86 Jaguar XJS V-12 convertible project

If your B bank fuel pressure regulator is leaking, then it’s not holding correct fuel pressure in the rail, and will cause loads of problems. The ECU is depending on a specific fuel pressure. It cannot detect what actual fuel pressure is. So it will be supplying the wrong fuel amount to the injectors.

For the 80s, our fuel injection system was quite advanced, most cars were still using carburetors. But compared to present day, it is extremely primitive.

It’s expensive, but i recommend Bosch for that FPR, as it’s so important. (And don’t waste money on genuine part. Its a Bosch in a Jaguar box)

Thanks for the information. When my new one shows up in 2-5 days I`ll update this post.

New regulator installed and no difference. It starts and barely runs. I tried to give it more fuel (acceleration) by turning the throttle capstan by hand and it dies and wont restart until tomorrow, maybe. Then the same thing will happen,if it does start.If I leave it run on its own it will stall after a minute or so. Also, this problem started after I fixed an oil leak on the valve train cover including the half moon. Before this it ran great except for the oil leak. I cant figure what may have happened to cause this problem. I`ll recheck everthing again. I thought maybe air pump connections, vacumn connections. Any input is appreciated.

Did you change both FPRs?
If not, try bypassing the A-Bank FPR to see if the engine will work.

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No I didn`t change both. I will bypass it today and repost any result. Thanks for the input.


I bypassed the A bank FPR, no luck. I ran a vacumn line from distributor direct to manifold vacumn supply, no luck. I also went back and regapped the throttle butterflys at 0.002 . I didnt have a 0.002 feeler gauge but I used a piece of doubled up aluminum foil as a gauge. I could feel slight tension as I pulled on foil while I adjusted throttle stop screw. Anyone know Is this a crucial measurement? I then adjusted the throttle rods to the capstan. Ill get a set and double check anyway.
It starts and still runs badly if I give about 1/2 throttle now, and then oil/gas started coming out of the dipstick hole. So I know that isnt a good thing. Im thinking so much fuel leaked into the crankcase it couldnt run. Ill post any progress and look forward for any input. Thanks

If they is that.much fuel in the crankcase, it shouldn’t be run as it needs oil, not an oil/gas mixture, for lubrication.

I would start with some basics to establish a baseline.

Drain the oil and see what it looks like and smells like.

Replace the oil filter and add required oil (likely 20W50).

Remove the plugs and disconnect the ignition to the coil.

That will allow you to crank engine easier (with no compression) to make compression tests in each cylinder.

While making compression tests, remove dipstick and place a baggy over the dipstick tube to catch anything which might come out when engine is cranking over so you can determine what is actually happening.

I’m just going on that it ran fine before cam cover gaskets. A lot of stuff had to be removed and replaced. I could be wrong, but it sounds like its running way too rich? Pull a spark plug to see if it’s fouled. Two things i think it could be are coolant temp sender and vacuum line to ecu. Both would tell ecu to over richen the mixture if they weren’t working. Also fuel injectors, if they are not triggering properly and flooding the cylinders.

If you have raw fuel entering the crankcase at enough volume to come out the dipstick, follow Jerry’s advice. You have a serious issue, do not try to run the engine until you identify what is going on.
You may have an injector, or bank of injectors staying open; which could be caused by a grounded injector control circuit, either due to a pinched wire or failed component. Find out which plugs are wet, then use a noid light to see if injector circuit is pulsing or on steady while cranking with the fuel pump relay removed. Pulsing is good, on steady bad. Change the oil, if gas diluted first.
Trying to run the engine in that state could melt down the catalysts, hydro lock the engine, or cause a fire.

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In my trek to get this car running again I have installed all new injectors, rebuilt injector wiring harness, plugs, another ecu which is what had made the difference in running the first time after being stored after more than 15 years. I checked the compression and it was fine then so I will assume it is still good. As I said before car ran well when I pulled it in to fix A side oil leak.
I wont run it with crankcase full and overflowing with oil and fuel so I will start there with new oil and filter. With B side FPR being bad (fuel in vacumn line) Ill look there first. My thoughts are that between the bad fuel pressure regulator and that I didnt gap the throttle plates properly the first time I unwittingly created a flooding situation. One question I had is how critical is the throttle plate gapping in the operation of my engine? With an obvious flooding situation Im beginning to think that between the FPR leaking and my self induced problem of the throttle plate gapping this may be the problem. My trying to start and run the motor has been over a period of time, not once or twice trying to start. Its been several tries trying different things at different times over a period of time. Pumping excess fuel into the crankcase each time I tried to start it. Someone mentioned the throttle plate gapping before and this seems to make the most sense at this time now that I think about it. Thanks for all the input and Ill post results,good or bad. Thanks all.

The throttle plate gap needs to be the same on both sides of the engine, and the throttle rods need to be carefully adjusted, so that “A” bank and “B” bank come off idle together, and pull equally, as you accelerate. If the plates are set too wide, your idle speed will increase, which should be adjusted using the AAV adjusting bolt. Once the throttle plates and rods are adjusted correctly, you can leave them alone. If, however, you disturb the capstan for some reason, the rod adjustment should be checked.

The throttle plate gaps not being adjusted correctly will just make it idle too high or idle roughly.

As Greg said, throttle gap is important for a smooth idle and of-idle acceleration, but not your issue here, the engine should start.
Taking into consideration that compression is good as you said, either something is feeding the engine with huge amounts of fuel, or the fuel that enters does not ignite.

Start with the basics.
Is there good spark?
Are the injectors clicking (all of them) and not staying wide open?
Short the Coolant and Air Temp sensors to be sure.
Check fuel pressure.

Good information here. Though Im going back to basics as suggested. The engine fired up after new oil and filter. I ran it for a short period when I then shut it down to see if it would start again and it did. I then started it again and ran it long enough to get the temp up then shut it down and again a no start condition, again. My in line fuel gauge reads around 36 when I turn the key on. When it isnt running the gauge drops slightly and holds around 30lbs. The gauge bounces all over when it is running.
Ill check for pinched wires again. The coils are original because it did run on the 2 coils. But Ill double check again. Then injector operation next. I have new coolant and air temp. sensors and will short them to test. The amp is a new delco insides. New plugs, wires, cap, injectors and wiring. Actually I didn`t remove any of these when I did the valve train cover gaskets.
Such a basic repair with new gaskets. I reopened the air injection airways in the head, new gaskets, new air injection valve, heater valve as well as all coolant hoses. Thanks for all the input and I will post good or bad results. Thanks again

Is your Tach behaving weird when it’s not starting?

The last I had it running it held at 1000 RPM. High yes, abnormal I dont think so. The only thing I accomplished yesterday was to check the coils. I checked the spark off the coil tower by creating a gap with a screw driver to ground and got good spark. I also checked with a new coil that I had and never installed. Same reaction as the old. Ill check spark at the plugs and check the injectors. First I`ll short the coolant temp sensor though I installed it last year, it is new. Thanks for the input

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What I meant to say Rodney, is if your Tach is going crazy when you crank the engine but it doesn’t starts.
It would be an indication that your Ignition Amp is not good. I know it’s new but thought to ask…

Thanks for the explanation Aristides. Ill check that. I have another of those in spare parts too. Ill be getting back to it this week.
My other problem that just came up is my fuel pump stopped working when I turn the key. I hot wired it and it still works so on to more trouble shooting. I`ll be checking the forum tonight for that one. Thanks again for the input.

The ECU activates the Fuel Pump relay, so either or…

Finally getting back to it. I bought another warranted ECU and I still have no fuel pump activation when I turn the key. So on I go. When I hot wire the fuel pump it pumps up to about 20lbs, not what I had when I checked before this (36 lbs). Not optimal but it does operate. The inline gauge tells me this.
Also there are times when inside the car a buzzer sounds when I turn the key on and when I turn the key off the buzzer still sounds. Even when I remove the key the buzzer is sounding and the only way to stop it is to disconnect the battery. I will check the archives for this issue and if I find the problem I will post the results. Thanks all for the previous help.