V8S misfire when cold

[Andy Lynch]

Hi can anyone suggest what may be wrong, my V8S has just developed a misfire when cold.

When the car is cold it idles ok, however if you dip the throttle it develops a single but very noticible misfire. As the revs increase, it doesn't back fire it just doesn't fire for a second, then carries on reving and running ok. As soon as it warms up it runs fine.

Thanks

Andy

[PYNEY]

i'm guessing it could be your idle speed control valve ?

[GreenV8S]

Not entirely sure what symptoms you're describing but from the sound of it it is either going flat, or cutting for a moment, as you open the throttle. That suggests you may have too much or too little throttle enrichment. It may be that the enrichment itself is correct but the base fuelling is out. And the most likely cause for that is that the coolant temp sender used by the ECU is mis-reading. It come be some other problem such as wrong fuel pressure causing a similar symptom.

[Andy Lynch]

Thanks GreenV8S

The car seems to be cutting for a moment as I open the throttle, as you said, best describes the symptoms.

Is there anyway of testing the coolant temp sender? or is it a case of fit a new one and hope that was the problem?

Do you know where I can get one? part number etc.

Thanks

Andy

[Ragtop]

Hi Andy,

Sorry to hear you're having problems. You can check the coolant temp sender quite easily in-situ by measuring its resistance. The value varies with temperature (obviously) and is given in the Haynes Range Rover manual, the 'bible' (I think) and here:

http://www.britishv8.org/Articles/Rover-14CUX-EFI....

I think the part number is ETC8496, and prices vary from around £5 to £40, eg:

http://www.lrdirect.com/ETC8496-Temperature-Sensor...

If the sensor itself appears to be working you should check the resistance at the ECU plug as well in case there is a wiring fault. That's a bit trickier 'cos you need to find the right pin - again it's listed in the britishV8 article and elsewhere. Open circuit is 'cold' and 'short circuit' is hot in the general scheme of things, but either may be read by the ECU as 'out of range' and give goodness-knows-what effect on running.

Having said all that, I would guess the problem lies elsewhere. Have you been fiddling with anything lately, like the idle mixture setting? Although the problem seems to be directly related to engine temperature, it may well be worth checking the usual things like ignition leads all tight etc.

Good luck...
Graham

PS - the Haynes manual has a pretty good section on the V8 engine, including fault-finding, and if you haven't got one I would recommend one. Cheap used ones come up on Ebay and Amazon quite often.

Edited by Ragtop on Sunday 17th July 17:39

[Andy Lynch]

Cheers Graham

The only thing I have been messing with is the Distributer cap and rotor arm, I pretty sure that everything went back ok.

However there is another issue, or two. (before I messed with the dizzy) Every time I reverse the car out of the garage and up the drive on to the road, it allways cuts out if I lift off the throttle, ever though it had been ticking over ok in the garage. It will restart ok and idle fine, and drive ok. Any Ideas?

Also when warm, if I stop the car and then restart it within a couple of minutes, some times its ok but sometimes it dosen't idle, and would cut out if I dont keep the revs on. after a few minutes driving its back to being ok again

Thanks for any advise

Andy

[Barkychoc]

Is your speedo working OK? The ecu uses the speedo signal to work out if the car is moving or not.

Also what petrol have you got in it? Mine gets mardy if it doesn't have shell VPower - it runs far better on that than anything else.

[Andy Lynch]

Yep speedo is ok.

Andy

[GreenV8S]

The hot soak problem isn't uncommon and can be caused by fuel boiling in the fuel rail and fuel lines due to heat soak when the car is stationary.

For the other problem, start by locating the coolant temp sender at the front of the intake manifold. You will have two senders there. One with a single wire drives the gauge. The other one has a 'mini power timer' style connector the same as the injectors use, and is used by the ECU. It's the ECU one you need to be concerned about. The resistance is measured with the sender disconnected. It should read about 5000 Ohms at freezing, and the resistance should roughly halve per 20C temperature rise. At 80C or so, that should take it to about 300 Ohms. That's just a rough figure so don't fuss if it's a bit out, but if it's far different you probably have a problem. You can check the sender itself just by sticking your head under the bonnet with a multimeter. If the sender checks out OK it's also worth doing the same measurement at the ECU end of the loom. That takes more work since you have to dig out the ECU, disconnect the electrical plug and then locate pins 7 and 25 and measure the resistance across them. If you don't already know which pins these are, you'll have to dig the seal out and unscrew the two screws that hold the clamshell on the back of the connector so you can see the pin numbers on the rear of the connector.

[v8s4me]

If you do decide to check the resistance at the pins on the ECU plug it’s worth noting that the numbering on the diagram in the “bible” is wrong, for the V8S anyway. The actual number layout on the ECU plug is a mirror image of the one in the book. It took me a whole Saturday to work this out! While you’ve got the ECU out it may be worth checking the wiring to make sure there is no break in the permanent live feed to the ECU and that the wires to and from the tune resistor are OK. You could also consider investing in a Steve Heath fault code reader.

[Ragtop]

v8s4me said:

If you do decide to check the resistance at the pins on the ECU plug it’s worth noting that the numbering on the diagram in the “bible” is wrong, for the V8S anyway.

Not so for mine! Mine's the same as the one in the 'bible' labelled '1990 onward arrangement' and is exactly the same as the one photographed in

http://www.britishv8.org/Articles/Rover-14CUX-EFI....

It has the same matching numbers cast in the plastic for confirmation. Find the numbers and you can't go wrong.

Have fun!
Graham

Edited to add: Joe, I bet you were looking at the pin side rather than the wiring side?

Edited by Ragtop on Tuesday 19th July 20:36

[GreenV8S]

Steve's book is correct, although he shows two arrangements which he describes as being different but are in fact the same thing upside down. The housing has the pins numbered and as far as I know there is only one arrangement and it matches what is in Steve's book.

[v8s4me]

Yes, the numbers moulded into the plastic under the seal are correct but on mine they didn't match the diagram when viewed from the front of the plug. That's what I meant when I wrote "mirror image". Condfused? You will be

[Andy Lynch]

Thanks for the info.

I have checked the resistance as asuggested, and it apears the coolant temperature sensor is ok, it measured 3000 ohms at room temp and dropped to 275 when the engine was at normal operating temperature. I checked the pins on the ECU and that was the same as across the sensor contacts. Thanks for the info about the pins being the mirror image, the heads up on the picture in the "bible", I to assumed the picture was of the front! anyway my copy now has pim numbers numbered from the front.

How on earth do you put the stupid flap back up that holds the ECU and what seems to be far too many wires for such a small car! I can see a forigner needed in our fab shop at work, anyone got any pics on how they fixed theirs.

New plugs leads dizzy next, lets hope that helps, By the way how much of the engine do I have to remove to replace the plug on No 7 cylinder? It looks a bit snug, but Im sure I will manage.

Thanks again

Andy

[Ragtop]

Andy Lynch said:

How on earth do you put the stupid flap back up that holds the ECU and what seems to be far too many wires for such a small car! I can see a forigner needed in our fab shop at work, anyone got any pics on how they fixed theirs.

Mine's held up with two quick-release tie-wraps that pass through holes in the front edge of the flap and around the padded crossmember immediately above. I suspect this is not standard...!

Graham

[Ragtop]

Andy Lynch said:

By the way how much of the engine do I have to remove to replace the plug on No 7 cylinder? It looks a bit snug, but Im sure I will manage.

A bit snug!!

I get all my plugs in and out without removing anything, using a 1/4" drive spark plug socket, ratchet handle and short extension bar. If you think removing them is difficult, wait until you try to put them back!

Graham

[v8s4me]

Try slipping a short length of plastic tube over the top of the plug. This will give you a bit of extra length which will help you get it in the hole. Once the plug is seated and you’ve got a couple of turns on it, pull off the tube and slip on the plug socket.

[GreenV8S]

V8S4me came up with a very clever sliding tray arrangement which would be well worth copying. What I did on mine is much cruder: I just drilled through the wooden frame that forms the bottom edge of the dash and fed a couple of bolts through from above with nuts on the bottom to secure them. I poked two small holes in the carpet that line up with these bolts. Now there's enough friction between the carpet and the bolts that you can just shove the carpet into place one-handed and it will stay there; I have a couple of wingnuts to secure it. I dread to think how much time I wasted trying to get those woodscrews into place and done up, trying to hold the screwdriver, screw, carpet, mess of stuff on top of the carpet all at the same time. Now it's a doddle.