Seriously rich V8efi - 6-7mpg!

[thecuth]

Hi all, I live in Amman Jordan and bought a fairly tired but straight and rust free '93 reg Disco 3.5 V8 late last year. Ever since I got it it ran a little rich and misfired/lost power on hills (and there's lots of them here!).

It's obvious that it's been badly maintained for years, the engine is quite corroded inside. It's a little tappety, but not terribly for it's age. I've done a lot of work besides what's listed below but this is a history of problems and work that relate to the engine problem that I've failed to get to the bottom of.

December - Got it.

Smelt a little rich poor economy (320km/tank - 11mpg), lumpy and severely lost power driving up long or steep hills.

- replaced spark plugs
- replaced vacuum advance (original one knackered)
- new rotor arm (original one knackered)
- new distributer cap
- new HT leads
- tested ECU temp sender

Easter time - Still dodgy.

- replaced lift pump (original had been tampered with)
- tested MAF (Just static voltage, it there a better way of testing this?), engine and roads speed sensors, injector resistance, throttle position sensor.
- changed spark plugs again - old ones completely sooted up

- I think my engine had lambda sensors & cat when new as it has that large plastic charcoal cannister under the bonnet. At some point the cat & lambda sensors have been removed, but the tune resistor has been changed to yellow (I think correct for non-cat)

Last week - still not good

- Had 7 injectors recondidtioned by a specialst and bought 1 new non-genuine one.
- Had pressure regulator checked by the same company.
- cleaned sooty spark plugs.

Verdict:

Even worse misfiring (sometimes runs on 7 and sometimes it seems like 4 1/2 cylinders) and worse rich smell. looks like I'm going to get no more than 200km out of this tank! (7mpg - SAME as my old 101)

What now:

1/ maybe pressure regulator is wrong and working at too higher pressure (but has allegedly been checked)?
2/ "injector recondidtioning specialist" did say that injectors can be sticky when new - could one be stuck open?
3/ non genuine injector I bought was for a 3.9, do both engines have the same injectors?
4/ Dodgy ECU
5/ could be weak spark but I've put strobe light on all plugs and it does seem to work (although when I rev the engine upto 2krpm it works intermittently - maybe dodgy strobelight)
6/ I've not replaced spark amplifier or coil - maybe weak spark would result in rich smell but surely not such poor economy?

7/ Clogged return pipe (there is no sign of physical damage)

Right now I'm still doing local mileage with a gentle right foot because I need to be mobile - Is this likely to cause the bores to rapidly deteriorate of will I get away with it in the short term? - It is costing me more in fuel than it would cost me in taxi fares!

[Nigelw]

I suffered similar poor economy with a 3.9, I replaced the lambda sensors and fitted a known good second hand MAF and it went from 10/11mpg to 18/19mpg and ran a hell of a lot better, further improved economy with replacing the worn out timing chain and sprockets.

The 3.5 in the Disco was hot wire and needs the lambdas to run properly if I'm not mistaken, it is the O2 sensors that tell the ECU what state the mixture is along with the other sensors that feed it info to perfect the running.

I would be looking to getting the EFi system back to as near factory spec as possible and going from there, if it's been hacked about, that is usually a sign of a fly by night mechanic who doesn't know anything about the system they are working on, if they did, they would be replacing parts, not simply removing them.

[Hybrid_From_Hell]

Cts.....prob failed. ..change it

[mickeyw]

That's coolant coolant temp sensor to the rest of us.

[Hybrid_From_Hell]

Sorry answering on mates phone

You kniw wgat my texting is like

[Hybrid_From_Hell]

^

Oops

[thecuth]

Thank all.

Nigel, sounds like you had a similar situation as me. I did a static voltage test on the maf a couple of months ago and it seemed within tollerance. But just this evening I got details of a really thorough test which I'll do tomorrow (details attached).

I had brainwave whilst reading that document... when I had the fuel rail off I did notice that the vacuum pipe to the pressure regulator was a little perished. If that's failed it'll run the injectors at too higher pressure so I'll look at that too.

Who knows, the slightly rich all year may be the maf and the drastic recently may just be the vacuum pipe.

I have checked the temp sender before, it's definitly fine.

http://www.actproducts.co.uk/2011/lucas-14cux-fuel-injection-system-%E2%80%93-installation-and-diagnostic-notes/

[thecuth]

Had a seriously interesting day, but going round in circles as normal.

I checked the vacuum pipe for the pressure regulator. Was perished as I remembered, but did at least hold a vacuum. I replaced it anyway with a new hose, checked the vacuum at the regulator end and sucked on the regulator to ensure there was movement and that the diaphram wasn't perforated. Verdict: that's all fine.

Then I checked the MAF and was surprised to find that the static and dynamic voltages were lower than they should be which should lead to lean running? It looks as if someone has tampered with the potentiometer in the past so perhaps someone tried to compensate. I cleaned the two wires with electrical cleaner and refitted it. I think I could usefully replace the unit sometime, but I doubt the MAF is the reason for the obscenly rich mixture...

Then I thought I'd check the fuel return pipe, I couldn't see any reason why it would have suddenly blocked other than the fact it had been disconnected for a couple of months whilst I was in the U.K. having the injectors serviced. However, I did have to blow very hard to clear what felt like some sort of obstruction! Maybe a little creature came to live in the pipe whilst I was away. Still I was excited to have found the main problem.

Still ran rough, so I took out the spark plugs and cleaned them. They were filthy and only 100km old. Re fitted them and it was still as lumpy as anything. The rich smell had almost gone from the exhaust but the engine stank of petrol. Checked the engine and sure enough the oil was full of petrol. The level was over an inch high, watery and stinking of petrol.

Tomorrow will be an oil change.

Rich running more or less fixed but engine is now more lumpy than ever. I've only done 140 km since this problem arose, surely I can't have worn the bore out in such a short space of time?

[Nigelw]

When I had my Discovery delivered to me by a friend of a friend from Portsmouth to middle of Belgium, he likened the fuel gauge to the count down timer LOL, he said it really was a real time visual thing watching it drop

I sat thinking about it and browsing the interweb and almost bought a brand new manifold and carb set for it, but then the sense suddenly kicked in, replace the suspect parts and enjoy a better MPG from the EFi than you'd ever get from the best tuned carbs.

Good luck.

[Tanuki]

Check that the return line from the pressure-regulator to the fuel tank isn't blocked. Disconnect it and blow it out with compressed air. There's no point having the fuel-pressure-regulator doing its thing if the excess-pressure fuel can't be returned to the tank!

And check the way the vacuum line to the pressure-regulator is connected - it sounds like yours may have been 'got at' at some time in the past and the suck-pipe's not connected to the right place on the intake-plenum - or the metal spigot on the plenum where the suck-pipe connects could be blocked with decades of black oily sludge...

[thecuth]

Hey Nigel.

Its always been a bit thirsty, but I've been able to tollerate that beacuse of the lower cost of fuel here. 320km to an 18 gall tank, the same in km as my tdi 90 does in miles to a 12 gall tank. At least the 80/ quarter of a tank is familiar even if the tank size and units are different

However, in the last week (since refitting the injectors) it did 140 km to three quarters of a tank - a different league... works out at about 6mpg! I never even got my 101 to much less than 8. Think I've fixed that now with the return pipe being cleared, just got more problems now...

I'll keep you informed.

[thecuth]

Hi Tanuki. You're a genius - dead right. It was the return line, i fixed that by blowing down it with my mouth, I did turn a little blue in the face! All repairs here are road-side. I wrote todays malarkey down a bit ago but I think my post wasnt approved so I'll give you all a summary...

I checked the vacuum pipe first and replaced it. Then I spent time checking and cleaning the maf. Then I checked the return line and found a blockage, blew it out. It still ran rough, but not so rich, so I cleaned the plugs which were covered in soot. Still ran rough. Smelt petrol and found it in the oil. Must have got in through the bores. Had a hell of a day!

Changing oil tomorrow. I hope engines not lost compression... I've only done 140km since the return pipe was blocked, surely I can't have done in the cylinders in that short time. I hope not!

[thecuth]

Lumpyness fixed as well now. It was one of my injectors. A brand new intermotor one, it seemed to be delivering too much fuel. Replaced it with a good secondhand one and it's finally running as well as it ever has since I got it.

[mickeyw]

Arrgghhh Cuth! Intermotor - a well known source of trouble. Nige (hybrid from hell) will go on about how good that brand is, lol.

Do you remember the time you towed me back from Chichester? That was due to a brand new Intermotor coil

[thecuth]

Not only is it working properly now, but it's going better than it ever has since I got it.

Looks like I'm going to get over 400km out of this tank which is 100 more than I've ever had even when it worked ok and 3 times what I was acheiving a few weeks ago. Ever since I've had the vehicle the plugs have got sooted up.

Not any more. Might be the 7 recon injectors I fitted or the fact that I cleaned the hot wire in the MAF.