I posted a bit ago about my left side (return) regulator seeping fuel into the vacuum line. The general consensus was...which makes perfect sense...that the regulator went bad.

No problem, I order a new one, it shows up today, and I install it. I fire the car up and check for leaks, everything looks good. I go for a test drive (maybe 5 miles or so, speeds up to 50 mph), park in in the garage for a few hours, then drive it to an event (maybe 15 miles)...again, it runs great...and I park it for about 2 hours.

I leave the event heading home, and notice that something seems to "drop out" occasionally. There will be a very brief power loss, but then the power loss becomes more frequent and more severe. Wondering about the tranny, I drop it into 2nd, and the behavior continues. In fact, when I was backing it into the garage, it just about "died", but the power came back and it's now safe at home.

Up until "now" (i.e., swapping out the return fuel regulator) I've never noticed any such behavior. While I'm tempted to wonder about the new fuel regulator, I would have thought that if it were bad from the start it would have revealed itself during the test drive or the drive to the event.

Questions...

Is the behavior consistent with a faulty return regulator?

Short of putting the old regulator (the one that was seeping fuel into the vacuum line) on, is there another way to diagnose this problem?

Palm mentions that the return regulator is the only one that seems to "do anything". When my old regulator was on the car, it ran fine even though it must have had a ruptured diaphragm since it was seeping fuel through the vacuum fitting. How critical is this regulator...after all, until visually noticing the leak, I had no idea there was a problem with it.

As always, thanks!

John
1987 XJ-S V12, 62,000 miles

 

I once had a problem with power "dropping out". It was quite severe, though. Heavy bucking. Long story short, the *inlet* regulator was faulty. I was able to diagnose it only after it went from bad to "no start".

Of course there could be many other causes. In your case, perhaps the fiddle factor.....the possibility of disturbing something else in the process of replacing the regulator. This isn't a criticism. It's easy to do, especially in a cramped V12 engine bay




Worth a try putting the old one back on.

The best way to check for a faulty regulator (other the visual leaks, as you reported) is with a fuel pressure test. Awkward on a V12 and useful only if the engine acts up with the pressure gauge attached!






Right. It actually controls fuel rail pressure by regulating how much fuel is allowed to return to the tank. The inlet regulator is for noise control.



It should've been running rich...but perhaps not so rich that it hurt performance. In fact, the engine may have liked a bit more fuel :-)




It's important.

Cheers
DD

 

*if* the return regulators are hard to get, there may be an alternative.

The 1987-1991 Supra Turbo and NA used a return regulator. The aftermarket versions have the added capability of being adjustable.

 

Agreeing with Doug +++.

If the RH is still in situ I would remove it and plug the vac port.

NOT related, but things that I have had go AWOL with almost the same symptoms.

1) Ignition module.
2) Shielded wire from the ign amp to the ECU.
3) Ignition switch electrical section gone hissy, they do that.
4) Ignition coil/s getting old.

AS Doug stated, something may have been dislodged/disturbed. There are lots of things that would have been moved/pushed/tugged to replace that FPR, so maybe a flaky wire/connector has died.

As Plums said, there are other options. I run a single PreHE FPR on the LH side only, and manually set it to 31psi, and 10 years on, still sweet.

 

I myself went AWOL for a week to sit in the Sun in Florida. I just had a chance to try a few things with the car, and as usual more questions are spawned...

1. I did fiddle with the wires to the water temp sensor. I couldn't make it hesitate at all. When I completely unplugged the water temp sensor, the engine quit, which I understand is normal behavior. These wires are all new and are soldered at both ends.

2. I cut everything out of the vacuum except the vacuum advance by unplugging it from the vacuum system and plugging it into the front port on the RH side. It didn't fix the problem, but it didn't seem to be worse either.

3. All the other wiring seems secure. I replaced all the wiring above the engine, and the car drove fine for several weeks in this condition (i.e., before I replaced the FPR). That doesn't mean there isn't a problem with it of course.

My (possibly faulty) impression of how both the fuel regulators work is that they are keyed of the vacuum system. If there is no vacuum to the regulators, what state do they default to? I'm just wondering if bypassing the vacuum system really told me anything.

From what I've read testing the coil(s) seems it would only reveal a fault if the coil was misbehaving during the test. I understand that later cars have a single coil in lieu of the two-coil system I have. If I end up having to fix this issue by replacing parts, is there a good reason NOT to just go with the single coil setup?

Thanks for all your help!

John
1987 XJ-S V12, 62,000 miles

 

No vacuum to the regulators = maximum fuel pressure. Not sure if the regulator would close 100% or merely close enough to give the maxium pressure within the design intent of the system. It wouldn't be fully *open*, though, that's a given.




Yeah, that's pretty much the case. A coil test sans any symptoms might reveal something to be suspicious about....but suspicion isn't the same a confirmaton, obviously :-)




Google "DAC6093 Jaguar coil"

I'm not sure what the original design applcation of the 6093 coil was but, somewhere along the line, it became the normally recommended replacement for the two coil Lucas system.




No, not really.

I think you can still buy new coils for the two coil system if you have a mind to but there's no advantage to doing so.

There's a certain novelty/curiosity aspect to the two coil system but I don't think too many people feel a strong sentimental attachment to it :-)

Cheers
DD

 

Doug et.al., I got to spend some more quality time with the car today, and got something of an unexpected result.

After fiddling with this and that, I put the "bad" regulator back on...and darn if the thing isn't purring like a cat again.

While that's certainly a good thing, it does leave me in a bit of a spot...

1. I paid $130 or so for a new regulator that doesn't seem to work. Not really a big deal.

2. I don't really want to be driving an air/fuel bomb down the road. For the test drives I was able to seal the vacuum port on the bad regulator, but that really isn't a permanent fix. I think that as a rule leaks get bigger not smaller, so if the diaphragm decides to completely let go some day fuel is going to be going somewhere it shouldn't.

3. Would I be crazy to tee the vacuum connection on the bad regulator into the fuel return line? That way if the diaphragm completely failed, it would only dump fuel back into the fuel line, which would at least be safe. While I'd prefer that it would just work correctly, I'm not sure how to get there from here.

Thanks as always!

John
1987 XJ-S V12, 62,000 miles

 

Can you explain what you did here? Are you saying that the vac hose was removed from the regulator?



Meanwhile, fuel in the return line would be sucked directly into the engine via the vacuum tee.

So, no, you don't want to do that :-)


I'd exchange the (apparently faulty) new regulator for another (hopefully good) new regulator, install it, and see what happens.

With any luck that'll be the end of the problem.

If the strangeness continues we'll have to dig deeper.

One quick question: as it stands, where on the engine is the regulator vacuum hose connected?

Cheers
DD

 

After re-installing the leaking regulator and letting it idle at various speeds for a while (and not hearing any engine hesitation, I took it back off and screwed a small sheet metal screw into the vacuum connection. I then ground the head off the screw, put about a 2 inch piece of vacuum line over the connection, the put a a piece of 180 PSI fuel injection hose over that. I put a metal rod (that was a very snug fit) into the other end of the FI hose, and secured all these connections with FI clamps. The idea here was to seal off the vacuum connection on the regulator, so any leaking fuel would be contained in the hose assembly. This worked for the test drive since no fuel was noted near the regulator at the many stops I made to check it.

I did state clearly the idea of teeing in my previous post. What I was thinking of doing was connecting the vacuum connection on the leaking regulator into the fuel return line, not into the vacuum line. In other words, I would unplug the vacuum line that runs from the engine vacuum system and block the hose that normally would go into the leaking regulator. The vacuum connecting on the leaking regulator would be connected to the fuel return line, so any leaking fuel would just go back to the fuel tank.

The new regulator I got mail order, so hopefully they'll exchange it.

The vacuum routing from the regulator is, as I understand it, supposed to go to the thermal switch on the fuel rail, and then two one of the ports on the front of the LH intake manifold. My thermal switch is broke (something else I need to get) so before the leak was discovered I had the outlet regulator vacuum going directly into the front of the LH intake manifold. This seems to be what EAC9485 shows as the correct routing.

Thanks!

John
1987 XJ-S V12, 62,000 miles

 

Okay, leak contained, good.

What I'm scratching my head about is how engine runs so well with no vac to the regulator....which should result in higher-than-needed fuel pressure in most driving conditions. But, apparently it doesn't go high enough to cause a problem.




OK, now I get it!






Most online vendors have a return policy for defective parts. Some are more accomodating than others :-)




Ok, good.


Cheers
DD

 

Doug...I don't know why it runs so well either! But having said that, both Plum and Grant have mentioned using adjustable regulators with no problems. I'm guessing they mean "static", i.e. you turn a screw or something and the pressure stays put at X psi, vs. dynamic (the regulator adjusts itself on-the-fly). Maybe my broken one is acting like an manually adjusted regulator, and just happens to have stuck in a nice place.

If I'm running too rich, how would this manifest itself? Really really bad gas mileage?

Thanks as always!

John
1987 XJ-S V12, 62,000 miles.

 

Hopefully they'll chime in but I *think* the adjustable regulators work dynamically as well. The "adjustment" aspect refers to adjusting the max allowable pressure. I dunno, never used one. There might be several different types.





I guess so. Or, the inlet regulator is limiting the effects of the faulty outler regulator? I'll have to do some mulling.




Slightly rich might go unnoticed by anything except an exhaust gas analyzer or emissions test....or a slight drop in fuel economy.

Very rich would mean black smoke from the tail pipes, sooty spark plugs, strong exhaust odor, larger drop in fuel economy.

Extremely rich and the engine wouldn't run or just barely run, spark plugs wet with fuel, etc. At this point "flooding" is a descriptor word than "rich".

Cheers
DD

 

I didn't get a chance to drive it tonight (winter is really hanging on in the Midwest), but I did pull three plugs. They all looked about the same, and a representative example is attached. Not a great pic, but the best I could do with the camera I had.

Anyway, to the naked (inexperienced) eye, my first though was that none of them looked sooty. There is no black residue at all. But would soot show up after only a few hundred miles of driving?

Thanks!

John
1987 XJ-S, V12

 

Looks good to me.

Soot can develop in just a few miles....10-15-20.... depending how bad the over fueling is. You won't have to drive hundreds of miles, no.

Cheers
DD

 

Doug, could you please elaborate on what you mean by noise control? Fuel pump noise?

I am always on the lookout for things to ditch from the engine bay and if I get get rid of the inlet regulator that would be great. One less thing to act up. Thanks

 

I think they may have had a problem with a "fluid harmonics" (or something like that...my education ends @ 12th grade [grin]) type of noise and the inlet regulator slowed down or otherwise altered the flow...

<shrug>

Many FI cars have pulsation dampners in the fuel pump or fuel lines for this reason. The inlet regulator was Jaguar's solution, I guess.

You can take it off and throw it under the workbench...and I'll wager you won't hear any difference. I never did.

Cheers
DD