Hate to start a first post with a question, rather than an answer, but no answers to give at this point.

Problem: Intermittent rough running/ missing/lack of power/poor throttle response/dying/coming home on a wrecker.

Vehicle: New to me 1995 XJS Convertible, AJ16 engine US spec, 115,000

Short story: - Purchased April, ran great, no codes, cool evening for test drive. Shortly – within 100 miles – would miss at idle – irregular, felt like 2-3 random cylinders would start missing just like someone flipped a switch. Took it out once, didn’t want to start when hot. Tried a trip, about 90 degrees ambient, got a high speed miss at freeway speeds, pulled off, lost all power, classic signs of fuel delivery – start, run in short surges, would not climb a hill, no more than 10 mph. Came home on flatbed. Problem is ongoing, seems to be temperature related – hotter it gets, worse the problem. Usually good on cold start-up, although will sometimes miss/bog down when first started, then run OK after 5 seconds – until it gets good and hot, when it will start again

• Replaced EGR valve
• Replaced plugs
• Replaced fuel pump/filter - tank interior spotless – fuel pressure OK - got it to act up in the driveway, threw a fuel pressure gauge on it (brazed a Schrader port to the fuel rail), 34psi running, 43 w/vacuum line unhooked, good response to throttle opening, so rules out fuel to me, missing with good fuel pressure.
• Replaced CKP (crank sensor)
• Cleaned MAF sensor, checked hose to throttle body
• Cleaned throttle body and IAC valve, IAC seems to work OK.
• Checked TPS resistance, OK, linear response, no dead spots
• Checked CTS, - had CTS circuit code pop up, did find loose connector at sensor, not fully plugged in - good sensor response, about 700 ohms @95 degrees, 300 ohms at 160 degrees, new sensor on order. Not much difference in running with sensor plugged in or unplugged.
• Quick test of injectors – coil resistance, spray pattern w/brakeclean can and 9 volt battery, all OK
• Checked coil primary resistance – OK when cold, boots look good, no gaskets fitted.
• ECM connectors secure, ground good. No water in area or corrosion seen.

I’m up for any thoughts that someone might have – I’m a heavy diesel guy, I have not really touched gas stuff since the ‘70’s So far, have about 400 miles on it, plus 100 or so on the wrecker. Was kinda hoping to use it for a trip at the end of September, so wanted to find a definite problem.
Next for me, failing any better ideas from any of you smart guys. Maybe –
• Back probe CTS wires at ECM
• Maybe solder dropping resistors to 12 LED’s, and try to back probe coils and injectors, try to get a failure in driveway, and see if coils and Injectors are still getting signals from ECM
• Pull coils, heat in oven, re-test? Not sure how hot – Maybe 170? They are OEM coils, I been hesitant to replace w/ aftermarket coils. Don’t mind buying coils if that is the problem, but don’t want to spend the money for OEM –grade coils just for troubleshooting. Maybe buy cheap set for troubleshooting? Heard tell they will go 10,000 miles or so?
• Rig flexible duct to home A/C ducting, try get car to miss in driveway, cool ECM and coils with ducted air, see if I can make it quit missing that way.

Do ECM’s have a history of heat-related failures? Anyone ever hear of heat-cycle testing an ECM? Or easier just to try to buy a used spare?

Or am I missing something simple. Car smells rich when missing at idle, so I assume not an ecm/fuel side problem. Coming down to coils?

Thanks for any thoughts,

Mike

 

1. Do you have the ability to see what the oxygen sensors are doing? I'm wondering if the cats are good. No smell? How about any rattle she banging the cats with a rubber mallet?

2. How's the idle? Do you only have a rough engine when giving it gas?

 

3. Is the coolant sensor operating properly?

 

Thanks for the replies. I can check 02 sensor waveform, but have not had the scanner with me when the car has actually acted up. Good idea to do so, I will stash the scanner in the car. I have not, however had any o2 sensor codes, and it seems like those are always the first to set.

On the cats, I had supposed that it used a monolithic ceramic core, rather than the older pellet-type, and that they would be either good or bad.

Most telling to me is the way that the "miss" for lack of a better word, will turn on just like a light switch - would kinda expect exhaust problem to begin at high RPM/load, and gradually work it's way down the power curve - wouldn't expect an intermittent problem. Still and all, I should be able to pick that up with a vacuum gauge - see if I still have one, and get it hooked up.

Re: the coolant sensor - high on the list from searching the forum. I did have a circuit error code, found the connector not fully seated at the sender. Checked sender resistance while the engine warmed up, about 700 at 90 degrees (F), dropped to about 300 at 160 degrees, measured w/ a temp gun at the sender. I don't believe I have the "Shielded" wire I see mentioned in the forum, looks to be a normal wire bundled with the injector loom.

I do have a sender on order, when I install it, I will test on the stove before I install, then back probe the wires at the ECM, and re-check fo a harness problem

Thanks for the responses - it's all good.

Mike

 

As long as you are sure you diagnosed/replaced the crankshaft position sensor, and not the camshaft position sensor, the coils are the last of the low hanging fruit options. You could always buy one cheapie and run it through, testing to see if it makes a difference, however I'd recommend you just bite the bullet and buy an OEM manufactured one to have as a spare anyways.

Make sure the car has gone into closed loop and is indeed taking data from the oxygen sensors once warmed up. I had a bad ECU (no water, no visible issues at the pins) that decided not to take data from those sensors. All of the other conditions seemed to have been met, it just wouldn't switch over.

I had to replace the ECU. Basically it idled ok, it ran poorly and had terrible fuel economy.

Keep us posted. We'll figure it out!

 

Sorry, VEE, missed the idle question - to early, and I was making assumptions. . Idle is and behavior is erratic. Will start up, might run rough for 5 seconds, then settle into a nice smooth idle. On a hot day - maybe 90 ambient - not today, just started raining, "Normal" behavior is that after 20 minutes or so it will suddenly start missing. Erratic miss, not like just dropping one hole, more like 2-3, but not a nice, steady miss, that you could pull coil triggers and isolate. Throttle response is bad, acts like no fuel available, or maybe TPS; with long delay and sputtering, maybe (rarely) even a backfire. Airflow (aurally) sounds good - leads me away from the cats, fuel rail pressure is at 34 psi, rises almost to 43 with the drop in manifold pressure, then re-establishes at about 35. Smells pretty rich at this point. I did see a reference in the '95 update saying the ECM would shut down injection on detected missfire, read this to believe it was on a cylinder by cylinder basis, but no other details. Kinda point me toward coils - but I have a hard time believing more that 1 or2 at a time failing, or heat-soak issues with ECM. Been kinda keeping an eye out for a spare to try.

Sorry for being wordy - you should see my failure analysis stff at work

Mike

 

VEE, sorry for the cross post.

Yes, replaced the crank sensor. From what I read, the cam sensor (Engine position sensor) - old distributor - is not used once the engine is running, and from what I gathered, even when starting, the ECM wiil use it's input, if a no-start occurs, it will change sensor input 180 degrees and try to start there. Not something that would affect the car once running, right?

Reluctor wheel was cleaned, was in good shape, air gap was OK. Not sure the reluctor is rubber-mounted or not,but I seemed to have a correlation between the gap and #1 TDC, also supposed that if it did slip, no way it would ever stop close enough to run again.

I will be honest, not sure how to check for closed loop operation. I'll try to dig up a manual for code reader, see what it says. I was able to pull up sensor waveform, so am assuming from that that the ecm is reading the data - but I have NOT had the scanner on it when it is acting up, I don't think the datalog function on my reader is adequate for diagnostics, but somewheer around I think I have one of the cheapie ELM cables - might try to find some free software that might help.

Thanks a lot for your help - as you know, the questions make you think down paths that you might previously have ignored.

 

I know you've checked for vacuum leaks, but your intake manifold gasket is probably tougher to check. I had a rough idle problem that ended up being the gasket. It didn't come all at once, the problem started off as poor fuel economy (14-15mpg) and eventually turned into a rough idle.

I don't recall having a bad driving experience. Once I put my foot on the gas, the car would drive smoothly, albeit with poor fuel economy, so I don't think it's that.

Your coils are probably original, I'm wondering if the coils are really starting to go. The ECU will not always throw a code with missing coils, however, when it decided to shut down a coil, I would get the P300 code, and it would stall out at a stop. That was unrelated to my intake manifold gasket...I think.

Strange situation you have developed. When my ECU quit reading oxygen sensors accurately, I never had a thrown code. That was the only problem I ever had that gave me a rough driving engine. I've had rough idles, but it always smoothed out when the gas was applied. Only the sensors gave me driving issues.

Let's check those sensors.

 

By the way, I use Yhasi Movi with a wireless ELM adapter with a MacBook. It cost me $100 a few years ago.

I also have something on my iPhone, which doesn't work as smoothly.

I also have a Jaguar IDS/Mongoose knockoff which is worse.

Uktimately, if you're going to pay for something like this, I don't think the iPhone apps are quite there yet. (I think it's OBDFusion) that I have.

 

I hate to leave something completely unanswered, so thought I would post a follow up if it helps someone.

Vee had suggested coils, possibly intake manifold gasket. I did go ahead and replace coils, with "Made in Japan" ones from SNG Barrett, no change. Tried a Mongoose knock-off with no joy, tried of all things a Harbor Freight scanner, was at least able to see STFT's and LTFT's, short terms were pretty well pegged at (as I remember) -24.6, but would jump into a normal range when the engine started to miss at idle. Car was going into closed loop, O2 sensors all seemed to be switching OK, and were readable through the scanner.

Somewhat unrelated, I replaced all of the coolant hoses and the water pump just because, the hose behind the intake was a little hard to get to, so I just removed the intake - checked the gasket, it was just fine visually. I had previously check with starting fluid, pretty sure it was OK, re-assembled with Hylomar for a sealant - love that stuff. I did find the PCV opening was clogged in the little heater assembly.

Still had the stumble off idle, cleaned the MAF sensor again, the decided to try the car with the MAF sensor unplugged, assuming the ECM would use TPS only and kinda run after a fashion. Car still stumbled, stopped, plugged in the sensor, it stumbled once on takeoff, then ran perfectly. As in drove it to work for a summer, took it to the beach a few times, sunny afternoon driving, just got back from a 4000 mile trip, to Denver/Santa Fe towing a trailer, never missed a beat running fine.

I did replace the MAF sensor - never got a rebuilt, bought a new one from England, I stripped out the entire engine/ECM harness, tested every wire and connection in it, and replaced it in the car, tried a replacement ECM (did not want to run with that item, put my old one back in), replaced the rear O2 sensors (had already replace the fronts) - didn't find anything, and nothing made a difference - car just ran fine.

Only issues I have now with drivebility is an occasional "Long term fuel trim lean" code mainly when towing a trailer - posts on here suggest that this is a common issue, and light pre-ignition at low engine speed (under 2000)/moderate throttle (about 40%) application - this disappears at higher elevations - towing a trailer does not seem to affect it adversely, it will also occur unloaded. I have traced the knock sensor wires, checked for a voltage spike tapping the block, but have not replaced the sensors as yet. Strangely, fuel grade does not seem to affect it at all - it does pretty well the same on regular, mid grade and premium. Most of the time it gets premium, but I will sometimes drop when I know I am going to burn the tank out cruising on a straight stretch of road.

Not sure if there is any moral here outside of there is a possibility of light at the end of the tunnel, good luck to anyone in the same situation.

Best Regards,

Mike.

One more thing - water pump I purchased was incorrect - as memory serves, it had bolt holes instead of studs on the flange for the fan - or maybe the other way around. I was going to set up and re-drill/tap as necessary - I am a machinist - but then I got smart. Just pressed to flange off both pumps, pressed the old flange on the new pump, 5 minutes and I was in business.

 

 

Thanks for the thoughts, there. Plugs and coils were one of the first things I did, plug wells are dry.As I had mentioned, no troubles with the car for going on two years now, and we do use it regularly. Just not really sure what had actually caused the troubles - they were quite significant at the time.

Again, thanks for the suggestions.

Off now to go chasing the turn signals on the X type, why couldn't it be simple, still have to change the engine on the X 358

Mike

 

Are theyre any good videos or how toos on getting out the transfer case for replacement

 

Hey guys,

I know this thread has been gone over several times. But I've been dealing with electrical issues ever since I got my XK. Mainly due to a shady mechanic which i had to take to Small Claims Court. I'm trying to fix the issue now, by replacing the battery, (previously replaced the alternator).

Which battery specifically should I use? I've seen everyone mention Group 49 batteries, and other have mentioned AGM batteries. I personally want to buy whichever is the better battery just to be done with these problems, but I don't know specifically which battery to buy.

Does any brand matter? Preferred brands? Size or voltage? etc. (I don't know anything about batteries) so please any additional information would be helpful.

 

XK you are n the wrong forum, this is the XJS site.

 

yes please pay attention to the forums

 

Now that I have been through this several times on the AJ27 NA engine, my condition followed the use of a fuel injector cleaner that appears to have worked TOO well. The AJ27 engine has no EGR in some configurations, so carbon will accumulate as the engine ages.

I have found - through disassembly of several top ends that when an injector cleaner has been added to the fuel tank, it may in fact dislodge large flakes of carbon and foul the intake and exhaust valves.

On one engine that had no compression and subsequent leak rate test showing all valves were being held open with verification that the valves and cams were in correct time and the crankshaft position sensor was indeed working, I removed the heads and lapped the carbon and pits out of the valve seats and valves as opposed to a regrind. This netted compressions across the cylinders close to new values of ~175 PSI. I have done that on now 4 different engines and it is quite time consuming, but netted a very satisfying result.

On my latest occurrence, I decided to try a carbon dissolve method and load each cylinder with about an ounce of WD40 and an ounce of B12 Chemtool, install the plugs, crank the motor for about 30 seconds to get everything coated, then let things soak for 1-2 days. If I had a can of Seafoam on the shelf I would have used that instead. Time is your friend here, so while allowing time for the soaking mixture to dissolve the carbon, I removed the battery, topped up the electrolyte and performed a deep cycle charge, and also deep cycle charge on a second battery to be used for a booster.

You will not succeed unless you have either a fully charged booster battery with a fully charged main battery or a commercial grade charger capable of full cranking amperage for 5 minutes to act just like a battery cold cranking amps.

On the second / third day I remove and clean the plugs, reinstalled, connected both batteries in parallel, sprayed a good 5 second spray of starter fluid using the High Load connection to the intake plenum and reconnected.

I then proceeded to crank the engine for 60 seconds or even much more at a time using varying throttle positions until I found a set of throttle positions that showed the most cylinders firing from off to full throttle and in-between. Sometimes that is zero throttle, sometimes 100% throttle, sometimes between 25%-50% and off and on

You may find that the engine may appear to "freewheel" with no apparent firing at some particular throttle positions and may intermittently fire at other positions or when moving through some throttle positions, so it is very much a tactical feel if you are getting any firing at all. IF you get some firing, you have some hope this technique will work.

Holding and/or moving the throttle at those positions I maintained continuous start cranking noticing more and more cylinders firing, keeping the starter engaged until the engine began and continued to run on its own before releasing the key. That was followed by a huge amount of smoke out the exhaust, and a large trail of carbon flakes out each exhaust pipe deposited onto the ground verifying the carbon fouling. Then let the engine warm up and drive as quickly as possible.

Beware that in some configurations, high revs of the engine in Neutral or park may cause some damage to some ZF transmissions so actual driving to warm up and perform some full throttle cleanouts is advisable.

Anyway, that is my experience with some of these engines that have carboned up. It does not resolve the valve & seat pitting problem, but it may get you started and running until you can the time to perform a top end refresh so you can do some further work in the garage.

Cheers!

 

I think you're in the wrong forum, none of the XJS had the V8 engine.

 

Agree with donut seal issue. Seems to be chronic on 4.0 motors I've owned. Sucking oil out of the well aint easy with the plug in. Try a turkey baster, then paper towels pushed down with a long screwdriver (gently). Oh, and buy the whole kit that includes valve cover, well seals and back-end cam seal.

 

Probably a stupid question, but when you said replaced the fuel filter, did you mean the one under the front wheel arch?
Have you had a close look at the fuel quality/cleanliness in the tank and coming from the fuel rail?