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Weird missfire problem...Please help


garetheves

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Just another thought on this. I had a similar problem on mine, changed the plugs - no change. Checked coil packs and connectors- still misfiring.

Would not start on first attempt only second. Would run like a pig when it did start if it was already hot. But would'nt do it all the time.

 

After tearing my hair out decided to check the fuel filter on the pump. Where someone had fitted the walbro they had left a burr on the metal pipe and this had cut through the rubber pipe from the pump. So fuel leaking back into the tank which is why i didnt notice it but thinking about it now the fuel pressure was getting lower as the pipe split more.

 

Hope you get it sorted.

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Just another thought on this. I had a similar problem on mine, changed the plugs - no change. Checked coil packs and connectors- still misfiring.

Would not start on first attempt only second. Would run like a pig when it did start if it was already hot. But would'nt do it all the time.

 

After tearing my hair out decided to check the fuel filter on the pump. Where someone had fitted the walbro they had left a burr on the metal pipe and this had cut through the rubber pipe from the pump. So fuel leaking back into the tank which is why i didnt notice it but thinking about it now the fuel pressure was getting lower as the pipe split more.

 

Hope you get it sorted.

 

Hmm interesting. Something else to try at least. Anyone care to give instructions on how to check the fuel filter, and Walbro.

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Underneath the spare wheel there is a plate with about 10 bolts. Take this off and you will see the fuel connections flow and return + power for pump. Disconnect all these and there should be a very large hose clamp around what looks like a very large plastic nut. You will see some alignment marks. Remove the hose clamp from the nut and using a screwdriver in the notches tap the nut ccw to remove it. Once this is off you can lift out the hanger and pump from the tank. REMEMBER - NO SMOKING! You will be left with a bloody great hole in the fuel tank.

 

There should be a small filter on the bottom of the pump and check the rubber pipe from the pump to the outlet pipe on the hanger.

 

After I changed that 50p worth of pipe, problem went away. :D

 

When fitting it back together make sure you line up the marks on the hanger and tank as this means the pump will sit in the baffle in the tank correctly.

Have fun getting the nut back on. :D A small amount of wd40 might help.

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Underneath the spare wheel there is a plate with about 10 bolts. Take this off and you will see the fuel connections flow and return + power for pump. Disconnect all these and there should be a very large hose clamp around what looks like a very large plastic nut. You will see some alignment marks. Remove the hose clamp from the nut and using a screwdriver in the notches tap the nut ccw to remove it. Once this is off you can lift out the hanger and pump from the tank. REMEMBER - NO SMOKING! You will be left with a bloody great hole in the fuel tank.

 

There should be a small filter on the bottom of the pump and check the rubber pipe from the pump to the outlet pipe on the hanger.

 

After I changed that 50p worth of pipe, problem went away. :D

 

When fitting it back together make sure you line up the marks on the hanger and tank as this means the pump will sit in the baffle in the tank correctly.

Have fun getting the nut back on. :D A small amount of wd40 might help.

 

Am i right in assuming that with the engine switched off there wont be any fuel in the pipes?? I dont want to disconnect them and petrol flow everywhere. Also do any of them need clamping off or anything?? Sounds a simple enough job, may as well change the fuel filter while im there.

 

Still not 100% convinced its fueling though as my AFR's stay ok throughout the miss, but cheers for the suggestion ill try anything at this moment.

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I've read through this entire thread, and come to the conclusion that the problem is heat related, therefore, my hypothesis is that the fault lies with mechanical error, not electrical.

 

I'd get a compression check done to see if your engines compressing properly. At least it'll rule out head gasket failure or worse.....

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I've read through this entire thread, and come to the conclusion that the problem is heat related, therefore, my hypothesis is that the fault lies with mechanical error, not electrical.

 

I'd get a compression check done to see if your engines compressing properly. At least it'll rule out head gasket failure or worse.....

 

The bit thats confusing me though is just after changing the plugs it ran fine for a week. This included a trip to see my parents (approx 40 miles return - motorway) and a very fast trip to leeds and back (approx 100 miles - motorway). Was in a mad rush to leeds as well so the speed was never below 80-90 leps. If it was a temperature issue then surely it would have been aparent then.

Also the missfire has changed recently. The orriginal miss only happened at cruising speeds on the motorway. Every day to day driving was ok, now though, after changing the connectors on my coil packs it is missing at idle as well as through the rev range. Its intermittant at idle but more rythmic through the revs.

Very wierd. Am going to try and get it booked it at HSR as soon as they can but my main concern is getting it there.

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Tempted to take my plugs back out, check them all and possibly replace them again. Maybe with all the fiddling about and changing coil packs etc ive buggered up one of the plugs or something.

 

Oh and noticed something a bit worrying last night. When i first start up the car, ie before it warms up, there is a faint amount of exhaust fumes in the engine bay, which increases when i rev the engine. This settles down once the engine is warm but is a bit worrying at cold.

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Tempted to take my plugs back out, check them all and possibly replace them again. Maybe with all the fiddling about and changing coil packs etc ive buggered up one of the plugs or something.

 

Oh and noticed something a bit worrying last night. When i first start up the car, ie before it warms up, there is a faint amount of exhaust fumes in the engine bay, which increases when i rev the engine. This settles down once the engine is warm but is a bit worrying at cold.

 

I'd check the plugs again mate, when you took the old ones out, did they all look the same at the tips or was one different to the others.

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First off,they are covered in sooty deposits, which leads me to believe the car is running rich. see here

 

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

 

Also, the bottom of your coil packs have what looks like oil on them, there should'nt be oil on them. If oil is getting there, your rocker cover gasket may be leaking into the chambers and interferring with the spark.

 

Look into these things and get back to me, it has me intrigued. ;)

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right then, i checked my plugs and coils as well. there was some oil around the plugs but the firms mechanic reckoned that it wasn't enough for the problems i'm getting. we reckon the oils coming from the 2 breather pipes across the top of the coils, both are 'wet' at both ends of the pipes and the pipes are 'rock hard'. so gonna clean it out, change the pipes and see.

also checked the blink codes on the dagnostic, it came up with a pressure problem, 3-4. but i have double checked all the pipes and intercooler pipework. no luck

checking against the problems i am having and the poss cures, again we reckon its around the butterflies. IAC, throttle control, etc.

i plan on putting some serious time into the checking on the 1st week of oct (im away next week).

 

Rob

 

ps if anyone knows the part numbers it would be much appreciated. trying to search paul e's thread on numbers now but cant see what i need.

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If oil is getting there, your rocker cover gasket may be leaking into the chambers and interferring with the spark.

 

Wow, old skool Slowdog :) Oil can't leak past the plug into the combustion chambers as the plug seals in rather a high pressure during the combustion process. And even if oil was oozing in in small quantities it wouldn't be as much as the breather system is burning in there already anyway.

 

-Ian

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Wow, old skool Slowdog :) Oil can't leak past the plug into the combustion chambers as the plug seals in rather a high pressure during the combustion process. And even if oil was oozing in in small quantities it wouldn't be as much as the breather system is burning in there already anyway.

 

-Ian

 

Dude, I wasn't talking about the combustion chamber, I was talking about the part where the coil pack connections attach to the plugs themselves, If either of the cam cover gaskets leaked the oil wold collect in the area mentioned.

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  • 3 weeks later...

First time ive had any spare time to have another go at solving this. PLanning on changing all the plugs again and giving the coil packs a clean but just a quick question:

 

Could a battery that was on its last legs give a missfire like this? Reason I ask is ive just gone out to my car, and its been sitting there a good 4-5 weeks without me touching it and the battery is completely flat, must have been on the way out for the last few months and the lack of inactivity has finished it off.

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Changed battery, spark plugs and gave the coil packs a good clean and still got the missfire. Booking it in at a garage tomorrow cos ive run out of options to try. Must say though, the plugs i took out, which only had 200 (yes 200) miles on them were black as the ace of spades and there was a faira mount of oil around the actual thread of numbers 3+4, which was a bit worrying. Just wondering, in light of the blackness of them, whether its overfueling, although my AFR's appear to be ok.

 

Ah well hopefully the garage can sort it out soon. Guess ill just have to limp there.

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Changed battery, spark plugs and gave the coil packs a good clean and still got the missfire. Booking it in at a garage tomorrow cos ive run out of options to try. Must say though, the plugs i took out, which only had 200 (yes 200) miles on them were black as the ace of spades and there was a faira mount of oil around the actual thread of numbers 3+4, which was a bit worrying. Just wondering, in light of the blackness of them, whether its overfueling, although my AFR's appear to be ok.

 

Ah well hopefully the garage can sort it out soon. Guess ill just have to limp there.

 

I have EXACTLY the same symptoms as yourself. Missfire but a lot more prominent when warm/hot. I had a 12 years of service lexus technician listen to it yesterday. It took him all of 2 seconds to look up and say 'number 3 injectors fooked mate'. :search:

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