Lotus Elan

Severe Misfire

PostPost by: types26/36 » Sun Nov 13, 2011 1:14 am

Well a crack in the exhaust manifold will certainly cause a back fire but I fail to see why it would cause a severe misfire, it wont improve the running of the engine as exhaust systems are designed to extract the burnt gasses as well as silence the car.
The engine is not taking air in through the exhaust valve on the exhaust stroke but expelling burnt gasses, the back fire is caused by air getting into the exhaust system through the crack in the manifold but air is not drawn into the combustion chamber.
You could run the engine with no exhaust system on and it should not misfire but it will be hell of a noisy.
Is the engine actually misfiring or is it just the impression you are getting because of the backfiring?
Brian
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PostPost by: archigator » Sun Nov 13, 2011 1:48 am

Brian, the engine does not idle as it did prior to this problem. Whenever I get the rpm's up, it starts to sputter and backfire. I assume the sputter is a misfire. Perhaps I should check the timing as well?

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PostPost by: ardee_selby » Mon Nov 14, 2011 6:58 pm

archigator wrote:Brian, the engine does not idle as it did prior to this problem. Whenever I get the rpm's up, it starts to sputter and backfire. I assume the sputter is a misfire. Perhaps I should check the timing as well?

Gary
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Gary,

+1 on what Brian has said...

Remote diagnosis is not easy without seeing, hearing, feeling, smelling, tasting what's going on, but FWIW...

Back to your OP, you wrote "I can only think that it's either ignition timing or bad gas"

So 1.0 Yes, check the timing and 2.0 I raised the question of duff fuel in Garys' saga. It has also been raised before when tuning Webers:

"Found recently that properly tuned Webers are a good way to identify having purchased sour gasoline. Can now tell within the first mile when it's a problem by the quite familiar bog, popping out the exhaust and the induction coughing. This has happened to me twice in the last month. First time it happened it caused me to take a different direction in my tuning procedure which left me totally mystified when it could not be repeated. It happened again to me last week while I was not making any changes this time. My local Chevron dealer has now really peeved me off. :angry: Only way I could have identified this problem before the Weber tweaks was maybe by the much more foul smelling exhaust fumes. Would-be tuners be wary".

(Ref: elan-f15/40dcoe-weber-tuning-t484-15.html)

So are you on the same tank of fuel since it was drained & re-filled?

Good Luck - Richard
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PostPost by: archigator » Mon Nov 14, 2011 7:50 pm

The tank was drained and refilled several months ago when I had my mechanical fuel pump rebuilt... an issue unrelated, I believe, to my current backfire problem. While I had the fuel pump sent off for repair I took the opportunity to totally replace the plastic fuel line (from tank to pump) with a new one, and I took out the tank and fuel sender to check out the inside of the st. stl. tank to see its condition. It was extremely clean. I also added an in-line fuel filter.

I've had a couple of refills since, and then my backfire issue started. I may drain it and refill this weekend. (I can save that potentially duff gas for my lawn mower.) Going to look at timing too. I'll report back...

Thanks,

Gary
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PostPost by: archigator » Sat Dec 17, 2011 2:11 am

Well, I'm back. :) I got the hole in my headers welded and patched the pinhole leak. I just reinstalled them... what a hassle!

The good news - my headers don't leak anymore!

The bad news - the engine still runs rough and there is still some backfire through the rear exhaust. I had the engine turned off and I pulled off the radiator cap and noticed that the water has fallen about 1/2-inch to where it's just visible above the top of the radiator core. (I had topped it up before I began the header removal work. No water was visible in the oil when I changed it prior to pulling the headers however. But since then (about 2 weeks) the radiator water level has dropped.) I then start the engine and as I give it gas at the carb linkage, the water in the radiator visibly drops. When I back off and let the engine idle, the water in the radiator rises again... but not to the full level that I had topped-off two weeks ago.

Is this looking more like a head gasket issue? Thanks.

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PostPost by: oldelanman » Sat Dec 17, 2011 9:46 am

Hi Gary,
Another thought......Not familiar with these new-fangled electronic ignition systems but I assume they just replace the points and condensor ? If so, when you fitted it and replaced the distributor cap did you also check the advance mechanism was moving freely? Possibly the advance cam is partially siezed on the shaft and upsetting the timing. This should be lubricated periodically but gets overlooked because it's so difficult to get to with the distributor fitted.

Also, could your varying water level simply be due to air in the system ? It's very difficult to completely fill the system with the standard set-up as the rad cap is not the highest point .. I jack up the front of the car and squeeze the top hose a few times which helps a bit to expel the air. Don't be in too much of a hurry to take the rad cap off after running the engine, make sure the recovery bottle has water in and leave the engine to cool down and top itself up from the bottle before you check the level in the rad. Sorry if this is obvious or has been covered already.
Good luck.

Regards,
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PostPost by: archigator » Thu Dec 29, 2011 4:26 pm

Mystery Solved! I revisted the carbs and found some crud in the front carb. No head gasket issues. No distributor or timing issues.
NOW SHE RUNS LIKE A SCALDED CAT! :twisted:
I'm looking forward to a happy new year in my Elan! Thanks again everyone!

Gary
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PostPost by: collins_dan » Thu Dec 29, 2011 7:52 pm

That's great! Any final determination on the water loss?

Dan
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PostPost by: archigator » Mon Jan 02, 2012 4:29 pm

Dan,

I found a small leak in the top hose connection... :?

Thanks,

Gary
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