Rover 2.5 KV6 Bigas - persistent regular misfire
Posted: Wed Jun 20, 2012 1:28 pm
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
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
).