Need advice on next steps. 92 XJ40 151000 miles. 2K miles since head gasket repair, new valve seals. Runs and drives in town OK, mileage poor. Will not run at steady 50-60 mph on freeway without a lot of stuttering, and bucking as if somethings not firing constantly. Had EGR code, replaced EGR and solenoid. All Vacuum lines check out. Recent new good set plug wires, Plugs, rotor, dist cap,donor car tps (old one appeared to have flat spot),coolant sensor. Just replaced coil (2nd time) with new Bosch, and last week new CPS, and new Lucas amplifier. Yesterday replaced the Oxy sensor, and while I had down pipe off (Just downstream of exhaust manifolds) noticed a lot of black Carbon in both pipes. Cats look open (can shine light through waffle lattice). Took car to local Muffler shop to check for excessive back pressure, he used hand to feel at exhaust pipe while partner revved up motor, said appeared fine to him. Did notice black smoke while testing. Have used Vacuum gauge to help check for symptoms but all tests appear normal. Injectors all "clicking" Noid lights all show equal, same resistance.
Whew. Sorry for long post, but open to all ideas going forward.MAF sensor expensive to replace as is ECM, but not sure what else to try. Either getting too much fuel or not burning it properly. If you stand on the throttle, takes off like a rocket to at least 85 with no problem; only has problem at steady speeds starting around 2k-RPMS. Ring any bells with anyone??

 

Shelby:
I've read this through a few times (and you've apparently stumped quite a number of people based upon the number of replies!), and each time I think to myself that if my Model A displayed these symptoms, the first place I'd go would to be adjust the timing. Now, I'm really not a mechanic of any kind; and despite liking to drive them, I don't really know tons about these cars. But, it does make sense to me that if you recently had the head done, if the timing was put off in reassembly, wouldn't it cause many of these faults? I hate to even suggest it...

Scott

 

Cam timing was dead on using cam timing tool during reinstall of head, double checked once already. Acceleration is fine up to as fast as I want to go. Problem seems to be during steady throttle "lean out". Have the older pre-gold plated MAF sensor connections, perhaps that is problem. Appreciate reply, hoping for more input.

 

Shelby,

Like Scott, I read and re-read your post several times. I kept thinking TPS, but then re-read and you stated you replaced it, but.... it was from a donor car ... correct? After you installed it, did you meter the output of the TPS through the full range? I'm sure you're aware the TPS has a variable output to the ECM, affected by the position of the throttle housing butterfly.

The only other item that comes to mind, which produces similar behavior at load, is the oxygen sensor, but you replaced that with a new one... right?

It sounds like you have spark and fuel is being delivered to the rail. Also, you state when it's opened up, there is consistent acceleration, so that leaves components that consistently control mixture. MAF, TPS, ECM and temperature sensor are the first things that come to mind. I'm sure there is something I'm not thinking about.

Sorry I can't provide "the answer", just trying to assist in thinking it through.....

 

Thanks for your input. Replaced the TPS after discovering "flat spot" during checking original through range. Donor TPS showed smooth range of values from idle to WOT,within values according to Haynes manual. Oxy sensor replaced with Walker brand new item. Just visually checked ECM connections, all look clean w/ no visible corrosion anywhere. Also checked resistance values of all plugs + HT coil wire today. All OK. Someone in past mentioned possible fuel pressure/injectors could be potential?

 

Very strange shelby,

Does your car have a nice idle? if it is 'hunting' an airleak perhaps?

inlet manifold gaskets & injector 'o'rings can perish over time.
151k may suggest worn injectors, but ive seen 250k xj6s run without fault!

have you changed the fuel pressure reg? though i cant see this causing your fault.
second hand MAF sensor is probably a sensible gamble.

cant really think of much else really; you've done everything!!!

hope you sort it!!

 

Shelby,

I thought about the fuel pressure, but your original post described the symptoms showing up when the rpm's reach aprox 2k, so I figured your idle must be ok. I would think if there is a fuel delivery issue (fuel pump and/or injectors), you would have a rough idle as well, so I didn't bring it up.

Do you have means of testing the fuel pressure at the rail? I saw your post regarding rebuilding the fuel injectors, is that post a tie-in to this one?

 

Car idles pretty well, with what sounds like an occasional "miss".
I posted another thread simply asking if a 1992 XJ40 w/ what appears to be original Lucas injectors had a built in filter. I ordered a "repair" injector set from O'Reilly's giving them the year make and model as well as Lucas injector#, thinking it would come with filters. They claim that inj. did not have filters, but I remember reading some Jaguar diagram that showed filters. Didn't want to pull fuel rail and injectors and find out they did have filters and have car down waiting to find filter set. Am wondering: If they did have filters, mine may be partially plugged, and while trying to signall a low demand for fuel (steady 55 MPH) it may be actually starving for fuel and battling input from OXY sensor etc. If no filters are present, I will go ahead and replace O-rings, although spraying carb cleaner or starting fluid around injectors while idling has no effect to indicate bad seals. Not too many more places too look w/o double checking what has been done.

 

Shelby,

Get your money back from O'Reilly's. Go to the web site I sent you and call those guys and ask them directly if your injectors have filters. Also, here' another site you can call, but mind you, he's in the business (makes his living) out of rebuilding fuel rails/injectors, but he may answer a straight forward question:

Jaguar Fuel Injector Service

I haven't used him, but have seen many recommendations for his service and it appears he's a Jag enthusiast, so just shoot it to him straight

I have learned the hard way, I do not trust any big-box auto retailer for information, or that the supposed "OEM" stuff they have are properly made to specifications. Research this forum and a few others for recommendations before you buy. The big-box retailers are ok for very simple consumable items (filters, oil, etc.), but don't get items you highly depend on for the smooth operations of your vehicle. There are a few vendors that I consistently buy from, if you send me a pm I'll send you the names. I have no affiliations with any of them.

Here's another site you might find interesting. It's a write-up on an earlier Jag, but the principles are the same:

http://www.backglass.org/duncan/jag/injectors/

 

Hi Shelby, was looking through the TSB's and came across a few that might apply to your situation - this one is worth a gander, but there are others on similar subjects - good luck!

https://www.jaguarforums.com/forum/a...s-stalling-pdf

 

Shelby
You could try another thermostat' if faulty and not bringing engine to right temp it will cause it to run to rich and foul your spark plugs'
I had a similar problem with my XJR 300. Its worth a try ; Good luck Ray ON EDGE

 

Same problem here, car running cold/rich - new thermostat was the fix, thanks on edge

 

Update on "Missing" problem. Found a set of new old stock Lucas/Bosch injectors and installed them. Some lots of visible rust in Injector rail (removed now); was sure I had found the main problem. STILL have same problem! Have been checking off items from Jaguar 4 page "stalling" tech bulletin, am down to replacing MAF sensor or ECM. Will change out thermostat today first, and recheck R values on TPS (used) throughout range. Hate to just keep replacing parts, but no codes to indicate problem.

 

Ihave in the past found that the crank shaft damper assembly to be a problem where as the rubber around the centre becomes perished and alter timing when load put on;
Or the timing ring could be cracked where it bolts to back of crank shaft damper and give similar problem. I have also found that some aftermarket rotors to be to loose on the shaft in distributor which at higher revs will give constant miss .Good luck well keep trying

 

Thanks to latest input from Lawrence and On Edge, and everyone who have weighed in.
Have installed new thermostat; engine comes to "normal" temp quicker now. Checked spark plugs, none fouled, but looks like running rich. Will check out crankshaft damper; have had that problem with GM motor in the past.Mileage has improved slightly and seems to run smoother with new injectors.Checked fuel pressure at rail and is good. Just to recap:Major problem is at 1500 rpm and up, esp.at freeway speeds when not accelerating. Steady throttle or backing off causes stalling, lurching, or missing; quits as soon as you open throttle back up and accelerates smoothly.

 

Maybe check the hose trumpet to air box is not split between the grooves or wrinkly bits and make sure hose clips at each end are tight.

cheers Ray

 

No leaks I could find in any air intake hoses. My son took it on a 260 mile round trip with no major problems other than the annoying "miss". Two days later got three codes; coolant temp sensor, egr solenoid circuit, oxy sensor. Looked at wiring diagram on Haynes manual for a 1992 Xj6 and looked like all three sensors were supplied voltage from the fuel relay.CTS and Oxy sensor Could not find new replacement for "yellow" relay, was sold a violet coloured relay by local independent Jag shop. Cleaned contacts and cleared codes and am now getting code 44 (running rich,oxy circuit). Two days later, car would sometimes stall at stop lights and idle would go down around 450-500 rpms. I had another used idle stepping motor and replaced, which stopped stalling and brought idle back up. Still getting code 44. all plugs look like burning rich but none fouled. Checked spark for each plug by using another new plug inserted into plug wire one at a time. Spark was consistent at each location but looked universally weak. Amplifier was replaced two week ago with NOS OEM Lucas.
Coil replaced 3 weeks ago with new Bosch.
Resistance values on coil are 2.1 on primary, 6,800 ohms on secondary. This is not within specs acc. to Haynes, but is corrct coil acc. to local import supply house by application. Could this be part of problem??

 

I have same problem with 1988 xj40 have changed the following no change.
Maf Sensor,
TPS,
Plugs,
Plug Leads,
Distributor Cap,
Rotor,
Idle Air Control Valve,
ECU with second hand unit,
All new injectors,
Fuel Pump,
Fuel Filter,
Fuel pressure regulator,
Temp Sensor,
Intake Bellows,
Have sprayed Easy Start round all possible vacuum leak spots no change in motor sound,
Someone suggested carbon on the pistons but have used a product to clean that.
All this with no results I love the old Girl but this is giving me the S---ts
Mine is running lean if I unplug the Maf sensor it runs ok but rich.
One thing you can buy a Landrover or Range Rover Maf sensor for a third the price of a Jag one and they are the same.
Please keep this thread going Im also desperate for a solution.