3.9 wedge 1990 misfire

[stevmale]

Please has anybody had experence of a misfire that starts at 2500rpm even when not under load , but occasionaly nearly disapears.
Its a hot wire system
I have :
checked fuel pressure
checked leads
checked plugs
checked the coil
by alternative units or gauge
the dizy as verticle play on the shaft and the head plate which holds the pic up head moves from side to side although the vac mechanisim seems ok.
reading thru all the topics it seems tobe well discussed subject.
thanks in advance.
steve

[ElvisWedgely]

When you say you checked the plugs, leads and coil, how did you check them? From my experience of finding a misfire is to eliminate these parts by replacing them with top quality products. Misfire detection is a pain in the backside which is one reason why I usually let the experts carry out this procedure as they have all the necessary equipment for detection and on the long run could work out cheaper by pinpointing the problem. I like to work on my TVR just like anyone else but when it comes to tuning, misfires and such, I let the experts do the job, preferably a rolling road tune. It should last for years and you'll know it's spot on. Sorry to sound a bit negative but that's the way I see it. Good luck and all the best.

Tony. TCB.

[stevmale]

Replaced parts with new and will continue to eliminate each area in turn.
I was just considering what was a common fault with a 3.9 "hot wire" V8
Thanks for the reply.

steve

[hallsie]

I had something kind of similar a few months back on on my 350.

It turned out to be the ignition amp, but I changed the Dizzy to do away with it rather than source another amp (I do have 2 spares now if you want to try that?)

Theres a company on fleabay that do both the dizzy and replacement amp.

Stu

[maston]

Not sure if the hotwire has one or not but I had the exact same problem with my 390 (flapper) and it turned out to be the Coolant Temperature Sensor.

[stevmale]

Thanks for your help.
This car as stood for two years so tonight i have stripped the the Dizy and rebuilt it.
I can not check the amp but the vac pin hole is elongated and the weights were seized
Its to late to start the TVR so tommorrow I shall report on what happens.
But for now I think its a dizy fault , so a new one is on the horizon.

Again thanks and i will check the circuits to see if the temperature sensor is feed to the ECU.

Regards
steve

[Brap_Brap]

After reading dozens of topics here like this over the past few years I finally realised why Englishmen like warm beer.

LUCAS also makes your refridgerators.

[grahamw48]

The dizzy is also probably 20 years old.

I'd be fairly happy if my fridge lasted 20 years.

[adam quantrill]

I've got a freezer still going strong after 17 years - only 3 to go ;^)

The ironical thing is that lucas original spares are now the best you can get, what with the likes of Intermoron on the scene... just not the bullet connectors....

[Danny Hoffman]

My guess would be the rotor arm, try a new quality replacement - not an Intermotor one!

[ElvisWedgely]

It may also be worth checking that the high tension leads are well separated from each other and any metal surroundings, as this sometimes causes an arc and misfire. Very difficult to detect, as such arcing can only be seen in total darkness, when the engine is running and revved through the range.

Tony. TCB.

[grahamw48]

Yes, that's the easiest way to find your stray sparks...in the dark.

[stevmale]

Sorry on hold for a while.
Regards
steve

[stevmale]

Hi found it to be a dizzy fault . A second hand replacement unit had been fitted with a damaged bent shaft.

Now there is a different fault a hesitation on full hard throttle , which disappears within 1/2 seconds.

Drive it quick but not hard its runs good .

As anybody any experence of this type of fault.

regards
steve

[grahamw48]

Rev limiter ?

[stevmale]

Never gave that a thought.
As a wedge have a limiter as standard !

thanks.

regards
steve

[matt-man]

Mine doesn't so no!!

[wedggie]

anyone get to the bottom of this? When i rev to about 3.5krmp there is a momentary cut out and then she fires up again... Only when i push her hard though.

[adam quantrill]

Is it OK when cold(ish) and then worse when hot?

[voltage_maxx]

Steve - I'm assuming this 3.9 engine is a retro fit engine?

If so, do you have the engine number?
It's been a while since I've played with a hot-wire system, but there are lots of small areas which can make a big difference to how the system runs. What tune resistor is fitted for example? Is your ECU looking for an input off the speed sensor - if it is there, is it activating the Range Rover 'joy kill' mode at high-speed?

If you can give us some more details, I'm sure we can help.