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engine misfiring especially when cold

katar83
Posts: 2996
Joined: Tue Aug 23, 2011 11:17 am
Location: Cambridge

Re: engine misfiring especially when cold

Postby katar83 » Sun Apr 11, 2021 5:53 pm

Since your car runs fine with disconnected MAF it means that fuelling and spark side of things are fine as it runs ok using default map, without looking at sensor inputs, even if its rich. I would concentrate on various sensors, one of them is fouling and reason for your misfire, sadly no OBD here so you'll have to resort to either measuring signals or substituting things. It will most likely be fuelling related issue so you should start looking at o2 sensor, coolant temp sensor, TPS and MAF itself. Just to confirm what MAF are you running? Check voltage on the CTS when engine is up to temperature, we should be able to translate it for you to something relevant in C.
You will also need to check TPS voltage and confirm that it runs ok in full range from 0.6V when closed to almost 5V at wide open throttle, key in position one is enough to check its voltage, you don't need to run engine to get the readings.
Check MAF plug for continuity and any broken wires, make sure it isn't messed up.
o2 sensor if its old, probably best to replace anyway, if not, you might be able to check it with either an analogue multimeter or you might have to resort to using an oscilloscope.
Failing that, next step would be to find a substitute ECU and possibly checking injectors for either leaking or poor patern(both common issues)
You could also check fuel pressure, or at least pinch return line, when its running, see if it improves things in any way.
1996, 3.2 SWB X300 - Relatively rust free daily driver!
1997, 4.0 LWB X300 - Unlucky car, sold 10.2020!.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, 10.2015. Gone!
1994, 3.2S XJ40 - First Jaaaag, long gone.

Clive Aintree
Posts: 53
Joined: Wed Apr 29, 2015 6:14 pm

Re: engine misfiring especially when cold

Postby Clive Aintree » Wed Apr 21, 2021 1:27 pm

Hello again,

Just checking the forum posts and I was sad to see that you had still not managed to cure the poor running. However when you said that "it runs great with the MAF disconnected" this reminded me of something that had happened to me. As the most recent post says, disconnecting the MAF causes the car to run I'm it's emergency " limp home" mode also known as "default map".

I had a problem with the lambda sensor ( also known as the "oxygen sensor"). This is fitted into the catalytic converter and sends signals to the ECU to regulate fuel supply to keep the air/fuel mixture just right.

I had a lambda sensor fail (simply due to old age). The symptoms were poor performance and cutting out at idle. My local mechinic could not remove the sensor from the catalytic converter. So he temporarily fitted a non-cat manifold with no lambda sensor and we set off on a 40 mile round trip to the nearest Jaguar specialist who was able to remove the old sensor using an oxyacetylene torch and fit a new one. The whole journey was done in "limp home" mode. The engine ran OK but acceleration was poor and the rev range limited.

I therefore think that as the lambda sensor should be checked. Take your car to an auto electrician and he will do a very simple voltage test. The sensor only has three wires and they run up the side of the wing inside the engine bay. Tested with a voltmeter and the car running, the voltage reading should "scan" continuously from 0 - 4v. Anything else, and it's dead. The car will still run with a dead sensor but goes into "limp home" mode.

New genuine Bosch lambda sensors cost about £60 and are easy to fit unless they are stuck in like mine was. So definitely get it checked - it is a vital component affecting running. Here is one on eBay but make sure it is the right one for your car:-

https://www.ebay.co.uk/itm/1x-BOSCH-UNI ... 3542108955

Let us know how you get on.

All the best and keep safe,

Clive
Clive

XJ6 3.2 1992
Land Rover Freelander TD4 2005
Austin A30 1955
Honda CB400A 1980

katar83
Posts: 2996
Joined: Tue Aug 23, 2011 11:17 am
Location: Cambridge

Re: engine misfiring especially when cold

Postby katar83 » Wed Apr 21, 2021 1:32 pm

FYI, normal 'meter' will unlikely show o2 sensor switching. Analogue should or use a scope.
1996, 3.2 SWB X300 - Relatively rust free daily driver!
1997, 4.0 LWB X300 - Unlucky car, sold 10.2020!.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, 10.2015. Gone!
1994, 3.2S XJ40 - First Jaaaag, long gone.

Clive Aintree
Posts: 53
Joined: Wed Apr 29, 2015 6:14 pm

Re: engine misfiring especially when cold

Postby Clive Aintree » Wed Apr 21, 2021 6:41 pm

That's a good point that Katar makes. It was just what I had been told to do.

So I did a search on YouTube and found this really good short video. It shows how to test the sensor just by using the resistance range on a cheap multimeter and without the engine running which is also safer to do. Most European cars of our era probably used the same Bosch sensor. So if you do not have a Jaguar manual, I am fairly sure that the figures would be similar to those given for this guy's Audi:-

https://youtu.be/7uqmYkl7t0c

And he also shows you how to replace the sensor - note the use of a hammer!

A final tip is to make sure that the wiring from the sensor is fully protected from heat - the cat and exhaust pipes can run at very high temperatures. It is a very good idea to buy a short length of heat reflective sheath such as this:-

https://www.ebay.co.uk/itm/294085621087

Well let's hope that finds the culprit.

Clive
Clive

XJ6 3.2 1992
Land Rover Freelander TD4 2005
Austin A30 1955
Honda CB400A 1980

fremaes
Posts: 33
Joined: Mon Oct 05, 2020 8:58 am
Location: Belgium / Netherlands

Re: engine misfiring especially when cold

Postby fremaes » Sat May 01, 2021 12:36 pm

Thank for all these great posts.

Meanwhile I found the cause. But I’m almost too ashamed to mention it.
It was a vacuum leak.
A small tube running from the intake collector to somewhere close to the battery was left open. (Still don’t know where is supposed to connect to) 5 months of searching finally paid off. But so stupid that it took 5 months to find something so obvious.

Anyway I found it thanks to a Toyota 4Runner forum that mentioned exactly the same behaviour as my car.
Where also a hose was disconnected.
I always thought vacuum related problems occur in the lower revs or result in poor idle since vacuum is most pronounced there.

Anyway I was thinking of buying a new O2 sensor and an adjustable fuel pressure valve an try to make it work since others have had the same problems and made it work again, with considerable poor mileage of course. But luckily I found the cause rather then fixing the symptoms.

Went to the MOT in Belgium, lights were off and hand break pulled only on one side.
Just before entering I pulled over and cleaned the whole engine bay which was full of steering oil. They didn’t see it but the pump definitely needs replacing.
First time driving I also noticed the front bearings went from whining to grinding so that also needs to be sorted out.

And last I noticed that when driving at constant speed with the engine fully warmed up the engine occasionally sputters, trembles for a split second, no loss of power or anything but it seems getting worse after a longer drive. Any suggestions, I was thinking dirt build up in the fuel line/injectors. O2 sensor has been replaced in 2004 , 60000km ago so might be needed to be replaced again? Or one of the posts said oil buildup in the spark plug holes due to bad seals? Since it is intermittent it might also be an electronic glitch.
Anyway your thoughts are welcome.

pimgmx
Posts: 3494
Joined: Tue Jul 08, 2014 12:07 pm
Location: South East of the Netherlands

Re: engine misfiring especially when cold

Postby pimgmx » Sat May 01, 2021 1:00 pm

fremaes wrote:Or one of the posts said oil buildup in the spark plug holes due to bad seals?


That scenario is VERY easy to check, although that also should occur when the engine’s cold...
All you need to do is open the bonnet, undo the HT leads and pull the spark plugs.

Dry & greyish plugs = good
Wet & oily = time for new cam cover/plug seals!

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abercanadian
Posts: 1535
Joined: Tue Oct 16, 2012 6:50 am
Location: Vancouver Island

Re: engine misfiring especially when cold

Postby abercanadian » Sat May 01, 2021 4:32 pm

Clean out the intake plumbing and throttle body.

Larry
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Frank123
Posts: 4
Joined: Mon Oct 12, 2020 7:53 pm

Re: engine misfiring especially when cold

Postby Frank123 » Wed May 05, 2021 9:16 am

Lambda sensor is pretty much a long service interval item. Their responsiveness slows down with age and use. Definitely a good idea to change it if it's original.

Having said that, I'm still running the one fitted to my car when I bought it years ago.


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