Hello all,
I've been plagued by an intermittent starting issue on my 1999 XK8 coupe 4.0. Sometimes, probably one time out of ten, when starting the engine catches then immediately dies.
When I try and restart, it runs really rough, misfiring, and will stall unless I keep feeding it some revs. After about 20 seconds it smooths out and when I take my foot off the gas it runs ok.

Whilst struggling there is a strong smell of fuel coming from the exhaust, which blows dark grey. The car usually goes into restricted performance mode for a few minutes afterwards - presumably because it's detected the misfires - then goes out of it again by itself.

The ODB2 reader reports misfires down the left side. It also looks like it's running rich down the left side - plugs are black compared to the right side which are a nice biscuit colour.

I've replaced the MAF with no effect, though doubted that was the issue as it seems to be limited to the left side. I'm thinking oxygen sensors next as these are the other components that give the ECU it's info to control fuel/ air mixture.

Has anyone else experienced this, or have any advice to give? Worth mentioning whilst we had very warm weather over the summer it didn't happen at all, any seems more likely to occur on a colder and/ or damp day.

I've also checked for vacuum leaks and haven't found any.

This only happens on first cold start of the day, and not very often.

thank you
Ash

 

If it keeps happening the cat on the bad side will likely be destroyed.

Being one side it's hard to see how any part used by both (e.g. MAF) could be to blame.

 

I think yours still has the 2 ignition control modules. You could try swapping them and see if the misfires follow it. If not, another possibility would be your ecm. Its possible the capacitors have leaked and corroded the traces inside. Other option might be your intake manifold gaskets on that side. You could try spraying some carb cleaner around thay side of the manifold while its running and see if the rpm picks up. If it does you have a leak

 

Thanks for the feedback people.

Can you give any guidance where the ignition control modules are?

I've checked around the air intake and fuel system with carb cleaner spray and cannot detect any leaks.

What has stumped me on this is the fact it is an intermittent issue - that normally points towards a failing sensor somewhere, if there were issues with the cat or ECM then I'd expect it to happen all the time.

 

The modules are mounted to underside of the cowl at left and right of centerline.

 

I replaced my ignition control modules once when getting an ignition related code. Don't think it made any difference in performance. By the way, the part lists for about $1,200, though I picked a couple up on eBay for 20 bucks. Before replacing the part, you could just swap the two modules from side to side to verify the problem is in fact the ignition module. There are not too hard to swap.

If I had to hazard a guess, I would also consider a problem with the Part Load Engine Breather. That it is located on the left side of the engine further makes me think the problem could lie here.

I've included a couple TSBs relating to the part. The first TSB is fairly simple. It advocates clearing the breather with a finger twisted 3/32" (2.5 mm) drill bit. The only warning for this is to not to use a larger drill bit and know that the breather is going to be brittle. I don't think it's too expensive if you break it. I replace mine a generation ago, but can't recall any cold sweats at the price.

chrome-extension://gphandlahdpffmccakmbngmbjnjiiahp/http://www.jagrepair.com/images/TSB/TSB2/XJ_XK/600Maintenance/600-03am3%20Part-Load%20Engine%20Breather.pdf

The second TSB is more involved and addresses a number of driveability issues relating to the part load breather which could be evidenced by fouled plugs.

chrome-extension://gphandlahdpffmccakmbngmbjnjiiahp/http://www.jagrepair.com/images/TSB/TSB2/XJ_XK/303Engine/303-47%20AJ26%20Diagnostic%20Flowcharts.pdf

My Jaguar friends are going to start calling me Mr. Simple or Simple minded because I always go for the simple (and cheap) approach first. It doesn't always work, but sometimes it does and at least it doesn't cost an arm and a leg.

 

Interesting! Never knew the XKs (up to 1999) had ignition control modules... Are they anything like ignition AMPs? And yes, looks like they can be had used on eBay and from a couple other sources.

When one side of an engine checks out or acts freaky, I always wonder about grounding. Unlike my 928, and especially my XJS, I just don't find as many dedicated ground points in the XKs. Are the ignition modules grounded? How and where?

 

Ignition modules are only for the AJ26 motor. The functionality was integrated into the ECM for 99MY-on XK8, 2000MY-on for the XKR.

 

I found the same thing, only the earlier AJ26 engines have the separate ignition control modules, from AJ27 onwards the ICMs are integrated with the ECM

Thanks for the advice on the park load engine breather, I will investigate further. I have already made sure the pipe that you disconnect from the top of the engine is clear, but didn't know about cleaning the port on the vehicle with a 2.5mm drill bit.

 

Not to sound stupid, but is there a known serial number when the change was made? As in, like my xjs, its a 1993 build year, but a 1994 "US" car model year. For example my xjs still has inboard rear brakes, even though 1994 MY came with outboard brakes. It only takes 2 seconds to do a quick visual check to verify if its possible that it doesnt have the modules. Just saying. If verified, then id still lean towards the ECM

 

From the Heritage chassis numbers doc (attached), I infer any VIN up to ...031302 for the XK8, and up to ...042775 for the XKR would be AJ26. The overlap was partly due to using up the remaining parts, apparently. It caught me out.

The 99 EG has a separate engine management section for each of the two models. I understand that the XKR wasn't available in the US prior to MY2000?

 

Each of the early ignition module pair fired 2 cylinders on both banks, as I recall. I have to guess that the engineers wanted semi balanced firing when running on only 4 cylinders if a module went bad.

I can't recall if the '99 XK8 has an EGR valve or not, but that would be a suspect for intermittent problems.

 

This quick YouTube video is very useful in terms of identifying your XK engine


The differences between AJ26 / AJ27 / AJ34 are very obvious when you see the three next to each other

 

Maybe I am stupid but as the ignition modules fire 2 on each bank it cannot affect only the left bank .
But as it has two catalytic converters and 4 oxy sensors then it stands to sense that each pair of oxy sensors controls the fuel on each bank . thus you must have a problem with the left-hand oxygen sensors.

 

Pistnbroke - that was my conclusion as well, that the left hand oxygen sensor(s) was a very good place to start.
I replaced the pre-cat sensor on the weekend - it's too early to tell if it's fixed the issue or not, as it was intermittent, but I've had no issues since and the car does seem to be running smoother.

It was a very tricky job to get that sensor out, I drained the expansion tank and removed it and got a long 22mm spanner onto the sensor - the issue was hardly any clearance to turn the spanner due to all the hard fuel pipes in the area.
I managed to get it loose in the end by cutting a slot out of the end of a 12 point ring spanner for the wires to go through, sliding it onto the sensor and turning as much as possible, removing it and swapping for the claw end, repeat loads of times moving a tiny fraction each time and so on... Photo attached,

I've since read apparently if you peel back the carpet from the passenger footwell there is a hole in the body work to put an extension bar and lambda sensor socket through. Sounds easy but it's pretty tight down there, so I reckon it would be 6 of one and half a dozen of another.

I'll post again in a week's time to confirm whether it solved the issue or not, last week the car had problems starting every other day so I would hope to know soon.

 

My understanding is that when O2 sensors fail on these cars the ECU just defaults to a preprogrammed map fueling,,, and economy drops some. Or am I talking about something different at this point?

Are y'all thinking that the occasional no start is due to an O2 sensor issue?

 

What OBD codes is the car reporting?

 

No. The sensors can't be used until VERY hot. (They're probably checked for gross errors. Probably. Or maybe.)

 

The car wasn't throwing up any codes related to this issue, which is why it's been a pain to diagnose.

I've been running it everyday for a week since replacing the left bank upstream oxygen sensor and so far so good - no issues with starting at all, whereas before it was doing it every other day.

So looks like the sensor was the culprit - the car is definitely running smoother and the MPG seems to be a bit better. It will be interesting to see what impact, if any, it has had on the emissions.

thanks everyone for your input and advice.

Ash