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Engine back firing..


Lotusdad

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I would greatly apprecaite any help.

I took the car on a rally today, covering about 300 miles. Its the first real drive I have given the car.

When the car gets up to speed and you ease off the throttle the rev counter drops to 0 and then bounces, the engine seems to stall and then it back fires.

It only happens when you DONT load the engine. I found that if I build up speed the boost guage climbs. The minute I ease of the throttle to maintain the speed

it happens. I find if I press in the clutch and dont touch the throttle its OK.

Any ideas... Am I looking at an electrical problem? (backfiring), why is the rev counter dropping to zero, and then boucing back to life?

Any advice would be appreciated...

Paul.

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Hey Paul,

I have an 85 TE with carbs, and I have noticed backfiring on my car also. I have kept track of when it happens, and have come to some conclusions. First off, when I am driving, and I have high revs, and let my let off the gas completely, so that the speed of the car in gear keeps the RPM's up, it gurgles and backfires. This is most likely due to the gas that goes through the engine from the carbs, with the butterfly valves closed, is a wrong mixture for proper combustion, and unburned gas gets through to the exhaust manifold, where it explodes in the typical burbling/backfiring.

The other case where my car backfires, and it does it with a super loud bang, sometimes equivalent to a seeming howitzer going off, is when I go to park my car, and have high RPM's, and turn off the ignition. The engine, as it does 40-50 revolutions before finally stopping, still sucks gas from the carbs, but with no spark, that unburned gas goes through to the exhaust system, where it takes a few seconds to heat up to the flash point, then BLAMMO!!!!. The way I found to completely eliminate the potential for backfire when turning the car off is to put it in second gear, have the clutch in, and the brake pressed at the same time, then slowly release the clutch until the engine catches and resistance slows the engine RPM's down, then at the same time turn off the ignition and release the clutch further, thus making the engine stop fairly immediately... voila, no backfire, not to mention huge embarassment, as wherever you are parking, usually has a crowd of people looking at you and the last thing you wish is for people to either get frightened, or laugh at you :).

Your Description of rpm's dropping to zero indicates an intermittent faulty ignition lead, or other wire issue in the ignition system, thus having momentary periods of time when you have no spark, but your engine is still sucking gas and air through.... thus ending up in the exhaust system, thus the eventual loud bang.

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Check all the wires on your coil.

I think from memory the rev counter is directly fed from it.

Letting off the gas in gear may jolt the car enough to disturb the connection, whereas letting off the gass out of gear will not jolt or jiggle anything and therefore not disturb the connection.

Pretty much had exactly this on an old 205 GTI of mine and the fix was as simple as squeeze the spade connector a little to make it a firmer hold on the coil.

Chunky Lover

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Certainly sounds like an electrical fault. If a car backfires it is usually when unburnt mixture dsuddenly gets ignited by the intermittent spark and the fuel in the exhaust system explodes.

As you say the rev counter drops to Zero this is certainly an electrical problem with a loose connection on either the coil or the ignition box. Good luck.

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Have a look at the connector in the lead to the distributor..three connections...notorious for intermittent faults. Also may have an issue with the leads where they go into the distributor itself, the insulation wears and they can short out to the metalwork, dumping all your sparks!!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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  • 5 months later...

Well I finally got my car back out after the long winter. All went well and after taking it for a run the problem came back

After reading the wiring diagram i am convinced its the rev limiter. I am not sure where this is located in the car any help in this area would be grateful.

Paul.

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easiest way is follow the wires. The dissy wires (not HT) lead into a black box containing the coil, attached to the rear boot floor panel (the upright section of that panel) and then a few wires come out of that box and head to the limiter, look on the rear wheel arch area on the side near the box with the coil in. They can be moved by owners, so not always the same location on every car.

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Its clearly not a carb turbo which I have and enjoy if thats the right word backfiring and gurgling on overrun - normally in 2nd gear. I have tried everything to get rid of of it to no avail and put it down to the ss exhaust system fitted, if you can call it an exhaust. It sounds fantastic but I have reached a certan age, have very grey hair and our high street is fairly narrow so I attract a lot of attention driving up and down it. The trouble is I enjoy it so much I have to keep going back, again and again.

I would like to get rid of the backfiring but then again I don't want it to sound like a washing machine so think I will live with it at age 60. Not many old folks of my age enjoy such things so enjoy the moment. Sorry but have had a few pints of sauce which is another of my failings in old age

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Rev Limiter should be on wheel arch near battery. There is a long thin plug with 3 wires that can be removed - the engine will still run fine. (mine is disconnected as it causes a misfire at high revs...) My rev counter dropped to zero whilst running with an almost flat battery while the alternator was accidentely disconnected, so I suspect the bad connection theory could be true. The rev counters themselves can also go 'intermittent' so it may simply be a faulty rev counter. Mine bangs, pops & crackles on overrun - its a tourist attraction in its own right when I can find a nice steep urban hill I can cruise down on a trailing throttle - No way am I getting rid of that!

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Its clearly not a carb turbo which I have and enjoy if thats the right word backfiring and gurgling on overrun - normally in 2nd gear. I have tried everything to get rid of of it to no avail and put it down to the ss exhaust system fitted, if you can call it an exhaust. It sounds fantastic but I have reached a certan age, have very grey hair and our high street is fairly narrow so I attract a lot of attention driving up and down it. The trouble is I enjoy it so much I have to keep going back, again and again.

I would like to get rid of the backfiring but then again I don't want it to sound like a washing machine so think I will live with it at age 60. Not many old folks of my age enjoy such things so enjoy the moment. Sorry but have had a few pints of sauce which is another of my failings in old age

Oh dear, Mike.....please don't start in with this nonsense about 60 being "old"!! I get to be 64 this year and still haven't grown up...I revel in the sounds of my Turbo, especially since by now I've pretty much built it myself...and I'm not alone on this forum; quite a few of us out there!! I'm currently building a single seater with the same 4.2 litre Audi V8 that Hilly used in his S3...now that ought to go quite nicely, I think. Better get back to hewing the engine mounts out of girders....!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Well its not the rev limiter. I took it for a run today, let things warm up and booted the car, turbo kicked in and it accellerated fine, on easing off the gas pedal, tacho dropped to zero, hunted up and down and then backfired backfired ...

If I press the clutch in and let it cost it calms down...

Any suggestions would be appreciated. I have not pulled the distributer yet as I am not sure how to get at it. The wiring to it seems to be fine.

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Cannot really help with your problem but just to cheer you up, you wouldn't be driving it yet if you lived in Quebec!

Good luck.

By the way, are you the Paul that bought a manifold (trough Steve) lately?

If so mine was in the same shipment...

Luc

Something I learned about cars or planes, it all works until it doesn't anymore...sometime there is no way around it!

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Try letting the engine idle whilst you waggle the ignition wiring about....not the HT stuff, but the rest of it. The rev counter going haywire makes me think you could have a broken wire or some failed insulation allowing the electrics to short out to ground somewhere. Scrutinise it with an intense scrute and check where the wiring goes into the distributor...

I've got a manifold paperweight too!!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Well I got up really early this morning with the intent of fixing this backfire problem. I followed everyones advice and eventually ended up at the distributor. I found if I taped it lighty the rev counter would bounce. I pulled the sprk plug leads, marked the cables with wire wrap numbers, and then proceeded to climb into the boot. I could not get my hand into the area required to remove the top clamp. I thought no problem I can flip it off with a large screw driver, but then how do I remove the lower clamp. Thats where I stopped, I could not get my hand underneath...Any advice here would be greatly appreciated...I thought that maybe the secret is removing the oil filter? So I carried on and replaced the front brake shoes...A cake walk by comparison. I took the car then for a test run to check the brakes out and boom bang the exhaust backfire was even worse, in particular climbing hills really started things off...The car rolled into my garage, and after an almighty bang I turned the engine off. wacko.gif

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By the sound of if, you're gonna need that new manifold soon!

Seriously, I've read the threads enough not to wish that to anybody.

Don't despair with the cap, time is often the solution, just make sure you have a new one standing by while you're in it.

Luc

Something I learned about cars or planes, it all works until it doesn't anymore...sometime there is no way around it!

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Well I finally found my problem of the backfiring and why it did it more on hills. It turned out to be a loose negative cable on the battery.wallbash.gif Dont ask me how but at rest the contection was good enough to start the car, but on accelleration or on a hill (battery sliding back) the connector would lossen and I would loose my ground. Since tigtening the connector, things are now quiet. I really appreciate all the help from everyone.

Paul. thumbsup.gif

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Enjoy the free fix Paul, those don't come around too often! :)

Something I learned about cars or planes, it all works until it doesn't anymore...sometime there is no way around it!

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