Thread: Trying to find a miss in 96 Discovery 3.9

I know this may sound silly, but I too went through the same experience and after replacing everything twice over etc I finally delved into to the pickup area of the reluctor pickup assembly. Nice HD brass and big nuts but the assembly became loose!, never seen this in normal cars but then again its why we love them so much, so yes, have a peek at the gap and check as this is not hard to do.

Cheers

http://www.carelect.demon.co.uk/rrmisfire.html

Worth having a shufti here as well as the rest of the RaRo links for Discovery.

I am starting to lean more and more towards a valve as it is popping out the exhaust every now and then. Cant get my hands on a compression tester this weekend so it will have to wait. I have checked or changed everything else to no avail bar cleaning injectors, next on list. The motor is starting and running perfect except for that constant miss cold or warm.

An Update. Did a compression test and they all came up between 100 and 105. Has new leads, sparkies, cap, rotor button, battery. Still has the miss. Will cruise at 100km hr no worries if you are just easing the accelerator on so slightly, any form of load and no good. Was wondering if a lack of fuel presure could posabably cause this. When unplugging injectors with motor running it seems the only one that does not change the pitch of the motor is the last one on the left bank. It is also last in line to get fuel. Will replace the coil today and then the injectors will get a clean. I guess if the problem still persists after that I will have to replace the fuel pump. The $$$ just keep racking up.
But I still love it!

I've been told that you can test the pressure in the fuel rail with a tyre gauge, as the rail has a schrader valve fitted. Use a cheapy gauge as the petrol will probably bugger the inards.

Should be approx 40psi running - keep a fire extinguisher handy .

If any one knows for fact why you shouldn't test it this way, please comment.


Bruce.

Ah, thats true, I will have to try that tomorrow as well.
So many things to play with. oh, the joys!

Tested the fuel presure as mentioned above and came up with about 40 psi. New coil did not fix the problem. When changing the plugs, noticed they where all quite black/fowled and blows black smoke when you give it a gut full. Is this a common sign when injectors are in a bad way? Is booked in for injectors to be cleaned Wednesday. Running out of things to replace.

Your water temp sensor may be bad. They are only $30 so a new one may be the go.

To test the injectors, switch the bad one to another position. If the miss stays in the same position, then the plug or loom may be bad, if it shifts then the injector is bad. I found with bad injectors that it would miss up to say 1500 , then the injector seemed to cut back in, or it may be that you cannot feel the miss after that.
Regard s Philip A