P38a 1 bank rich on LPG

[Rudolf]

Hi Guys
Having some difficulty with the car when running on gas. RR4.6 Thor, Stefanelli SIS system has been fine for 35k now missing on gas. Runs fine on petrol

Live data read of OBD shows O2 sensors working correctly and short term – long term fuel trims as expected. No fault codes

When first switching to gas car misfires heavily. Bank 2 O2 sensor shows rich and STFT moves to minus 25% as stays there. This improved the misfile some. Eventually LTFT also reduces injector times and misfire reduces to a degree where it’s almost gone.

Looking at the injector times I can see that, on petrol both banks are even and on gas bank 2 is shorter, which given the above is what I’d expect.

So, what’s the problem?
As part of a service I’ve fitted new plugs and leads.
Compressions test ok
Swapped the injectors bank to bank, no change in behaviour
Swapped O2 sensors bank to bank, no change in behaviour
Whilst running on gas removed the fuel pump fuse to kill the fuel pressure, no change in behaviour, so it’s not a leaking petrol injector
Even with heavy misfire removing plug leads one at a time or disconnecting gas injectors one at a time does not really show a specific cylinder is the cause of the misfire, it’s a case of all have about the same effect.
On gas with the misfire several fault codes come up, all refer to rich mixture and o2 sensor behaviour, but this is because the mixture is rich and it does send the sensor out of range some times.

So what’s making one bank rich on gas? I’m beginning to think it might be a gas injector wiring issue or even the gas ECU, but then the injector times all show even bank to bank albeit short on bank 2 as a result of fuel trim.

Also, does anyone have a pin-out diagram for the SIS ECU , I want to check the injector wire continuity
Does anyone have the calibration instruction for the Stefanelli SIS system?

Rudolf

[rossko]

Use a stethoscope (improvise with screwdriver) to listen to the gas injectors, a silent one may be always-open.

[classicswede]

If you have swapped the injector rails over already then that should rule the injectors out.

The vapouriser could be leaking gad into the manifold and depending where the connection is it might only make one bank rich. This would settle out under load.

Is it very rich ar idle and smooths out under load or rich in all conditions?

Try and do the basics before looking at compression loss or worn cam issues

[Rudolf]

Thanks Rossko but been there done that. even connected an Oscilloscope to each injector and checked out the voltage pattern, all look the same and all sound the same.

As classicswede says I'd expect swapping the injectors over to move the fault too, but it didn't. I've checked all the pipe work and can't find a leak, additionally gas pressure is held at the injectors when stopped overnight, so no leaks there. The rich condition is present under all load conditions.

I tell you guy's I'm running out of ideas!

[andy evans autogas]

Try clamping off gas injector pipes 1 at a time in case you've got a faulty gas injector .... It sounds like 1 or more is overfueling

[classicswede]

You could try swapping the coil packs over. It could be the coil for that bank has gone weak.

[classicswede]

You could try swapping the coil packs over. It could be the coil for that bank has gone weak.

[Rudolf]

Thanks andy evans autogas and classicswede

I agree it's over fuelling as shown by the O2 output and fuel trimming and so tried clamping teach pipe some time ago, even disconnected each injector in turn, even so it's not easy to detect which cylinder is missing or making a difference. it's almost like they all contribute to the problem a little bit.

New coil pack already fitted and spark checked, trust me when I tell you, it's considerable on each cylinder!

I'm beginning to smell the scent of a new ECU.....Still before that I'd like to try and inspect all of the wiring, although that means removing the upper inlet manifold

Rudolf

[classicswede]

If the wiring loom is anything like AEB then the injector cuts will have a multi plug for each bank. You could swap the injector cut banks over and switch over the LPG injector plugs. If either ECU or wiring are at fault then the problem will move with it.

[Rudolf]

Interesting idea classicswede, bit of a trial getting the upper manifold off for an experiment, but, as I say, I'm getting a bit desperate. If I follow the above process the problem should move, am i correct in thinking that the EUC has no preference - knowledge of which bank of injectors are which, it simply matches a bank of four petrol injectors with a bank of four gas injectors

R

[rossko]

What does the other bank do while all this is going on ... it's very easy to get partial cross-bank swaps on these engines, I expect we've all seen one or two that have run like it for thousands of miles and the odd wobbly put up with, it's not as obvious as you might think.

[Rudolf]

I agree, it's very easy to cross the injector wiring over and, surprisingly, running is not that different to the feel, however, watching the o2 sensor output in live time reveals no change in the reading or fuel trim on the 'good' bank, only the 'bad' bank is rich (o2 reading around 0.85volts) which then induces STFT until a max -25% is reached when, some times, that bank goes open loop and the petrol ECU runs on the default mapping.

I would like to confirm the gas injector firing order just to be sure the leads are on correctly (mind you I would like to set fire to it and claim the insurance too) but since the wiring harness colours are pretty much the same each bank though it's hard to be sure. 1 harness is yellow, green, red, blue the other ,yellow, brown, red, blue.

Just to add insult to injury the Stefanelli web site and instruction don't refer to the harnesses being different, both are shown as being yellow, green, red, blue.

Also, it's always possible the petrol injector cut in has been made out of the expected order and so the gas injector colour line up was never correct.

Has anyone any good ideas for checking the injector firing order? if so I could then match that to the ign firing order to be sure of a match (allbeit 108 degrees earlier)

Appreciate all the ideas guys, thanks

Rudolf

[classicswede]

The good bank should have started reading rich.

has the LPG wiring been wired upto the lambda on the problem bank?

[LPGC]

Another point might be worth a mention here...

I have corrected a lot of Stefanelli systems with two reducers, some have had no balance pipe between gas outlets, some have only had one reducer's vacuum reference connected... With such a setup it can be expected to have one bank richer than the other as all pressure readings are only relevant to one bank of cylinders, the other bank might be running with a much higher or lower pressure and therefore always be a lot richer or leaner....

Simon
Lpgc

[Rudolf]

Evening all. Thanks for all the suggestions. So, what’s been happening over February? Well, over a period of days, I exposed the petrol ECU wiring and, using my duel trace oscilloscope, probed each of the injector control earth wires in turn whilst at the same time probing each gas injector control earth. In this way I’ve been able to establish which gas injector is connected to which petrol injector and so, the gas firing order. I've also been able to look at the injector trace pattern and pretty much all 8 are the same.

I’ve removed the upper manifold and checked all the wiring on the petrol injectors and also the inlet manifold gaskets for leaks. The gas harness on bank 2 was trapped under the manifold, but the wiring looks ok.

I’ve remove all the gas pressure pies to the injectors to be sure nothing has collapsed internally and nothing is blocking the feeds.

I’ve checked that the feed from each injector to the manifold is clear and not blocked or restricted.

I’ve swapped the O2 sensors side to side (although I don’t know why since it runs fine on petrol!)

I’ve cursed a great deal, since none of this made one iota of difference.

I noticed that the temperature in a morning seems to have a bearing on the running, when it’s really I have a misfire which is much worse than when it reasonably mild. When it’s cold the misfire is bad for the first 2 – 3 miles and then suddenly improves. I put this down to the ECU going open loop, but, running with the OBD reader connected and ‘saving’ the journey for later analysis proved that this is not the case. Certainly the level of fuel trim differs a lot but the ECU does not go OL.

So now I’m thinking bad connection somewhere. I took the gas ECU PCB out of the case (quite easy only 3 screws) and thoroughly inspected, guess what? Nothing to see.

As it was late I put everything back together and went to bed. Next morning the bugger ran perfectly….. a day later it was back to square one, but hey, this IS progress.

ECU removed again and re-inspected, still nothing to see not even with a strong magnifying glass, however, although they look fine I cleaned all the pins and also inspected the harness connector. I ‘flexed’ the pins on the ECU over a little to make the bind on the harness connector for a good connection and……… it’s running fine!

It would seem that the problem lay in a poor or partial connection on the gas ECU, I guess you live and learn.

I’ve recalibrated the system as far as I can but, since I don’t have any really knowledge of the Stefanelli software, it’s a bit of a guess. It seems that the only option is to do an automatic calibration and then modify three parameters, Idle, Charge and TI Exe. After auto-calibration Idle comes up at around 1 -1.2 depending on how often your run the calibration, and doesn’t seem to have much influence on the idle. Charge comes up as 1.2 and has a huge influence on the idle, so I’ve set it where it matches the O2 and STFT behaviour when running on petrol. TI Exc seems to make no difference at all and is usually set to 0.
So, does anyone know how to calibrate a Stefanelli SIS system?