I picked up an 88 XJS a few months back, and it's developed some issues recently.

When it started was about a month or two back. I had only driven it for maybe an hour at a time at this point. I took a 4 hour roll around the highways, and noticed that it was running a little differently by the time I got back to town, couldn't place why. Then, ever since, it's been a bit more rumbly at idle, and will hum quite ferociously between 1000 and 1800 RPM no matter the gear. Also seems to have a bit less go juice in those revs than before.

Since then, it has been hard starting about half the time from cold, and occasionally when hot, where it would not have any problems starting before this.

What I know is that it is *louder* and less peppy than before. There is some soot in the exhaust, but not much and I admit I wasn't clever enough to check that before I bought the car. The fuel rail pressure have been around 50 since this fiasco started.

What I think is that it's running rich because of the high fuel pressure. I've read that it's supposed to be around 34 and I'm way out of that range.

What I have done was replace both fuel pressure regulators. The old ones still worked in that if I removed the vacuum, the pressure went up even more, but I smelled some gas in the vacuum line and just went ahead and replaced them. Not sure if that was a good idea or not in hindsight, the rail pressure is still around 48 when idle and 46 when hot. The new regulators also appear to work, since again removing the vacuum makes the pressure go up. I have also check the return fuel line and fuel seems to flow, I disconnected the return to the gas tank and let it flow into a can.

I have had no stalls at any point, it does any speed I ask of it with no problem, but I am dead certain the cat is not running right.

Cheers if anyone can help me out here

 

Hmm. Some other folks will jump in here and clean up my thinking and limited understanding but

And ALL of my experience (if ya can call it that) is with a 1990 Merelli Car.

Taking the advise of good folks here, I eliminated one of the 2 regulators, using only the one that controls the return fuel on the LH side of the rail. Simplifying moments like this. The feed side I simply plugged the hose right into a barbed connection on the rail. Careful cutting the old hose off to NOT gouge the barbed connection. And,,, are the regulators OEM? Because I went the one regulator route I was able to afford the one, and I did. Seemed like the right thing to do to spend extra here. Cant afford all OE stuff.

I changed all plugs (correct gap or checked pregap is vital) made sure rotor and cap (rotor at least) was ok... New coils can be had and it ain't a million bucks... Rock Auto, United Automotive Products, I think. Had a great experience with them.

I don't know how long your car sat (if it did) but spending a day cleaning ALL ground points, a good number of + electrical connections generally (battery disconnected), keeping track of what you have and haven't done, less and more. Definitely the resistor pack connection at the RH front corner of the car that signals all the injectors. Make sure that the injectors aren't shorting if you can and if possible pull the injectors loom OUT of the floor of the V... Hot environment down there and if there are any splits in the wire insulation injectors will not fire (which just may account for higher rail pressures?) or fire rightly. That last bit is a theory I just made up so it could be a dumb *** theory.

Then, there is also checking the reading at the potentiometer in the throttle capstan. Should be like .32 to .36v at idle position...car off taking measurements.

My Brother, I don't usually offer all kinds of advise because with my fairly limited experience I could lead you wrong AND because I am pretty sure the 88 is Lucas stuff. Again, my experience is with my Merelli Car...

Hope others will help clear up what of what I've said will and won't apply. I want to know myself.

 

Where are you taking your pressure reading?

Cheers
DD

 

Also,,, you have to have good balance on the left and right side of the intake. This can be tough. But a feeler gauge and getting roughly (.002 .003???) at the TOP of the butterfly valves at the throttle bodies is an important area for right and smooth running at any speed and rpm... Check the little bushings that carry the throttle shafts at the back of both sides of the intake,,, linkage points that transmit movement of the peddle, throttle capstan TO the throttle body butterfly valves. Little plastic thingies...

 

Hi Spooky Horn

It sounds like your Coolant Temperature Sensor may be on the way out

Which can lead to over fuelling, which could make your Car very hard to Start or may Start running and then suddenly Stop and all sorts of stuff like that

You could always try the 'Paper Clip Trick' and Bridge the Wires with a 'Paper Clip' or even a piece of Wire and see if that makes any difference

As this will Trick the ECU in to thinking the Injectors have already got enough fuel, rather than the other way around

 

Thanks for the input ya'll.

I'm taking the measurement right before the downstream/left hand fuel pressure regulator, right after the fuel leaves the injector rail.

I believe I checked the throttles and they were seated right shortly after I got the car but I will have to double check... Sounds like I need a checklist. I don't know how much these things jig out of place and I definitely didn't check the bushings.

If I read Jag's docs correctly, the resistance of the sensor goes down when the temp goes up, so a dead short will make it think it's up to temp. If I do this when the engine is cold, and it doesn't run any differently when I short it, the sensor is definitely bad, right?

Is this the sensor that the gauge cluster uses? It seems like the temp gauge reads a sane value, I can't say for sure if it's correct but it rises to just below half staff when it's fully up to temp.

This is a Lucas car for sure.

My regulators aren't OEM, or at least I did not go out of my way to get OEM ones, I got them off of fleabay. If you can run the engine with just the left hand regulator then I suppose I'll remove the right hand one just to keep the variables down. I still got the original ones and they aren't totally hosed, if I need to I can pop the old ones on while I'm figuring this out.

The car didn't sit for too long (I think about 6 months judging by the documentation I got) but it's humid and I don't know what state the wiring is really in. I'll go ahead and do that this weekend.

I'll go over your other points too, I appreciate it

 

Spooky, you be new, WELCOME to the Forums.

When the beast is sorted, please do an Intro in the New Members Area.

I am with Doug, where the pressure is taken is important. I use the hose from the rail to the B Bank FPR.

You "appear" to have return fuel. I say this because many an issue like this can be the return steel pipe under the LH side of the car has been "crushed" by tyre fitters etc NOT using the supplied jacking points.

The B Bank (LH) FPR is the pressure control FPR, the A Bank (RH) is some damper device for pulse etc, and causes more issues than it sorts. Most owners remove that FPR, and for some unexplained reason, things settle down. The A bank and B bank FPR are NOT, repeat NOT, interchangeable, just saying.

The TPS (Throttle Position Sensor), sounds to me like it is out of range, and/or going flaky.

The CTS (Coolant Temp Sensor) as mentioned, may be having a bad day, and at about $30, I would change it, and carefully check the wiring, inside the boot and plug, they do fail.

There is a vac hose, from the centre of the Balance Pipe (that big sucker that runs across the rear of the engine), that travels to the ECU in the boot. This hose blocks up, mainly with rarely used cars, and in some cases, splits at the ECU. That ECU relies on a steady vac signal to calculate fueling requirements. Example: Less vac = MORE fuel, More Vac = LESS fuel. So if that hose is damaged/plugged/restricted. the ECU will get confused.

Your altering idle could be that hose, mainly the section inteh boot, where it travels around under the battery, and terminates at teh ECU. I have seen many, over the years, have split at the ECU spigot.

Read the stickies at the top of this section, it might clear a few things up for you.

I will keep thinking.

 

More thought.

ALL that above will NOT give the fuel pressure you are stating. Fuel pressure in 100% the task of the LH FPR. If you are at that 50psi mark, you either have a return restriction, or a dud FPR. Again the test port position for the pressure is important.

All the others WILL give weird running and rich mixture, etc etc. Its like a Domino thing.

 

Good Morning Alllll 😊

Where is the best right place to test fuel pressure? If I've removed the RH FPR can I insert a two ended barbed pressure dial in the line going IN on the RH feed tube/line? Just wondering.

Would a set up something like this (not exactly this) suffice? ​​​​​​

Amazon

Amazon

Amazon

Amazon

EDIT. Grant, you answered my question! As usual. I had to go back and read more carefully. Still a question is,,, where in the B bank line. I literally ready to go open the hood now and have a look. From the rail I have this manufactured rubber steel line that bolts (I think) into the LH FPR, then from the regulator to the cooler (yes, experimenting I've reconnected it) then to the return UNDER the brake reservoir... Where to place a permanent FP gauge? Is it possible to place one on the feed side, in the line from the pump, near where the removed RH FPR would be?

Sorry. Don't mean to hijack,,, but it's all kinda part of the same convo.

 

JJJ
If you have removed the A bank FPR, you can measure the fuel pressure anywhere between the pump outlet and the B bank FPR inlet.

 

Right on.... Thanks!

 

Jason,

In that B Bank hose/pipe is the hose that MUST be changed of course as part of the post purchase catch up. BUT, that is the hose that I used until the A Bank FPR went in the trash, then as Greg said, anywhere in that Inlet hose.

Nothing fancy, just a barb "T", and sacrifice that hose each time, as I HATE joins etc in fuel hose, looks crap, and just gives me the heebies, must be old age.

 

Got it... I would like a quick look gauge for my fuel pressure. Not expensive and an easy thing... Thanks y'all?

 

Hey Grant, thanks for the info. I figure I can test the regulator easy enough, just remove the vacuum and see how it behaves.

I took a look at the fuel return line under the car and it doesn't look it's been crushed at any point, just a touch rusty but it seems fine enough. What's a good way to test for a restriction? I checked before and there is some flow, but I don't know how much flow I should expect in the return line.

 

Hi Spooky Horn

If you have a look on YouTube, there are Videos on how to Test the Coolant Temperature Sensor, so I would have a look at those first and then do the Test

The Coolant Temperature Sensor Tells the ECU to give the Injectors a bit more Fuel when the Engine is Cold and then less as it warms up but it isn't an exact Science as factors like Ambient Temperature may also play a part, so shorting the plug of the CTS when the Engine is Cold won't necessarily indicate that the CTS has gone bad
Unlike the Multi Meter Test that they show you how to do on YouTube, which should give a much more definitive answer

You also need to bear in mind, that it may not be the CTS that is making your Engine cut out, as the CTS is only one of a number of possibilities, like for instance Fuel Pressure or a Failing FPR on 'B' Bank, as was mentioned by 'Greg'

 

Hey Spooky,,,

My understanding is that the FPR and its function has to do with what in essence is a very sensitive and precise diaphragm system that if OFF WILL return fuel to the tank, and WILL function without blowing fuel back into the vacuum control side, WILL hold a pressure in the rail - and WILL look shiny and new, etc BUT that all FPRs are not the built the same (as they say). There are certain things (and it been a rough journey figuring out what these things are) I will buy aftermarket and there are certain things one (I) should not - Im learning. I fitted a genuine subaru MAFlow sensor (cheaper than the Jag version) to my XK8 cuz folks on the forums said it would work, and it did, but I was tempted to purchase one of the many alternatives that were MUCH cheaper than even the subaru forester MAF sensor. There is a level of precision in the engineering that must be met, MAF is delicate function. Sometimes one gets what one pays for... I dont mean to lecture,,,

I would replace the FPR with a known Jag 5.3 V12 unit and keep it moving. That's just me. Eliminating the RH FPR as was taught to me by folks here.
I also replaced the temp sensor with a known GOOD produced part (as OB above is saying) right away when I got the XJS. I cant remember the supplier.
I replaced ball joints (mid priced) and reported here to learn that others had used the same brand and ended up re-replacing after just 1- 1 1/2 years, while the Lemforder parts will last much much longer. Then, the are the bushings - Metalastic - which folks say are a must - and I was looking at the 1 million cheaper alternatives. A no no.

Its hard to know when to save a buck or two or when to spend the big bucks.... I have made mistakes.

 

Spooky,

There are probably specs somewhere, but I have never bothered. Blow some Comp Air down that line, 20psi or so, NOT 100psi, from the engine bay, and with the fuel cap off, someone will hear the rush into the tank. If its undamaged under the car, I would call it OK.

I would remove that A Bank FPR, and then work from there. PDF attached on that.

As Jason mentioned, some parts suppliers "group" fitment specs too much,. and that can reek havoc. I use OE Bosch for FPR, and YES, they can be $$, but no price on satisfaction.

I will think some more.

 

OK, rummaging in the shed and found:

Old FPR 0 280 160 214 = B BANK, = 2.5Bar (36PSI).
VERY OLD FPR 0 280 160 234 = A BANK = 3.0 Bar (43.5PSI)

These correspond to
EAC2606 = A Bank
EAC4862 = B Bank.

SO, the B Bank FPR is 36 PSI FLAT OUT, and vac modulated for the application. If you are testing AFTER the A Bank FPR, and getting 50PSI, that FPR is wrong or a dud.
IF you are testing BEFORE the A Bank FPR, 50psi would NOT be unusual in my opinion, although I have never taken a reading on any of my cars in that position.

If it were mine, A Bank FPR removed, and then take a reading with the B Bank FPR only as normal. Once that is done, and there is still a problem, then the B Bank FPR is highly suspected to be wrong or a dud.

It all gets back to where you are taking the pressure reading from, as Doug asked way back.

CTS = 0 280 130 026, and is NOT Jaguar specific, it is used on many makes and models with Bosch EFI.

 

I've gone ahead and removed the A bank FPR and getting more or less the same readings, been measuring it right before the B bank FPR. Guess that narrows it down a little...

Gonna order an OEM FPR and in the meantime brush up on the other stuff you guys mentioned.

 

WELL BLOODY DONE>

I am impressed, working quietly and systematically, you will go far in Jag ownership.

Lots to read at the top stickies, and ALWAYS, ask questions, thats what we are here for.