Hi Ramon. Sorry for not getting back to you sooner. Of course it's good news. One dog-rough car that wouldn't drive into the lockup, versus a sweet beauty that has recently got me up and down to London. Good news in my book and anyone else's with a degree of sense!
Back to Basics really does work.
It's always a good start point. From there I fitted a Lumenition electronic ignition system, and at some point I will return to the original setup to fix it. Part curiosity and part not liking getting beat by something!
Two step backwards and nil steps forwards is the way to the future because time really can go backwards in Scotland (or London). (Time is the mechanism that prevents everything happening at once).
You've been watching too much Star Trek! 800 miles forward, as a matter of fact, London and back recently.
Disappointed? Moi? Not at all!
Only jesting, Dr Spock!
Your convictions have carried you through to a successful conclusions
You bet.
without needing any help at all, so the whole thread has been a virtual waste of time, except for thee and me.
You really are on a different planet now. This thread is far from a waste of time. I found it most useful getting the thoughts of other contributors. The thread isn't over. I will fix the original setup and post the solution (not any time soon though).
Me? I'm a happy bunny cuz I'm researching electronic ignition systems for an upcoming essay and pissing about with other people's systems is the only way to drag out a potential diagnosis because in 15 years of dabbling I never had a major ignition prob on any one of my 4 SD1's that went beyond changing a rotor arm or the odd plug lead.
I wish you well with it. I used to have 2600 SD1. Fab car.
Mind you, whether I can find the balls to recommend reverting to a points system is another thing altogether.
There is a LOT to be said for it and it's simplicity, especially for guys like me who don't know a great deal about electronics. I ran the points for only a few days before fitting the Lumenition kit. It was never my intention to run on points all the time (mentioned that earlier, I think).
So maybe you do have the balls to recommend a points system with a Lumention kit? Easy to change back to points if the electronics pack in (very rare with Lumenition). This redundancy was a huge advantage for me. Much cheaper too than the original amp I bought.
And for thee, when you get the urge to revert to modern technology all you have to do is plough thro' the dross on this thread because hidden somewhere is the answer from one of the contributors.
"modern technology"??? Would that be the Lucas under-coil amp versus my shiny new Lumenition kit??
I don't see any dross on this thread from other contributors, all worthy, valuable contributions.
On the other hand you might commence a new thread and draw in better expert diagnosis from future contributors who will try to deal with these electronic issues for you.
Perfectly happy with the contributions here. It's not just for me. This isn't email, it's a publicly accesible forum. All good info, for all to read.
If you are getting wet plugs, you simply MUST consider over fueling and not just a dodgy spark.
I don't know if you have read the thread. I could see the spark failing, in front of my eyes, on a test plug OUTSIDE the engine. How can that be caused by fuel? Turns out it had nothing to do with fuel, which couldn't be more obvious. The plugs were wet because they weren't sparking.
Things do not always happen in singularity so think outside AND inside the box.
Thanks for the advice (I'm not eight years old, btw). I once had a Renault 5 with a leaking rocker cover gasket. The oil leaked into the timing hole in the bellhousing, onto the clutch, causing horrendous judder, which in turn broke an engine mounting and strained the heavy positive lead on the starter motor solenoid, causing the plastic body to crack, making it work intermittently. The dodgy starter was cured by fitting a new rocker cover gasket.
When faced with a dodgy starter motor and looking for the root cause, not many people would start off by looking at the rocker cover gasket. That and a hundred other things has taught me to be open minded, but I'm sure your advice will be of use to some readers.
Equally, when I see a plug fail in front of my eyes, outside the engine, I know I have got an intermittent spark.
That's exactly what Ramon does and I would trust him anytime with ignition stuff.
Hmmm. He thinks a plug failing outside the engine can be a fuel issue. Too busy playing with his dolls, I think.
Forgot to say earlier. Ramon said this thread was full of dross and a waste of time. Chris' suggestion alone about the LED lights on the amp, was first class and will be the first thing I try when going back to fix the original system.
For me, and I'm sure others reading it, not dross, and not a waste of time.
Range Rover 2 Door wrote:Forgot to say earlier. Ramon said this thread was full of dross and a waste of time.
Hello Charles, Good Holiday? The actual quotation was:
all you have to do is plough thro' the dross on this thread because hidden somewhere is the answer from one of the contributors.
Apparantly in gold smelting - where even the dross has value - its always on top so it just looks like its all dross. Aneasymistakatomaka.
Indeed the lamp/led suggestion was valuable, as were the voltage hunting suggestions, as was the diagnostic process, as was your condenser enlightenment, as was the night time arcing observation suggestion, as was the voltmeter/led/oscilloscope teach-in. The only dross came from me, so i feel entitled to comment.
Sadly despite all the incoming golden suggestions, you, me and everyone else still dont know what the original fault was. The damn thing is still out there, undiagnosed, waiting to trap the next victim.
Cupie dolls? Raw nerves? You are right there. Too good a prize for our collective failure. One of these perhaps?
Last edited by ramon alban on Wed Jan 07, 2009 9:19 pm, edited 1 time in total.
I suppose the easiest thing is not to contribute in any way.
Really what can one say against such an articulate and obviously well educated individual who seeks a rocker cover to fix a starter motor.
Still that is inside the box though. It's the big bit where the engine sits and is covered by things like inner valances, and a big flappy thing that has hinges called a bonnnet.
Hello Doc, By the way - barring unavailable HD bed - new knee next Tuesday.
Dangerdoc wrote:I suppose the easiest thing is not to contribute in any way.
No, surely not, because that would be pre-judging the patient after just reading the symptoms. Your oath makes you follow thro' the best you can? I'm just a glutton for punishment.
Anyway, we are both on a diagnostic mission, aren't we? You to cure the sick and me to improve my ability against those untenable problems that seem to defy logic, currently ignition related.
Every time one offers a wrong LOGICAL diagnosis the forum will always come back and say so. Chris, is a great, polite, example of refocussing those of us who stray too far outside the box.
But it is infrequent, the problemee already decided an action plan to solve a fault by fast forwarding into a previous time warp, not following through with complex diagnostic suggestions. Even novices give it their best shot
Really what can one say against such an articulate and obviously well educated individual who seeks a rocker cover to fix a starter motor.
Dont forget to mend the damaged cables?
30 years - still has to ask for help tho.
By the way, I love your prior observation "done something for one year, 30 times" that was most succinct. Does tha happen in doctoring too? May I borrow it please?
You're not paying attention Ramon! I will go back to the original setup and fix it, then post the solution here (not any time soon, though). Then we, and the millions who read this archive in the future, will all be very happy bunnies, dolls and spoons!
Range Rover 2 Door wrote:You're not paying attention Ramon! I will go back to the original setup and fix it, then post the solution here (not any time soon, though). Then we, and the millions who read this archive in the future, will all be very happy bunnies, dolls and spoons!
Charley, In the interim, whilst it remains unresolved, bags I hold your wooden spoon for my singular failure of earlier diagnosis and directing you into the wrong universe.
Reviewing notes and reaasembling clues, I now have the highly probable diagnosis (ignition, not fuel, of course) of the original fault, simple, basic and non-electronic. Kevin mgbv8, was right, he said it would be simple. Its all there, just a matter of reviewing the basic ignition process looking for those missing sparks.
I know its only a theoretical exercise now, with the system being cut adrift, as it were, and being pretty much impossible to refit, wire for wire with the fault intact, given its likely simplicity, your first hand presence, the host of components replaced, all the measurements, signs/symptoms revealed, amidst an electronicky confusion, if you were a betting man, what, in your opinion, was the single thing that got missed?
This is quite possibly the weirdest thread I have seen on this forum.
But, to add my tuppence worth of weirdness, I once had an intermittent misfire/exhaust fart at idle and low rpm, on my 3.5SD1 motor. A whole ignition system later, another dizzy fitted, Real Steel springs.
No improvement.
I then did all the mods recommended in the amplifier upgrade thread, etc etc.
No improvement.
I swapped out engine earth wires, checked connections etc.
No change.
I then bought a Weber 500 carb, £210, and binned my old and tired 38dgas. The new carb didn't fit my Offy manifold.
oh how I laughed.
So, I bought a £200 Edelbrock manifold, fitted that with the carb on.
No improvement.
I fitted a carb jet kit, to stop it doing 12mpg.
No improvement.
I'd now got about £700 invested in this misfire hunt, and it was still exactly the same.
I did compression tests. Nothing amiss there. I gave up, and lived with the misfire for months.
And then, one day, for some reason I forget, I swapped the dizzy vacuum pipe from manifold vacuum to ported vacuum.
The misfire disappeared.
Luckily I had no razorblades or sharp implements to hand that day.
Paul B wrote:This is quite possibly the weirdest thread I have seen on this forum.
Hello Paul, you can say that again!
Paul B wrote:This is quite possibly the weirdest thread I have seen on this forum.
Yup, may i follow up on two points in your post.
I'd now got about £700 invested in this misfire hunt, and it was still exactly the same
So it seems that after chasing out non existent ignition fault you pursued a fuel related solution - again to no avail.
Question #1 - When the misfire was present did you at anytime establish that the ignition was faulty, ie missing sparks, weak sparks, etc, or was it simply a process of elimination by substitution, until, as it were, all possibilities of an ignition related fault were eliminated, thus you had to move over to a fuel possibility?
And then, one day, for some reason I forget, I swapped the dizzy vacuum pipe from manifold vacuum to ported vacuum. The misfire disappeared.
I was previously unfamiliar with the term "ported vacuum" so I looked it up to find it is where there is no vacuum present until the throttle plate moves away from the idle position, which is the same for Efi system, but they don't have the unported option for vacuum advance.
Question #2 - Have you any idea why that phenomenom was occuring?
I cant figure it out, but might it be because the manifold vacuum changes with engine load, this induces the dizzy vacuum advance system to oscillate on and off because the vacuum itself was being affected by feedback from the change in spark timing?
Question #3 - have you ever reverted the pipe to the manifold vacuum to check if the fault was manifesting itself as intermittant sparks or more simply unstable timing?
Paul B wrote:
Question #1 - When the misfire was present did you at anytime establish that the ignition was faulty, ie missing sparks, weak sparks, etc, or was it simply a process of elimination by substitution, until, as it were, all possibilities of an ignition related fault were eliminated, thus you had to move over to a fuel possibility?
And then, one day, for some reason I forget, I swapped the dizzy vacuum pipe from manifold vacuum to ported vacuum. The misfire disappeared.
I was previously unfamiliar with the term "ported vacuum" so I looked it up to find it is where there is no vacuum present until the throttle plate moves away from the idle position, which is the same for Efi system, but they don't have the unported option for vacuum advance.
Question #2 - Have you any idea why that phenomenom was occuring?
I cant figure it out, but might it be because the manifold vacuum changes with engine load, this induces the dizzy vacuum advance system to oscillate on and off because the vacuum itself was being affected by feedback from the change in spark timing?
Question #3 - have you ever reverted the pipe to the manifold vacuum to check if the fault was manifesting itself as intermittant sparks or more simply unstable timing?
Regards
Ramon
I thought I had a 'weak' spark, not too healthy looking, so swapping the ignition parts was a cheap start, unfortunately I could not let go of the issue and followed it for months. A couple of people told me it could be cracked valve seats, cracked heads and other desperate measures. I even came close to pulling the heads off and substituting a pair of spares I have.
At one stage, after fitting the new carb/manifold I 'fixed' the problem for a couple of weeks, but then one day whilst tweaking the timing it suddenly came back, and nothing I could do would get rid of it.
I forget the reason for swapping the vacuum pipe over, but the idle dropped so I had to tweak that up, and I noticed it was running smooth and even after that, with none of the occasional 'fart' from the exhaust.
My theory is that with so much advance at idle (full vacuum) it was firing before the exhaust valve had fully closed, or at least right on the ragged edge, but I've never looked deep enough into the cam timing details to establish if it is the fault.
I did swap the vacuum pipe back once or twice just to test the theory and the misfire returned. When you do it you need to back off the idle, as you end up with some 1500rpm tick over, as the advance moves 30+ degrees with the full vacuum depression.
The embarrassing thing is that I have preached for years that manifold vacuum is far better than ported vacuum, for both efficiency and economy.
Ramon, here's the article that made me feel manifold vacuum was the be all and end all of vacuum controlled ignition advance, long, but interesting:
TIMING AND VACUUM ADVANCE
The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn
time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is
still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.
The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the auto cam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at
high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of
spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at
50mph).
When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.
The key difference is that centrifugal advance (in the distributor auto cam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based
on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and
oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was
inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum
advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.
What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full
load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they
don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.
Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren't fully-deployed until they see about 15" Hg. Manifold vacuum, so those cans don't work very well on a modified engine; with less than 15"
Hg. at a rough idle, the stock can will "dither" in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15" Hg. of vacuum at idle need a vacuum advance can that's fully-deployed at least 1", preferably 2" of vacuum less than idle vacuum level so idle advance is solid and stable; the
Echlin #VC1810 advance can (about $10 at NAPA) provides the same amount
of advance as the stock can (15 degrees), but is fully-deployed at only 8" of vacuum, so there is no variation in idle timing even with a stout cam.
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum.
Thinking back, £700 on parts was a bit of an overstatement, as the bits probably topped out at £500, with pre-owned ignition parts I had kicking about.
oh how I laughed. 
