be the regulators. They are supposed to modulate the pressure, i.e., close a bit when the pressure is low, open a bit when high. The left one is most critical in this. If it is stuck full open the fuel just rushes back to the tank and there’s no pressure at the rail…. Well, maybe a little.
BTW, what is you’re year model? If it’s a PreHE there’s a check valve that screws into the fuel pump, and the fuel feed line forward connects to it. The symptoms of its failure is quick pressure drop after shutdown, making restarts problematic, but otherwise the engine runs fine.
Ed Sowell
'76 XJ-S coupe, red
is there really pressure coming out of the filter…or is it just flow…?..What is the fuel pressure, how much is the fuel flow …gal per minute…@ require injector pressure…call me if you have a cheep rate…Art…
Hi Ed: it’s an 88 xjsc. V12. Had the wife turn the key, then shut it off, I then carefully pulled one side of the fuel line off the filter with a pan under it and towel over it and still got sprayed with fuel. Re-tightened the hose had the wife turn the key on again this time unbolted one and then the other regulator and just a drop of fuel! Missing something just don’t know what. If you saw my original post about this where I stated that this all started when I accidentally hit the interface relay to the trip computer with my wrench as I was tightening up the battery terminal and saw a spark even though the interface has a plastic case you can see why I thought I shorted out either the interface unit or the fuel relay but obviously it’s pumping fuel and if I use ether in the butterfly it will fire though die quickly so it’s getting spark but…I’m at a loss!
Regards: Dennis Cunningha
1988 xjsc 53,000 mile
2003 xj8 VDP 90,000 miles
2006xj8L 75,000 miles
Hi Dennis, I have an 88 XJ-SC with the same set-up as you.Based on how MY car behaves, here’s my 2 cents.When the fuel pump is energized, pressure builds in the line from the pump to the primary FPR- up to about 43 psi. At the same time, the pressure in the fuel rail should be around 38psi. When the fuel pump shuts off, if the FPR’s are working as they should, the pressure in the rail should stay at 38psi or so, but the pressure IN THE LINE from the pump to the first FPR should collapse, as your pump should not have a check valve. Why is there still pressure in the pump to FPR line? Maybe a plugged fuel filter. If you could be more specific about WHICH lines you loosened on the FPR’s, that would be helpful, I think, too. As far as the interface unit- I’m no expert, but I would check fuses #4 and # 15, as a start! Kirbert must not be awake, yet!
Hi Ed:
still trying to narrow down the problem. I keep going back to the spark that jumped to the interface unit next to the fuel and main relay . Is there a way I can test the interface unit to see if it is fried?DAC2589
Regards: Dennis
Hi Dennis,
Sorry, I don’t know anything about the trip computer interface.
Ed Sowell
'76 XJ-S coupe, red
Dennis, you tell us that the car will run briefly when you spray ether into an intake. So you must have spark, but no fuel. Why don’t you investigate the fuel situation further, ie- fuel pressure?
hi Dave, finally got time to work on the jag again. Here is what I’ve
done: I cut in a fuel pressure gauge on the passenger side (American)
fuel line before it hits the FPR with a shut off in the short line from
the tee to the gauge. When I have my wife turn the car on the old fuel
pump pumps but doesn’t get past 15 psi. I changed out the fuel pump with
a new one. Wide wasn’t there so used a spare battery to “Jump” the new
fuel pump and at first no pressure at all so I thought it was sucking
air so I opened the small lower tank checked the filter (Which was
clean) and added fuel to the lower tank and tried again after about 30
seconds, I got up to 15psi!!. Loosened the line from the tank to the new
filter and got a mixture of air and water. Again put some ether into the
butterfly and the engine caught so the electrical side still seems to be
ok. I’m running out of patience! You said the pressure to the rail feed
should collapse but it is still reading 15 psi. Help!
Sounds like a bad B bank FPR. Do you have a replacement?
If not, pinch the line after the B FPR and see if pressure goes up. If so, order one.
Late edit: sorry did you say air and water? Not air and gas? If that’s right ignore my comment and drain that tank.
I forgot an important question. Did this engine run ok before all of these problems appeared?
1 Like
[DavetheLimey] DavetheLimey
http://forums.jag-lovers.com/users/davethelimey
February 7I forgot an important question. Did this engine run ok before all of
these problems appeared?
Visit Topic
http://forums.jag-lovers.com/t/no-start-on-my-xjsc/350007/13 It was
hunting badly with the OEM 16 CU computer and not as badly when I
changed it to a spare 6 CU. That was a combination of the butterflies
being out of adjustment and the tps set completely opposite of where
it belongs. Kirby helped me straighten it out. I then put the 16 CU
back in and when I did and re-connected the battery my battery wrench
hit the plastic interface unit to the trip computer and I saw a spark.
Don’t know how because its not metal like the main and fuel relays
next to it but just in case i changed them out. This is why I thought
the problem was either the relays or the 16 CU computer but I’ve tried
the two spare 6 CU’s and the same result.
In Reply To[Dennis_Cunningham] Dennis_Cunningham
http://forums.jag-lovers.com/users/dennis_cunningham
February 6hi Dave, finally got time to work on the jag again. Here is what I’ve
done: I cut in a fuel pressure gauge on the passenger side (American)
fuel line before it hits the FPR with a shut off in the short line
from the tee to the gauge. When I have my wife turn the car on the old
fuel pump pumps bu…
Visit Topic
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Hi Dennis, if you want to send a “PM” all you do is click on the “avatar”, in my case, the blue car, then click on “Message”. After typing your message, click on “Message” again to send it! Let me ask again- Has this car ever run “just fine” or is it a project car? PM your reply, please. Edit- Never mind responding- I went back in your “Summary” and discovered that this IS a restoration that you have been working on for several years. That is helpful in figuring out your problem! Do what I suggested in my previous PM and let me know the results, in a PM!
Dave.
A final question Dennis. Is there an air compressor with a regulator handy to where you are working on this car? A rubber-tipped blow-gun would be useful, too. There are easy ways to test the FPR’s. Let me know!
Hi Dave: Not a project car low mileage v-12 runs fine. I do have a large
compressor in the garage and am going down there now to blow out the
line with it. Will let you know how I make out. Oh, clicking on your
avatar doesn’t do anything on my desktop or i phone.
HI, I’m having a similar problem with my '88 XJS, I put the battery charger on the battery without disconnecting the terminals. Oops… and now the XJS won’t start. Hmmm… it’s been this way for nearly a year, also there’s a gas leak I’ve need to chase down cause evidently all of the gas has leaked out of the tank. Ugh…
I have too many Jags, keeping them on the road is a full time job. My main focus is on either the XJ6 Series II or Series III cause these are my daily drivers. I’m not too sure why I posted this.
I am curious as to what the final repair is. Also what’s a FPR or B FPR Fuel ??? Rail?
Cheers!
MLee,
FPR is an abbreviation for Fuel Pressure Regulator. The right side of the Jaguar V12 is referred to the A side or A bank, and the left side is the B side or B bank. The A side Fuel Pressure Regulator (FPR) is on the right side and the B side Fuel Pressure Regulator (FPR) is on the left side.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA
P.M.Novak7@gmail.com
Hi The FPR is the fuel pressure regulator at the end of the fuel rail on
each side that the fuel injectors are attached to.