Thread: Engine miss when warmed up.Disco 1996 3.9

Originally Posted by bee utey

Water I suspect. 1. Lift the oil filler cap, look for condensation. 2. Lift distributor cap, look for same. 3. Pull out the plugs, look for moisture/rust. You may have weakened head gaskets, its common to have the engine run fine until you apply a good load. If its wet plugs, leave them out for a few hours then reinstall, should drive OK.

I changed the plugs last night with some new ones but still did the same, the ones I pulled out have about 1000km on them and look a bit black with a slight grey on one side, Did not show any signs of mosture on them. There is no sign of water under the dissy cap. I'll go out and check under the oil cap for moister.
Cheers, David.

Originally Posted by Landover

I changed the plugs last night with some new ones but still did the same, the ones I pulled out have about 1000km on them and look a bit black with a slight grey on one side, Did not show any signs of mosture on them. There is no sign of water under the dissy cap. I'll go out and check under the oil cap for moister.
Cheers, David.

David .... you have got one of those hard nut problems, where everything has been changed and it's not working

Just for hips & giggles ..... Grab your old Amp & reinstall that, cause the amp you got was 2cnd hand ...... You just never know
The other thing to look for is a very fine hair line crack in the Distributor cap, as over heating a motor can cause ANY cap to stress and fracture / so change that for old one?



Usually if water is getting in the bores from a bung head gasket (wiping out the spark plug) You would see the sign's on the spark plug / Steamed cleaned / and a totally different colour to the others .... But your saying they are all black, so I'm not suspecting head failure at all .... but a compression test may resolve this Q

It'll be something "Dumb" thats causing the problem / Loose connection or some part that got disturbed when you changed the fan / Did you hit something with the Hammer by any chance?? .....



Another thing to try is take ALL the wires off the back of the alternator (isolate it), and then fire it up & see if that makes a difference


Lastly .... do one thing at a time, otherwise you won't be able to find which part is at fault


Mike

I think I might have it sorted (lets hope).

As Mike suggested I was going to put the old Amp in as it did not stop the car from starting. I unwapped all the connection and just before I pulled it out I through I better check to see if it starts as it was all still in pieces from the night before. I gave under the Dizzy cap and working a quick squirt of WD40 and refitted and made sure all the leads are in tight. Found the plug off the connector on the termistat cover (probley knocked trying to remove Viscous) and checked all other connections. Turned the key and it started up straight away. Let it idle for about 20 plus minutes and is purring like a kitten, no sign of any miss and smooth to rev. Unable to road test as I have stuff hanging off it everywhere. Stopped it and tried starting it from time to time and starts straight up.

So I'm thinking one of two thing could have happened,

- first is that the engine was still flooded when I tried last night and even the new plug got to wet. It dried out over night and started.

- second is one off the connection was loose or dirty posibley around the amp causing issues.

I don't think the engine it's self is stuff as I could not find any signs of moisture under the oil cap or anywhere else. It was also idling smoothly so I think it was electrical.

I'm still not 100% convinced it is fixed yet so I will let it cool over night and see how it goes tomorrow and do a road test. For now I had to drop everthing and rush to work. Will let you know how it goes.

Cheers, David.

Dirty and loose electrical terminals can be a health hazard, I call it TERMINAL DISEASE!!!

Originally Posted by Landover

Found the plug off the connector on the termistat cover (probley knocked trying to remove Viscous)

David ..... Just out of interest ..... can you post up a picy of this "connector on the (thermostat??)" .....

Mike

Ok, there's bad news and good news.

First the bad - Went out to start it this morning and would not go. Back to missing and spluttering but would not fire. I put the original Amp back in and was the same. I check the voltages cross the coil and found with the Ignition on about 0.6 to 1 volt cross the coil. Coil Pos to earth was 12v and coil Neg to earth was 11.7v. Could not get it started so don't know the voltage across the coil when running.

Now the Good news - I took the coil out of my boat (GT40) and put it in. First kick off the engine and fired straight up. Turned on and off several times and start very quickly. The Voltage across the coil when running is 12V. It look like the problem may have been a week spark from the coil making it hard to start but runs ok when going. Can coils be intermittently good then bad, maybe it's been slowly failing.

This coil is a points coil so can I run it for a while for testing. It's the GT40 not the GT40R so it's a 12V coil. Will this cause any harm. I see others are running them. The original one is a Black Bosch with a reddish top, looks original but sure.

Mike, I'll take a picture of this plug on the thermostat housing for you and post it up. It's a two wire plug with spade terminals in a black plastic. It's not for the temp gauge as when I remove it the temp still shows. I suspect it may be for the thermo fans but not really sure.

Anyway does any one know a good place to get a coil and which one should I get.

Cheers, David.

Originally Posted by Landover

It's not for the temp gauge as when I remove it the temp still shows.

That's what I was thinking ... Hence post a photo of "your finger pointing to the plug"

Originally Posted by Landover

Anyway does any one know a good place to get a coil and which one should I get.

I recommend that you ring up Stuart at Rovercraft & get the right coil


BTW ... Does your model have that spider alarm ... If it does, then get a bypass plug for it .... available at where the coil is ......


Mike

I recently had issues with a coil that really went haywire. See this:

Confusing - distributors for 3.9L V8

I'm also in Sunbury. If you're interested I can try your suspect coil in my 3.9 and see if the problem follows the coil.