Rover 2.5 KV6 Bigas - persistent regular misfire

[stewart_ingram]

I have posted this info elsewhere with no response so far, so a little bit of cut & paste:

Rover 75 KV6 2.5 ‘Y’ plate

This car was diy converted a few years ago, and was checked over & certified by a reputable fitter. He commented at the time that it took a while to calibrate but eventually it
took ok. (See later comment). It seemed ok to drive; being the 4th conversion of mine I felt ok with it, though there were 1 or 2 minor issues of fitting that I wanted to tidy up later, mainly for tidiness. Eventually, I felt that it wasn’t quite right & started investigating; 1st replacement was a single known faulty ignition lead. From then on things started to go wrong. As part of the investigation I also decided to get on with the tidy up, and have never been able to cure the fault, though it has mysteriously gone for a while before re-occurring.
At this point I should add that I am not a trained mechanic, though since I started driving in 1967 I have done all my own car maintenance, only recently have I ever trusted a garage to do anything for me. I was overseen by my grandad in the early years, he was in the car trade. Myself, I am an electronic comms engineer by trade.
The car is fitted with a Bigas system, with 2 banks of 3 injectors, each bank serving one side of the V6 engine. The fault I am trying to rectify is a regular misfire, which I have deduced is on no.5 cylinder. This is proven by idling the engine on lpg, and in turn disconnecting the injector electrical supply plug for each cylinder. If a difference in running is noticed, then that injector/cylinder is proven as running ok. But if no change, then that cylinder is the faulty one. The fault has gone at times, for no apparent reason; then suddenly come back in a similar fashion. This seems to happen whilst the engine is stopped; upon restarting & changing to gas the condition has changed. There is no occasional misfire, such as noticed with a dirty plug problem. If the engine is revved on lpg to say 2500rpm, then on switching to petrol it increases to 3000rpm & runs smoother. (Coincidence that 1 cyl not working is 1/6th of o/p which equates to 500rpm in this instance?).
I will in a moment list all things that have been changed or checked; but during this process I have effectively re-installed the system, and discovered that (possibly from new?) I had crossed over 2 wires on the ‘cut leads’ to the petrol injectors – hence the initial calibration problem? Whatever, that fault is now rectified.
In no order of checking, but more an ease of listing, the following have been done:
Tank connector/fuel gauge float (pickup was faulty)
Metal pipes rear to front etc checked for damage
Front solenoid valve & internal filter (damaged by me)
Vapouriser replaced (faulty thread which was originally repaired)
Inline filter (removed with no effect, now replaced as assumed ok)
Lpg Injectors relocated, so as to allow heavy ends to drain. One in the original kit was damaged before the original install; I asked Tinleytech to sell me another bank, which he initially refused as he said they were balanced pairs. However 1 bank was eventually purchased & fitted ok. Later on, I found another one had been damaged by the bonnet. Luckily I had bought a secondhand bank of 4 from ebay; I rebuilt the damaged bank with bits from the 4-bank, it is very easy to do. At this point I found the 3-bank I had purchased had different strength springs to the other 3-bank, so these were replaced with parts from the 4-bank, so that all 6 are the same build. This gave a distinct improvement but not full repair. I have also swopped wiring & o/p hoses over from cyl5 to other cylinders to try to eliminate the original injector 5; the fault remains on cyl 5. Also the 2 banks have been similarly swopped over. This includes the large diameter feed hoses from the ‘Y’ just after the vapouriser.
o/p hoses have been replaced due to re-routeing. Brass nozzles have been blown through with air, also physically removed and visually checked as clear.
An early failure of a relay in the lpg ecu, controlling the solenoid valves, saw this wired out & the solenoids wired via the ignition switch. This relay has now been replaced. 2 other relays in the ecu have also since failed & been replaced; these were for the petrol injectors.
Water flow through the vaporiser has been checked for air bubbles and bled in different ways, there is no problem here.
Spark plugs were replaced with new. Not good; within a few months I replaced them again (quite recent) with new iridium plugs – a startling change!.
New plug leads have been fitted.
Plug/lead/coil from cyl 5 has been swopped with cyl 3; fault remains on cyl 5 proving components ok.
Voltages on injector i/p plug for cyl 5 compared with other cylinders & shows ok with a digital meter.
Voltages on lpg injectors compared ok with a digital meter, also waveform with a usb oscilloscope. Though I haven’t at this time gone in depth with this, they appear ok between cyl 5 & others.
Petrol injector voltages also checked with a digital meter to prove they are being turned off when on lpg
Continuity checks of cableform from lpg ecu to lpg injectors, petrol injectors, petrol ecu, etc checked.
Calibration of the lpg software has been done numerous times. Sometimes it refuses to calibrate but at other times does go in.
I’ve not had access to a T4 but have had other readers on the car at various times and cleared past faults. The last time I was left with air intake motors as a fault, though I had recently rebuilt them. I’m not sure if this is therefore current, but can’t see this as having any effect?
Obviously with this fault I do get engine warning lights. However if I run solely on petrol for a few days they do clear. On occasions though, when clear, I do get a quick ‘check engine’ flash up with in 30secs of startup on petrol.
(As an aside, a recommendation of a suitable cheap reader for the car would also be helpful – I have purchased one a while back but cannot get it to talk with the car).
Any suggestions welcomed

Stewart

[stewart_ingram]

Further to originally writing the above, I have done a little more work. From someone else's suggestion, I have clamped in turn each of the injector o/p hoses to the brass nozzles. No.5 makes no difference thus once again pointing to a cyl 5 fault.
I have a USB oscilloscope, which I have used to check the pulse waveform to the injectors. Now it is not the most user-friendly piece of kit, but I did get some interesting results. Firstly connecting to a good injector feed, actually on the o/p of the gas ecu (so eliminating car wiring) I got a representative trace. This was also confirmed the same on a 2nd injector feed. When checked on the no.5 feed however, the top half of the trace was almost totally compressed, but if the actual injector was unplugged then the top half of the waveform showed though at a lower level than the good ones. Possible low pulse o/p being attenuated by the load imposed by the injector?. I had a look in the ecu; potentially there was a dry joint on the o/p transistor but this was resoldered and had no effect.

[Tubbs]

Hmm, personally i would firstly get yourself a code reader that works and reads live data, because you are pissing in the wind without one.
If you suspect number 5 then change over the injector to number 6 on the pipes and see if you can move the problem. If the fault still shows on number 5 then swap coils over and see if the fault moves. If it doesnt swap the spark plugs. If it stays on number 5 do a wet and dry compression test...
But ideally you want to change all 6 injectors for new ones.
If you suspect number 5 injector channel ecu side then swap the wires over number 5 to 6...does it move to number 6 ?

[stewart_ingram]

Just to clear up confusion.

I have swopped coils of injectors over (ie stripped injectors down to do this).
I have swopped whole bank of injectors over.
Ihave swopped o/p pipes to nozzles over.
I have swopped spark plugs/leads/coils over.

The fault remains on cylinder 5

I have checked with oscilloscope on ecu o/p connector (before the car wiring to the injector) which is where I've found the odd waveform).
I have conn checked wiring from ecu to all injors (lpg/petrol).
I have done compression tests on all cylinders.

[rossko]

Well if you think the fault is ECU output no.5, swap the connector with some other injector on the same bank. The injection sequencing isn't desperately important.

I spent hours looking for a single cylinder hiccup that turned out to be a flap of rubber inside the relevant injection pipe.

[Charlie Renard]

Suspect injectors - as I understand it, they are set at the factory using dial gauges (to adjust the height of the seat) randomly swapping parts from one set to another will never give good results.
Connect one of your 'good' injectors to cylinder 5 to eliminate the ecu/wiring.

[stewart_ingram]

Suspect injectors - as I understand it, they are set at the factory using dial gauges (to adjust the height of the seat) randomly swapping parts from one set to another will never give good results.
Connect one of your 'good' injectors to cylinder 5 to eliminate the ecu/wiring.

I repeat again - I have swapped good injectors to no. 5 and the fault stays on no5.

[stewart_ingram]

Well if you think the fault is ECU output no.5, swap the connector with some other injector on the same bank. The injection sequencing isn't desperately important.

I spent hours looking for a single cylinder hiccup that turned out to be a flap of rubber inside the relevant injection pipe.

All hoses have previously been checked and swapped.
Strangely enough, whilst driving this morning, I had the inspiration to use no.7 o/p from the ecu! The sequence is not set in stone within the ecu, it can't be as different engines have different firing sequences. The i/p signals (for each cylinder) to the ecu are derived from the 'cut leads', effectively the pulse derived from the petrol ecu for the respective cylinder, and diverted via the lpg ecu for use either by the petrol or lpg injector as required. Cyl 5 is ok on petrol so I know that the i/p wiring is ok; and I get an odd pulse waveform at the o/p of the lpg ecu, which just leaves the internals of the lpg ecu. By my reckoning, swapping 5 i/p, 5 petrol o/p, & 5 lpg o/p, with those for no.7 *should* hopefully find a good route through the lpg ecu. The proof of the pudding....? If this rain eases off this morning, I shall give it a go. If it works that is £300 saved!

[rossko]

I think the difficulty with using a "spare" channel is that the ECU would like to know if it is 6 or 8 cylinders, and will complain about "missing" ones. You could always try the swapsy for diagnosis before going to trouble of rewiring ...

[stewart_ingram]

Well if you think the fault is ECU output no.5, swap the connector with some other injector on the same bank. The injection sequencing isn't desperately important.

I spent hours looking for a single cylinder hiccup that turned out to be a flap of rubber inside the relevant injection pipe.

All hoses have previously been checked and swapped.
Strangely enough, whilst driving this morning, I had the inspiration to use no.7 o/p from the ecu! The sequence is not set in stone within the ecu, it can't be as different engines have different firing sequences. The i/p signals (for each cylinder) to the ecu are derived from the 'cut leads', effectively the pulse derived from the petrol ecu for the respective cylinder, and diverted via the lpg ecu for use either by the petrol or lpg injector as required. Cyl 5 is ok on petrol so I know that the i/p wiring is ok; and I get an odd pulse waveform at the o/p of the lpg ecu, which just leaves the internals of the lpg ecu. By my reckoning, swapping 5 i/p, 5 petrol o/p, & 5 lpg o/p, with those for no.7 *should* hopefully find a good route through the lpg ecu. The proof of the pudding....? If this rain eases off this morning, I shall give it a go. If it works that is £300 saved!

OK had a brief look this morning and CURED IT
Though I was musing over changing cut wires as well as lpg injector feed, in practice I only needed to change the plug over on the lpg injector. I had a look at the diagram, and the wiring table I had created showing my install, and found it not necessary to vary the cut wires. So no need for any dismantling to get at the ecu's!
I have actually used crimped bullet connectors to join the leads anyway, polarised too, and everything colour-coded with cable ties, so it would have been an easy unplug/replug job, but as I said, not necessary.
So it is now running sweetly on lpg, no rpm variation from petrol, just needs a re-calibration to check that it is ok. As I have to go out shortly that will wait till later.

My supposition of how it works is this.
The petrol ecu is programmed with the basic firing order of the cylinders, and checks various sensors around the engine to adapt any o/ps that it makes as necessary. Basically for each cylinder in turn, it will provide a pulse to the ignition coil, which in turn sends a hv spike to the spark plug. This is modified to requirements by the ecu. Also a pulse (call it an 'impulse') is sent to the petrol injector; again modjfed in shape/duration as required, by the petrol ecu.
When modified for lpg running, the impulse lead is routed via the lpg ecu. In petrol mode, it passes through the contacts of a relay at rest, to get to the petrol injector. This occurs individually for each cylinder.
In lpg mode, the impulse lead goes into the lpg ecu as before, is cut off from feeding the petrol injectoras the relay is now energised, and feeds instead to internal circuitry in the lpg ecu. I have no diagrams for the internals, & can only hazard a guess at what happens there, so will refrain from comment in case I am wrong! However it is theen processed by the lpg cpu in there - common to all cylinders, as this adapts during calibration to optimum settings - then is fed out on a dedicated pin to reach the lpg injector.
It must do this sequentially, as told to do so by the petrol ecu, because if it is only using 6 cylinders the remaining 2 are ignored. There is nothing in programming to set up the order of use. So swapping no.5 (faulty) with no.7 (spare) substitutes that in its place.
Anyone know different please enlighten me, all I know is that it now works!

Stewart

[rossko]

How it works all depends what sort/age of Bigas system it is and how you have it configured (sequential, group) . So you now have no connection to LPG cyl 7 input and no connection to LPG cyl 5 output, but output 7 connected to the real LPG injector 5?

[stewart_ingram]

Originally I had 1/2/3/4/5/6 connected with 7 (bank 1) and 8 (bank 2) disconnected. All I have done is make the feed to 5 a spare, and used 7 as the new feed to 5. All works ok and it calibrated in a remarkably quick time. Never actually had it as good since installation.

[Tubbs]

So what you are saying is that all the injectors fire irrelivant of how its configured ? So it fires all 8 regardless ? I know the new ecus dont. You would have to move the cut injector loom over to one of the spare channels. And then as ross says it may well complain about the missing pulses on an 8 cylinder configuration. But hey if its sorted, its sorted ! So thats good news then...are you sure its set on sequential, not part or full group ?

[stewart_ingram]

Definately set on sequential.

My theory is that it sees the 1st impulse, and directs that out. Then follows through in sequence; directing the o/p to the next available port. If 2 are missing (ie 7/8 on a 6-cyl car) then it only routes those 6 out. You don't actually tell it via programming that it is 5-6-7-8 cylinders so how does it know.
I always assumed that as the injector leads are numbered (lettered?) A-B-C-D that it would do these in sequence, but again, if the firing order changes on different cars, again you don't program that in? All it has to go on is the order of impulse signals that it gets.
I suppose again that the spare cut-wire on each bank should have been used, but that surely would have confused it over what it is seeing as impulses from the petrol ecu?

Anyway, it works and that is what matters.

As regards the injectors, I used to believe what I had been told, about precision calibrated items etc, but on stripping one down, through necessity, there is no way that is true. Component parts made to good standards, yes, but just the method of assembly can lead to differing standards of precision adjustment. They are only a steel piston, spring loaded, in a brass tube, with a 'rubber-like' cushion on the head. When I discovered the differing springs inside mine, I could see the lack of spring pressure was not seating it properly in the closed position. In fact I stretched 1 spring to give more pressure at 1st, and it worked! Never believe all you are told, especially if you are used to repairing things! (Old age/old school engineering showing here ).

[rossko]

You don't actually tell it via programming that it is 5-6-7-8 cylinders so how does it know.

Because you tell it
http://www.motogas.com/software/ISGI036 ... _7_ENG.pdf
(page 7)
or this is an old SGIS (not SGIS-N) system?

All it has to go on is the order of impulse signals that it gets.

Yes. In your case it ought to wait forever for a number 7 trigger ...

Anyway, it works and that is what matters.

Just so long as you are sure it is actually running gas on cyl5 and not leaving it in petrol mode - later ECUs wait for trigger pulses before switching individual cylinders. Early ones are as simplistic as you describe. I did mean what I said about operation depending on age/version of system.

I used to believe what I had been told, about precision calibrated items etc,

Regardless of what you feel about the build quality, the important thing about any injector (including petrol) is that this kind of system is totally dependent on all injectors performing alike. Opening times, closing times, flow rates must all be well matched.
There are many threads on here about poor performance, entirely due to simple deterioration of the rubber cushion affercting open/close times.

[stewart_ingram]

OK last call I think.

Just for peace of mind on my part, today I also swopped over the 'cut-leads' from cyl 5 to cyl, so they now match the injector 7 (which is of course feeding injector 5). There was no change in performance. TBH in my mind I should have done this anyway, it sounds more right in my opinion. But hey-ho, it worked the other way too!.
I also checked yet again that it is definately running on lpg, by clamping each feed hose in turn.

[Tubbs]

Tbh i wouldnt be happy about leaving the injector wiring on a different channel to the one that was firing the gas injector either....