I said the older ECU's were not truly sequential.. This does depend on definition of truly sequential... The modern definition of truly sequential is that the LPG system follows the petrol strategy exactly.. i.e. waits for pulse on individual petrol injector wires before pulsing relative individual LPG injectors and calculates pulse times for individual LPG injectors based on pulse times of relative individual petrol injectors. With this type of strategy you don't really need any software fuelling adjustment for acceleration, the LPG ECU doesn't need to do much about acceleration compensation if it follows the petrol enrichment strategy because the petrol system has already done the compensation.Tinleytech wrote:For info, the above description regarding the function of the 'enrichment in acceleration' slider is fundamentally wrong - please see below direct from the AEB software guide (apologies for the rather poor English), this also calls into question (as mentioned previously) Simon's persistance that the AEB ECU is not truly sequential - which it is and has been for many years :
4.6.6 Enrichment in acceleration
Many engine management units have transient enrichment of petrol injection, during
accelerations. Sometimes this causes jerking or hesitation, on gas. You can fix it with this filter:
· By default the filter is defeated, with its fader all the way right; in this position, the petrol
transient is copied to the gas injection, applying all the enrichment.
· As you move the fader to the left, the Dream XXI-N ECU will follow the petrol transient
slower and slower, thus applying less enrichment to the gas injection.
Whenever the enrichment is filtered, the box of the filter will glow in red, on the screen.
Older ECU's don't match the above because channel D LPG injector output pulses even without it's corresponding input wired up (yellow and yellow with black stripe wires). On these ECU's channel D LPG injector pulses for the same duration as channels C, B and A LPG injectors, with all of them based on channel A input (blue and blue black stripe wires). Given that channel B, C and D LPG injectors pulse for the same duration as channel A input and given that B, C and D don't wait for a petrol injection pulse before pulsing the relevant LPG injector, these ECU's don't match the above definition. Just seen this again on Himselfunknown's vehicle... We swapped channel D output onto injector C, plug C now not connected, and even without yellow yellow black stripe wires connected the engine will run on all 6 cylinders. This is something that anyone with a 3, 5, or 6 cylinder engine with an older AEB ECU can confirm for themselves, they may just need an interface cable to disable diagnostics (to prevent errors for unplugged injector C) occurring and forcing a switch back to petrol on ECU's that are old but new enough to have diagnostics enabled.
The newer ECU's are truly sequential - They follow the above modern definition. Just seen this again on Himselfunknown's vehicle... Swapping channel D plug onto injector C, plug C now not connected, yellow and yellow black stripe wires not connected, the engine will only run on 5 cylinders because channel D output does not pulse without the yellow yellow black stripe wires connected with the newer ECU.
I'm not sure when the 4.6.6 you quoted was published but I fully accept that it is a totally accurate description of how the acceleration enrichment works on the newer ECU's. I would add that with the newer ECUs being truly sequential, this is not really a very useful function - We both seem to agree that it is really a leaning in acceleration tool (and a more correct term for it would be 'acceleration leaning slider' on newer ECU's).. Quite often when this needs to be applied it is because the map (usually at low rpm high load) is too rich, or vacuum or gas pressure sensor piping means the map sensor momentarily reads incorrect pressure when blipping the throttle. 4.6.6 Is not an accurate description of how the acceleration slider works on older ECU's... Since older ECU's only calculate gas injector pulse duration from blue blue with black stripe wiring then would expect them to give cylinder A fuelling which corresponds to petrol injector input A (same as the newer ECUs so far), then (4 cylinder install in this example) for C, D, B (in that order according to firing order) give each LPG injector increasing fuelling to account for rising load when noticing quickly increasing map (so 'acceleration enrichment slider' is an entirely appropriate term on older ECU's)... The enrichment is a fudge factor / approximation on older ECU's, only necessary because they do not actually use signals from red red with black stripe (cylinder 2), green green with black stripe (cylinder 3), yellow yellow with black stripe (cylinder 4) wires, instead they have to approximate the enrichment for cylinders 2,3 and 4 and the 'acceleration enrichment' slider is a control which affects this amount of enrichment. The default position for slider in newer ECUs is full right, which we agree is the off position on newer ECUs. The default position in older ECU's isn't always full right (and full right could often bring about misfires on CDB due to overfueling during acceleration).. the default position was in the middle in some older AEB ECU's depending on brand and year and this would allow a fairly wide range of adjustment during acceleration, with even the default middle position giving some acceleration enrichment. The slider was/is far more useful on older ECU's because the ECU does need to compensate for acceleration on channels CDB, because it bases LPG injector pulse length only on petrol injector A pulse length, while engine load can increase in the time between injector A pulsing and any of the other injectors pulsing during the same 720 degree complete cycle of the engine. The fact that the difference between individual cylinder loads can be more different at low rpm than they can at high rpm (for any given rate of change of throttle position / manifold pressure / engine load) also goes a long way towards explaining why correct setting of the acceleration enrichment slider position is more critical at low rpm than at high rpm (manifold pressure / engine load can increase at a particular rate regardless of rpm, so at low rpm there can be a greater difference between individual cylinder loads than at high rpm). In any event, this seems to be the way the older ECUs really work regardless of what documentation says, and from a technical point of view for ECU's that base a full cylinder bank of LPG injectors pulse durations (4 in case of 4cyl or V8 engine, 3 in case of a V6 etc) on the petrol injector duration of only the first cylinder (1 of the 4 or 3) in that bank this certainly makes sense. There have been several ways in which the acceleration enrichment slider works and it's default position depending on brand, year of ECU (board), firmware and software. Changes to the acceleration slider and even the basic principals of operation of the ECU's have seemed to come about quietly without announcement from AEB.
Edit - I just dug out old Bigas instructions (in Italian) and entered the text regarding acceleration enrichment into an Italian to English web convertor.. The English conversion reads 'The acceleration enrichment function is used to grease the carburetion during acceleration, to make such a change, you need move the cursor'.. No mention of full right being off or of 'leaning sometimes being necessary' and in the diagram the default position is in the centre. Dunno about you but 'greasing' doesn't imply to me that full right is off with anywhere to the left leaning the mixture - to me this seems like cursor in the middle is an ECU designer anticipated amount of enrichment required during acceleration. This was in documentation that came with software version 5.. You'll know what year V5 Bigas software came out
I haven't written any of the above to criticise any ECU's, old or new, at all, and I would never go out of my way against TinleyTech, a great supplier. Just observations and points that had to be taken into consideration during the repair on Himselfunknown's vehicle (he is considering fitting the newer ECU so will need to know that if he does he will need to reconnect plug C to injector C, disconnecting injector plug D). Years ago I started out almost exclusively fitting OMVL ECU's (sometimes Bigas, etc) - Those I fitted years ago are by now the older ECU's I refer to above and I still like/rate them. These days I fit new AEB ECU's on most 8 cylinder vehicles I convert. The 'fudge factor' necessary on older systems generally worked well - this will be because it was in any case only a fudge factor in a similar way to the fudge factor petrol ECUs also employ during acceleration. Waiting until a petrol injection pulse is received before beginning LPG injector pulse should be the aspect that makes newer ECU's a better bet in many cases on modern engines (some of which run Atkinson cycles, variable cam timing, cylinder shut-down, extra injection on only some cylinders on a bank, etc) rather than more accurate fuelling - both are capable of accurate fuelling during acceleration but the newer ECU's also in theory supply that fuelling at the correct moment and with filtering done on individual cylinders. No need to explore my choice of wording in the last couple of sentences or that might unfortunately open another can of worms. Some of the most basic processes in firmware would have to have been much re-written during the change from only reading petrol injector pulses from one petrol injector on each bank (and having to calculate enrichment for other injectors) to the more recent fully sequential method of operation (reading all petrol injector pulses, where the default for 'leaning during acceleration' is off). Might expect there to have been hardware changes too, in which case this might be further reason for changes to firmware. The look of ECUs (8 cylinder versions particularly), the wiring looms, the external sensors and look of software are the most similar aspects between old and new ECU's but they do the job in different ways - some of the software controls have different effects as a consequence (the acceleration slider is an example).
There are other ECU's around that have been described as fully sequential when really they are far less fully sequential than older AEB systems.. AG on many sequential petrol injection V8's employ only four cylinder's worth of LPG injector driving outputs with LPG injectors wired in parallel - so that's putting a half group LPG system on a sequential engine. Despite this, AG was/is regarded as a premium system in other European countries, even though it cannot match the fuelling strategy of even a very old slave type sequential AEB ECU... It doesn't matter much with LPG (especially on older engine designs) if it is injected way ahead of the particular cylinder's inlet stroke way ahead of when the petrol injector would usually inject fuel because LPG will not wet the manifold or port walls like petrol would, but even the old AEB ECU's do account for enrichment on acceleration, which is something which cannot be done for all cylinders if LPG injectors are wired in parallel.
Simon