Really bad MPG on Rover V8 4.6 - Help!

Def west ender · Post by **Def west ender** » Tue Dec 16, 2008 5:14 pm

Will this do the trick?

http://cgi.ebay.co.uk/LAND-ROVER-V8-ECU ... 240%3A1318

Def west ender · Post by **Def west ender** » Tue Dec 16, 2008 9:34 pm

I called RPi and talked to someone called Ian, he said that these 2 items would do the trick, any thoughts? Since it's running massively rich on petrol too, surely there's a common fault as these items seem to be targeted at just LPG.

Thanks again guys.

http://cgi.ebay.co.uk/Land-Rover-V8-eng ... dZViewItem

http://cgi.ebay.co.uk/LPG-Lambda-loop-u ... dZViewItem

ChrisJC · Post by **ChrisJC** » Wed Dec 17, 2008 8:21 am

Def west ender wrote:Will this do the trick?

http://cgi.ebay.co.uk/LAND-ROVER-V8-ECU ... 240%3A1318

Provided you have the same ECU as the one in the blurb, and also the connector to attach it to, then I would say that will tell you what's wrong.

Alternatively you could try to bribe your local Landie garage to get them to use theirs.

But I would certainly try to establish what the fault was before spending money on new parts.

Chris.

CastleMGBV8 · Post by **CastleMGBV8** » Wed Dec 17, 2008 1:51 pm

RPI's prime initiative is to sell you something, check carefully to make sure it's something you really need.

Kevin.

Def west ender · Post by **Def west ender** » Wed Dec 17, 2008 4:44 pm

I agree, although I'm not saying what he offered me won't solve the problem, he didn't really listen to what I had to say before he told me what I needed.

The gas installer said it could be that the cam could be 1 notch out on the timing, I can't imagine this is what's wrong, would it still run?? as mine is just lumpy an eats fuel, any thoughts?

Kev · Post by **Kev** » Wed Dec 17, 2008 7:33 pm

My cam was 1 tooth out and ran OKish. I bought a Piper 285 cam for my Serp engine. Fitted it carefully and timed it to the marks. No adjustment on the Serp cams.
The engine ran but it was down on power and I had a lot of problems with the mixture.
Cutting a very very very long story short I checked the timing with a cam degree wheel and found it one tooth out even though the marks lined up. I contacted Piper who told me that I should have checked when I fitted it

as they sometimes index the blank one tooth out if they can't get the grind on and no they don't indicate if they do that. Bastards !!!!!

Kev

edit: have to agree with castleMGB, RPI's prime motivation is to sell something. I'd not use them for impartial advice

Def west ender · Post by **Def west ender** » Wed Dec 17, 2008 8:33 pm

Cheers Kev, useful info, I wonder if mine is the same. Just to pick your brains a little more... ...when you say ran OKish can you describe it a bit more. Mine seems 10-20% down on power, revs round to 5,500rpm but sounds a little harsh and is a bit lumpy through the rev range (more so on low revs), eats fuel and blackens plugs in seconds. Similar to yours?

PS While I was fiddling under the engine bay I had a gas backfire (no not a fart

) and it blew my intake hose to pieces

Just bout a silicone one on ebay for £18

CastleMGBV8 · Post by **CastleMGBV8** » Wed Dec 17, 2008 11:07 pm

If there have been backfires through the airflow meter I'm told it usually damages them which could be one source of your problems.

I also understand that the 3 or 5AM is a little small for a 4.6 engine and fitting a 20AM? from a Jaguar can be beneficial.

Kevin.

CastleMGBV8 · Post by **CastleMGBV8** » Wed Dec 17, 2008 11:07 pm

If there have been backfires through the airflow meter I'm told it usually damages them which could be one source of your problems.

I also understand that the 3 or 5AM is a little small for a 4.6 engine and fitting a 20AM? from a Jaguar can be beneficial.

Kevin.

Robrover · Post by **Robrover** » Thu Dec 18, 2008 7:21 am

Also check your engine's reaching it's full running temperature, has the correct thermostat which is not stuck open. My hotwire Disco was running rich because it wasn't getting hot enough so the ECU overfuels. Not apparent on the temp gauge on the dash. The Disco has an 88 degree thermo and enrichmnet from a cold start doesn't cut out until the engine reaches 80C.

Def west ender · Post by **Def west ender** » Thu Dec 18, 2008 11:14 am

Robrover wrote:Also check your engine's reaching it's full running temperature, has the correct thermostat which is not stuck open. My hotwire Disco was running rich because it wasn't getting hot enough so the ECU overfuels. Not apparent on the temp gauge on the dash. The Disco has an 88 degree thermo and enrichmnet from a cold start doesn't cut out until the engine reaches 80C.

Yep done that, just put a new 88 degree thermostat in and set my dail to 90-92 degrees, the fan will now cut in after the thermostat opens. Mind you the fan only cuts in when the cars parked as when I'm driving it won't as it's winter (cold air through the radiator grill) does anyone block/cover their grill like the London taxis do to keep them warm? I've been running mostly with gas the enrichment wouldn't effect it would it?

Also regarding the backfire, it's the first one it's ever done and I was fiddling, I hope it's not blown the AFM.

kiwicar · Post by **kiwicar** » Thu Dec 18, 2008 1:20 pm

From my 42K of experiance of LPG on a 3.9 injection RR.
1/ the plugs last 6-8 k miles before they need replacing.
2/ distributor lasts about 35k before it is worn enough for the scatter to cause a significant increase in the number of back fires.
3/ leads rotor arm and cap last 9-12k
4/ a backfire hard enough to split the pipework stands a 25% chance of killing your AFM
5/ you are better off running without Lambdas as it is one thing less to put it into limp home mode (remember disconnecting the power to reset the ecu will only take it out of limp home mode IF you have fixed the problem that put it there in the first place)
6/ if you have been running with the LPG still burning when it goes out the exhaust valve for more than about 3k miles then you should rebuild the heads as the exhaust seats and valves will be shot.
7/ five common causes of the above are insuficient compression, old distributor, poor mixing of the gas with the air, limp home mode, old plugs and not enough ignition advance.
8/ If the cam is advanced it will result in 6 but it will also make it prone to backfire.
After 42 k miles I reconed it would never pay for itself and sold the car
Mike

Def west ender · Post by **Def west ender** » Thu Dec 18, 2008 2:09 pm

Wow, cheers for the the detailed reply, thanks for putting the time into it.

1/ the plugs are new
2/ distributor looks in good shape, but don't know how many miles it's done and don't mind spending on a new one if it'll help.
3/ leads rotor arm and cap all new
4/ backfire: I put my AFM back on and the bracket holding it was at a bad angle and was stretching the hose, I have a new better hose, how can I tell if the AFM is broken? I put my finger over the hole with the wires and it did alter the revs, does this mean its working?
5/ It has a 4 branch manifold without Lambdas
6/ I've done 300 miles on LPG
7/ insuficient compression - new engine/heads, old distributor - I'll look into that, poor mixing of the gas with the air - been set up, limp home mode - not sure, old plugs and not enough ignition advance - been set up.
8/ If the cam is advanced it will result in 6 but it will also make it prone to backfire - this is what the gas installer says it may be.

Kev · Post by **Kev** » Thu Dec 18, 2008 5:38 pm

Def west ender wrote:Cheers Kev, useful info, I wonder if mine is the same. Just to pick your brains a little more... ...when you say ran OKish can you describe it a bit more. Mine seems 10-20% down on power, revs round to 5,500rpm but sounds a little harsh and is a bit lumpy through the rev range (more so on low revs), eats fuel and blackens plugs in seconds. Similar to yours?

PS While I was fiddling under the engine bay I had a gas backfire (no not a fart ) and it blew my intake hose to pieces Just bout a silicone one on ebay for £18

Mine was a bit similar in that the power was less than expected, the power band was narrower than normal and higher up the rev range than expected. I had to tweak the mixture right back from what I'd expected. i run a megasquirt so I was able to compensate for many of the probelms. The number of times I checked the ignition timing was unture

as people kept telling me it must be out.
My next door neighbour is a bit of a guru and after some head scratching he was the first to suggest a cam problem. I tested the cam timing roughly, with the engine in-situ, and it apeared to be a bit out but I wasn't convinced. I then removed the front cover and a rocker cover and measured the timing accurately with a degree wheel and got my neighbour to check 'cause I didn't believe it.
My advice would be to do a rough and ready check with a timing disc on the crank pulley and a clock gauge on a rocker; don't forget there's 720deg. per cycle.

good luck
Kev

kiwicar · Post by **kiwicar** » Thu Dec 18, 2008 5:55 pm

If the lambdas have been removed the ECU needs to be told by fitting the right tuning resistors otherwise it looks for the Lambdas and when it does not get the right signal back it goes into limp home mode straight away.I would check this first.
With the rather slow burn design of the heads on the rover you really need more CR on gas than the engine is happy with on petrol. The guys on here who have success with LPG use higher CR in the region of 10.5 :1 or more, they run gas only, as this is the very top end of what petrol will run on without detonating under full load. If you are running less than 10:1 on gas I don't think you will avoid trouble on LPG.
Many of the kits try and get around the issue of low CR by putting in alot of ignition advance when the kit switches from petrol, trouble here is that the amount of extra advance combined with a worn distributor giving you alot of spark "scatter" ends up with cross fire onto the wrong plug in the distributor and you get a backfire on gas.
All this adds up to needing all the ignition components, especially the distributor, in new condition. Also if the engine is old it will need a rebuild sooner or the CR drops and the exhaust valves and seats burn.
I'm not saying you can't get an engine to run LPG, you can and many do, however end up consuming bits far more quickly, this plus the initial cost of the kit and the higher servicing costs means you take far longer to see a return on your investment.
Mike
Edit If you are in limp home mode your plugs will be dead in about 50 miles

so sort out this before you put more miles on the engine.