Engine Check Light on 2004 Monaro cv8
Discussion
This is a follow on from the spark plug thread I was running to see if I can get any help diagnosing a problem I'm having with the engine check light coming on.
Synopsis:
I've had an LPG conversion done to the car. This is the Prinz injection system (Not the old ventura system).
The car was running rough when in gas with the boot down. Also after the car was warmed when sitting in traffic sometimes the engine warning light was coming on, in either gas or petrol. So I took it back to the LPG fitters. They've spent a week going over the car with a fine tooth comb to track the problem down. It looks like they were running too much gas into the engine when the boot was down, this causing the roughness to they've reduced the gas flow when booting.
However as part of the investigation they checked the spark on the cylinders as a poor spark could also have caused the poor running under gas (more sensitive to poor spark than petrol) and if there was a misfire due to poor spark it could also cause the engine check light to come up.
What they found was the HT leads on several cylinders were arcing. I suggested changing the HT leads to Magacors but when I asked Vauxhall they threw their toys out of the pram and said I couldn't put Magnecors on. They then wanted to charge me £46.50 each to replace the 8 HT leads on the car. At this point I decided to take the car to them and let them sort the arcing under warranty.
After a couple of hours work they called back saying there was nothing wrong with the car and arcing on the HT leads was to be expected and they didn't need replacing. The engine check light didn't come on for them and the only recorded event in the computer was two occasions where the engine was running lean on banks one and two which had resolved itself. So there was nothing they could do.
While driving the car back from the dealers the engine light came on, then again when I got the car home and again this morning. The roughness seems to have stopped but I haven't really pushed the car yet.
The help I need is this. If vauxhall can't find the problem and just keep saying 'My experience says problems like this are always caused by the LPG installers' I don't think I'm going to get far with them. So we put the car on a diagnostic machine so we could watch the O2 sensors (previously suggested as a possible cause of the problem).
What we found was this.
Both banks pre cat sensors varied between 0.15 and 0.85 volts in both petrol and gas. (As expected according to the gas guy)
Both banks post cat sat at 0.442 to 0.448 volts in both petrol and gas. (As expected according to the gas guy)
While we were watching this the check engine light came up while it was running in petrol. Nothing moved out of these ranges at the time and e didn't hear or feel anything like a misfire, but then again it's not certain that we would anyway.
Has anyone got any ideas as to whats going on here, remember that the vauxhall diagnostics computer only showed two instances recorded of both banks runing lean and the warning is coming up regularly.
Thanks in advance for he help.
Stu
Synopsis:
I've had an LPG conversion done to the car. This is the Prinz injection system (Not the old ventura system).
The car was running rough when in gas with the boot down. Also after the car was warmed when sitting in traffic sometimes the engine warning light was coming on, in either gas or petrol. So I took it back to the LPG fitters. They've spent a week going over the car with a fine tooth comb to track the problem down. It looks like they were running too much gas into the engine when the boot was down, this causing the roughness to they've reduced the gas flow when booting.
However as part of the investigation they checked the spark on the cylinders as a poor spark could also have caused the poor running under gas (more sensitive to poor spark than petrol) and if there was a misfire due to poor spark it could also cause the engine check light to come up.
What they found was the HT leads on several cylinders were arcing. I suggested changing the HT leads to Magacors but when I asked Vauxhall they threw their toys out of the pram and said I couldn't put Magnecors on. They then wanted to charge me £46.50 each to replace the 8 HT leads on the car. At this point I decided to take the car to them and let them sort the arcing under warranty.
After a couple of hours work they called back saying there was nothing wrong with the car and arcing on the HT leads was to be expected and they didn't need replacing. The engine check light didn't come on for them and the only recorded event in the computer was two occasions where the engine was running lean on banks one and two which had resolved itself. So there was nothing they could do.
While driving the car back from the dealers the engine light came on, then again when I got the car home and again this morning. The roughness seems to have stopped but I haven't really pushed the car yet.
The help I need is this. If vauxhall can't find the problem and just keep saying 'My experience says problems like this are always caused by the LPG installers' I don't think I'm going to get far with them. So we put the car on a diagnostic machine so we could watch the O2 sensors (previously suggested as a possible cause of the problem).
What we found was this.
Both banks pre cat sensors varied between 0.15 and 0.85 volts in both petrol and gas. (As expected according to the gas guy)
Both banks post cat sat at 0.442 to 0.448 volts in both petrol and gas. (As expected according to the gas guy)
While we were watching this the check engine light came up while it was running in petrol. Nothing moved out of these ranges at the time and e didn't hear or feel anything like a misfire, but then again it's not certain that we would anyway.
Has anyone got any ideas as to whats going on here, remember that the vauxhall diagnostics computer only showed two instances recorded of both banks runing lean and the warning is coming up regularly.
Thanks in advance for he help.
Stu
Yes, you need to read what the check engine light is. If as the dealer says its banks 1 and 2 lean then there may be an issue with fueling or the o2's. Did it used to come on with petrol before Lpg?
The voltages sound about right. The whole idea is that they switch as the car changes from lean to rich and back, moving fueling around to "switch" the o2's constantly. This is what closed loop is all about.
I still think arcing is bad and shouldnt happen. Misfires can cause unburnt fuel and o2 to enter the exhaust making the o2 sensors read lean (due to excess o2). If bad enough this could cause the o2 lean codes to trigger. It can also force the pcm to dump in more fuel to compensate, making a real mess of things.
>> Edited by ringram on Thursday 13th April 13:13
The voltages sound about right. The whole idea is that they switch as the car changes from lean to rich and back, moving fueling around to "switch" the o2's constantly. This is what closed loop is all about.
I still think arcing is bad and shouldnt happen. Misfires can cause unburnt fuel and o2 to enter the exhaust making the o2 sensors read lean (due to excess o2). If bad enough this could cause the o2 lean codes to trigger. It can also force the pcm to dump in more fuel to compensate, making a real mess of things.
>> Edited by ringram on Thursday 13th April 13:13
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