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As of yesterday I'm the excited owner of a V12! I've always wanted a car with a V12 and for my 50th bday (which is tomorrow) I bought a 1989 XJS coupe. 63K miles and in ok shape. Pics attached.
I've spent the last couple of weeks watching videos and most of last night looking around here. What refocused my attention to a XJS was you tube videos with manual transmissions and ferrari like music. (v12gents)
Mine is a running, driving car. However..... It starts and revs just fine in park and neutral. In gear at anything over 10% throttle, it bucks, spits, and eventually stalls. I searched for hours here last night trying to find info from another post. I understand that's the protocol before barging in and asking for help. However I couldn't find anything. I thought I might have more information to post tonight as I spent some time today poking around and testing. I gunned it in reverse and smoked the tires. However the next time I tried that is did the same thing as in drive. I scanned the engine bay checking the vacuum hoses and associated parts thinking it would be there somewhere. I'm new to this engine but soaking up information rapidly. After seeing how many knowledgeable people there are here, I suspect one of you will point directly to the culprit!
My plan was to see if I could sort this issue so I could actually take it for a short drive. Then I'm going to start sorting things based on that wonderful pdf in the stickys. I'm sorry I forgot his name but thank you to our friend down under. I'm starting with the fuel system. None of my injectors are leaking but those hoses are showing signs of cracking. I'm going to put together a little parts order for the fuel items, vacuum hose and bits, and change all the fluids and filters to start. Time for a spreadsheet.
I usually write a check for my car repairs/maintenance/upgrades but I sure am looking forward to this project. I'll attach a pic of my other car too. It looks amazing but the only thing I did was pay for it.
In gear at anything over 10% throttle, it bucks, spits, and eventually stalls.
The 'could be' list might get a little long on this.
My first thought is the the TPS is on the blink. It can be checked with a digital volt meter. We can tell you how if you haven't already found out thru your previous browsing.
My '88 V12 had a terrible bucking problem when throttle was applied. Long story short, the inlet fuel regulator was on the blink, as verified by a fuel pressure test....which is something that is probably in your future.
I'd also make sure the left and right throttle blades are properly adjusted, throttle bores cleaned, and the linkages properly synchronized. You'll probably need new throttle bushings before adjusting the linkages.
Any of us can help you thru the above items.
Others will chime in with other ideas.
At some point we'll need to know if you have Lucas or Marelli ignition.
After you get this bucking problem fixed there are other very important things to check and service on this car....thing that need attention on virtually every used XJS V12.
Welcome and congratulations! One question: Do you want a reliable super-condition XJS and are you prepared to do the work steadily and methodically?
If the answer is "yes" I can guarantee you will get there, and I can guarantee you will be amazed at the long-distance capability of the car. As to fixing the car, and how best to do it, I would think in terms of "systems".
Your problem is either fuel or spark. My money is on fuel, as what you describe sounds like it is running out of fuel at the intake - but no guarantees! As Doug mentioned the Throttle Position Sensor, although electric, controls the engine ECU's fuel input by telling it how open the throttles are and hence how long the injector pulse should be (my apologies if you already know all of this).
So in your place, I would work though the fuel system systematically:
Test the FPR as Doug mentions
Clean out the sump tank (under the battery) and change its internal filter
Change the main fuel filter
Blow out the fuel line to the engine
Put some good injector cleaner in the tank very strong concentration, and run it through a bit and let the engine stand with it in the system for 24 hours
Test the fuel pressure delivery to the engine and the flow. Flow is important, some clown may have jacked up your car and pinched the under-car fuel line!
Remove the intake-side pressure regulator and connect the feed directly to the fuel injector rail, then test fuel rail pressure as the car is revved. If a problem renew the FRP on the exit (downstream) side of the rail. (In my case I would always replace the fuel rail exit pressure regulator as a matter of course on a car this old, 40 or 50 dollars well spent).
Once done retest pressure, if still a problem, renew fuel pump.
Renew injector hoses and test the injectors for a good spray pattern
Test the vac hose from the engine to the ECU in the boot for holding vacuum.
Look CAREFULLY at the injector loom, if the insulation is dry and cracking, make a new one or buy a new one.
This all seems a lot of work, and you may luck into the first cause of your problem with the first or the last thing you do, BUT if you want a reliable car, do the lot. ANY 35 year old car will need all this done to be a dependable vehicle.
Also, while the list looks long, it is only a couple of day's work once you find out where everything is, and everyone, everyone, on here will be more than willing to help you with each stage of the work. Do not hesitate to ask!
And, worst case, even if none of this fixes it, and it turns out you have an ignition-related problem, none of the work will have been wasted - you want a reliable car right? So it all has to be done , anyway!
Doug, Grant, Greg, Stephen, Thank you guys for the kind welcome. And to answer your question, yes, I'm looking forward to methodically going through this car and making it right! And to Grant, it's a Marelli ignition. I've spent the last several hours at my shop playing around with the Jag. One of my better birthdays! I thought I would share the results before I head home.
The TPS was reading 0.18V at rest. I adjusted per Grants pdf. I was thinking this was it for sure! Tested and it was actually worse. No bucking just instant stall. However with no throttle input, it would roll just fine. Re-tested and it was 0.338, right where I set it. Then I slowly revved the engine while watching the meter and everything looked fine but I noticed two things. One was when I put it back to idle, the reading was now 0.44. I suspect I didn't tighten the screws enough. Two...and this could be important, as I rotated the throttle (with the engine off) all the way my meter overloaded at the range I had set. Meaning it went over 9.9V. Should it top out at 5V? The throttle bushings looked fine and I popped one air cleaner to look at the throttle body. It looked clean. I think next I'll reset the TPS, check the fuel pressure/flow (what should it be/Flow?), set the throttle linkage, and order whatever this leaking part is in the pic below.
I'm going to search here for info on checking the fuel pressure. I have a gauge but I'm sure I'll need to buy fittings. You always do.
I did notice a fuel leak. Pic attached.
Any recommendations on service manuals and where to buy parts?
DO NOT run that engine or even try, until those very sad looking hoses are replaced and the "fuel leak" is NO more.
As for the TPS, USeing the Red and Yellow TPS wres, you should have 4.99 - 5.0 v at WOT. It should only be getting 5v reference from the ECU. I cannot see anything that would give more than that 5v, even in my pickled grey stuff.
For TPS integrity, I use an old style analogue meter, as the needle swing is always more sensitive than the digital stuff.
I reckon you have a TPS that has gone AWOL.
Check the engine main earth strap fiasco at the LH engine mount.
Look at any and ALL the earth wires in the engine bay, there may be a flacky one for the EFI system, it is getting common now, and the few alongside the battery, they be special, as in their integrity. Many a V12 has been hissy due to them being shitty.
The EFI resistor Pack, RHF corner of the engine bay. Unplug it, Lemon Juice the plug and socket, WD40 rinse off and replug, Wonders have taken place with that little gem.
Have fun.
Parts, you be up there, so any of the operators that support this site are good, and I use SNG a lot, both UK and USA.
Not much from a general service point of view is Jaguar specific, so shop a bit, ask questions. I simply cannot remember the last time I darkened a Dealer door, even with the later "plastic" type Jags in my fleet.
beaUTiful car!!! Wise, slow, humble and right to the point guidance is given on this forum. Some great members. Everything is going to work out.
You must stabilize that pot and the readings in the tps...
For the fuel leak,,, I believe that the other end of that vac hose (one of them) goes to one of the fuel pressure regulators on the LH side. That little brown contraption, when working, will signal the FPR to allow extra fuel to leave the rail due to heat build up in the fuel-in rail. Many have removed this contraption... Anyways, If you have fuel there and in the vac system it is a good indicator that the FPR, the diaphragm inside, has ruptured and the FPR is dead. Could be causing or contributing to the bucking problem...
I like that work "bucking"... I could see it becoming quite useful in working with and describing Jag issues,,, without offending the Jag Forum Moderators, lol
Yes. The other night when I got home I started reading and figured out it was probably a bad FPR causing the fuel to go in the vacuum line up to the fuel temp sensor. I ordered both the left and right side FPR's. I've probably read a few hundred pages of that 700 plus page "book" posted in the sticky's. What a wealth of knowledge.
I plan to replace all the fuel lines myself. From what I can gather there are two sizes of fuel lines, 5/16"/8mm and 1/2". Am I missing any others?
Once I can take a short drive or two in this car, I'll pull it in my shop and start the real work. I'd like to feel what it drives like before, and then after all this work.
I'm working on a spreadsheet of parts to order, breaking them down into categories. This will be based on Grants post purchase worksheet and a few other things I've found.
I would delete the A Bank FPR, it is not needed, UNLESS your market legislation states otherwise, which I doubt.
The engine bay EFI hoses are in fact 7.5mm. Most suppliers are selling 8mm, and nobody reports ant issues.
Some cars, repeat SOME cars have a 9.5 - 10mm return hose, from the B Bank FPR to the spigot in the firewall, some are standard 8mm, so that is an unknown until its dismantled.
The only 1/2" are the 2 in the boot. Tank to Sump tank, Sump tank to pump Inlet. The Sump to Pump is a "formed" hose, the other is straight hose.
Update. I replaced the left bank FPR and that was the fix. My TPS issue wasn't the TPS it was the throttle cable. When I put it back the last time I must have turned that outside nut a little and it was holding the throttle open just enough to read 0.44V.
I floored it in my shop parking lot and oh my. The throttle stuck open for a bit. I noticed a tight spot when I was turning it by hand in the engine bay. I was puckering for a minute as I was standing on the brakes! I'm not sure if my car has abs yet, but if it does, it's not working. I laid a nice 20 foot skid mark. Ha.
I'll be pulling it in my shop this week and starting the tear down. I'm going to do all the fuel lines, and everything from Grants pdf in the front end of the car. After that's done perhaps I'll put it on the road and enjoy the fruits of my labor before dropping the IRS and doing the back end.
I suppose this ends this thread. I'm sure there will be more. Thank you guys. I'll keep you posted. I plan to at least take lots of pictures and maybe even some video of the process.
If you're in teardown mode, you might also want to look at the cooling system. The V12's cooling system is plenty adequate if working as designed, and by now most are not. As a first step, I would take the radiator out. It's very common to find them 1/3 to 1/2 blocked by leaves, dirt and debris sucked in-between the radiator and the AC condenser. Rad out is the only way to properly clean everything.
The second thing about cooling is the thermostats are almost certainly wrong. They have a foot that moves with the thermostat to block off the bypass, and most are too short and do not block off the bypass. There is quite a bit in the archives here about thermostat's, but as a shortcut pick up the Gates 33188S from rockauto.com and drill a small (5/64") bleed hole in the flange of the thermostat and install that with the bleed hole up to purge the air.
When you'd refilling the radiator, it can be difficult to get everything fully bled. I usually jack up the front left corner of the car, and remove the small bleed plug from the radiator. Fill the system at the crossover pipe, ( not the expansion tank on the LH inner fender) very slowly to let the air purge as the coolant level rises. Fill it too fast and it traps the air. V12's can be tricky to get completely bled, and thus full. If it isn't completely full, the cooling ability is compromised.
Other thing to check while you have the mechanical fan out is the condition of the fan blades. The early white (now aged to yellow) fans are known to crack, the later black fans are better, and also more efficient. The clutch probably needs replacement by now too.
12-23-2020, 10:31 PM
Bucking bronco
