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Blowback.....could this be MJ related?.
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I'm in Southampton so it's a fair old drive for me.........I've heard good things about NMS, and if I don't sort this soon they will be getting a call Smile

Cheers.

Paul.

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Post Another update..... 
A fellow MJ user RichB (also on this forum), took a look at the car this weekend.....I'll cut and paste his comments, as it's useful, and may also trigger some thoughts Smile - needless to say, MJ looks like it might be OK...

Firstly, a test-drive to get a good feeling for the overall problem. Apart from the 'rev-limiting', the engine feels fantastic - smooth power delivery across the rev-range, with great mid-range pull. Throttle response at all points in the rev-range was also excellent. This makes me think that the engine is fundamentally sound, with good compression, reasonable ignition timing, and well set-up carbs.
As to the 'rev-limiting' - well until I experienced it, it was hard for me to appreciate. It is a real 'brick-wall' effect, with it *very* unwilling to accelerate further. There is a very marked change in sound coming from the carbs, and the smell of unburnt fuel, even from the windswept cockpit at 60/70 mph, is incredably strong - it must be blowing *huge* quantities of air/fuel mixture out of the carbs. It occurs both under full-throttle rapid acceleration, and part-throttle gentle acceleration - so appears to be rev-related, rather than airflow-related.

Back at the ranch, we looked at several things:

1. Carb balance/idle mixture adjust: The tip of one of the idle mixture adjustment needles had sheared off and was stuck in the carb, so no adjustment was possible on this barrel. This needs replacing/adjusting. Despite this, idle quality was good.

2. Carb mounting: Thee were quite 'solid' (misab's + cosworth rubbers), so were eased off a bit.

3. Fuel pressure: Found to be very low, and the pump is under-specified for the engine potential. Pressure increased to its maximum of ~1.5psi, but needs improving to give the recommended pressure (~3.5psi) into the Webers.

4. Momentarily blocking the inlet trumpets with your hand: On the barrel with the broken idle screw, air could be heard sucking in somewhere else, and the engine continued to run. Removing the idle screw and blocking the hole with a finger, air was still entering somewhere else (On the other three barrels, blocking the trumpet would quickly slow the engine to a stall). Upon removing the trumpets, one was slightly distorted with a slight ridge on the sleeve that goes inside the carb body (unfortunately don't know which barrel this was in). This air entry needs investigating/solving.

5. Ignition (MegaJolt): The problem occurs both with and without the MJ ECU, i.e. also on EDIS-only 10degrees BTDC timing. Tried a different VR sensor, EDIS module, MJ ECU and complete wiring loom (all from my car!). Using a timing light, at a constant rpm, timing was mostly solid, but with some 'random' flashes, which could also be detected in the engine note. During the 'rev-limiting' condition, again timing was mostly as expected, but to be honest it was very hard to tell the occurrance of errors, as the limiting is so violent (and LOUD) it very much discourages you from maintaining the condition (plus the risk of explosion due to all the unburnt fuel in the air!). Reducing the VR-trigger wheel gap seemed to give less 'errors', suggesting there still maybe a signal quality issue. The trigger wheel also is not fully proud of the crank pulley - maybe still room for some improvement here.

6. Plugs: Looked OK, re-gapped from 0.6 to 1.0mm (seems typical for high-energy EDIS systems).

So overall, we didn't find a 'quick fix', but there are several issues requiring attention. Whether any (or the sum of) these could resove the problem is to be seen. At least it didn't rain on us.


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Thanks for the write-up.

So the one thing that made any sort of difference was to adjust the gap between sensor and wheel. Have you verified the trigger wheel is centered on the crank pulley? I would imagine so, but it's worth asking.

Do you have an original distributor setup to fall back on for A-B testing? That proved useful in a different thread here on the forums.

Also, do you have access to any test equipment, like an oscilloscope? It would be interesting to see what the various signals look like at the moment the problems happen- I would be interested in seeing the VR sensor signal, the 12V supply to the EDIS module, and the coil pack drive signals.


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Hi Brent,

I have checked the gap on the Trigger wheel / Vr sensor, and it seems pretty consistant........I now have the VR as close as I dare Smile....


I sold my origional distributor / ht leads / coil on flea bay...which I'm now regretting...but plugging RichB's in was a big help as my next step was to start replacing VR sensor / edis.....

I do have access to scopes so this may be a possibility (need to find one with hold and save facility).........

having swapped to Rich's MJ / edis / vr, the only common components left were the coil pack (which I have tried replacing), HT leads and plugs, and the trigger wheel.......

I also had another thought that the other item common to the engine speed is the alternator (i.e. it spins at the same time as the engine irrespective of load), a real long shot, but am also going to try removing it for 1 run....

Anyone else watched timing using a strobe and noticed the occasional flicker, or is MJ / Edis 100% rock solid.....?????

Anyway, will keep this forum updated.................


CHeers, Paul.

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Post Update.... 
Just wanted to run something past you......

A friend of a friend m(who is an engine builder) has looked at the vid and immediately siad it looks like the ignition is firing at the wrong time (note 'Wrong time', not 'not firing').....Just wondering if you know what would ever cause MJ to do this?...Again, there are many theories floating around so I'm folowing up on this one like the others....

Meanwhile, I have another couple of vids for you all:

This one shows is taken from looking down the barrel of what seems to tbe the worst effected cylinder (cylinder 2):


http://s34.photobucket.com/albums/d102/jenkosrugby/?action=view&current=DSCF1627-1.flv

And this is me holding the car at a steady 5.5krpm:

http://s34.photobucket.com/albums/d102/jenkosrugby/?action=view&current=DSCF1628.flv



Ta for now......Paul.

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have you checked the poundage of the valve springs??? or fitted a new set?? or checked that your current ones are fitted corectly and are compatible with the rev range the cam is trying to pull?? it sounds a little like valve bounce in those second pair of videos!! im going against the engine builder purely because if it was firing at the wrong time id be expecting to see flames thru the carbs not just air and fuel!!


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I wouldn't worry too much about the occasional glitch in the firing of the ignition - it sure won't cause what your vid shows!
Deal with that later.

Have you tried longer intake trumpets? If so, what happened?

In checking the cam timing, have you done so with a degree wheel (or tape) and dial indicator?
Checked both intake and exhaust profiles on all cylinders for correct timing?

Doesn't sound so much like valve bounce as reversion stutter.

The vids make me think of the intake pulses synchronising with the valve closure event resulting in the intake charge bouncing off the valve and back through the carbs.
Your earlier comment about the mixture going very lean at the time the engine stopped winding up is exactly what I would expect.

Just how much length have you got in the intake manifold?
If real short, can you make and fit spacers at least 6mm thick between the manifold and head?
Even 'craftwood' or similar composite material will do to try this.
Don't expect a radical change in the limiting event revs unless you can change the butterfly to valve length by at least 20%.
What you will be looking for is a small change in the revs at which the event occurs and more importantly a 'softening' of the sound given off.

You mentioned that this started after a winter rebuild but I get the sneaky feeling that it was a lot more than a 'rebuild'.
Something along the lines of a change in ignition, cam, ports and a few other things all at the same time!!
You may have got yourself a combination that needs a lot longer manifold runner in order to work properly and I can see that being a problem with the very restricted engine bay width you have in a Westie. Trumpets and sock filters through the side might be on the agenda!!

Get back with a bit more detailed / itemised report. Someone wil click to the problem!

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Thanks for the comments Gents....

OK, to answer the questions....

First off valve springs.....This was my very first suspicion, and consequently, spent a tidy sum of money changing to a very nice set of double springs....Alas made no difference.

I tried much longer trumpets (in the shape of some plastic tube), and again did not shift the the point of the problem. I checked cam timing with a degree wheel on the crank pulley, and a dial guage reading inlet valve lift on cylinder 1 (tried on valve cap and follower)...so am confident that cam is set to the 106 degrees as recommended by piper...also worth mentioning that I can swing the vernier pulley on my cam from one end to another without it making any difference to the point of the problem. I have not checked the exhaust valve timing though!....That may be worth a look.

The inlet length is fairly standard for this engine (I would guess at it being 80mm)...there is a nicely matched inlet manifold (to the ports) bolted to the carbs, and as trumpet length does not make any difference, I was thinking this would not be down to inlet tract...

You are correct, it was not just a rebuild.....IN fact the block was new, the head was ported, new camshaft lifters, valve springs.....BUT, directly after I built the engine and installed it, I get it rolling roaded (at this point it still had a distributor)....it reached peak power at 6000rpm (155bhp)...However, as I was still running in the engine, I rarely revved it above 5000rpm....Meanwhile I decided to convert to MJ, I installed MJ, and while still running in, our club had a rolling road day...It was at this point on the rolling road the fuel spit back was noticed...however when I data logged the problem it seemed to occur at around 6000rpm.....I've since fitted trumpets and a sausage filter, and now the problem seems to occur at 5500rpm.......

Obviously this points to either MJ or the fitment of the new filter....but, having tried a different MJ system, it still did the same thing.. also removal of the trumpets did nothing to change the point of the problem.....

So, the obvious things I have tried but I can't even get the pointof the problem to move...I feel if I could move it either up or down the rev range, I would be 90% there...But so far have drawn a blank on everything.....

The only thing I havent changed are the HT leads (that were new), and the plugs......I'm trying to hunt down a dizzy at the mo and see if by putting that back on it works!....fingers crossed.

Anyway, keep the questions coming Smile

Paul.

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another idea that was flung my way is the carbs! are they mounted correctly? if webbers are too tight and not fitted with the correct rubber seals and washers that allow them to move that can do some very strange things all due to the vibration of the engine! aparantly at certain revs it can start to froth up which im told would cause this lean mixture and missfire you are finding!


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Alas, have looked into this one......And measured the movement at the trumpet end....all looks well. I'm using the cosworth rubbers and Misab washers, am getting approx 10mm movement at the end.... Smile

Thanks.

Paul.

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I assume the faults (air leaks, fuel pressure etc) identified by RichB have all been corrected? Can the engine be stalled on all four intakes now?

Just ticking fingers:
Tried alternate MJLJ system from RichB and new coilpack - no difference. Not likely to be ignition fault.
Tried longer outside ram tubes - no difference. Won't make much difference unless the overall carb/manifold/port combination is very close to perfect.
Tried different valve springs - no difference. Absolutely no audible indication of problems here.
Varied cam timing with vernier adjustment - no difference. Interesting - I would have expected at least some variance but maybe the problem involves a gross error in configuration that masks any change due to cam timing.

You mentioned having checked timing when it was around 5000 - was this with a timing tape or degree wheel on the crank so that you can get an accurate indication of the true timing to compare with the timing set in the MJLJ map? Did the displayed timing agree very closely with the map?

Is the trigger wheel attached to a part of the damper that is 'outside' any flexible material or is it absolutely rigidly attached to an unmovable part bolted to the crank? No possibility of an elastomer damper section affecting the relationship of the trigger wheel to the crankshaft in case of harmonic vibration?

You mentioned the manifold is ported to match the head. Is there any possibility of borrowing an unmodified manifold to try? An increase in the cross sectional area of the manifold runner will SLOW the mixture velocity and just might have altered the intake pulse timing enough to upset things. A small step from a smaller runner to a larger port won't hurt appreciably and often helps in acting as an anti-reversion dam.

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What is the mapping you are using?
Another off-the-wall possibility is oil - you are using a 'normal' oil and not some heavy weight competition oil I hope.
I've been caught with 'anti-pumpup' lifters and 60 weight oil - the lifters might as well have been solids at high revs!
Contact Piper and ask for their suggestions on oil.

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Post reply...... 
To answer the questions:

Th faults Rich round have not been corrected....but not through want of trying Smile - I bought a new idle mixture adjustment screw, only to find that someone has bodged the idle hole in the weber.....By chance, it does seem to allow the correct amount of fuel and air in, so actually, the set up works perfectly well....just means it has no adjustment..........As to why the car does not stall, that one is still a mystery, but at a guess, I would say the idle adjust hole can leak with eonugh vacume, so when you put your hand over the trumpet, air can be sucked in from around the screw thread......Not perfect, and I will sort this, but I'm sure it's not related to my problem

Timing was checked using a strobe light....but, I only have the marks on the engine to go by....So I know the idle timing was spot on at 10 degrees...and this advanced perfectly well as the revs built up.....But, I do not have a perfect comparisson between the MJ map and the real timing....needless to say, the limp home mode seemed to be spot on at 10 degrees, and the engine still behaved in the same way on limp home....So, from that the conclusion that the issue was not timing related.

For the trigger wheel attachment.....see this picture:...also I have now moved the VR sensor further out (towards the outer edge of the trigger wheel, and further away from the alternator belt pulley).....But this shows the trigger wheel mounded against the pulley wheel, it's very secure at this point

http://i34.photobucket.com/albums/d102/jenkosrugby/DSCF1447.jpg

This pic shows the porting of the inlet manifold through to the head.....as you can see, it looks good. and I'm running 34mm chokes which for a 2ltr should be fine......The change of trumpet length made no difference, and this (I think is also taken into account when looking at the inlet length.....
http://i34.photobucket.com/albums/d102/jenkosrugby/Westfield%20Engine%20out/DSCF0646.jpg

However, point taken...if I can figure out a way of changing this I'll give it a go.....

Many thanks for the advice.....will carry on trying.....

Paul.

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Hello to all,


For my experiences installing MJLJ in 4 cars, i have learned some important things about VR sensor installation. From your photo of the sensor installation, i can understand the sensor bracket is solid. but i have had a similar problem with a solid bracket (5mm of iron), think, the sensor is longer, and it isn't soo rigid (you can bend it a little with fingers) In a car, i had placed the sensor with a thick spacer in the original sensor bracket of the engine (because the bore of the original sensor is bigger than the ford VR sensor). The bracket design can vibrate but at high rev because the long distance from the bolt to the sensor, longer distances can vibrate more.

When i have mapped 2 of my MJLJ in the rolling road dyno, when i have had vibrations of the sensor, usually, the rpm indicator in the configurator goes to 0 rpm and the actual rpm of the engine. When the EDIS loose sync, the result is no spark. ( The same problem is with a excessive runout of the trigger wheel). If when you accellerate the engine at the rev of the problem and see the rpm signal goes intermittently to 0 rpm in the Configurator sw, you have finded the problem.

If this type of problem are LOAD dependant, the usually cause is the length of the runners and the resonances in the intake runners. But this isn't your case because is independant of the LOAD and only related with the rev reached.


Cheers!! Wink

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Post Thanks for reply....and update...... 
I 100% take your point re the sensor bracket....the previous bracket I thought would be fine but at a certain rev vibrated....

The new one that you see in the photos however, is fine...I cannot physically move it with my hand it's that solid......

However, it's now not relavent as on the weekend I swapped back to a distributor based system to see if made any difference........It did not!.....Still blowing out fuel at the same point!.

I also tried some different lifters....again made no difference.....

So....I can now totally discount the ignition system....it's either mechanical or the carbs...As it's not load related, I doubt it's the carbs, but I'm going to try a different main jet, emulsion tube, and air corrector to see if it changes anything.....If not, then I'm stumped again....... Smile

Thanks mfor the comments.

Paul.

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