Thread: Engine miss when warmed up.Disco 1996 3.9

It could possibly also be an alternator fault. The tacho is fed from the alternator and a poor alternator output (spiking, etc) could interfere with the ignition.

The TPS is on the throttle body front, directly inline with the throttle shaft.

Originally Posted by Landover

Hello to all.
I’m nearly ready to through in the towel on this Disco, It spends more time in the shed than in the bush. While I enjoy tinkering with it I want to get out and have some fun.

The Disco is a 1996 3.9efi, Auto, 177000km.
The problem this time is it gets a miss when it gets warmed up, after about 10 to 20km. You can feel it through the car when you hold a steady speed or if it ideals for a while it is like its missing a few pots when you give it a rev then clears out and rev freely for a bit. The Taco also fluctuates a bit on ideal. If you let it cool down it’s a lot better. The temperature gauge sits about half way.

History: Initially had starting problems and flooding and had replaced new injectors, fuel pump, fuel pressure regulator, return fuel line unblocked, Spark plugs, MAF second hand. It now starts and runs ok but this miss problem is getting worse the more I drive it.

Things I have checked:
-Spark plugs new NGK BPR5ES
-Distributor Cap looks ok, Original
-Rotor looks good, Lucus.
-Coil connections Bosch
-Maf, Set to 1.3 volts as per Another post. Originaly 0.07 volts.
-Checked leads and resistance ranges from 9.5kohm to 13kohms, What’s normal. I went to get some Magnecor leads but the guy was not there so still to be done. Are there any other leads recommended.

During my investigation I found the Vacuum Advance is not working, I suck on the hose but keep getting air. I read that this does not make a big difference though and will get to that next.

I want to check the TPS as per other post but cant find anything that looks like the one picture, Any Ideals where it is.

If you are still reading this long post I feel as it’s a heat related problem that possibly the coil Amp is getting hot and freaking out. I don’t know how to check this other than replace it with some ones for testing

Any Ideals would be greatly appreciated.

Thanks in advance (one frustrated Disco owner)

Cheers, David.

rover craft in fern tree gully is very cheap for the advance vac on the dizzy,

Originally Posted by Landover

During my investigation I found the Vacuum Advance is not working, I suck on the hose but keep getting air. I read that this does not make a big difference though and will get to that next.

O yes it does ......

Originally Posted by matthewk

rover craft in fern tree gully is very cheap for the advance vac on the dizzy,

Mike

Could be in need of some new leads. I use Bosch black leads bought individually from Supercheap - just measure them up first. They are cheap and have always worked well, much better than some other types. Magnecore are good but very pricey.

You could also have sticking valves, common with D1 V8s especially autos that are not hard driven and run on standard ULP. Drop a bottle of Nulon fuel system cleaner or Redex in it when the tank's almost empty then rev it right out in the lower gears. I use super unleaded and run the auto in 3 instead of D around town.

The coil Amp needs to dissipate heat through a heat sink, remove it and apply heat transfer paste (available at computer shops), Vacuum advance needs to be working, replace Dissy cap and rotor, use only genuine Lucas parts, replace plug leads and come back and let us all know the result, Regards Frank.

Thanks for the info guys, looks like I will have to get the Vac advance sorted and getting some new leads ect. Also got an Amp module on it's way to see if that helps (Thanks It'sNotWorthComplaining!). Any other ideas to throw out there might help. I'll keep you updated.
Cheers,David.

Ok it's been a while so it's time for an update. And some urgent help needed

I have change the Amp module, new magnacor leads, replaced the vaccum advance set timing to 9deg btdc and new rotor button. Cleaned the stepper motor and TPS. Everything seem to be running quite well but when I was taking it on test runs it kept over heating.

So got the radiator rodded and flushed the system and new coolant added.

All back together and seems to be running at about 95%. The ideal fluctuates a bit on ideal but no big deal. Have had it out for a few runs and been alot nicer to drive. Starts first pop and drives smoother.

Now here where the problem starts. I went out for a 4wd bush run to test it out and went well for most of the day. It wasn't until I did a long hill climb that it over heated a couple of times. Let it cool down and topped up with water and headed home, the engine had a bit of a miss since getting hot but drove home ok and not hot.

I put it in the shed and got a new Viscous fan and fitted it after much trouble getting the old one off.

Now the car wont start, It's tries to fire but just wont run. It's like it's only firing on three cylinder and splutter a bit and stops. I've checked all the connections, checked the leads are fitted both ends, replaced the spark plugs, put in my spare MAF, ECU and rotor. There is fuel pressure at the rail as when I press the valve fuel squirts out. I pulled out a plug and had a nice blue spark. The plugs are wet with fuel. Checked engine oil for water and coolant for oil but both clean. A couple of times it has started and runs ok, sounds like all pots a firing and idles ok. but when I try later it wount start again.

I don't know what to try next. The AULRO gathering is at Blackwood this weekend and I don't want to go it the wife Holden Frontera.

Any help would be appreciated. I can't even drive it to a LR mechanic.

Cheers, David.

Ps: sorry about the long story, I though it might help with a bit of background.

Originally Posted by Landover

O

I have change the Amp module, new magnacor leads, replaced the vaccum advance set timing to 9deg btdc and new rotor button. Cleaned the stepper motor and TPS. Everything seem to be running quite well but when I was taking it on test runs it kept over heating.

So got the radiator rodded and flushed the system and new coolant added.

All back together and seems to be running at about 95%. The ideal fluctuates a bit on ideal ] but no big deal. Have had it out for a few runs and been alot nicer to drive. Starts first pop and drives smoother.

Now here where the problem starts. I went out for a 4wd bush run to test it out and went well for most of the day. It wasn't until I did a long hill climb that it over heated a couple of times. Let it cool down and topped up with water and headed home,

Now the car wont start, It's tries to fire but just wont run. It's like it's only firing on three cylinder and splutter a bit and stops.
The plugs are wet with fuel.

David .... Background stories are good

is the Amp module located on the distributor? ... or remote mount near the coil?
Also ... Where did you get / buy the Amp from???? ... and did you install the Amp with the heat paste to the heat sink??


Also, (nothing to do with the not starting) when you removed the TPS to clean it, Did you recalibrate it with a multi meter?? as this affects that fluctuating idle

Mike