What was the Necam Distributor Stepper Motor System all about?

[CNG]

Until my recent conversion I had a Necam Stepper factory-fit system running on my Volvo. The LPG trade don't seem keen. Always seemed to work, hence i never really questioned it, or found a strong reason to remove it.

What in essence was the reason for its distributor? Appears to be not much more than a dressed-up Lambda-fed single-point? (a la Leonardo) It IS a Leonardo save the dizzy, isn't it? Did any other manufacturers produce similar or was it a Koltec/Necam only thing?

[Brian_H]

As far as I know its just designed to reduce the amount of gas in the manifold, making it more suitable for engines that have a plastic manifold?

[LPGC]

There were a few aftermarket multi-point continuous (as opposed to pulsed injection) systems that worked in a very similar fashion to the early Koltec systems, including Tartarini (Etagas) and Landirezo

As Bri says one of the advantages of these systems compared to mixer or gas carb systems was that they injected gas close to inlet valves (a feed to each engine cylinder close to it's inlet valve) instead of a common feed to the manifold, which helped prevent backfires (if the manifold only contains air there's no explosive mixture in the manifold).

The aftermarket versions of this type of (continuous injection) systems are usually considered a stop-gap before standalone electric pulsed injection systems came along.

The early standalone multi-point electric pulsed injection systems were themselves a stop-gas before slave type multi-point electronic pulsed injection systems came along.

Even most of the early slave (gas injection output is based on petrol ECU injection pulse lengths so the petrol ECU provides the closed loop functionality) electronic pulsed systems didn't entirely follow the fuelling strategy of the petrol injection system... and some modern systems still don't.

Some of the best modern systems can just about entirely follow the petrol fuelling strategy (if set up properly) but there is a differences between a modern sequential system (sequential just means it pulses gas injectors in a sequence) and systems that can more accurately follow the petrol fuelling strategy (especially over a wider range of vehicles). Just a couple of examples - A sequential system might not wait for start of a petrol injection pulse on individual cylinders before it begins pulsing the gas injector on the respective cylinder, a system that can accurately follow the petrol ECU's strategy will. A sequential system might base LPG injector pulse lengths solely on the input from a single petrol injector pulse length, a system that can accurately follow the petrol ECU strategy will base individual gas injection pulse lengths on individual petrol injector pulse lengths.

It is (or was) quite common to have potential customers say things like 'I used to have a 1996 Merc running on LPG converted using X system, I've now bought a 2006 Honda Vtec and based on X system working very well on the Merc I'd like to have my Vtec converted using the same X system please'. What they didn't realise was that although X system could be expected to give great results on one (especially older) model of vehicle, that didn't necessarily mean it would be capable of the same great results on a different (especially later) model vehicle. The old vehicle probably didn't have VVT or run a pseudo Atkinson cycle or do extra injection, the newer vehicle probably does have those aspects, the older vehicle probably had manifold referenced petrol pressure, the newer vehicle probably has atmospheric pressure referenced (constant) petrol pressure.

[CNG]

Thanks for the full answer Simon. Although I've yet to see it on any single-point I've run, I'm sure back-fires do happen. It's not popular to say it, yet I liked Volvo's factory Necam. A Leonardo with one of those anti-blow-back intake tubes still seems attractive.To be fair to KME Nevo - it's not finished, I've yet to get the KME Nevo I have in substitute for the factory Necam to run as well.

[LPGC]

Nevo is one of my favourite ECU's, problems you're having won't be due to having fitted Nevo.

Bit different running CNG to running petrol, there's the limited parts availability for CNG for items such as reducers and the timing advance processor aspects.

Not sure if I've mentioned this before (though I expect I have) - When I've replaced Koltec systems on Volvo's with aftermarket kit I've found that remnants of the Koltec system can prevent the petrol ECU running in closed loop mode when running on gas... As memory serves there's a connection from the original solenoids (tank / reducer) wiring to the petrol ECU which causes the petrol ECU to run in open loop mode whenever the solenoids are powered up. Use an OBD scan tool to see if you're up against the same issue... If you are you'll have to break that connection between solenoids wiring and petrol ECU or it will be more difficult to tune. I might find where/how I broke that connection in my notes but again as memory serves I think it's at the dash switch for the Koltec system, disconnecting the factory switch might solve it.

[Brian_H]

To be fair to the Necam stepper system I had, it worked well for a long time with relatively little needing doing to it. When it did pack up (or got to the point I had to swap it out) it probabbly could have been fixed but the car was getting to the point where it was going to be going shortly as well, so wasn't worth putting too much effort/money into trying to get it working again, over swapping the front end out and reusing that front end kit later on (which as it happens, is a KME Nevo as well).

Unpicking the Necam wiring was interesting to say the least though!

[LPGC]

Different things happen on different Koltec equipped vehicles if you connect power to the original tank (and/or) reducer solenoid wiring (as in to utilise existing tank wiring by connecting to the aftermarket ECU's solenoid output wiring).

[Brian_H]

I'd guess that has something also to do with the fuel gauge arrangements, I know you've said some of them will drive the petrol gauge to show lpg level, the Ford implementaion (at least the one I had) had its own gauge on the switch like most other systems do.

[LPGC]

The fuel gauge arrangement, so for example on some of the Vauxhalls you can set them up so that when running on gas the standard dash petrol gauge reflects LPG level instead of petrol level (as it does on the same car with the Koltec LPG system fitted). But on other makes/models including the Volvos sending power to the solenoids using the factory solenoid wiring makes the petrol ECU run in open loop mode, which is obviously a problem for an LPG slave type system.

[CNG]

I'll cover the details in the thread, Currently the car lacks grunt and is not economical.. Necam wins - for now. If this was LPG it'd be sorted long since.
I'm convinced the issues I see have nothing to do with the KME Nevo or the legacy of the Necam. The prior Necam factory-fit has made things easy in many ways. The subsequent LPG lash-in less so. I'm using the factory-fit gauge, and the factory reducer/tank mount etc etc. The job looks very 'factory'. The whole conversion by its very nature is obscure, this makes it awkward. Yet, not truly obscure - just obscure here.

AEB's tech-sheets allude to such things - it's been done by Simon and Dai's Russian/Polish/Argentinian/Italian cousins to the point that we're tripping over Volvo white-blocks running CNG. Somewhere. Just not here. This means I can't find information too easily, or becuase of COVID, getting the frikin' parts! The bill for Nevo has the time and parts bill at mad levels. To date I'd be infintely better to have stayed with Necam. A combination of COVID / my inexperience /obscurity sits at the root of this, over Nevo per se.

i'm pretty sure a proper TAP, and Dai's eye over the now half-baked Nevo configuration will sort most of the problems. As I said I'll continue deatil in the main thread.

viewtopic.php?t=17145

[LPGC]

Still using the dashboard fuel gauge for LPG tank level when running on LPG....

Have you monitored OBD live data when running on LPG and checked to make sure that...
It is running in closed loop mode (not running in open loop mode due to legacy Koltec bits)?
With decent fuel trims?
Fuel trims change correspondingly if you adjust LPG calibration (it isn't getting an emulated lambda voltage that makes it seem like fuelling is correct on LPG when actually fuelling could be anywhere but emulation would make the petrol ECU see correct fuelling - again this would be due to legacy Koltec bits)?