Thread: 3.9 EFI Flat spot / slight misfire

The vss is driven off the transfer box There's a Bowden cable between the box and the vss. This drives a chopper wheel in the vss which creates a square wave signal which goes to the ecu so the ecu can work out that you're moving. From this data it also provides a signal to the electronic speedo. What can be confusing is that the vss has a blanked off mechanical output- if you don'thave the electronic speedo another Bowden cable would run to a gearbox at the back of the speedo. That blanked off outlet looks a bit like a sensor that should point to the road...it's not.
In short- it being a 3.9 post 89 rrc if your speedo works so does your vss.
Hope that helps

Well I am having difficulties, and things got noticeably worse today.

I was ment to be heading to rover this pm but I have no tail lights on the trailer (another mystery)... So I hooked everything up in preparation to leave tomorrow morning. But upon driving home the car was stuttering badly, more so with the lights on.
Every time I intend on going away the car throws a tanty!!

Anyways I got home with the camper on the back and a engine that stuttered and strggled to hold 60km/h and frustratingly started pulling wires apart and re routing cables.

I have minimized the miss substantially, but it is still present. I need to run a grounded sheath over the signal wire from the dizzy as per PhilipA previous post.

Still yet to receive the Magnecor leads, hopefully they help as the old leads are in need of replacement.

Not to mention prior to all the above, this morning when I went to leave for work I noticed a puddle of oil under the car and a heavy drip trail from when I arrived home the previous night. Oil pressure sender unit had failed.

That's three planned trips and three times the car has developed a new problem within 24 hours of my intended departure.

The last trip the starter motor died exactly 24 hours prior to my departure.

And before that I had an earth problem, as well as a battery isolation switch failure that caused the vehicle not to start...
Fingers crossed I can get away tomorrow morning.

Originally Posted by Hobbes

Jim,
Mine does exact same - misfire that feels like injectors cutting for a millisecond. It's intermittent, but seems most prevelant when driving through 2000 ish rpm. It's got new bosch plug leads, NGK plugs. Dissy cap & rotor a few months old.
Checked the TPS and that's tracking fine with no drop outs - and of course everything else!

What's the symptoms of the ignition amp going west? - is it gradual death or..

Just a note on the VSS - it also drives the electronic speedo so no speedo means no VSS input to ECU.

& Grimace - had a similiar problem to your a/c months ago - the heaterblower motor bearings had gone tight so turning on drew a lot of current - could actually hear the alternator whistle! it was enough to drop the voltage enough to upset the ignition and make it run really rough...

Yep that's bang on the button, the rev range is correct, from round 85kmh thru 115kmh, i've ran for around 15km's with the vac advance disconnected, still the same, ran this tank of fuel dry, filled up with some 98 to see if that could cure it, or the fuel pump was overheating.

The only thing i have done over the past few weeks was to clean up my wiring around the air filter, jack, through to the brake servo,the OEM clipping had all broken way over the years, so used some plastic tubing around the old wiring, could have that have caused it????

Had to do a 150km's round trip today, it was pretty well bang on the button cruising up at 120km'hs, it did miss slightly in the rev range but not as much.

This evening i plan to check for any HT leads arcing in the dark, then replace my amp, from what i've read its a slow death, then its a complete shutdown, something i want to avoid.

The OEM one is nearly 100GBP, who makes these Bosch, Lucas, Intermodel etc most likely go down the upgrade route if u can get hold of one of those Bosch amps out here.

Grimace mate- if I was in qld I'd lend you mine!
Comparing notes in the pub the other night (otherwise known as Rangie baiting) I won on the basis of no breakdowns in 15 years ( but failed to mention replaced a power steering pump, a fuel pump, 2 head gaskets, 1 cv, 1 fuel tank, dash out 3 times etc etc) Not a great help but..

I think Phillip's point about isolating the HT circuit (and LT) ignition from the alternator wiring is really wise. The Landrover workshop manual is very specific about HT cable routing for good reason and I suspect it's something oft overlooked - I'm going to rewire mine from scratch this weekend.

Jim - I'm pretty sure that I need to replace the ignition amp as everything else checks out. i also know my dizzy is worn (Ward at GC has rebuilt it, me twice)
I'm looking at replacing the whole thing with this - 123/ROVER-8-R-V
It's about 400GBP but maybe worth it... PhilA , beeutey - what do you guys think?

Did the test in darkness of the HT leads, i've never seen leads literally glow in the dark i could see blue flashes tracking through the leads, the lead from the coil arced every so often, but piston 2 & 4 were shocking.

New set of OEM leads in the morning, together with the change of the amp, lets see what this brings

Found this link for Lucas dizzys from a company in Bromsgrove, looks a tidy price!

http://www.simonbbc.com/distributors/8-cylinder'sort=20a&filter_id=4

It's about 400GBP but maybe worth it... PhilA , beeutey - what do you guys think?

It looks an interesting product , but probably not one that I would buy, as it appears to offer a selection of advance curves (electronic?) rather than the ability to set an advance curve on a dyno.

This is OK if you have an unmodified engine.

If I were looking at say AUD 800 I would probably go for setting up an EDIS system for the same money
Megajolt ECUs for Rover/TVR engines

I realise that this probably not for everyone , but it removes the timing chain slop as a limitation, however it still will not give an optimum result as you really need knock sensors as well.
Regards Philip A

Originally Posted by PhilipA

It looks an interesting product , but probably not one that I would buy, as it appears to offer a selection of advance curves (electronic?) rather than the ability to set an advance curve on a dyno.

This is OK if you have an unmodified engine.

Thanks for that - it looked attractive as quality diz with an amp built in. Incidently, I understand they're due to release a version called "123/tune" which is fully mappable via USB to laptop & then gives you two dash switchable maps - handy for lpg.
But you're right - the inner fiddler in me would probably go with the megajolt system!

Originally Posted by jimbob292

Found this link for Lucas dizzys from a company in Bromsgrove, looks a tidy price!

http://www.simonbbc.com/distributors/8-cylinder'sort=20a&filter_id=4

That looks very reasonable - thanks!

Think we deserve some pics of the HT light show though! Actually the Bosch website mentions that the corona effect is quite normal but rather more prevelant if you buy the cheaper range of leads...

I've been trying to find some of those nylon combs with fixing hole that separate the HT leads - no luck at the usual Repco/Supercheap outlets - anyone know an off the shelf supplier?