The V8 Owners Forum -

Hi Guys, first post on here and sorry it's a question

I have a Land Rover Defender running a 4.6 V8. The thing is eating Petrol and LPG (8-10mpg at best), I've tried everything but am at a loss (both mentally and pocket) so am asking for help.


It's a 1984 Defender with:

Brand new from crate 4.6 (just 1500 miles done), 4.6 heads, new cam, timing chain etc.. the whole works mated to a 4 speed ZF auto box. Just fitted new leads, plugs, cap, rotor arm too and all set up as best as possible. It also has no cats with 4 branch headers, distributor (new), hotwire system, brakes not binding either.

It runs reasonably fine, but not as powerful as it should be (my opionion), a bit lumpy and not as smooth as a V8's I've had in the past, but by no means awful. It's been to a couple of mechanics the last one deals with LPG and races Rover V8's and seems like he knows what he's talking about, but even he can't quite work it out.

It runs very rich and on petrol will foul the plugs in 3 minutes (very sooty and black), he first thought it was a very worn out cam, but when we removed the inlet it was perfect (inlet then cleaned and put back), he now thinks that perhaps when the engine was put back together the cam may have been put back a tooth out, he says that the ecu would compensate for this so it would run ok'ish but just run very rich. The last car I had that had a cam 1 tooth out (K-series) did run but was very noticeable it was wrong. You can pull leads 2 and 6 off and it doesn't make much of a difference as with some leads (spark is fine).

Any ideas? Big thanks in advance.

What injection system are you using? If Hotwire.
1) Disconnect battery
2) Leave disconnected for 1 minute
3) Reconnect

It resets the ecu
To me it sounds like it is in safe mode / get you home mode

An yes that is RICH on mine in back garden it made our eyes water with the fumes! And mine was down about 6mpg!

Ian

Cheers for the reply Ian.

Yes it's hotwire.

The battery was disconnected for over an hour the other day, but made no difference.

How much less power is the safe mode? As I can still accelerate quite fast/good top speed too, about as fast as a 3.5 V8 Defender and it's a 4.6.

I've not checked if it has a 3.9 or 4.6 ECU, are they the same?

Safe Mode is very rich nd I believe also messes on the timing so it will not rev so well. Power was still reasonable but fumes terrible.

Perhaps you have a mix of 2 systems
A system set for cats with a non cat tune resistor in so it is getting screwed up readings and trying to over compensate!

No doubt Ramon will be along shortly and he will have some ge=reat ideas for you to try

Ian

Ian Anderson wrote:Safe Mode is very rich nd I believe also messes on the timing so it will not rev so well. Power was still reasonable but fumes terrible.

Perhaps you have a mix of 2 systems
A system set for cats with a non cat tune resistor in so it is getting screwed up readings and trying to over compensate!

No doubt Ramon will be along shortly and he will have some ge=reat ideas for you to try

Ian

Thing is it's not only giving bad MPG on petrol it's doing even worse on LPG (around 8mpg) it's just a basic single-point system which just sticks in the same amount on LPG/air no matter what the ECU does, unless it's advancing/retarding the timing way off, I guess that would just throw unburnt fuel through (if I had cats on I'd check to see if they were glowing).

Does sound like limp mode to me.

Did anybody ever scan in the troubleshooting instructions for Hotwire? It's probably a duff sensor.

BTW - Hotwire doesn't alter the ignition timing - it can't.

Chris.

ChrisJC wrote:Does sound like limp mode to me.

Did anybody ever scan in the troubleshooting instructions for Hotwire? It's probably a duff sensor.

BTW - Hotwire doesn't alter the ignition timing - it can't.

Chris.

If the hotwire was up the spout would it effect it running on LPG though? As the LPG system is just a straight forward single point which is set (the more you put your foot down the more it sticks in - no more or less no matter what)

Depends, but from the sound of it, the LPG is completely independent of the Hotwire system, so yes one should not affect the other.

You could have two issues, a fault with the hotwire, and a completely separate fault with the LPG. I would think that the LPG would be easier to get right because it's simpler.

Has the LPG system been set up properly with a gas analyser?

Chris.

ChrisJC wrote:
Has the LPG system been set up properly with a gas analyser?

Chris.

Yes it has, it's been to 2 places, last guy seems to really know his stuff.

If the Hotwire was faulty would/could this effect the ECU's timing at all?

PS: Cheers for all the help everyone, really appreciate it.

Def west ender wrote:
If the Hotwire was faulty would/could this effect the ECU's timing at all?

How do you mean? The Hotwire ECU only controls fuelling, the ignition system is completely separate.

Chris.

Which ECU is it, If its from an earlier engine of smaller capacity won't it meed modifying to run properly with a 4.6, also is it a standard cam as most uprated cams will upset a standard hotwire system.

If your running an earlier front cover to drive a distributor was it just bolt a drive cog on the nose of the cam or were other mods done?



Kevin.

CastleMGBV8 wrote:Which ECU is it, If its from an earlier engine of smaller capacity won't it meed modifying to run properly with a 4.6, also is it a standard cam as most uprated cams will upset a standard hotwire system.

If your running an earlier front cover to drive a distributor was it just bolt a drive cog on the nose of the cam or were other mods done?

Kevin.

Not checked the ECU (not even found it!) It's an old 1984 that has been re-bodied and tons of stuff done, so things aren't in the same place they should be, I'm guessing it would be a 4.6 ECU (I thought the 3.9 and the 4.6 was the same though) as I'm guessing the engine/loom was initially from a donor Range Rover, I'll do a proper hunt to try and find it.

If it was the ECU how would I be able to sort it, short of replacing it with the 4.6 one, is there a management system, like Emerald/ICON that can tune it correctly? I know RPi do a chip, but £395 for £20 worth of bits is insane.

Not sure about the distributor, I know it has a J&P Duplex Chain/Standard cam.

Do I taike it that the engine change was done by someone else?

Are you sure it's a Hotwire system if the vehicle is 1984 it could be a flapper system for a 3.5!

What does it say/ numbers on the airflow meter?

Kevin.

CastleMGBV8 wrote:Do I taike it that the engine change was done by someone else?

Are you sure it's a Hotwire system if the vehicle is 1984 it could be a flapper system for a 3.5!

What does it say/ numbers on the airflow meter?

Kevin.

Aha, this maybe the problem. Can't find the ECU, I believe it's behind the bulkhead as I've looked everywhere else and there is a cover over it with the LPG bolted to it, but the airflow meter is a Lucas 3am which I believe is only fitted to the 3.9, I've attached a picture of one similar from ebay as my camera phone is crap.



If this is the fault is there a way round it, by fitting correct ECU and airflow meter or is the wiring different?

Def west ender wrote:
Not checked the ECU (not even found it!) It's an old 1984 that has been re-bodied and tons of stuff done, so things aren't in the same place they should be, I'm guessing it would be a 4.6 ECU (I thought the 3.9 and the 4.6 was the same though) as I'm guessing the engine/loom was initially from a donor Range Rover, I'll do a proper hunt to try and find it.

If it was the ECU how would I be able to sort it, short of replacing it with the 4.6 one, is there a management system, like Emerald/ICON that can tune it correctly? I know RPi do a chip, but £395 for £20 worth of bits is insane.

Not sure about the distributor, I know it has a J&P Duplex Chain/Standard cam.

There's no 'standard' Hotwire ECU for the 4.6 engine. There are only standard ECUs for 3.5, 3.9 & 4.2 in Hotwire.

Most likely you've got a stock 3.9 Hotwire ECU which is mostly OK on a 4.6, although not optimised.

If you don't want an RPi chip, and you want it right, then you need Emerald, VEMs etc.

But it's definitely worth making sure that it's not in limp mode before changing stuff.

Chris.