hi everyone,
i'm new to this forum.
I have bought a 92model XJ40 4.0 in november last year but i have not been able to register it because the engine is running rough.
it is not as bad as the other topic with the same title. the engine goes up all the way but it starts like misfiring at 1500 revs when cold and around 2000 when warm
idle is running nice.

I changed the CPS with a new one
checked in intake manifold for airleaks (also checked with spraing starterspray around it) and cleaned everything in the neighborhood.

I did some tests
unlpugged the MAF and started it and the rough running was a lot less.
unplugged the sparkplug leads one by one and none made the running worse. meanwhile saw my ignition coil was arcing between the center pin and the pin on the left

these two things stumbled me

my reasoning is that probably the ignition is very weak. so replacing things with new leads and sparkplugs not sure for the ignition coil
and that the MAF is not doing its job properly. so i'm diving in finding a new one.

The MAF in my car has the following code DBC5917 but these ones are practically unavailable in the aftermarket. but the later model DBC10852 are around for something 100 Euros because also being used in landrover and saab
I found that the DBC10852 doesn't have the idle adjustment screw whereas mine has.

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

 

Hi, I would definitely start with new plug wires. If it were me, I would change cap and rotor too as a precaution. Then see how it runs. As for the MAF sensor I think the one with the adjuster screw could be replaced by the one without, but the ones with the gold terminals for the 93-4 were different somehow. Sorry I don't know more. You can check this by part super cession in the Jaguar heritage parts listings or possibly by SNGBarrats. Good luck!

 

thanks for that.
going to order that stuff today.

I have also to let you know that I bought this car with rough running symptoms thinking it would be an easy fix, the arcing came only very recent but certainly needs to be addressed.

I have been looking around concerning MAF sensors. on pistonheads someone wrote that all the lucas 5AM are interchangeable but they use them for tuning other cars not jags
someone else reasoned that probably they could be, since the mapping is done in the ECU and not in the MAF
but no-one seems to have facts
I read about an italian who drove around with his MAF disconnected for quite some time because it drove better without.

probably our engines use the MAF to fine tune not to set parameters in the ECU-mapping
Is saw from mine that in no time my plugs were completely black when i disconnected my MAF
before they where rather pale suggesting a very lean mixture maybe causing the rough running.

so i think a new MAF might be needed. Probably they do wear out in time

I'll keep you guys updated if the DBC10852 works for me.

 

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.

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

 

Here's hoping it works for you!

 

Good luck, keep us posted. I would pay extra attn to the ignition cap, especially if you noticed arcing track marks, that's usually a sign there's a crack in the cap, wouldn't cost much to replace it, I always believe in doing the simple inexpensive things first. Btw, did you get a cel code?

 

I think he'd definitely get a CEL flag running with the maf unplugged!

Larry

 

of course i did get a code driving without my MAF plugged in
with the MAF connected i didn't get any code. which means the MAF is still working.
contacts have been thoroughly cleaned but with no success.
also I cleaned the two sensor wires itself with a soft contact cleaner leaving no residue
i also opened the MAF for a visual inspection and to check for any cracked solderings but it looked like brand new. if any where cracked it would definitively throw me a code.

I think this MAF still measures within specs from the ECU (min and max voltages registered must be OK) but the values measured are definitely off.
I could notice this with a more white deposit on the spark plugs suggesting a lean mixture. (without MAF they turned black in no time which i think is also not very OK)

MAF is ordered but takes some time to arrive in the Netherlands due to the brexit.
i'll keep you guys posted

 

Did you check and/or replace the distributor cap?

 

Dear all,

sorry for the delay,
i ordered some parts but none really helped so I’m getting a bit desperate. This car is sitting since I bought it in November on my driveway.

Things done so far:

New CPS
New coil
New leads and plugs
New distributor and rotor arm
New MAF
Checked for air leaks in the intake trajectory
Checked for compression (everything within specs)

Symptoms are: running on like 5 of the 6 cilinders from 2000 rpm and above (earlier when cold)
Doesn’t matter which lead you disconnect (in the problem rev zone) it still runs as bad. Disconnecting 2 is a major difference.

Disconnecting the MAF solves it completely but then plugs gets black in no time.

What on the world could cause this, I would really appreciate your advice.

 

Do you have catalytic converters, could they be plugged? I ask because of another current thread.

 

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.

 

Hi fremaes,

Welcome to the Jaguar Forums! It's great to have you with us!

As you've already learned, we have some friendly and very knowledgeable members who are happy to help.

The manual at the link below contains much of the data required to test various sensors for proper operation as mentioned by katar83:

Jaguar AJ6 4.0L Engine Management System / OBDI DIagnostic Guide

For example, the chart on pdf page 51 gives the correct resistance readings for the Coolant Temperature Sensor at any given coolant temperature.

One place to begin your diagnosis would be to check the Vehicle Condition Monitor for any stored diagnostic trouble codes. To do so, turn the key to position II (ON) but do not start the engine. Press and release the VCM button on the trip computer next to the steering wheel. Watch for a message to appear in the odometer window below the speedometer. DTCs appear in the form of FF or Fuel Fault and a two-digit numeral, such as FF14 or Fuel Fault 23. You can find explanations for these codes in the manual at the link above, or in the Haynes manual. You can download a mostly-complete U.K. edition at this link:

Haynes Jaguar XJ40 Repair Manual

Cheers,

Don