While I've come a long way in improving the engine in my newest Jag since I bought it in June, it still has a couple issues that are becoming increasingly annoying as I bring other parts of the car back up to snuff.

Here's what I've done so far: Replaced all fuel lines, had injectors cleaned & flow tested, new injector harness, removed & rebuilt distributor advance mechanism that was seized, set timing, new rotor, cap, vac advance, champion spark plugs & gapped properly, MSD ignition wires, thermostats, adjusted throttle linkages & throttle bodies (cleaned throttle bodies too)

The first issue is that the car idles at a different speed every time I start it. Anywhere from 600-1300 rpm. Almost certain that this is the AAV so I have one on order.

The biggest problem however is how the engine runs once it's warmed up.

When cold it idles fine. But once warm it idles slightly rough & I can hear what I think is a misfire on the B bank exhaust. When I blip the throttle and let off it spits and coughs as the revs fall back to idle. If I increase the revs gradually with the hood open I can see that the rough running is not just at idle, but does become less perceivable the higher the rpm. It also surges +/- 50 rpm when in Drive with the car at a stop. If I shut the engine down and try to restart it while it's still warm it will sputter and surge rapidly from about 100-500 rpm until I give it some gas and then it will settle at about 400 rpm and run rough. When it does this, the exhaust smells like it's running super rich.

It still feels strong though in the higher rpms. If I hit the kick down switch it'll put me in the back of my seat and rev out to redline and sounds healthy when doing so. It's still drivable when warm but the surging and rough running shake the car at stop lights; once moving all of these symptoms are imperceivable to the driver.

Of note is that when the engine is surging in "D", at a stop light for example, the voltmeter surges in unison with the tach. The PO gutted the air injection system and replaced the OE alternator with an aftermarket one located where the air pump should be. I have wondered if this alternator is my problem as it sometimes reads at 13v and other times will drop to 11-12v. But I haven't been able to trace any correlation with the way the engine runs and what the gauge is reading out. The battery also seems to have plenty of charge at all times.

I've also wondered about the ignition amp or coil. The PO already installed the new style single coil so I would think it's fine but who knows?? The amp could be suspect.

Finally I've thought maybe it's a bad fuel pressure regulator. The one on A bank still has its zinc plating so I think it's relatively new, but the B bank one looks original.

As you might be able to tell I have my theories but they're all shots in the dark at this point. Before I start throwing parts (and money) at the problem I thought I'd run it by the forum if anyone has any thoughts.

 

Hi Ecb Jag

Although you don't say what Car you've got, I'm 'guessing' an 88 Lucas?

From what you have already said, I am also thinking that it could be the FPR (Fuel Pressure Regulator) on 'B' Bank that 'could' be the cause of your problem

Although it won't be the one on 'A' Bank as you could even eliminate that one altogether

But don't get the 'Plastic' out just yet, as it may be a related problem with a very easy inexpensive fix

If the Diaphragm on the FPR on 'B' Bank is either leaking or on the way out, then this could result in a loss of Fuel Pressure, as there is nothing to build this up before any excess fuel goes back to the Tank

Though it could also equally be a loss of Vacuum from the Pipe that goes on the end of the FPR on 'B' Bank (The Same FPR!)
because the FPR on 'B' Bank is Closed by default and needs the Vacuum to regulate the Pressure

So Just to Sum it up a bit and make your head Spin Slower

Leaking Diaphragm on 'B' Bank FPR (could result in Low Fuel Pressure where on some occasions She may not even Start)

Loss of Vacuum on 'B' Bank FPR (could have the opposite effect by increasing Fuel Pressure which could result in Over Fuelling)

So what do you do now?

(1) Check all the Vacuum Pipes from the Inlet Manifold and then take the Vacuum Pipe off the 'B' Bank FPR and see if you've got any Vacuum and if you have that's good! though get a 'Shop' to do you a Favour and Check it over with their Vacuum Gauge

(2) Then while you are about it, 'Sweet Talk' the 'Shop' into also checking the Fuel Pressure and then you will know 'almost for sure' if it is the Diaphragm on the 'B' Bank FPR that is leaking

The reason I say 'almost for sure' is that a loss of Fuel Pressure could also be down to a Blocked Fuel Filter or a Lazy Fuel Pump, that is on the way out (plenty around on ebay for around $30-$40) no need to pay IRO $200 as they are Generic!

(3) The other good news being that the FPR on 'B' Bank is the cheaper one of the two and also you won't have to buy an FPR for 'A' Bank as the later Cars don't have them anyway

Although before you go 'Splashing the Cash' it may be better to hang on and see if that New AAV makes any discernible difference

 

TPS out of range.

Work just called me in, I will post the write up on that tonight, OZ time.

See ya.

 

On Second thoughts:

'I'm with 'Grant' What 'The Wizard' doesn't know, you don't need to know!

 

Here ya go.

Some of the scribe is not needed as you appear to have covered those items, and I know you are clcever enough to skip them, you are a V12 owner after all, superior intelligence being a must.

I have included the AAV rebuild, just because.

 

Hey all, finally have an update on this issue. Didn't have a lot of time to work on the Jag over the holidays. Many thanks OB and Grant for the input.

Grant I followed your instructions and sure enough you were 100% correct. The TPS was all the way out at .56v so I adjusted it down to .34v but also discovered dead spots in the travel so a new TPS was ordered. I was pointed towards a TSB that advised the retrofitting of the newer red TPS style to older cars. So I ordered the TPS EAC9634 and the adaptor EAC9567. Fitment was a huge pain as I had to make a custom adaptor for the flat shaft of the new TPS and the "D" shape of the pedestal shaft.

I successfully installed it but I immediately noticed some issues. For one, the new TPS has many more degrees of rotation than the old TPS meaning that it will never achieve WOT as the capstan only rotates about 90 degrees. This may be the reason why at WOT the new TPS only reaches 3.98v instead of 5.02v like the old one.

More significantly the engine now surges violently when you crack the throttle past idle. It idles fine, and runs well after about 25% throttle but there's a dead space between about 5% and 25% where the engine has no power and does the surging thing. Electrically checked the new TPS and it has no dead spots like the old one. It seems as though the scaling of this red TPS is all wrong for this ECU.

I followed the Technical Service Bulletin from Jaguar exactly but I fear I've just wasted a bunch of time and money and should have ordered the proper Bournes style TPS EAC2670. I had to modify the spindle of the new TPS and the adaptor so now theres no returning anything so I guess I just made this job twice as expensive

Unless anyone has any experience with this red TPS I guess tomorrow I'll be putting the old one back on and ordering the much more expensive EAC2670.

 

Bloody hell.

I used a TPS from an XJ40, found in the U-Pull It way back before computers and Forums. Made my own "adaptor/s".

Prior to that, my V12 HE was operating just fine with a Mazda TPS fitted.

That flat spot/surge may be:

1) Throttle discs not synchronised. They are critical, to a point, up to about 1800rpm, after that the care factor of that engine is zero.
2) Vac pipe/hose TO the ECU is not vac proof, OR, contaminated with oily goo.
3) The mixture "pot" inside the ECU needs trimming.
4) The AAV is not closing 100%, and I am assuming this surging is on an engine AT operating temp??
5) Good old USA emission junk reeking havoc.
6) The PCV valve is "bouncing" on its spring, and that will create an unmeasured vac leak.
7) Ignition timing is out, maybe advanced too far??

We have ZERO emissions where I call home.

Vac advance hose is direct to the spigot on the underside of the RH throttle body.
Engine breaths to atmosphere.
So much so that the engine is really back to basics.

Always remeber, this is NOT a V12, it is a Double Six, in V formation. Meaning 2 X 6 cylinder engines on a common crankcase.

Sooooo, when cracking idle, if the mechanical bits are out of phase, one engine will fight the other, and surging will be your friend.

That TPS getting to just 4v at WOT is a concern, but only dimly, as once this engine is over 3000rpm, its basically doing its own thing. I like to see 4.7 or better, but 5 is not critical. With it that low at WOT, MAYBE it is too low at that lower end, SOOOOOO, bump up the idle split to 0.36, and try it, and VERY importantly, REMEMBER the beer.

Some more beer reading for you. I have some others, but waaaaay too big for this system, so PM your direct email and I will send them.

 

ONE too many beers with dinner and I found myself back in the garage tonight determined to at least get the car back to where it was before today's TPS adventure. OCD electrical readings on both new and old TPS revealed that I was correct about the scaling. The new TPS (EAC9634) distributes the same range of around .26v-5.00v over more like 160 degrees of rotation rather than the Bournes original's 90-100 degrees. (EAC2670). My conclusion is that even with the new TPS dialed in to .34v @ idle, as soon as it comes off idle it begins sending an increasingly low signal to the ECU given the actual throttle input causing the surge.

EAC9634 is the TPS called out for 1989-1991 V12 xj-s but a technical service bulletin from Jaguar in 2001 instructs the use of it for all HE V12's using the adaptor kit EAC9567. I don't know if part numbers have changed or if the TSB is flat out wrong, but in my experience EAC9634 is a NO-GO for Lucas HE V12s originally fitted with the Bournes (larger black) TPS.

I'll be ordering the correct TPS tomorrow and report back when it arrives. As of now I've reinstalled the original TPS and the car is back to running at least as well as it was before this fiasco.

 

Yes, you have been supplied the wrong TPS. The correct one goes through 90 degrees.

 

I'm a little surprised at your experience. Recollecting 20+ years I don't recall this being a problem....but I'm on my first cuppa coffee.

Was your EAC9634 a 'factory' part or aftermarket substitute? Just wondering. Sometimes the aftermarket provides incorrect substitutions. Although, to be honest, in the last few years I've found Jaguar itself doing the same in their own replacement parts scheme.

I had a severe surging problem last year. Go to post #11 of this thread and watch the video:

https://www.jaguarforums.com/forum/x...88-v12-193753/

Replacing TPS did indeed solve the problem. I used the present-day "Bournes" replacement offered by various vendors. A bit pricey. On this car (and on my old XJS) I had used a Mustang TPS (only $25) with good results....right up to the point where it failed

Cheers
DD

 

Doug- My EAC9634 was supposedly an OEM Jag part (and was priced as such!); but now that you mention it neither "Jaguar" or "Lucas" or "Anything" appears anywhere on the unit. It's just solid red with no script whatsoever. Can't rule out the possibility that I got a cheap aftermarket or defective part although my electrical tests would suggest that it is working as it was designed and it looks identical to the one pictured below. I find its 160ish degrees of rotation quite strange because I can't think of an application where any sort of throttle system would rotate that much.

I watched your video and that is exactly what my car was doing when cracked off idle.

Here is the TSB mentioned previously:


Far be it from me to contradict information coming straight from Jag but it certainly didn't work for me as it caused the surging/ dead spot issue. And now since it appears that the older style Bournes TPS is back in production I would advise anyone to avoid the headache and go with the straightforward replacement route.

 

Just a quick update on this thread. Further TPS Woes.

My replacement TPS showed up this week. It came from SNG Barratt and I opted for the aftermarket one for $140 as opposed to the OEM one offered from Jagbits for $370.

To make a long story short it was no good. Grant's excellent instructions on calibrating the TPS calls for it to read .32v-.36v @ idle. Well, the lowest this one would adjust to was .86v before cutting out to .00v. Not only that, it would land on a different number each time it came back to idle i.e. .86 then .94 then 1.02 then .87 etc. The movement of the potentiometer was rough and it felt cheap.

So I'm returning that one and will spring for the OEM one I suppose but right now my attention has been diverted to a broken bolt in my water rail. See my thread "AAV Bolt Snapped Off". As soon as that's sorted out, I'll be back onto this idle issue.

Cheers

 

 

The Bourne's style pot is available (whether made by B or not no idea) from Manners. As is also the new red style.

 

So the brand new OEM AAV is finally installed after the water rail debacle aaaaaaaanddddddd.. *Drum Roll*

It's resulted in zero change whatsoever. zilch. nada. null.

Even with the idle adjustment backed all the way out the car still runs cold at about 600 rpm and sputters. When it warms up it idles at about 800 rpm and still surges +/- 50ish rpm. You can hear it and feel it and see it on the tach. This is frustrating because I didn't expect the new AAV to fix all the issues but I certainly expected it to at least run differently. The old AAV was totally gunked up inside with disintegrated rubber that evidently fell into it and melted from the upper hose.

Seems to me that with the idle adjustment screw all the way out the engine should be idling well over 1000rpm but nope. The AAV screw has no effect on the idle speed. The idle speed at any given time is really anyone's guess. Sometimes as low as 300rpm (stumbling and sounding like its going to die) and other times as high as 800 but all the while surging and shaking the whole car when in "D" at a stop. It also cuts out for a split second when throttle is applied.

Still waiting on new TPS #3 to show up but does this sound like it could all be due to a flaky TPS? My gut is telling me that something else is up. I haven't been able to find any vacuum leaks as of yet, and the ignition system is all new with exception to the amplifier.

I'm still suspect of this aftermarket GM alternator as I mentioned before. I'm sure the prince of darkness isn't too pleased with this American made part invading its realm. The voltage gauge in the car surges with the tach. Also the needle is always in the "off charge" part of the gauge at the very bottom of "Normal" but I've never had a dead battery and the "lightning bolt" is not illuminated on the cluster so inconclusive. Could something screwy be going on electrically that's affecting the ignition system or am I barking up the wrong tree?

 

On the upside, took the Jag on a really nice drive to the California coast today after being laid up in the garage for a month. It's a shame I can't get it to idle right; it drives really nicely otherwise..

 

OK, BUGGA>

Re-read this whole thread, coz I forget stuff now.

The old AAV full of hose bits is bizzare at best, but so be it.

Couple of thoughts, based on that strange idle set up you are seeing.

Trace that AAV Inlet hose, the one that goes to the rear of the B bank air cleaner. Make sure it is NOT plugged. Better still remove it, fire up the beast, and the suction from that AAV should be like Mums Dyson. That adjustment bolt is for HOT engine setting only, YES you know that, just saying.

BEER TIME

The mechanical advance INSIDE the distributor is "Sticky" and not returning to the zero position, and thus holding the timing in an advanced state. Havoc is now your friend. Pop the cap, CAREFULLY remove the rotor, and dribble some Diesel Fuel down the guts of the shaft, then work that shaft, until its "snapping" back to zero with a resounding CLACK. Once satisfied, dribble some Synthetic Engine/Trans fluid down that same hole.

REMOVING THE ROTOR

DO NOT simply pull up on it, the shaft it is attached to will rise up and DESTROY the springs etc in the depths, SAD day.
Use a screwdriver, a BIG sucker, and PUSH DOWN on that star wheel as you pull up on that rotor. Aussie talk: "push down as hard as you pull up, so the shaft STAYS where it is", simple.

HOWEVER

If the car has had some Wombat in there before you, and he has simply pulled UP on the rotor, the springs may already be toast, hence the odd idle speeds, due to the Mechanical Advance not being able to return to zero, and satisfy the system.

I have had to cut some rotors off, as they simply would not part company with that shaft.

BEER TIME

THEN, the vac capsule may be going AWOL, so simply reach in and remove the vac hose, plug the hose (no vac leak allowed), and try the thing, it may be that simple.

I'll keep thinking,

BUT

That AAV should be factory set for 1200rpm COLD, and then you can set the bleed off when hot, with that screw to the desired 750ish rpm.

 

Many thanks Grant. Wish I could buy YOU a beer.

I removed and rebuilt the distributor back in July, complete with a new vac advance unit, rotor, & cap, but leaving no stone unturned I opened it back up today. The mechanical advance is still nice and snappy- added some trans fluid to the rotor shaft while I was in there. Found a couple plug wires that may or may not have been clipped onto the plugs all the way- not sure but they're all definitely on now. Also checked the timing. 17 degrees BTDC @ 3000 rpm w/ vac advance disconnected. Good stuff.

Checked the AAV inlet and yep- plenty of suction there.

Since the AAV adjustment was already dialed way out and the old beast was still idling too slow it seemed logical to check the butterflies again. I had already checked and set the throttle but it was a day of double and triple checking my own work.

Well it turns out the butterflies were too tight. No idea why/how. I checked them several times over the course of this saga. Maybe because last time I did it with a cold engine and this time with a hot one. Set them right and viola, the engine roared to life and idled at about 1300rpm and I was now able to dial in a 750 rpm idle with the idle screw on the AAV.

I still have a slight wander of +/- 50rpm but I'm hoping new TPS #3 sorts that out. Will update when it shows up.

For now, I'd say the idle has gone from a 4/10 to a 8/10. Although, we'll see if it's where I left it come tomorrow. Fingers crossed.

 

You could test this theory if you slacken the drive belt off the alternator and see if that stopped the surge.