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engine misfiring especially when cold

Distinguished Mbr
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Re: engine misfiring especially when cold

Postby NMV 1E » Sat Dec 19, 2020 2:40 pm

I'm wondering whether you may have an "injector" problem or a loom / connector issue. Discovering which cylinder miss fires, would help to some extent :?: ;)
Life begins at Forty ! I was born with nothing, I seem to have most of it left.

2002 Titan Silver BMW 316ti Auto Compact
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1989 White V.W. Golf Cabriolet (G.T.i.)
1968 Anchor Blue Ford Cortina 1600 GT

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Re: engine misfiring especially when cold

Postby fremaes » Sun Dec 27, 2020 3:16 pm

Sorry, it has been quiet for some time. Busy with other projects.

Maybe I used the wrong term misfiring where it should be rough running.
I don’t think it is a injector related problem since she runs fine at idle only vibrates occasionally
But she really trembles around 2000 revs to around 2300

I looked at checking the MAF with a multimeter but it can only say wether it gives a signal or not. This is the same what the VCM is checking
There is apparently no way of checking if the MAF still measures correctly.

Meanwhile I found an easy way to check for vacuum leaks. Gently spray starter spray and see if the engine picks up speed.

Still have to buy starter spray though. I let you know what it does.

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Re: engine misfiring especially when cold

Postby guy » Fri Jan 08, 2021 4:35 pm


Not sure if you've got to this, but I had a very similar problem on my '93 3.2. After going through everything mentioned above (including replacement injectors!) the problem was solved by replacing the crank position sensor. You can get a cheap one on ebay but as yours is a later car you might have to fiddle with the wiring - but it does work ;)

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Re: engine misfiring especially when cold

Postby fremaes » Fri Jan 22, 2021 3:50 pm

Sorry for the quietness.

Still no improvement with the starter spray nothing changed so probably the inlet is airtight. Although it need quite some staterspray to notice the engine picking up speed when you blow it in the air box it only responds very little.

I did some other test when in the problem revs I unplugged one plug lead it didn’t influence the poor running. I did one by one and NONE made the engine make run worse which is very strange to me :shock:

On the other hand it moves the problem back to an ignition problem and not a mixture problem.

Measured compression: all of it within a tight range and within specs ( forgot the numbers (something 12,3)

@ guy thanks for the suggestion.
Although it seems there is already a replacement fitted ( having a white wire)
Can you explain your symptoms ? Did it also vary when the engine is cold and hot?

With the strange plug lead symptoms I’m thinking towards CPS ( which is the one saying which cylinder should fire)
So ordering one soon.

On the other hand it is strange that NONE changed the poor running. :shock:

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Re: engine misfiring especially when cold

Postby Aidan » Fri Jan 22, 2021 6:12 pm

Hello Fremaes,

I also suspect (hope) that your CPS is the problembecasue it's a quick and easy fix. I had intermittent starting problems on my 3.2 litre a few months ago. I replaced the CPS and the problem hasn't returned. I can't say 100% that the new CPS was the cure because the starting problems were intermittent and replacing the CPS might just have been a coincidence, but so far so good.

It seems that these cars suffer so much from CPS failures as they get older that replacing the CPS is probably a good thing anyway.

Good luck and please let us know how you are progressing with this cold-start problem.


1994 Moroccan Red XJ40 3,2 Sport ("Ruby")
1995 Jade Green X300 3,2 Sovereign ("Jade")
2005 Cedar Green Pearl Volvo XC 90 SE - Sold
2007 Colorado Red Ford Galaxy Ghia

Clive Aintree
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Re: engine misfiring especially when cold

Postby Clive Aintree » Fri Feb 12, 2021 1:55 pm

Hi Fred,

These same problems come up now and then. So I Googled "XJ40 rough running" and I found this earlier XJ40 forum link marked "CURED". It was the MAF. The guy had even tried other used MAF's but only a new one cured it. Here's his story:-


So what would a new MAF cost? First get the part number - for your 92 4.0 it should be DBC10852. Put the part number into a Google search and then look for the cheapest seller. Here is a reasonably priced one from a UK seller who could almost certainly ship to you:-

https://www.daytonagblimited.co.uk/all- ... 10852.html

But before you order, give the seller your car's VIN number to double check that it is the correct part.

But I agree that just swapping parts without knowing the cause is not really sensible. There comes a point when it is better to pay a Jaguar specialist a couple of hours' labour to find the cause. Then decide whether it is a job that you can do yourself or one for a garage.

Well I hope this helps.

Good luck he stay safe,


XJ6 3.2 1992
Range Rover 3.9 Vogue SE 1994
Austin A30 1955
Honda CB400A 1980

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Re: engine misfiring especially when cold

Postby fremaes » Fri Feb 19, 2021 6:24 pm

hi everyone,

Clive thanks for the interesting link.
i previously opened my MAF sensor no worn soldering everything looked brandnew inside but i will definitely measure it using mellow's suggestions

fitted a new CPS sensor today, thinking this would solve the problem but it didn't. :(

but in the corner of my eye I saw my ignition coil arcing. (from the center pin to the small pin on the left)
not sure this could cause my problem.

again today i tested the ignition when it was running roughly (1500+ rpm) by pulling out one sparkplug at a time again none made it run worse (pulling out two made a big difference)
so maybe my ignition coil might be shot and doesn't make enough spark anymore? or doesn't my reasoning make any sense.
any thoughts are welcome.

old del boy
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Re: engine misfiring especially when cold

Postby old del boy » Sat Feb 20, 2021 12:36 am

The arcing on the coil would suggest the HT lead has broken down which would lead to a reduced spark so i would renew the lead , this is more likely than a coil failure but who knows it may be faulty , same as the ignition amplifier , they rarely give trouble but sometimes swapping parts is the only way to eliminate a fault ,

https://www.sngbarratt.com/English/#/UK ... plifier%60

'93 4.0L Daimler, solent blue,
'93 4.0L Daimler, Westminster,
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Re: engine misfiring especially when cold

Postby fremaes » Sun Feb 21, 2021 9:07 pm

@ Clive. my MAF is a DBC5917 not the DBC10852 you suggested
these DBC5917's are apparently unavailable as a new part.

I found a older thread on this forum about the differences between all the different MAF codes for our XJ40's but there no real answer was given.
another guy said his car drove better without a MAF then with it. which is highly like the behavior of my car.
I asked for a quote to get my one fixed (210Euro) which is double of a new one of the DBC10852 type.

so hence my question: does anybody knows if MAFs are interchangeable? can i replace a DBC5917 with a DBC10852?

any thoughts on this will be very helpful

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Re: engine misfiring especially when cold

Postby fremaes » Tue Feb 23, 2021 1:29 pm

a little update.
i did a small test drive without the MAF connected and man this car flies
it never had that amount of power :o

so definitely going to buy a new MAF hopefully it fits.
​​​​​​​i'll let you know!!

A very happy Fred

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