V8 Power Drop

[GreenPig]

Hi,

We own a Range Rover classic 1992 J 3.9 EFI Auto which has an intermittent problem.
When driving it suddenly will loose power for a second or two then power kicks back in and it runs as normal. This seems to happen around 2000 rpm, the power drops off, but the engine doesn’t stall completely it drops to tick over then kicks back in. As you can imagine this is quite alarming if you are on the motorway etc.
We have a fault code reader and nothing shows up also we have done the obvious like change the HT and plug leads. Can anyone point us in the right direction?
Thanks

 

[classic kev]

'92 on a J..... cat or non-cat? If non cat you won't get as much info from ECU as it won't "see" lean or rich conditions from lamda sensors or misfires.

First thoughts are possibly ignition amplifier or dying ECU. Would suggest trying a substitute ECU. My '91 RRC had a similar problem some years ago, that was the ECU, put in a second hand one and not looked back.

 

[GreenPig]

Hi Classic Kev,

Thanks for that, its a non cat version.

Any clues as to how I make sure I get a good second hand ecu or should I look for a recon one?

My other landy is a 2.5d 110 so electronics (electrics even!) are a new thing to me.

Thanks again

 

[classic kev]

Part of the problem with intermittent rough running is deciding where to look first.

What you don't know is if the problem is an injection problem or an ignition problem. What you describe sounds a bit like the engine "stumbles" then runs fine for a bit then does it again. I've had similar issues over the years from various causes.

Do some basic things first - check battery and alternator output; see what happens when you drive with heated rear screen on, heater on max, main beam and driving lights. If it coughs and splutters chances are the alternator is in need of an overhaul.

Check and clean main earth points, good earth is essential for good running. Remove and clean the big earth from battery to chassis, undo and clean the earth point under the expansion tank.

Next run basic ignition checks - do a search these have been posted a couple a times.

You say you have changed dizzy cap and leads - what about rotor arm? use only genuine Lucas ignition parts.

Check your coil.

Assuming ignition checks out you'll need to move on to the EFI. Injection pulse is triggered from the negative side of the coil, check the condition of the wire and the spade terminal - they corrode and break. (Also remember the injectors are earth switched)

Using a multi-meter, check the air flow meter (search for how to check this). Then check the throttle pot and the coolant thermistor.

If all this appears to check out try substituting the ECU, either get hold of one from a known running vehicle or take a chance on a used one from fleabay. Any 14 CUX ECU will do, it doesn't matter if it comes off a Disco or RRC or what the part number is, it should work. (Don't use a TVR one though).

That should keep you busy for a bit. Good luck.

 

[GreenPig]

Classic Kev,

Thats super helpful and has sorted my weekend out!

Thanks again.

 

[West Slope Rover]

Thanks kev! Great tutorial. I've bookmarked it for future reference as I do with other pertinent posts.

Isn't this a great place?

 

[Mr Noisy]

Looks like kev's got this one sorted, nice one

 

[classic kev]

Thanks chaps! I'm only passing on what I have learned from owning an RRC that refused to run properly for a year and of course the input from LZ!

To the OP, put up your location and maybe introduce yourself in the appropriate section

BTW Noisy, did I remember reading you ditched your original heater box? Might have a use for it, if it's available how much might you ask for it? Drop me a PM.

Cheers.

 

[classic kev]

FWIW have a breeze through this wee thread, I just did a search for "engine stumble" coz this all sounded vaguely familiar!

http://www.landyzone.co.uk/lz/f42/mystery-mid-rpm-misfire-93628.html?highlight=engine+stumble

 

[Mr Noisy]

Thanks chaps! I'm only passing on what I have learned from owning an RRC that refused to run properly for a year and of course the input from LZ!

To the OP, put up your location and maybe introduce yourself in the appropriate section

BTW Noisy, did I remember reading you ditched your original heater box? Might have a use for it, if it's available how much might you ask for it? Drop me a PM.

Cheers.

Hi Kev

I did yes but I passed it on to 200tdiayre but unfortunately it got broke in postage! What a waste!!

 

[classic kev]

Hi Kev

I did yes but I passed it on to 200tdiayre but unfortunately it got broke in postage! What a waste!!

Oh dear, never mind, it happens but thanks anyway.