Trying to find a miss in 96 Discovery 3.9

[SpeedWayRover]

Hi ppl'z,
Just trying to fix a miss that my car has picked up, it started with it being intermitent, but now permanant. I have replaced the leads, cap and rotor button and checked plugs so far without any success and was wondering what is the next best direction to head in? I was thinking getting the injecters cleaned would be the way to go. What are others thoughts? Also when turning the ignition off now it seems to have an electrical type buzz. Any help would be greatly appreciated.

thanks.

Leigh

[Scouse]

Can you trace which cylinder the misfire is in by removing HT leads ?
Make sure you earth the disconnected lead, the electrics dont like open circuits too much.
If you can trace it to one cylinder, carry out a compression test. If the pressures are OK & you have plenty of spark at that cylinder, then start looking at the injector.

How many Km on the engine ?
Worn camshafts are common but generally don't knock one cylinder out completely.

Not too sure on the buzz. You have to listen where it's coming from. Engine bay, underdash.......more info req on that one.

[p38arover]

Can you trace which cylinder the misfire is in by removing HT leads ?
Make sure you earth the disconnected lead, the electrics dont like open circuits too much.

As an aside, I think that unplugging the HT lead is not recommended for the P38A and the D2 V8 owing to the possibility of damaging the electronics. Dunno if it is OK to earth it or not. An interesting point. I think they recommend unplugging an injector connector.

Ron

[SpeedWayRover]

Woops, I did the unplugging leads thing before I replaced them and could not make out any difference. The Buzzing is from under the bonet, posabably to the paseenger side. maybe I hurt it unplugging leads. :o
The engine has 195 000 km on it. Never blew any smoke other then fuel smoke, seems to be running rich but still getting same km out of tank, if not more, then they have been reportd too. Compression test might be next on the cards.

[4bee]

Depends on the miss of course ie. when, but have you checked & thoroughly cleaned & lightly lubed the Idle Air Control Valve?

[LRCounty]

Woops, I did the unplugging leads thing before I replaced them and could not make out any difference. The Buzzing is from under the bonet, posabably to the paseenger side. maybe I hurt it unplugging leads. :o
The engine has 195 000 km on it. Never blew any smoke other then fuel smoke, seems to be running rich but still getting same km out of tank, if not more, then they have been reportd too. Compression test might be next on the cards.

I had symptoms like this. For me it turned out to be the Injector O-Rings. If this is the reason for the miss, it will be sucking an audible amount of air. You can check each injector easily, by getting a small diameter piece of hose, stick one end in your ear, and move the other end around the base of each injector where it plugs into the manifold. You can easily hear the difference between one that is sealing properly, and one that is sucking air.

Cheers
Andre

[chunk]

the buzzing noise could be coming from the ABS pump. i had a problem with mine last year, i had to unplug it when i turned the ignition off and reconnect it when i was going for a drive. i did this for about a week and the problem fixed its self, no problem since.
:burnrubber:

[DirtyDawg]

I had the same problem once in the rangie, turned out to be a broke piece of plastic on the electrical coupling to an injector, it essentially made worthless the steel retaining clip so Idling it would be fine and reving whilst stationary was good but road movement was enough to break contact and cause a miss.
I tracked down the offender by looking for the rich cylinder and concentrating on that till I found it.

[SpeedWayRover]

Thanks for all the the tips. I will be going through everything till I find the problem this weekend. Hopefully I will be able to let you know what it was by Monday.

[Michael2]

Trying to find a miss in 96 Discovery 3.9


I read that, and thought you were looking for a young lady who might have caught your eye as she sped by.
:oops2:

[SpeedWayRover]

AAAAAAaah, if only it was that simple.:D

[mousie]

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

[4bee]

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

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

[SpeedWayRover]

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.

[SpeedWayRover]

:eek: 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.:mad:
But I still love it!:angel:

[BMac]

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.

[SpeedWayRover]

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

[SpeedWayRover]

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.:rolleyes:

[PhilipA]

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

[Quiggers]

This may sound obvious, but having read your prob, you haven't put in new plugs - or have you? Plugs may work fine at idle test but may fail under load - I - like others have been thru this -

one plug in eight will fail and herein may lie your problem - 20,000ks or more and plugs really should be renewed.

GQ

[V8chops]

Had a similar problem with my 2001 Disco.
Turned out to be a coil pack. "they never go wrong" yeah right. Only one in Oz and had to ship it from Sydney to Kalgoorlie...

Check all your plugs - you'll get a black carbonisation on just 4 of them if it's a coil pack, mine was missing on 2 with the other 2 just showing some black staining by the time we found the problem. Platinum tipped buggers too, $$$. To be sure, check the numbers against the firing diagram in your manual - it tells you which plugs go with which coil pack.

Coil pack was about $400 I think, plus pulling apart and re-assembly. Then the new pack stressed the old leads which probably hadn't felt that much juice for a while, and they neede replacing too.....

[SpeedWayRover]

Yes, to new plugs. Coil pack??? Did not relise it had one as it has a Electronic dizzy and coil. Have not got a manual, will have to purchase the AULRO manual CD.

[Scouse]

Coil pack??? Did not relise it had one as it has a Electronic dizzy and coil. Don't worry, you don't have a coil pack:cool: .
Later cars did away with the distributor & ran coil packs.

[SpeedWayRover]

Ok, updates, After getting all injectors checked and still having the problem I decided to play around with the adjustment in the airflow metre. It did not seem to make any difference so I ended up putting it back to where it started. I then went for a 30 minute trip and beleive it or not the problem has nearly ceased. now this brings me to the conclusion, that just maybe the airflow sensor was all gooed up or something and with the moving I did with the adjustment, it just might have helped it get working again? Is the airflow sensor able to be pulled apart and cleaned? Could a dodgy airflow metre cause the problems I have been having? PLEASE HELP!!! I Am Desperate!!!:o

[4bee]

It can be, carefully.
Remove the screws on the inlet, I think, & gently seperate the 2.
You will see the bypass canal in which the hot wires are situated. I cleaned mine with Metho, although there was no obvious crap on them.

Wasn't aware there was an adjustment, & I don't think I'd go there anyway.

[loanrangie]

Hmm, wont she be in the passenger's seat ?

[SpeedWayRover]

oK, The miss is back yet again and I have run out of time as I am going down to Victoria this weekend, sooooo, I need to find a good mechanic in Western Sydney that will be able to find and fix the problem while I am down Vic, before I come back to Syd in a week or so to drive the Lovely "fixed" Discovery back to Vic. Any help would be very much appreciated, thanks.

[PhilipA]

I doubt that the problem is the airflow meter. If it goes bad the ECU will revert to "limp home" mode and you will get increased fuel consumption but it should run well.
I would still look at plugs, leads, injectors, injector leads.
What about the temp sensor. If you have a multimeter check that the resistance across the two terminals is 300-400 OHMS while the engine is at operating temp.
Regard s Philip A..

[4bee]

Good point. I looked at mine this morning before I read this reply & suspect the spade terminals were loose-ish & dirty.
Not surprising really, the way it's tucked in behind the alternator & air stream.:(

Anyway have cleaned them up & reset them.

Are those readings for the Lucas 3TT ECT or doesn't it matter?


Not sure yet, but It appears as though it may (?) be running a little better. I have not had it up to normal optng. temp yet & I will then also check the resistance.

'Placebo Effect' in action maybe? Fingers crossed.:eek:

[4bee]

Have been for a run to the big smoke today & worked the engine hard-ish coming home.

Checked the resistance across the ECT with the engine quite hot & that read 0 ohms. ie. Open circuited.

Remove the leads & no difference in the running of the engine. ????


Odd thing is now I can adjust the Base Idle speed over a range where-as before I couldn't much without it going ga-ga.

Temp. gauge seems to be now reading higher than normal for this time of the year. ie. midway.

So, what came first? The chicken or the egg? While in town, the engine seemed more responsive.


Now, to check the ECT when it's cold.

Stuffed, maybe? Thoughts please.:confused:

[4bee]

Update.


Cannot get a resistance reading through the sensor. I am using a digital meter but it has been suggested it's the wrong type.

Maybe I have fried it once & for all?????? :eek: :(

[4bee]

Can anyone help with the P/N for the 'Engine Coolant Temperature Sensor' for the 3.9 V8 please?

[PhilipA]

Cooper has invoiced the one I bought as ETC8496 sender W/temp ECU at $27.89 plus GST.
Regard s Philip A

[4bee]

Thanks Philip.:)


What was your problem then, & did it fix it?

[DEFENDERZOOK]

your run into town may have given the engine a bit of a clean out.....
if you do short trips they clog up with carbon.....

[4bee]

Hhhmmmmm, how so, zook? The sensor is in the coolant circuit & not in any contact with carbon.:confused:

[PhilipA]

I didn't have a problem. I fitted new sensors to the Thor manifold that I put on the car. Just to be sure that any problems that arose during the install were not caused by faulty sensors.

You know , through all of this , I still do not have a clear idea of under what circumstances that your car plays up. If you are just driving along at 80Kmh and it starts to miss, drops out, then the odds are your TPS has died. Also , tip in after going down a hill and resuming progress will be jerky, as will taking off from a stop.
The TPS is the only "wear" item in a 3.9 injection, in that its a variable resistor "volume control" basically, with a contact that rubs along a resistance track.
Its pretty expensive so you should check it first. The way to check it is to put a multimeter " on resistance if off, volts if on" across the signal wires and see that you get a smooth transition eg increase in volts or reduction in ohms with no backtracking or dropouts. Most problems of drop out will be just after rest, ie idle.

Regards Philip A

[4bee]

Thanks Philip.:) It is open circuit at all temps. When it was hot yesterday & cold 1st thing this morning.

I feel it is tied in with the crap intermittent idling (usually at traffic lights) which I have experienced over some years & have mostly 'blamed' the Idle Air Control Valve & Base Idle adjustment, but could not see how this could 'unadjust' itself. The IAC has recently been replaced with a new one.

http://www.kemparts.com/scripts/140.asp

It's better, but still has it's moments so after reading some of these posts & browsing the web, I checked the continuity of the TPS/ECT & found it lacking, to say the least. There were moments when I 'thought' I had readings, but now deffo not. Maybe my intermittent problem has now become permanent?

[SpeedWayRover]

Thanks for all the tips, I have decided i will take the risk and drive it to vic and then find the problem there, as i have alot more contacts there. goes good on long runs so i think it will be fine, maybe use a bit of extra juice if anything. Again, thanks for all the help to all.