Ben Jordan Posted February 2, 2006 Share Posted February 2, 2006 As you have all probably noticed by my threads lately in am having a right s##t time with my Land rovers. A couple of days ago my Rangie was brought out of storage to be used as my daily driver for three to six months. It is a 3.9 Efi with LPG. Anyway due to the LPG garage not being open i took the Rangie to work on petrol for the first couple of days, no problems. On the way home from work on the second day i stopped of at the garage and filled up with LPG. As i set off i changed to LPG and every 50-100 foot it backfired. I thought that this was very strange, as I have never had one problem with the LPG. I thought it was through lack of use and would clear up. After half a mile it was still doing it and i changed back to petrol as i did so the engine died, i managed to get the Rangie off the road before i lost momentum. I tried restarting it and all it did was hunt between 1000 - 1500 rpm for about 10 seconds before stopping. I tried getting it into gear and moving to totally clear the road but it would stall as i got it into gear. I got the bonnet up, started it up and ran around to the engine to see if i could find the problem, as i did so i could hear a large sucking and saw that the Air flow meter to Manifold hose was sheared in half. I assumed this was from the back firing as the LPG injector was very close to this point. I was outside a DIY so i went and brought some black nasty and bodged the hose back together and went home on petrol. Does anybody know what is causing the back firing and surely the LPG didn't find ignition inside this hose to blow it in half? Quote Link to comment Share on other sites More sharing options...
Fatboy Posted February 2, 2006 Share Posted February 2, 2006 Ben, I replied on your other post, I'd go for: Camshaft (worn) . Timing. because it is cheap to adjust. Little trumpets causing or contributing the rough running. Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 2, 2006 Author Share Posted February 2, 2006 So if i didnt have one problem with it before parking it up, what would be the problem? Quote Link to comment Share on other sites More sharing options...
Fatboy Posted February 2, 2006 Share Posted February 2, 2006 So if i didnt have one problem with it before parking it up, what would be the problem? Ben, Maybe the dizzy cap, rotor and plugs have oxidised a bit therefore your spark is weaker than it was and now its amplifying the deficiencies of the cam? Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 2, 2006 Author Share Posted February 2, 2006 I have just taken it out on petrol, on tick over its seems as if its missing. You can feel a rhythmic lumpiness. Its same on cruising the power seems to be pulsing. Faboy, you are convinced it's the cam aren't you? Quote Link to comment Share on other sites More sharing options...
Fatboy Posted February 2, 2006 Share Posted February 2, 2006 Ben, You could spend a couple of hours and check: Plugs, Distributor Cap and Rotor Arm. Whip the plenum chamber cover off and check the trumpets. Check the timing. You are still running with the bodged up hose so that won't be helping airflow control... Look at the state of the oil as an indicator for piston rings etc. I don't think a compression test necessarily confirms the state of the cam because mine was fine but the exhaust lobe on No3 turned out to be almost as round as a bearing surface The cam isn't really a massive job but if you were going "in there" you may be tempted to do the head gaskets, timing chain and gears (for sure) etc. What mileage has it done ? Quote Link to comment Share on other sites More sharing options...
nas90 Posted February 2, 2006 Share Posted February 2, 2006 What LPG system? Do you have 8 injection points in the plenum or single point injection for LPG? Clean the filter in the LPG vapouriser (regulator), clean the stepper motor plunger, fix the airflow hose. If you have single point injection this will probably be the cause of backfire with your engine. Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 2, 2006 Share Posted February 2, 2006 What LPG system? Do you have 8 injection points in the plenum or single point injection for LPG?Clean the filter in the LPG vapouriser (regulator), clean the stepper motor plunger, fix the airflow hose. If you have single point injection this will probably be the cause of backfire with your engine. Mine tends to backfire if I start on LPG (common on all venturi type setups, I think), but the only time I've had a really serious misfire it was ignition timing. Ironically I ended up limping home on gas because once it had blown the intake pipe apart the petrol ECU was too confused to run. In fairness, though, that was a really serious ignition timing problem. Some pillock (that'll be me then) had put the ignition cables on wrong, despite rechecking them several times... Quote Link to comment Share on other sites More sharing options...
Niall_CSK Posted February 2, 2006 Share Posted February 2, 2006 Almost certainly ignition, especially if it's been laid up for a while. Distibutor bob weights could be stuck, look out your storbe and do a search on my posts for how to test. Pulsing on petrol indicates you could have another air leak caused by your "frontfires" on LPG. Look over all the hoses carefully, older hoses that have hardened could be cracked or broken and just so rigid with age, wish that happened with me!, that you can't see the break. Quote Link to comment Share on other sites More sharing options...
Rocket Posted February 2, 2006 Share Posted February 2, 2006 Ben The backfire is an ignition problem. LPG puts a much greater strain on your HT system than petrol. by that I mean it is harder for the voltage at the spark plug to jump the gap when running on LPG. This means that the voltage on your HT system is higher which means it will take the easiest path and if there is any weakness in your Distributor cap or HT leads it will take this route rather than the spark plug. Eventually it will ignite the LPG on one cycle effectivley causing an explosion in your inlet tract and rupturing your airflow meter hose. Classic symptoms! This can also be exacerbated by a weak mixture. My suggestion. Go through your HT system and replace anything old and weak paying particular attention to HT leads buy the best replacements you can afford. Magnecor are the best. Drain out your LPG Vapouriser or better still strip it and check the diaphragm. The lumpy running on petrol could also be the HT system now showing its deficiencies on petrol but my bet is an air leak between the airflow meter and the manifold. First make areally good job of your taped up bodge. DO NOT PUT A NEW HOSE ON YET, until you have cured the problem. If you have to because yours is too badly shredded, don't do the clamps up too tight so that if it backfires again it simply pops the hose off rather thn destroying it. Check that none of the vacuum or vent pipes have been blown off the plenum housing (giving rise to air leaks0. Your ignition timing would be better advanced by a few degrees for optimum running on LPG and running on petrol won't be too adversely affected although the best solution is an RPI ignition amplifier which gives lovely sparks and different ignition advance depending on which fuel you are running on. A new Diaphragm, a set of Magnecor leads and an RPI ignition amp completely transformed my EFI disco into a totally reliable supersmooth LPG running beauty. Cheers Quote Link to comment Share on other sites More sharing options...
Red Rover Posted February 3, 2006 Share Posted February 3, 2006 Hi all, I had a similiar problem with backfiring.My 88 runs on petrol or lpg.Every now and again I switch back to petrol just to make sure it's working OK.The last time I did this,it would not run on petrol.I went back to lpg and when I got home I did a little troubleshooting.I remember having a few backfires while on lpg and I pulled the hose off the air flow meter and found that the flapper was binding.I thought the shaft was bent but it turned out that the diecast flapper was distorted.I managed to straighten it by belting it with a drift and a hammer until it was free again.Now it runs on petrol again,idling is a little erratic but it does not stall.I think my backfires were caused by too large throttle opening at too low a speed(too lazy to change down) on a cold motor. Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 3, 2006 Author Share Posted February 3, 2006 First off im going to buy a new set of Magnecor leads and service the Dizzy. What do i need for the Dizzy? A Dizzy cap? Rotor arm? Anything else? As for the Magnecor leads will i notice a difference between the 8mm and 8.5mm leads? Where is the cheapest place to get this stuff? Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 3, 2006 Author Share Posted February 3, 2006 A new Diaphragm, a set of Magnecor leads and an RPI ignition amp completely transformed my EFI disco into a totally reliable supersmooth LPG running beauty.Cheers Where does the RPI ignition amp fit into the system? Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 3, 2006 Author Share Posted February 3, 2006 Has anybody dealt with these people? and what do you think about these leads? HERE!! Quote Link to comment Share on other sites More sharing options...
Rocket Posted February 3, 2006 Share Posted February 3, 2006 Where does the RPI ignition amp fit into the system? Ben I don't know the cheapest place but RPI can supply your needs and Chris is very helpful and knowledgeable on LPG and anything Rover V8 http://www.rpiv8.com/electrics-1.htm#Poweramp Basically you remove the ignition amplifier already bolted to the side of your Dizzy and replace it with the RPI unit although it is big to mount on the Dizzy so you can mount it on the wing. Close to the coil and your vapouriser is good as you need to run wires to both. The thickness of the Magnecor leads just makes it more difficult to clip them into the cable guides on your engine but they will fit. Good Luck B) Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 4, 2006 Author Share Posted February 4, 2006 The thickness of the Magnecor leads just makes it more difficult to clip them into the cable guides on your engine but they will fit. Will the thicker ones give better results or would i not release the full potential with the thicker ones? Quote Link to comment Share on other sites More sharing options...
Rocket Posted February 4, 2006 Share Posted February 4, 2006 Will the thicker ones give better results or would i not release the full potential with the thicker ones? Thicker is better from an insulation point of view. There is no possibility of voltage going astray! Plus they are guaranteed for 10 years I beleive. Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 5, 2006 Author Share Posted February 5, 2006 So it is only the insulation that is thicker not the core? Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 5, 2006 Share Posted February 5, 2006 Has anybody dealt with these people? and what do you think about these leads? HERE!! I'd say they're overkill... A set of decent Mallory or similar (or even new OEM) should see you good. Just steer clear of cheapo leads. Lund engines will do a set of Mallory 8mm leads for about two thirds of that, assembled to your spec (so turn around might not be so quick, but the ends will all be done for you). Direct link here, but it's a frames based site, to click here if you want navigation (it's under engines -> ignition). Plenty of other places do Mallorys as well. Thicker is better from an insulation point of view. There is no possibility of voltage going astray! Plus they are guaranteed for 10 years I beleive. I'm not an expert, but I thought the current was carried on the surface of HT leads? Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 6, 2006 Author Share Posted February 6, 2006 I have just spoken to somebody at RPI, think it could have been Chris. Anyway one of the checks he told me to do was check the vacuum advance. i pulled the vacuum advance pipe off the plenum and sucked on it. No movement, nor was there any suction to hold in the pipe if you know what i mean. So this could be my problem. What is the best way to cure it? Can i buy just the vacuum advance unit? Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 6, 2006 Author Share Posted February 6, 2006 Would having no ignition advance cause me to lose power with higher RPM? And make the fuel consumption go up? Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 6, 2006 Share Posted February 6, 2006 I have just spoken to somebody at RPI, think it could have been Chris. Anyway one of the checks he told me to do was check the vacuum advance. i pulled the vacuum advance pipe off the plenum and sucked on it. No movement, nor was there any suction to hold in the pipe if you know what i mean. So this could be my problem. What is the best way to cure it? Can i buy just the vacuum advance unit? Yep - they're about thirty quid and dead easy to change. Would having no ignition advance cause me to lose power with higher RPM? And make the fuel consumption go up? Could do - I ran without vacuum advance for months. Not sure it affected the fuel consumption much but it definitely lost power at high revs. Quote Link to comment Share on other sites More sharing options...
Rocket Posted February 8, 2006 Share Posted February 8, 2006 I have just spoken to somebody at RPI, think it could have been Chris. Anyway one of the checks he told me to do was check the vacuum advance. i pulled the vacuum advance pipe off the plenum and sucked on it. No movement, nor was there any suction to hold in the pipe if you know what i mean. So this could be my problem. What is the best way to cure it? Can i buy just the vacuum advance unit? Ben they are hopeless things, I think if you checked 10 of them most wouldn't work. I replaced mine when it failed (bloody expensive!!!!!) but didn't notice much difference in running but then the V8 s don't seem particularly fussed about ignition timing so I can't see what a couple of degrees of vacuum advance is going to do. I certainly don't think it is the root cause of your problem although if there are other faults this probably won't help. Quote Link to comment Share on other sites More sharing options...
Ben Jordan Posted February 8, 2006 Author Share Posted February 8, 2006 I have a new vacuum advance unit and on the way from Steve Lund i have a set of leads, a dizzy cap, rotor arm and a new set of plugs. Lets see what that does when fitted. Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 8, 2006 Share Posted February 8, 2006 Ben they are hopeless things, I think if you checked 10 of them most wouldn't work. I replaced mine when it failed (bloody expensive!!!!!) but didn't notice much difference in running but then the V8 s don't seem particularly fussed about ignition timing so I can't see what a couple of degrees of vacuum advance is going to do. I certainly don't think it is the root cause of your problem although if there are other faults this probably won't help. They are when they're running on LPG... That said, I ran my old engine for months without a working vacuum advance - it noticeably affected acceleration on petrol and very noticeably on gas, but it didn't cause any other problems. Quote Link to comment Share on other sites More sharing options...
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