Discovery V8i (3.9 EFi) - Overfuelling

[Ian Seale]

Help!

My Disco's V8 has turned into a fuel pump.
It startered running lumpy at low revs, woudn't pick up from tick-over very well and started to stall now and again - it also had a slight misfire at around 2,000-2,500 revs.

Its been to a 4x4 specialist and put on, what looked like to me, a very basic diagnostic tester.
They first thought it was the Lambda probes (strangely, even the though the test showed and imbalance between the sensors - one bouncing around 15 the other around 7) they said that they'ed tested the sensors and they were OK.

Next, at a shade under £400 they reckoned it could be the Airflow meter, a quick change out made no difference.

All else is OK, and the problem came on suddenly, like something let go.

If you can get it to start, and when it does, it tends to be first time, it can run quite well, especially if given a run - but not always!.

If it doesn't start first time, the overfuelling just make things worse, and you can't guarantee then if it will start at all.

I'm now facing taking to LR, as I reckon they might have a more comprehensive diagnostic test than this 'specialist' I've just been to.
But before I do, I thought I'd throw this one out there to the combined minds of the forum.

Cheers, and fingers crossed,

Ian

 

[Ian Seale]

This is a PS.

The '4x4 specialist' diagnostic oddly showed that although overfuelling it was withing limits and pass an MOT, also that the overfuelling seemed to be in the lower rev range.

Hope that helps

 

[Belle427]

ive heard of all sorts of problems with these,the ones you have already done and the coolant temp sensor,ecu and stepper motor,best to get it to a dealer and on the diagnostics

 

[Heyyouitsme]

check all the little tiny rubber pipes that are on the top of the engine, i bet it s the vac sensor for the top of the engine, if the pipe is split or not connected or the vac sensor is dodgy it will overfuel and run lumpy

 

[Ian Seale]

Heyyouitsme & ch427,

Thanks for the replies.

I stopped by my local Land Rover dealer yesterday, to be fair they were pretty good, and honest, and said their diagnostics were just the same as the specialist (they knew them well), and they'ed do just the same things, but start again from scratch.

The specialist is happy with the stepper motor, but we haven't done a change out of the ECU just yet, or any check on the coolant sensor either.

I have checked all the vacuum pipes (Haynes point to that one too) they all seem OK, but I' have a look at the Vacuum sensor too then.

I guess where I get frustrated (coming from a diagnostic test background) is that the diagnostics don't pick up irregular signals from the sensors and flag them up, OR how the test the buggers, it's a pretty simple task to whack a multi-meter on a sensor IF you know what a good reading should look like - and no one tells you! - Everything is a change out!

Cheers,

Ian

 

[jonnyfishing]

Which sensors do you want to test ? Is it possible that the ignition amplifier (incorporated in the distributor)could be faulty?I would look in this direction first.

 

[Ian Seale]

jonnyfishing.

The next place to look seems to be the Coolant and the Vacuum Sensors, if they're not too pricey it might be beeter for me to but them and change them out one by one, than pay the garage to do it.

But there should be some form of test spec for a sensor that can be performed on a multi-meter to see if it's alright. I'm just surprised that the diagnostics aren't smart enough to flag a dodgey sensor reading if one has gone west.

I really don't think the spark is the problem (Leads, Plugs, Cap & Rotor are all less than 5K old - and nothing was touched just prior to the fault occurring). To add to that, the spark is well fat when tested against the block.
Everything is pointing to overfuelling, and everyone who's looked at, or smelt it, says so.
Having said that, I'm grateful of any advice, and the beauty of this site is that people can look at things from a different perspective (or experience) from you - so that will be the next thing I check if the sensors prove OK either by test or change out.

Cheers,

Ian

 

[Belle427]

http://www.v-8.org.uk/forum/index.php
the guys on here may have a better idea regarding sensor readings
jim,the guy here is also **** hot and very helpfull
http://www.jrv8.co.uk/

 

[Ian Seale]

ch427,

Thanks for that, useful websites!
The first one even had a guys with the same problem as me!

I had a good read through Haynes, and, in addition to your own and Heyyouitsme's advice (vacuum sensor) I'm going to take a look at the By-Pass Air Valve at the rear of the plenum chamber.
Haynes states that 'it controls idle (mine is lumpy, and prone not to start - i.e. on idle). Also, it says, when triggered by the ECU it allows extra air to pass into the inlet manifold, fooling the system into supplying more fuel.
Now, if that valve was sticking, staying open, or basically just not behaving itself it seems like it could produce the symptoms that I'm experiencing.
Also some days its bl**dy murder, others it not so bad, although always overfuelling, this would be conducive with something like a valve sticking, but not always in the same place.

I'm going to have it off tomorrow and give it a good old blast with carb cleaner, and see whats what.
If it works I'll let you know, and the guy on the other website.

Mucho cheers.

 

[jonnyfishing]

Ian

I still think you should look to the amplifier,if your spark is not constant at all engine speeds you will get misfires. Unburnt fuel going down one side of the twin exhausts would make the lambda readings bounce around a bit. A faulty amplifier will deliver an erratic strength spark,so when your spark is weak you get unburnt fuel and wet plugs=poor starting (cold engine).Erratic running with a hot engine.
However, here are some sensor tests you can try:-

cooling sensor temp resistance ohms
0c 5700-5900
20c 2400-2600
40c 1100-1300
60c 500-700
80c 300-400
100c 150-200
********************
Crank Position Sensor (CKP) (incorporated in distributor) remove ignition amplifier (ignition off)
check resistance between CKP terminals........2000-5000 ohms
*******************
Ignition Amplifier. TEST 1
ignition off--disconnect plug--ignition on--check voltage between plug terminal No3 and earth....should be battery voltage.
TEST 2
Replace plug...ignition on...check voltage between amplifier mounting screw and earth...0.1volts MAX.
*******************
Evap.Canister Purge Valve.
Disconnect plug and test valve operation with a supply from the battery, listening for the valve operating.
*******************

A Haynes Manual might come in handy to guide you.Good luck.

My money is on the IGN. AMP.

 

[Ian Seale]

jonnyfishing,

Wow, Thanks for that!

This site is a fantastic mine of helpful people.

As I'll have the bonnet up tomorrow, I'll get my probes out!

Cheers once again,

Ian

 

[Ian Seale]

Guys,

Progress Report
Whipped out the Bypass Air Valve (Haynes Description) or the Idle Control Valve (LR Description) at the rear of the Plenum Chamber, and it was black as the ace of spades, all sooted up, and looked like it wasn't seating.
I took off the whole assembly and checked the vacuum hoses all seemed OK.
So I cleaned the Air Valve and the Valve Seating within the assembly with Carb Cleaner and polished the valve head where it looked like it had scaled up a little, and re-assembled it.
QUESTION (For anyone that might know)
The valve itself didn't seem to have much travel on it, and the spring around the shaft looked to be as compressed as it could be (i.e it's natural, unenergised state seemd to be in the 'valve open' mode).
Energising it would seem whould push the valve out, into the seating and close the vacuum air path from the hose on the filter side of the butterfly to the plenum chamber. The purpose of the valve is to 'trick' the ECU to overfuel when there is load, on idle, to increase engine revs. It does this by allowing extra air to pass - so you'd think 'Valve Open' for that condidtion Valve Closed normall.
Thing is, reassembling the Valve in the housing, the valve was not closed, and you could blow through from the vaccuum hose spigot.
Testing the valve, with it connected and grounded to the block and switching the ignition on gave no movement to the valve, just as slight vibration when switching the ignition off.
Having said all that, the clean-up seemed to have worked and she started first time. The road test was good too, seemd much smoother.
However, I'm not entirely convinced that it was just 'gunk' in the valve causing the problem, and wanted to check it out against a good one, or find out, from someone who knows, what the idle state of the valve is (i.e is it closed - no blow through).
That was put paid when enquiring with LR parts that they don't do just a valve, only an assembly @ £102, and they can't order one in just for me to look at it and compare.
They also said that they never have this valve go wrong, hence none in stock.
I'd like to nail this one completely, but £102 is a bit of a gamble.
Over to the forum, it might help the guy on the V8 website with the same problem too.

Cheers,

Ian

 

[Belle427]

forgot to add you may find more info on that site by visiting the old forum link at the top of the page,its changed lately

 

[Ian Seale]

Guys,

Final (Hopefully) Progress Report

After I'd Whipped out the Bypass Air Valve (Haynes Description) or the Idle Control Valve (LR Description) at the rear of the Plenum Chamber, (it was black as the ace of spades, all sooted up) and cleaning it with Carb Cleaner I have had no further lumpy tick-over or pick-up problems.

Initially, it was difficult to start still but ran well.
Taking it on a few long runs seems to have sorted that out.
The V8 engine really seems to get itself fouled up whe it gets overfuelled and would appear to generate additional problem symtoms.
I've just done 241 miles on a tank (14 mpg average) including 2 hours of nightmarish stop-start congested traffic jams, and about 40 mile sof when I still had the problem, and lots of running to warm up during diagnosis.

Some feedback from the V8 forum indicated the Air By-Pass Valve is a big problem with TVR idling too.

I reckon Disco's get driven in a different way (very light right foot) and spend a lot of time burbling around between 1,000 and 2,000 revs - so a problem affecting idle can also impact on normal road use too.

I'd recommend anyone with Rover V8 idling problem to whip out the Air By-Pass Valve, the housing too if you can, and, if it is sooted up, give it a good clea with Carb Cleaner, it appears to have worled for me.

Cheers (till the next little challenge),

Ian