Escape Posted January 5, 2009 Share Posted January 5, 2009 OK guys, I could use some help. My V8 is not running as should, and I can’t seem to find the cause. Better start from the beginning, but this does mean it will be a lenghty post. Thanks in advance for reading through it. Car is a 1995 Range Rover P38a, originally a 4.0 but after overheating the previous owner had a 4.6 installed. Not much of a quality built unfortunately. Running mainly on LPG, single point system. About half a year ago, I started getting frequent backfires. I found a faulty plug lead, replaced all plugs and leads but still got the occasional backfire. At about 50mph, when the torque converter would lock-up, the engine would run very poorly, almost like it was missing one or more cylinders. The whole car would shudder forwards-backwards with it. And fuel consumption was increasing. I then did a top-end rebuild, with some much appreciated pointers from HFH and his rebuild topic. Changed the cam for a Torquemax, heads skimmed and mildly ported, new rocker assemblies, new timing chain and gear. Started up great first time, but found out one of the cats was blocked. Took 'em both out and afterwards had a hell of a time getting her to start again. Plugs, leads, coils and CKP replaced, no definite solution but all of a sudden she came too life again. After resetting the GEMS she ran just fine, decent MPG, all on petrol as I wanted to replace the LPG system with a more performant one but didn't get round to it. Then, about a month ago, after being left in the cold for 3 days, she started, immediately stalled and wouldn't fire again. Changed the (relatively new) plugs after reading about similar experiences, and once more she was running smoothly. The plan was to use her to tow the trailer with the Defender to Slab. I did get occasional stalling when idling, but an adaptive values reset cured this. But when visiting family on Christmas day, the lumpy running with lock-up reappeared. I again hooked it up to the Rovacom, but could not find anything really wrong with it. Temperature rose as expected, from 11°C when parked inside overnight up to 90°C when driven for a while. Idle showed no more problems. Only odd thing I could find was a lowish reading for the air intake temperature (about 10°C lower then expected) and the left O2 sensor switching much slower compared to the right one. The ECU also frequently throws code ‘1021: invalid fault code’, but also did this when the engine was running fine. Consumption is through the roof and there’s always a smell of petrol about, warm or cold. So she must be running rich and thus quickly killing the plugs. I tried changing both the air intake temperature sensor and MAF, but to no effect. Plugs (standard Champions) seem to have a tendency to coke up, but giving it some revs seems to clean them OK. The air intake temperature sensor does respond to ambient temperature, when holding a lighter close to it, the reading immediately rose. I also installed a different set of O2 sensors (coming from a car with an LPG-conversion), causing the engine to run open loop all the time with maximum negative fuel trim. But the poor running remains and if anything has gotten worse, building up the revs doesn’t go as smoothly as it used to. Fuel pressure was checked at 2.5bar. Injectors seem unlikely, as the problem occurred first (last year) when running LPG and now on petrol. Next on my list are replacing the engine temperature sensor and ECU. Thanks for the pointers Nige Any other ideas you might have would be very welcome! Best regards, Filip Quote Link to comment Share on other sites More sharing options...
disco_al Posted January 5, 2009 Share Posted January 5, 2009 I would ditch the Champion plugs and slap in a set of NGK's. Oxy sensors shouldn't cause a problem on a single point LPG system, unless it uses them to regulate the mixture. Cold weather can cause havoc with LPG too. Quote Link to comment Share on other sites More sharing options...
Escape Posted January 5, 2009 Author Share Posted January 5, 2009 I would ditch the Champion plugs and slap in a set of NGK's. Oxy sensors shouldn't cause a problem on a single point LPG system, unless it uses them to regulate the mixture. Cold weather can cause havoc with LPG too. I was running NGK's, when she wouldn't start. After lot's of searching and finding the topic from HFH, I changed them for Champions (easiest to get around here) and all was fine, that is, for about a week. Only running on petrol at the moment, want to get the engine sorted out good before installing the LPG. Quote Link to comment Share on other sites More sharing options...
SteveRK Posted January 5, 2009 Share Posted January 5, 2009 Does the 4.6 use a vacuum fuel pressure regulator as per the 3.9? If so its worth checking the vacuum hose is intact. I dont quite understand what the o2 sensor/s is/are doing if you have removed the cats - are they simply feeding a fixed voltage to the ECU? Quote Link to comment Share on other sites More sharing options...
ramon alban Posted January 6, 2009 Share Posted January 6, 2009 Consumption is through the roof and there’s always a smell of petrol about, warm or cold. So she must be running rich and thus quickly killing the plugs. Thats it, right there. Nothing else matters until you fix the mixture problems, changing plugs will make no diff to the root cause. Generaly, Five component issues will cause the overfueling. # Coolant temp sensor or associated wiring faulty, check characteristics with ohm meter and continuity tests # ECU check by substitution. # Throttle position sensor. measure for electrical noise when rotating # Pressure reg, vacuum control tube not bringing pressure down when needed. # weeping injectors - perform a pressure leak down test., Less likely - the AFM is faulty - check by substitution. Quote Link to comment Share on other sites More sharing options...
Escape Posted January 6, 2009 Author Share Posted January 6, 2009 Does the 4.6 use a vacuum fuel pressure regulator as per the 3.9? If so its worth checking the vacuum hose is intact. I dont quite understand what the o2 sensor/s is/are doing if you have removed the cats - are they simply feeding a fixed voltage to the ECU? Yes, the 4.6GEMS also uses a vacuum fuel pressure regulator. The hoses have been replaced recently and I can find no leaks. The O2 sensors are upstream from the cats, as I understand it they are used to adjust the mixture to obtain a correct lambda value (lean or rich), which is necessary for correct operation of the cats. The cats don't have any effect on the reading, being downstream, so it shouldn't make a difference. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 6, 2009 Share Posted January 6, 2009 I also installed a different set of O2 sensors (coming from a car with an LPG-conversion), causing the engine to run open loop all the time with maximum negative fuel trim. But the poor running remains and if anything has gotten worse, building up the revs doesn’t go as smoothly as it used to. Can you explain how a new set of O2 sensors causes it to run open loop? I can't quite see how it can be running open loop AND applying fuel trim Cats or no cats the O2 sensors will/should still be doing their thing. I'd ignore "lowish" or "highish" readings from the coolant or air temp sensor, if they fail they usually fail either short circuit or open circuit so if they're reading somewhere near reality they're probably working - automotive sensors are rarely very accurate. Can I ask what air filter you're running? The oil from filters such as K&N is known to kill hot-wire MAF sensors. It's unlikely since you changed the MAF to no effect, but worth an ask. Quote Link to comment Share on other sites More sharing options...
Escape Posted January 6, 2009 Author Share Posted January 6, 2009 Can you explain how a new set of O2 sensors causes it to run open loop? I can't quite see how it can be running open loop AND applying fuel trim Cats or no cats the O2 sensors will/should still be doing their thing. I'd ignore "lowish" or "highish" readings from the coolant or air temp sensor, if they fail they usually fail either short circuit or open circuit so if they're reading somewhere near reality they're probably working - automotive sensors are rarely very accurate. Can I ask what air filter you're running? The oil from filters such as K&N is known to kill hot-wire MAF sensors. It's unlikely since you changed the MAF to no effect, but worth an ask. - I used the O2-sensors from another GEMS V8. But they differed from the ones I took out. Maybe they were replaced when the LPG was installed, to provide a signal for the electronic feedback system. The Rovacom indicated both banks were running open loop, with one sensor reading 'defect' and the other one 'not yet satisfied'. Fuel trim after the adaptive reset was maximum negative, but you're right I can't be sure the engine is actually using this trim value. Because the symptoms remained the same, I did conclude the O2 sensors are not to blame. - The temperature readings are changing with temperature, my guess is also those sensors should be working OK-ish. - I did run a K&N filter, but when I replaced the MAF I put a standard filter in instead. Furthermore, I believe the MAF has little or no influence on a single-point LPG system, so a bad MAF can't explain why I had similar problems on LPG before. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 6, 2009 Share Posted January 6, 2009 - I used the O2-sensors from another GEMS V8. But they differed from the ones I took out. Maybe they were replaced when the LPG was installed, to provide a signal for the electronic feedback system. The Rovacom indicated both banks were running open loop, with one sensor reading 'defect' and the other one 'not yet satisfied'. Fuel trim after the adaptive reset was maximum negative, but you're right I can't be sure the engine is actually using this trim value.Because the symptoms remained the same, I did conclude the O2 sensors are not to blame. So both O2 sensors are a different type and in a faulty state, and the ECU is either trying to lean things off massively or just confused / ignoring them and working in a default mode? I can't imagine that's helping matters Quote Link to comment Share on other sites More sharing options...
Escape Posted January 7, 2009 Author Share Posted January 7, 2009 So both O2 sensors are a different type and in a faulty state, and the ECU is either trying to lean things off massively or just confused / ignoring them and working in a default mode? I can't imagine that's helping matters Sorry, I don't think I explained right... The original O2 sensors are both working, but the left one seemed to be switching slower and with less amplitude than the right one. So I decided to replace both with those from a different car, which resulted in the left one throwing a defect and the right one not getting satisfied. The ECU did look lat is was trying to lean things of, but still a smell of petrol about and the same poor running. If I find the time, I'll install the original sensors again today. Quote Link to comment Share on other sites More sharing options...
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