Thread: Discovery 1 running rough when warm

Check the rotor and dissy cap, plug leads and plugs themselves. Could also be an air leak, check around plenum and tightness of inlet manifold bolts.

Other culprits could be AFM and possibly TPS. D1 autos also suffer from sticking valves if driven lightly on ULP. Let tank go down to nearly empty, chuck in a bottle of Nulon FI cleaner or equivalent and take it for an Italian Tune up - i.e. rev it to 5000 rpm in lower gears (or manual shift the auto box). Afterwards fill it up with premium and if an auto drive it round the city in 3.

You don't say you have overheating problem so in addition to Traco's advice I would also look at overall timing particularly as symptoms of power disappearing at 3K is also reflective of a seized mechanical advance.

I would take the terminals off the coil one by one, tighten, and refit. A loose terminal complete with a bit of corrosion will do that. Also take the cap off with the engine warm, look for condensation.

I'll add some real simple checks.....



Suck on the Vacuum advance unit and see if it holds vacuum

In total darkness .... Lift the bonnet and start the car ... You will instantly see any ignition Sparks Arcing out from the leads & coil / cap

Start the car & pull the plug on the MAF .... Go for a drive



It'l be something silly ....

Mike

The temperature sensor in the middle of the V is know to cause issues. Might even be loose. cheap to fix. That is where my money is.

Hi All

Thanks for all the tips. Over the weekend the car has gotten worse so I am now getting desperate.

The car will no never rev past 3500 in neutral. I can start teh car and from cold it will not free rev past 3500. As the car gets warm or the air temperature rises the car will not free rev past 2500.

Under load the car will not rev past 3000 even when cold.

I have found out that the other driver of the car has been putting E10 fuel in the car for a few months. I usually use Premium or just ULP when I can't get it. I am not sure what E10 will do to the car though as the compression is so low on D1's.

I have tried the following this weekend with no improvement noticed.

I put a bottle of Nulon injector cleaner in half a tank and ran it to empty. I then put a full tank of Caltex Vortex Premium ULP in and have so far run through half a tank. All I have noticed is slightly better idle and better fuel economy.

I have looked at the engine in complete darkness when it was misfiring and can see no signs of sparks around the coil or distributor.

I have checked the rotor button and distributor cap and both look fine with only minor burning on the cap contacts. Both are about 5 months old.

I have checked all coil wiring and cleaned all connections and all are fine.

I checked the vacuum advance and it is holding vacuum fine. When vacuum is applied I can see the baseplate moving. I checked the bob weights were not stuck and they seem fine and free.

I checked the static timing and it was 6 degrees. I can't see how this would have just changed from when the car was running fine.

I tried unplugging the MAF while the car was idling and it almost stalled. The car could not be driven with the MAF unplugged.

I checked the voltage going to the coil and ignition module while driving and they sat solid at 13.9 volts even when the engine was misfiring. I had heard of an alternator fault causing misfiring so it was worth a check.

One rubber boot on the coil lead looked a bit sad so I tried another coil lead.

I checked the other leads and they looked fine. All measured OK for resistance.

I pulled the plugs and all seem to be burning fine.

I am at my wits end with this car.

I would appreciate any further thoughts on trouble shooting.

Regards

Richard

Fuel pressure. I can't help you with specifics but if you can read fuel pressure before the regulator, it is a good diagnostic for fuel delivery problems. I have made a tee for a different vehicle once, you are looking for a rise under load as the manifold vacuum drops. It is probable that your fuel pump has a pressure leak, especially if someone has repaired it. Perhaps also regulator problems. Pinching closed the return hose will raise pressure if the pump is OK, do this carefully and listen to the engine.
The fuel pump is quite easy to access, lift the cargo area mat and unscrew the hatch. Remove the pump and check for loose/ split pressure hose.
Someone else posted about an ECU that they changed fixing his running problems, find an owner willing to swap, ask here if there are any problems with that first.

I had a similar prob with my 95 3.9 disco i ended up replacing all the ignition system dizzy coil amp leads the whole lot got canned and in went the crane system from my old rangie and what a difference it made no more prince of darkness for my disco