Uprated Ignition System?

[tref]

Gentlefolk,

Probably a question for the turbo tuners, does anyone know of an "uprated" ignition system that might work on a 944 S2?

Following the Dyno day I am reasonably confident that the Ignition system on my S2 is relatively healthy - I certainly have new plugs, leads, dizzy cap and rotor arm etc, and it runs fine. However... LPG seems to be somewhat more demanding on the ignition system, so whilst it works fine on petrol, I wonder if this is possibly part (if not all) of the problems I have of a high-speed miss-fire on LPG.

Ideally, I don't want to replace the LT side, just the HT side, so am thinking I guess of a go-faster coil. I seem to recall "WUF" had a coil per plug, but does this require an entirely different ignition "brain" or other major changes?

My reason for looking at the ignition system is two fold - firstly the majority of poor running problems that I have seen solved in LPG conversions seem to be the ignition system rather than the LPG system itself, and years ago a discussion with Jon Mitchell, and his commenst that he would like to see what difference a twin-spark conversion to a 944 might make to it's performance... this stuck in my mind in terms of perhaps the existing arrangement might not be ideal in the combustion chamber, and of course, LPG will have entirely different burn characteristics.

Any suggestions gratefully received!

 

[Ex Skyline]

You should really be speaking with Jon' Mitchell again Tref and, NOT with us mere mortals [8|][][]

 

[tref]

But sometimes us mere mortals remember the obvious, that if you are to "into it" you forget, like "Have you looked at your earth strap recently?" (Errr, no[])!

Plus of course, The Ark was built by amateurs, the Titanic by professionals! There are a lot of people who have played with stuff like I have on here, and learnt a lot along the way... I'd be interested to hear of (and avoid) the blind alleys as much as the good solutions.

 

[944 man]

I think that he should actually be speaking to Tom Barker. Im not sure that he has cracked the 16v Motronic yet though, but when he has then coilpacks and MAP will all be possible with a plug and play solution.

 

[ChasR]

What spark plugs are you using Tref?

Many people say that Copper plugs are the best, but IME whilst this may be the case for their spark strength capability they are pants when it comes to durability, that is before you get to how they fare with modern fuels (a certain Triumph Stag specialist was saying to me how he had seen plugs worn down to almost the nub after 10k due to (in his opinion) the higher ethanol content in fuel (going by the difference that occured with my Stag when I went to fresh plugs after 2 years (around 3,000 miles) I would agree (it would misfire/backfire (at the exhaust) as soon as the car went above 4k))). But even on friend's cars on LPG where copper plugs were specified they were misfiring within 5k of the plugs being changed (an '07 Wrectra 1.8 where it came with copper plugs from the factory).

Platinums and Iridium may not be the best but at least they last (on my Mondeo 1.8 (and previously my 3.0) on LPG the platinum plugs do a reasonable amount of miles, however they will probably last around 30k at best if I am honest even with Flashlube (a valve saving product) being used (as opposed to 60k on petrol). The lack of lubrication LPG provides has been blamed (even unleaded (in its new ethanol form) lubricates things a little more than LPG).

As a stop gap you could try to narrow the gaps a touch on the new plugs you try out (even if they are copper items ).

 

[tref]

Thanks guys, I had been keeping half an eye on Tom Baker's work, as it looked to provide a useful solution to failing ECUs as much as anything else. Shame, as you say, it isn't suited to the 16v yet.

Chas, that is really useful stuff... I was thinking that I'm not so worried about messing with the timing (as Tom Baker's system might allow), but primarily "fattening up" the spark. I cannot remember what plugs I have - I suspect they are cheap Bosch ones, as somewhere I heard that LPG works better on cheap plugs rather than anything flash.

Given the miles I cover, following your mail I was wondering if it might be that the plugs have simply worn out, but the problem was there from the outset. I have another couple of sets kicking around somewhere so I will have a look at what they are and change them at the weekend. Certainly the misfire sounds similar to your experience, and wonder now if what I was thinking (creating a bigger spark) could in fact exasperate the problem.

 

[ChasR]

Before going too far down the misfire theory how long have you had the misfire for upon the car being on LPG? And what system are you running in the car?

 

[tref]

The problem has been there from the off on LPG. It is like "hitting a soft rev-limiter" at anything from 4-6k rpm. On a light throttle you can drive through it. It seemed like fuel starvation, and indeed, that was the route we went down looking at the LPG system - the injectors have been changed, the multi-valve, filter, anything which could result in a loss of fuel pressure. All the time the fuel pressure measurement at the injectors has been good.

It went on the rolling road at Ray West, and indeed, it mapped the petrol curve pretty damn well until it hit that "wall", and was showing "lean" - which again, pointed at fuel starvation, so we have again been through all we can think of which could be restricting fuel at higher revs. I understand that the signal from the coil isn't "the cleanest" they have seen, so the coil has been changed since, and various other "electriceral" methods have been tried to overcome that.

From my prior research I understood that ignition problems are commonly blamed on a newly fitted LPG system so I did go through that before it was converted - new plugs, leads, dizzy cap, rotor arm, and indeed, the dyno would suggest the car is healthy and running well.

That said... it wouldn't be the first time I have fitted new components only to find them not as good as one might hope, hence the plugs will indeed be my next thing to look at again.

The system is now entirely Prins VSI 2. - yellow injectors...

Oh... the running lean on the dyno... This is something I haven't checked, but it was suggested that unless it was a "five gas analysis" (which I don't know yet) If it were just measuring oxygen, then a miss-fire would cause it to show as running lean, as of course, no ignition means unburnt fuel, but also oxygen going through the exhaust, so oxygen will read high, suggesting it is lean... Hence, having again been through the fuel side, looking again at the possibility of an ignition system not quite doing all it needs to on LPG.

 

[T3rra]

Tons got quite a few projects on the go, try him. If there's a demand then it put push things on. Won't hurt to give him a call

 

[ChasR]

Seeing as it is a Prins kit, was it installed into the car from new and by a Prins approved dealer? If so, how did they go about solving the issue?

Normally in this instance I would say to hook a laptop up and to look for data where there appears to be an abnormality in the parameters. Prins software however seems to be awkward to acquire software due to their relatively closed dealer network. I shall have to look up what the injector and vaporiser specifications are for your car before condemning the wrong thing. It is easy after all to spend someone else's hard earned reddies .

One more thing, do the AFMs in the S2 work as they do in the Turbo? Basically where after 3.5krpm the ECU guesses how to chuck the fuel in...

 

[tref]

Yes, new Prins kit installed by an approved Prins dealer (14 years working on/fitting LPG), and they are still working on solving it. They came up to the Dyno day to see what was going on, and if it gave any clues, hence the further fiddling following that, and leading to this now.

We have been out with the laptop connected (he doesn't seem to enjoy the ride at the revs where it is a problem[]), and the next thing is to go back to the rolling road and see what we can do to sort it out... but... Unless we have something to change, no matter what we do on the rolling road isn't going to change anything, and if we find something to change (like for example ignition components) then in truth, we can probably change them prior to that so we can use rolling road time to put the cherry on top. The only other thing the rolling road will be good for is the five-gas analysis at the revs where the problem lies, as that is something which we cannot do on the road or static. That should tell us if it really is lean (fuel) or showing lean because of a miss-fire (ignition).

What is this you say about the ECU guessing how much fuel to put in???

Many thanks for your comments, most appreciated...

 

[Indi9xx]

Tref can you upload a picture of your plugs? ideally a side on photo of them.

I personally think there is a chance that your temperature range of the plugs you are using is too hot or too cold.

It is possible to remap your ECU so that when it is in the "LPG" mode it uses a different ignition map, which can be done with your standard DME and a very installation of an extra wire into any of the coding plugs, which can in turn to coupled to whatever switches you from LPG to petrol, perhaps using a simple relay to keep it electrically isolated.

But before you go down that road, I would recommend uploading a photo of your plugs and I will be able to tell if you need to try one step colder or hotter.

 

[Indi9xx]

If it does turn out that your plugs seem to be running in the correct temperature range, you can get a few more KV to your plugs by widening the gap a little.

 

[944 man]

Two maps on an otherwise standard DME (apart from the ICs) Jon?

 

[944Turbo]

Most of the aftermarket chips have several maps selected with the region coding plug (external of the ecu) or the fuel quality switch (on the ecu) or variations of the two
Tony

 

[tref]

Sorry, I really am rubbish with pictures on here, and to be honest, I don't think they will tell a lot - I moved the car around before taking them out, so of course, it was running on petrol in cold-start mode. They are Denso rather than the usual Bosch ones I fit (I never have been able to see any great advantage in flashy spark plugs, not in smooth running, longevity, economy, the basic Bosch ones always seem to do just as well), and they have a gap you can drive a bus through... but they may have had the gaps opened up already by the LPG chap - I know it was something he mentioned... So... I have now put in a set of standard gapped, Bosch plugs that I would usually use as a baseline, and can then play around with them.

My first thought on a different map for LPG was "why?". Up until the point at which it starts to misfire, it matches the curve on petrol almost identically, just a few hp down. If it continues to do that without the misfire I will be very happy.
The thoughts following that were, "but it could gain a bit more power?", to which I countered that if I wanted power, I wouldn't be fitting LPG! I would rather have the economy, because if I do want the extra power, I hit the button and flick it back to petrol.
Then of course I realised that it might be possible to map it for better economy (stop yawning at the back there!), and there I could see a real benefit...

Tempted to fit nitrous and water injection though, just to see how many injectors you can fit in an inlet manifold[]

 

[944 man]

My thoughts are that you can significantly advance the timing (due to LPGs amazing octane rating), making more power for the same amount of fuel used, enabling you to back off a little for any given speed or performance requirement, therefore saving money.

 

[ChasR]

That is a little strange Tref.

Most LPG chaps I have seen tend to go for a colder plug due to the LPG burning hotter than petrol (possibly due the effects of the timing not being advanced enough (LPG has a higher RON rating than even V-Power ) as a result of it lacking lubricating properties of even unleaded.

However. many LPG installers do report sucess in shortening the electrode gap, not widening it as you. For me, simply keeping them as the car left the factory has left me with satisfactory results. Sometimes shortening them can result in an improvment but IMO this down to part of the ignition system being in poor order (which you seem to have covered).

In your position (as the cheapest fix) I would be tempted chuck in some stock plugs but at a shorter gap and progress from there .

 

[tref]

I'm afraid my comments about the plug gap was as a result of Jon's comments above, and the LPG guy muttering something about the plugs, which I promptly forgot! It could therefore be that the plug gap was always like that, or eroded open in service, I honestly don't know now.

Standard plugs with standard gap now fitted, and it maybe runs a little smoother on petrol, maybe the changeover to LPG is a little smoother, and maybe it is all placebo, but it certainly hasn't affected the missing at higher revs.

 

[Indi9xx]

Widening the electrode gap results in a slightly retarded ignition source but with higher KV, narrowing it causes a more advanced ignition source but with lower KV. This is just due to the field in the coil collapsing and it taking more energy to bridge a wider plug gap, and therefore has to saturate further.

So some LPG tuners may find benefits to a narrower gap due to it advancing the ignition timing just a little.. However in tref's case he seemed to be looking for an upgrade to the KV available, possibly thinking that his ignition source was too weak at higher rpm, which could, or may not, be the actual cause of his fault.

For the pictures, if you are looking for fueling clues, it is best to whip out the plugs right after a power run... However for reading the plug temperature reading and deciding if you need to go hotter or colder on the basis of if the plug on average is running too hot or cold, you can do this even if you have moved it around since the last run, as long as you have not coked it up so badly that you cant see the heat pattern on the side electrode or electrodes.

As a rule of thumb (apart from detonation avoidance tuning of plug temp, which is another kettle of fish) on the side electrode you will see a band of heat tempering, ideally this wants to be around 50% of the electrode length, if it is closer than this to the plug body your plug is too hot, if it is further away than this it is too cold for the average duty cycle of that engine.

On turbocharged cars, you need to look for other clues to see if the plug is running too hot and could be causing a pre ignition source, as this could be happening in short on boost periods.