3.9 V8 running issues - cutting out, rough idle and running rich

Hi everyone,

I have just purchased this week, a Disco 1 3.9 V8 with an LPG system.

Unfortunately it does have a few issues that I need to address quite quickly.

Last night, when I was trying to work out where a whine was coming from, I put the autobox into neutral whilst the car was rolling. It then cut out on me. I am guessing this is to do with the idle control valve (stepper motor). I was wondering if there are any other suspects though to check out. Tonight I am going to climb in and take it off and give it a clean to see if that does it.

It is also under powered, or so I feel, I have nothing to compare it to, so I have boughgt a load of new iginition parts, dizzy cap, rotor, leads, and coil, air filter etc. Is there anything common that I can check.

It is running rich, very rich, but I have found a slight leak from one of the manifolds, possibly causing the lamda sensors to miss read? Any other suggestions on why it would run rich.

I will of course address all the things I know about, but it would be good to know what else can be checked, especially if it means I will get an extra mpg

Sorry for all the Q's :-D

Steve

I don't know anything much about LPG but first thing first, disconnect your LPG and get it running right on petrol.

Stalling - it sounds like this happens when you come off the throttle? If so, check base voltage on throttle potentiometer.

Replacement ignition parts - Please put genuine Lucas arm and cap on. Do not use a "Performance" coil get a genuine item. Use good quality leads.

Running rich - check the air flow meter. If AFM (or MAF as it is also known) is O.K. you may need to check the lambda sensors if they are dead or dying they could easily cause rich running.

Check and set your ignition timing. Check that the vac advance and mechanical advance are both working correctly.

I know I always say this but trust me, remove and clean the plenum and ram housing and set the throttle disc. Also clean the flame trap and the little breather at the back of the right hand (when facing the engine) rocker cover. Make sure all the vac lines are clean and clear. Might also be worth replacing the air filter.

HTH good luck.

A few things to do then!!

I have read a couple of threads on how to check the afm, but I have noticed a few differences between them all. I think I will see if I can have a borrow of one and swap it out, see if that makes a difference, possibly easier for me than playing around with my cheapie multi meter

It only stalls when it is moving at speed in neutral, I think it is possibly the stepper motor. I whipped it out last night to have a look at it, it didnt seem to dirty. I might try and take it off and plug it back in and see what it actually does. If anything at all.

Thanks again for the ideas.

Ill post back when I have been through everything one at a time, and let everyone know what the culprit was, if I ever find it that is.

I should also mention, that if in gear, whilst stationary, the idle is fairly smooth, sits around the 650 rpm mark. It is idling rough whilst out of gear, and slightly higher rpm.

I just noticed, you are only up the road from me as well. Small world!

Stevd said:

I should also mention, that if in gear, whilst stationary, the idle is fairly smooth, sits around the 650 rpm mark. It is idling rough whilst out of gear, and slightly higher rpm.

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Sounds like u have a misfire if there is a problem at higher revs, the stepper is only a piston arrangement moving in and out make sure u reset it to as it was if operated while removed otherwise you will have a problem as it also functions with starting, also required will be a new fiber sezaling washer.

discool said:

Sounds like u have a misfire if there is a problem at higher revs, the stepper is only a piston arrangement moving in and out make sure u reset it to as it was if operated while removed otherwise you will have a problem as it also functions with starting, also required will be a new fiber sezaling washer.

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Sorry that was poorly worded. I should have said, whilst the car is out of gear, it will idle slightly irratically and a couple of hundered revs more than if it was in Drive. Whilst in drive, the idle is constant.

Right, in that case I wont play about with the stepper motor whilst it is out of the engine Thanks for the heads up on that!!!

Steve

The stepper is there to balance out the idle speed so there will be little difference between the loads placed on the engine , in gear or not, a/c on or not, revs do drop slightly but in milli-seconds or so return back to their idle speed setting.

Unplug and remove the valve by all means but don't do it with the ignition-switch turned on.

There is load of post on this stating anything from IC Valve air or vacuum leaks to the ignition system plus all the other related stuff.
I haven't see anything that hits the spot so to speak... but when my tick-over gets a bit erratic I just pour a can of injection cleaner in the fuel-tank and it back to normal.

Going to run a load of cleaner through, its a good idea.

Been having a play around with it tonight.

Took the maf sensor connector of and gave it a good clean, no difference.

Took the stepper moto out again and gave it another good squirting. Also gave the housing a good squirt with carb cleaner too. No difference.

Tried taking the plenum chamber apart. Unfortunately some inconsiderate Ba$t@rd has rounded one of the hex bolts. It has to be the one which is recessed as well. So unfortunately I am not getting into that any time soon.

I have made sure that all the feeds are nice and secure. They all seemed to be ok.

I do have a new air filter on order but it hasnt arrived as yet, but I have tried running without the airfilter, still no joy.

Many more things to try tomorrow though. I will keep trying and updating.

There are many posts on this, but unfortunately, as with a lot of forums, when people do sort out their motors, they don't return to complete their posts with their final solution. :-(

Thanks for the tips so far.

get a punch the same size as bolt head and hit hard till its squashed enough for key to knocked in to fit ,the knocking will be loosening it at the same time repeat till it comes out

That's a clever idea!! Took me a minute to figure out what you meant, but yeah....that makes sense, although they do look fairly tough things to bend, which can only mean one thing.....get out the whopping persuader

See how you get on, if you can't get it to settle down and you're not too far away I have an ECU code reader, also spare ECU and AFM so might be able to narrow it down by substitution. I think I might have a couple of old Lambda sensors too.

You might find it useful to have a look at the EcuMate webpage - www.ecumate.com, look at the user manual, might give you some clues.

Thanks for that offer Classic Kev!!! I might take you up on that offer, but I will continue battling for a bit first, as I would hate to waste your time!

I actually managed to get the plenum cover off today. The punch idea worked a charm!!

Cleaned all that up, but unfortunately hasnt made a difference. I have been reading about cleaning the 'fire trap' (read that the other night so I may be mistaken) if not, what is the fire trap? and where is it located? Also I have read about cleaning the vacuum hoses, are they just the hoses going to the plenum. Sorry for the basic questions, I have read these things need doing, but the other threads dont explain what or where they are?

It called a crankcase-breather I don't know why it's so called "flame trap" in my 27+ years with a V8 I have never bothered to find out, not that I'm that interest.
Anyway see attached pic just remove hose and unscrew the canister and clean both in petrol and refit, job done. Don't know why u would want to clean a vac hose.

I had similar issues to you a while back, turned out to be the fuel pump in the tank was delivering intermittent pressure and eventually stopped and the fuel pressure regulator at the end of the fuel rail. The diaphragm was gone in the regulator meaning it got to much fuel pressure at lower RPM.

If you do buy one DO NOT buy a britpart fuel pump, I had 2 from them, one lasted 3k the other 2k. Absolute junk. I think I stumped up for an OEM after that!

Stevd said:

It is also under powered, or so I feel, I have nothing to compare it to, so I have boughgt a load of new iginition parts, dizzy cap, rotor, leads, and coil, air filter etc. Is there anything common that I can check.

It is running rich, very rich, but I have found a slight leak from one of the manifolds, possibly causing the lamda sensors to miss read? Any other suggestions on why it would run rich.

Click to expand...

Have you done a compression test? Might be worth a shot.

Running rich - check coolant temperature thermistor. I don't know if there is an efi warning light on a Disco dash (Rangie has one!). If there is a fault somewhere in the efi the ecu will go in to limp mode, this makes it run very rich like single digit mpg rich. Throttle potentiometer might also be a culprit, might also explain poor power? Does it pick up smoothly and quickly when you gas it? do the revs drop quickly when you get off the throttle?

HTH

classic kev said:

Have you done a compression test? Might be worth a shot.

Running rich - check coolant temperature thermistor. I don't know if there is an efi warning light on a Disco dash (Rangie has one!). If there is a fault somewhere in the efi the ecu will go in to limp mode, this makes it run very rich like single digit mpg rich. Throttle potentiometer might also be a culprit, might also explain poor power? Does it pick up smoothly and quickly when you gas it? do the revs drop quickly when you get off the throttle?

HTH

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Yeah disco has a light to, states nice and clearly - CHECK ENGINE lol.