3.9 V8i low power and missing on different fuel

Hi Landyzone,

I am a new member today and this is my first ever post!

I have a 1998 Disco series 1, 3.9 V8i Auto.

I have had this vehicle for about 2 years now and has been a great car.

I have a problem which has crept into the mix slowly over the last few months and is frustrating.

My Disco is experiencing quite bad power loss and seems to be running rough and missing.
The problem is not constant and I am convinced that is related to petrol. I say this because the engine will be ruinning ok (never perfect with full power though), then If i fill up at a petrol station, sometimes it will immediately miss badly and have even less power. So much to the extent of it struggling to climb gentle hills. Sometimes, it will run better after a top up and sometimes worse.
I think it could be bad fuel in my tank or blocked filter, but am not convinced because the problem has been going on now for over a year and I assume that a blocked fuel filter would be constantly blocked and not change performance from day to day.
Also, when running at its worst, it will stall constantly when the revs are at idle- at lights, slowing down for a roundabout, just after starting and selecting reverse etc.
Also, this might seem like a silly question, but where is the fuel filter located?
I have run several bottles of injector cleaner in the fuel tank over the period and have run the highest octane fuel also to clean out the system but nothing has made any effect yet.

Can someone please help me and steer me in the right direction to fault find this problem.

Matt

where are you? someone may be close.
you could have **** in the tank and possibly blocked filter.

had a rover 75 petrol with weird running and it turned out to be the filter solid with crap, joy of joys on this filter not avaliable but housing 104 pounds + vat so stripped it, cleaned it and refitted as they didn't want to spend any money

rockliffmt said:

Hi Landyzone,

I am a new member today and this is my first ever post!

I have a 1998 Disco series 1, 3.9 V8i Auto.

I have had this vehicle for about 2 years now and has been a great car.

I have a problem which has crept into the mix slowly over the last few months and is frustrating.

My Disco is experiencing quite bad power loss and seems to be running rough and missing.
The problem is not constant and I am convinced that is related to petrol. I say this because the engine will be ruinning ok (never perfect with full power though), then If i fill up at a petrol station, sometimes it will immediately miss badly and have even less power. So much to the extent of it struggling to climb gentle hills. Sometimes, it will run better after a top up and sometimes worse.
I think it could be bad fuel in my tank or blocked filter, but am not convinced because the problem has been going on now for over a year and I assume that a blocked fuel filter would be constantly blocked and not change performance from day to day.
Also, when running at its worst, it will stall constantly when the revs are at idle- at lights, slowing down for a roundabout, just after starting and selecting reverse etc.
Also, this might seem like a silly question, but where is the fuel filter located?
I have run several bottles of injector cleaner in the fuel tank over the period and have run the highest octane fuel also to clean out the system but nothing has made any effect yet.

Can someone please help me and steer me in the right direction to fault find this problem.

Matt

Click to expand...

Have you changed the plugs n leads

Nathan,
No I havent as yet changed the plugs and leads.
I Did think of this as an option, but I thought that if there was a problem there, the symptoms would be the same all the time.

I did however, remove the plugs, cleaned and checked the spark gaps.
All seemed OK to me.

Do you think I should go down this path anyway?

When did your disco have a full service as that includes the fuel filter which can be seen behind the o/s rear wheel. As mentioned by Nathan above, plugs & leads do make a difference.
Also clean the crankcase breather and it's pipe located on the drivers side (rhd) rocker cover. Check the contacts on top of the coil are clean and tight and also that there no air leaks around the plenum camber or the attached hoses.
Stalling may require the resetting/adjustment of the 'base idle' as mine did, it's easy but I got LR to do mine.

:doh: And :welcome2: to the Forum

Great, thanks.

I will give all the above mentioned a try as soon as i get home from work in 5 days time.

I will let you know how I go!

I think I would go with changing the fuel filter first - cheap and normally easy if the unions and pipes aren't too corroded. Be careful though, the fuel pipes from the tank rot like crazy and if delicate are very easy to break; consider putting flexible fuel hose in.

After that you're in for tracking a mystery misfire. There is a lot on this subject (I should know!!) so do a search. Do start with the obvious stuff like plugs, leads, dizzy cap and rotor arm - only genuine Lucas will do; trust me on that. Check your ignition timing. It may be you have a stretched timing chain and the ignition timing is wandering, also check vac advance and mechanical advance.

Let us know how you get on.

discool said:

When did your disco have a full service as that includes the fuel filter which can be seen behind the o/s rear wheel. As mentioned by Nathan above, plugs & leads do make a difference.
Also clean the crankcase breather and it's pipe located on the drivers side (rhd) rocker cover. Check the contacts on top of the coil are clean and tight and also that there no air leaks around the plenum camber or the attached hoses.
Stalling may require the resetting/adjustment of the 'base idle' as mine did, it's easy but I got LR to do mine.

Click to expand...

Looks good advice to me

You might also want to check/clean the stepper motor (idle stabilisation valve).

Had exactly same problems almost, changed leads to 8mm last weekend and running like new.... well symptoms all gone and even managed an overtake. First time I have smiled for a while

Fuel pump!

I had it on a bmw. change the filter too!

There is a little known bit of legislation about petrol; we have two grades, summer and winter, and every autumn we get a spate of curiouse 'fuel maledy' questions crop up, when, by law, the petrol stations have to switch from summer grade to winter.
Shouldn't REALLY effect the running of the car, but it does tend to show up or highlight weaknesses that are already there, and it can confuse some EFi black-box brains, when you fill with winter grade at a station that has switched over early, then fill at a station that still has summer grade fuel..........
Anyway, that's purely of accademic interest, but worth a note, if you are using different stations each fill, and the onlt nugget out of it, is that while fault finding, try and stick with a single filling station to eliminate the variable.
If the fuel filter is blocked, it would choke flow on wide or full throttle opening, on its own, that wouldn't account for stalling near idle or general rough running.
However, as said, its hung in the feed line on the outside of the chassis rail at the rear of the off-side rear wheel arch, connected via two short lengths of rubber hose and conventional hose clips, and wouldn't be a bad thing to swap out just to eliminate that idea from the list.
As said though, pipes are fragile, or at least get so with age. worth buying new four new clips and half a meter of new flex hose to make fitting new filter a tad easier and reduce risk of stressing the hard-pipes.
Tank & pump.
Should have submerged electric pump, and they normally work or they dont.....
But, crud / rust in tank can make them play up, as they sit in a sump, so any crud that gets washed in will choke them, but can be dislodged when you go over a bump or fill from near empty etc.
If a plastic tank rust accumulation shouldn't be an issue, but check.
Lift the boot floor, undo the six bolt mounting flange, disconnect the pipes and lift the pump out, and look for rust / sludge in the tank.
they can be 'flushed', but to be honest, if its a metal tank, I'd check the ecconomics of getting a new plastic one, becouse if they have enough rust in the sump to effect the pump, then they will normally be thin and about to pin-hole or start leaking at the seam.
the other one to check while in the area is the pipes on the pump and the runs from it.
Otherwise, back into the engine bay, and as other advice, start with the ignition and the cold start squirter.
running higher octane or injector cleaner through rarely doies much on a motor that is showing symptoms of needing it; by that point the injectors are too far gone to see any effect.
Injectors on the RV8 I think should be changed every 60K miles or something....... but usually dont.... so in all prob, yours are long past thier best, but an expensive fix, the major benefit of which is oft largely lost as motors of rthat age have as also said, sloppy timing chans putting the valve timing out.......
Essentially, it SOUNDS like it's in need of a thorough service in the engine bay area to get it back on form, and pulling its weight, but, it probably wont be as good as it once was, as its basically starting to show its age.

Hi again!.

Here is an update for you helpful people.

Because of work commitments and general near Christmas business, I only got a chance to give the Discovery a once over today.
This is what I did and what I found.

I checked a few easy things first, to check and access.......all were mentioned by various posters.

I first looked at the throttle area and noticed that the springs and link arrangement was squeeky and a little stiff. A soaking in penetrating lubricant resolved this nicely.
- Result was not noticeable apart from smoother operating but still the same rough running and missing.

I then traced the vacuum hose from this assembly.....( I think maybe its the vacuum advance???) any way, it joins a main vacuum line on a T section, they were split along the joiner about 3/4 of an inch.
I stripped this off and re joined. - Result was not noticeable.

I then got my pliers and tried to press on each plug lead on top of the distributor to make sure this was all tight and well connected (while the engine was running). The result was a spark emitting from 2 of the plug lead boots on the dizzy to my pliers.
mmmmmm this was a revelation! The spark was intermittent but accompanied by a snapping noise like a fly zapper....I then realized that I heard this noise 3 days ago while inside a drive though bottle shop of all places! it was nice and echoey and I noticed it.
I then did the dark test.....(turned all the lights off and run it in the dark and tested for sparks).well............many sparks. The plugs on the leads were sparking. One was very badly sparking to the distributor suction hose, one was sparking to the frame, and one was sparking to another lead..(crossover firing???...)...anyway, the spark to the dizzy suction hose was considerably bad compared to the others.

So.....it was straight to the Auto spares retailer for new leads.
I also picked up while I was there, an inductive spark plug lead voltage tester.
Very handy tool and when I returned home and used it, I found that one lead was in very poor shape and 2 others were suspect...Just the result I was after!

Anyway, I changed the leads.... Result:...................................Brilliant, the Discovery is now running beautifully and the V8 is back!

Maybe not quite 100 percent yet, but I think maybe 95 to 98 percent. (not too sure as I have had the disco for about 2 years and its probably going as good as it been since ive had it)....maybe its running at 100 percent!...time will tell!
I will next follow a few other suggestions and see how it goes, but that will have to wait another 5 weeks when I return home from work again...I leave on Monday.

Anyway, thank you very much all who have posted suggestions and I am very grateful and I will keep you informed of any new developments.

The V8 is back!!, and it will now tow my 3 tonne boat with ease! It was struggling to pull its own weight up hills up until earlier today!!

Matt

Glad it worked , I have tried 3 different sets by three different brands and still the fireworks display!

On a similar vein I had problems with loss of power on hills on both fuels. Worst on petrol. Everything changed plugs, leads etc and a mate now reckons one of the cylinders not firing which is cause of problem. Def a spark to it. Any quick checks recommended before it goes to garage for what I suspect will be a stroke of a chin, shake of a head and a large bill. Cheers

only use genuine parts on the ignition pattern are crap