Electrical issue, can anyone suggest a parts source please?
Discussion
Hi peeps, got no feed from the distributor to tell the coil to work.
It's a stock 350i. As the nice AA man explained to me:
It's either the pick up in the distributor at fault, or the amplifier.
Either way, there is nothing coming from the amplifier.
My garage will tell me this week which is causing the problem.
So, could any one tell me where I might get a replacement amplifier,
or can I get the pick up fixed, or will I need to replace the whole distributor?
Thanks in advance chaps.
It's a stock 350i. As the nice AA man explained to me:
It's either the pick up in the distributor at fault, or the amplifier.
Either way, there is nothing coming from the amplifier.
My garage will tell me this week which is causing the problem.
So, could any one tell me where I might get a replacement amplifier,
or can I get the pick up fixed, or will I need to replace the whole distributor?
Thanks in advance chaps.
No, the pickup can be replaced... last one I got was £18 from an Ebay seller whose name I forget.
If you have a multimeter you can do a quick check: undo and remove the two screws that hold the igntion amp to the side of the dissy and measure across the two terminals you'll find poking out of the dissy. You should see about 3000 Ohms (3k): if it's significantly higher (mine was 19 MegOhms!) then it's gone open-circuit and won't be supplying any trigger pulses.
If you have a multimeter you can do a quick check: undo and remove the two screws that hold the igntion amp to the side of the dissy and measure across the two terminals you'll find poking out of the dissy. You should see about 3000 Ohms (3k): if it's significantly higher (mine was 19 MegOhms!) then it's gone open-circuit and won't be supplying any trigger pulses.
adam quantrill said:
If you replae the pickup do you need to set the timing again to get it spot on, or will the new one go in pretty much the same place?
I think it has locating pips so goes back in the correct place.I'm assuming that he auto-sparky has ruled-out the coil as beng open-circuit? The ignition amp. gets its supply through the coil winding so if the coil dies the amp. will appear to be doing nothing.
adam quantrill said:
What I meant was - are there any tolerances in the pickup manufacture that might mean the timing gets shifted slightly? I would imagine only by a degree either way so it will run normally without adjustment.
Fair point: it's quite a hefty bit of steel as a former with just a bobbin glued (or moulded) on... I guess there may be some piddling tolerance but with the slack in everything else, I don't know if you'd notice it. I just dropped my replacement in and away it went.
pacman1 said:
bought replacement amplifier ------ fitted in 2 minutes ----- jobs a good 'un
An interesting and satisfactory outcome - wonder if the AA man who said it could be either the dizzy pick-up coil OR the amplifier, would have like to have narrowed down the choice with some intelligent diagnosis such as:Test the Amplifier and Distributor Pickup Coil Together.
o Remove Distributor Cap.
o Disconnect ECU trigger wire from the 6.8k ohm resistor to prevent spurious signals getting to the ECU.
o Disconnect amplifier wire from coil negative.
o Connect a 12v 21W bulb from the same amplifier wire to coil positive (12 volt supply).
o The 21W bulb acts as a substitute coil load.
o (courtesy TVR forum) Turn ignition on and rotate distributor rotor arm back and forward against the vacuum/mechanical advance springs.
o As the toothed reluctor wheel triggers the pickup coil, the amplifier should flash the bulb.
o If bulb flashing is positive and consistent the amplifier and pickup coil are working correctly together.
o If lamp does not flash or is inconsistent/weak either the amplifier or pickup coil is faulty.
Check the pickup coil independently
o Remove the amplifier connections to the pick-up coil and measure the resistance of the distributor pickup coil for a steady value between 500 ohms to 1500 ohms on the ohm-meter. Flex the wires at the same time to test their integrity.
o Outside the above range, short or open circuit indicates a croaky pickup coil.
o By process of elimination, if the pickup coil is OK, one might conclude the amplifier is faulty but nothing is ever that simple with electronic components, so to be sure:
Test the Amplifier independently
o What follows is an elegant but slightly complex test process.
o Use a 1.5 volt pen-cell battery connected in series with a (say} 2,700 ohm resistor and two flying leads to simulate the pickup coil.
o With the coil and amplifier connected normally and the distributor pickup coil disconnected from the amplifier, connect one flying lead to one of the amplifier input connectors and touch the other flying lead intermittantly across the second amplifier input connector.
o This emulates a pulsed input thereby activating the amplifier in sympathy to generate sparks from the coil?
o Polarity of this simulation is non-critical as neither flying lead is connected to earth, only to the amplifier input connectors, and the pulsing voltage from the pen-cell via the 2700 ohm resistor acts similar to the pickup coil input without causing stress or damage to the amplifier.
o The above test can be performed with the 21 watt bulb as the coil substitute as previously described, except in that circumstance, the pick-up coil simulation will flash the bulb.
Alternatively (for even more elegance), going one step further:
o Construct a small test box complete with switch, 21 watt bulb/holder, pen-cell battery, 2700 ohm resistor, 12 volt pos/neg power connections (from a car battery), spade connectors to the amplifier, etc.
o Connect up the 12 volts power and the amplifier to the test box and flick the switch repeatedly to emulate the pulsed input from a pickup coil and see the 21 watt bulb flash in sympathy to show the amplifier is working correctly.
Now, dont get me wrong! The above tests are not that easy to set up if an owner/enthusiast is unfamiliar with electricity, multi-meters, simple wiring, and the Ignition wiring/components involved, but a competent AA man should have the wit and ability to determine which component is faulty. Bring back real AA men, I say!
And for any RV8 owner/enthusiast, such home brew test procedures could save loadsa money before replacing components that have not croaked.
Elsewhere on the forum are the full range of ignition component tests - search for - TESTNG IGNITION COMPONENTS
pacman1 said:
Quick update, identified and bought replacement amplifier from the local parts shop, fitted in 2 minutes by my own fair hand, jobs a good 'un.
Make sure you use thermal compound (normally white stuff) when fitting the amp or it might go south fairly quickly. If you can't get the right stuff then apparently toothpaste is almost as good...adam quantrill said:
pacman1 said:
Quick update, identified and bought replacement amplifier from the local parts shop, fitted in 2 minutes by my own fair hand, jobs a good 'un.
Make sure you use thermal compound (normally white stuff) when fitting the amp or it might go south fairly quickly. If you can't get the right stuff then apparently toothpaste is almost as good...Its consistency was quite thin, so I could only put so much on, but I have kept the rest. Perhaps I should consider putting some more on at a later date?
The pops n bangs are summat else at the mo and a tenner's worth of juice lasts no time. I can't put this solely down to the fitting of the amplifier, I just think it needs a good tune after four years and 5k miles. Driven quietly with the roof on I have got north of 30mpg in the past, but it doesn't get the use these days. I did 200 miles in her last year, but hoping to get some better runs in before garaging for the winter.
Drives, sounds and smells great though!
pacman1 said:
Thanks, it came with a small sachet of clear looking syrup of sorts which I applied to the back of the amplifier prior to fitting.
Its consistency was quite thin, so I could only put so much on, but I have kept the rest. Perhaps I should consider putting some more on at a later date?
The pops n bangs are summat else at the mo and a tenner's worth of juice lasts no time. I can't put this solely down to the fitting of the amplifier, I just think it needs a good tune after four years and 5k miles. Driven quietly with the roof on I have got north of 30mpg in the past, but it doesn't get the use these days. I did 200 miles in her last year, but hoping to get some better runs in before garaging for the winter.
Drives, sounds and smells great though!
Heat transfer compound should be used sparingly; just a mere smear is all that's required... otherwise it has the opposite effect and acts as an insulator! Somewhere I have a tube of Dow Corning that I've been using for almost thirty years... and it was half-empty when I got it! That's how litle you need.Its consistency was quite thin, so I could only put so much on, but I have kept the rest. Perhaps I should consider putting some more on at a later date?
The pops n bangs are summat else at the mo and a tenner's worth of juice lasts no time. I can't put this solely down to the fitting of the amplifier, I just think it needs a good tune after four years and 5k miles. Driven quietly with the roof on I have got north of 30mpg in the past, but it doesn't get the use these days. I did 200 miles in her last year, but hoping to get some better runs in before garaging for the winter.
Drives, sounds and smells great though!
I paid £1.48 a litre for some cooking 95RON last night at Woodall Services, that equates to £6.72 a gallon. So it's no surprise that a tenner won't get you far
I tightened the amplifier tight, but not too tight, if you see what I mean, allowing the slpit washers to do their thing.
Any excess compound will have squeezed out, but I shall check again for tightness in a week or too.
As for the price of fuel, well, I console myself that I'ts possibly the cheapest V8 to run on the planet!
Any excess compound will have squeezed out, but I shall check again for tightness in a week or too.
As for the price of fuel, well, I console myself that I'ts possibly the cheapest V8 to run on the planet!
honestjohntoo said:
pacman1 said:
bought replacement amplifier ------ fitted in 2 minutes ----- jobs a good 'un
An interesting and satisfactory outcome - wonder if the AA man who said it could be either the dizzy pick-up coil OR the amplifier, would have like to have narrowed down the choice... [plus an interesting lot of technical stuff you said there as well]
It took less than 15 minutes for him to narrow down the fault to two possibilities.
He then took the time to detail his findings and answer my questions.
Whether he might have been able to diagnose further is of no consequence since he was unable to fix it at the roadside, and recommended my garage investigate further.
Their auto electrician did... it fecking well started didn't it.. which led them to think it was most likely the amplifier no longer wishing to work every time in the engine heat, rather than the dizzy pick up giving up the ghost.
So that was the first, most likely, and cost effective item I chose to replace, and it worked.
Edited by pacman1 on Sunday 31st July 23:25
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