Flat Spots while driving issues

[Stef]

So my Elan is not used that often currently but has been driving really well until couple weeks ago.

She started to experience flat spots upon acceleration, first experienced at high speed on the A14. Also experienced from pulling away.

Initially I hoped it was damp somewhere but surely that should of cleared after a few minutes if so?

I'm suspecting electrical or fuel. Any advice appreciated.

Thanks!!

[theelanman]

Id probably suspect the engine......

[Rambo]

My 1st thought was coil breakdown.

Have you done the paperclip test to see if any error codes appear

Have you got Elanscan ? Maybe worth a shot ?

[lotusflasherman]

Think you suspect the right area. Everything cold and damp at the moment. Like Rambo, I'd be looking at coils and HT leads - they don't like being damp. If it's consistently bad an easy check is run the engine when it's dark and look if you can see 'bright blue gremlins' running down the leads or across the coils - electrical people call it 'tracking'. Either way, wipe coil and HT leads dry and spray with WD-40. (Not with engine running unless you want to jump around a bit ) One of the few things that WD-40 is right for...

[Artaban]

I would have thought electrical as well but if that proves not to be the case how old is the fuel in the car if you don't drive it much? My daughters gone off to Uni so her car isn't driven and I had similar problems cured by putting a can of SeaFoam in the fuel tank. No harm in doing that anyway as it clears the fuel system better than any other snake oil additive I've used.
Andy

[Simon_P]

I'm suspecting electrical or fuel. Any advice appreciated.

Yes that covers it!

As others have said most likely electrical.
The key is you say it is on acceleration - to test driving along slowly with a light foot, then floor it.
If you get a misfire consistently when you do this and it recovers when you ease off it is most likely leads or coils. They don't get any better and aren't expensive so just change them anyway - the ultimate test is to keep doing this until it gives up permanently but then you've broken down so don't go further than you can limp home

The spark has to jump the gap in the spark plugs. By flooring it you make this much harder and electricity always takes the easiest route, which might not be through the spark plugs.

Also in your diagnosis be clear on the difference between a flat spot and misfire does it just feel a bit dull or does it sound as though something is wrong.

[John_W]

Also ensure the plugs are correctly gapped (31 thou).

[Danevansgolf]

Personally I'd change your spark plugs, they may have broken down or even the ceramic might have a hair line crack in. For £12. I'd start there. If you suspect coils I have an old spare set which you can borrow. Good luck.. My spark plugs were only a year old and they broke down completely, hence the flat spots at high throttle.

[lotusflasherman]

... a can of SeaFoam in the fuel tank. No harm in doing that anyway as it clears the fuel system better than any other snake oil additive I've used. Andy

SeaFoam? - Never heard of it so went on 'net to find out. Now wouldn't touch it with the proverbial 'barge pole' after watching Official and amateur Vid's on Youtube, though this one was interesting... https://www.youtube.com/watch?v=YOkNDdtuHp0

In one vid' a guy looks in cylinders of a Honda Civic with boroscope through plugholes to give a before and after view. After dosing running engine with the mix injected in the intake he takes it for a good blast and reckons he can see carbon has come off the edges of the pistons. Not sure about that but if it has it's gone out of his exhaust with no problem. On any car with a turbo it's going through the exhaust turbine blades, not something I'd be too enthusiastic about !

In 'the old days' my Dad used to ask for a shot of RedeX with each gallon of petrol but we still had to 'decoke' the engine every 30k / 40k miles, but reckon it was more to do with carbs and manual choke, than fuel. Much more accurate fueling by fuel injection & ECU's and I've seen 130k engines with just a brown 'glaze' on the pistons. Must get the boroscope out at next plug change..

Do wish I could keep old fuel in my Elan ...
I normally use Shell V-Power Nitro+ Unleaded as it contains engine cleaning agents that cheap supermarket petrol does not. Bit expensive but have a Drivers Clubcard and they frequently send me a £5 voucher. I see on my account I filled 18 times last year, so it rarely gets to 3 weeks old!

[Rambo]

I remember the old RedEx dispenser at garages back in the '60s/70's. My parents went and filled up and asked for "four and four shots" ie four gallons and four shots of FedEx. I still use RedEx added to a tank of petrol every few months and in between times I alternate cheapo supermarket fuel with the more expensive Shell Optimax as I too think that it contains better detergents and additives. And if it's good enough for Ferrari then.....

[Saltire]

I still use RedEx added to a tank of petrol every few months and in between times I alternate cheapo supermarket fuel with the more expensive Shell Optimax as I too think that it contains better detergents and additives. And if it's good enough for Ferrari then.....

Goodness! I had no idea you could still get RedEx. Great idea to use it in conjunction with mixed fuel brands. I too like Optimax; my only problem is that the nearest pump is 25 miles away.

[Artaban]

Good excuse to go for a drive with the petrol station 25 miles away.
Ref SeaFoam, ignore the youtube videos I never find those helpful. I got the recommendation from other car forums and then read the reviews on Amazon. Noticed a difference with SeaFoam but none with RedEx and I used RedEx last month. I just put SeaFoam in the fuel tank if you want to clean the rest of the system Terraclean might be better. Though finding someone local to do it might be tricky.

[lotusflasherman]

Keep up lads... Optimax became V-Power Nitro several years ago...

Don't intend to use any additives in the M100 as that was designed for unleaded but older engines' exhaust valves suffer without lead in petrol so the Plus2 twincam engine really needs an Octane Booster and Lead Substitute.
STP-LEAD-SUBSTITUTE-REPLACEMENT-ADDITIVE-OCTANE-BOOSTER
Used to run a Copper S with 13.5:1 compression ratio and that was fussy about whose 5 star leaded petrol I used. 5 star had a range of RON 100 to 105 and I learn't who was near 100 and who was near 105. (Cheap Jet 5 star was a 'No No")
Couple of years ago I was in Austria in the Subaru and filled with OMV 101 Octane Unleaded. Noticeably more power from the turbo and got more miles out of that tankful. (I reset the trip when I fill up). Wish we had it in the UK.
V-Power Nitro in UK is usually 98 but they do list Nitro+99 as available but never seen it. Tesco Momentum 99 is highest octane commonly available and is my alternative choice. Interesting that in Italy and Germany Shell V Power has always been 100 RON. Always wondered what happened to EU standardization, and that was before Brexit!

[Rambo]

Would the extra power from the turbo you experinced in Austria also have anything to do with the cold and increase in altitude as well as the OMV 101 ?

I always seem to experience better oomph and boost when it's very cold and quite a bit above sea level

[CalElan]

If I'm not sure what my Elan useage plans are when I'm filling up I just put half a tank in..
If it's sits for a while before the next run I just pep it up with a splash at the station..

However, Sods law usually dictates that I burn off the half-tank that day and have to fuel again..
It could be poor planning, or just the fact that it's quite infectious!

[Saltire]

Good excuse to go for a drive with the petrol station 25 miles away.
Ref SeaFoam, ignore the youtube videos I never find those helpful. I got the recommendation from other car forums and then read the reviews on Amazon. Noticed a difference with SeaFoam but none with RedEx and I used RedEx last month. I just put SeaFoam in the fuel tank if you want to clean the rest of the system Terraclean might be better. Though finding someone local to do it might be tricky.

Actually, Andy, the local motor engineer who looks after the Elan for me has a Terraclean agency. He's shown me photos of some of the results which he took, and I must say it looks very impressive.

[Saltire]

Keep up lads... Optimax became V-Power Nitro several years ago...

Crumbs . . . You'll be telling me next you can no longer get National Benzole. Or Regent

[Simon_P]

Would the extra power from the turbo you experinced in Austria also have anything to do with the cold and increase in altitude as well as the OMV 101 ?

I always seem to experience better oomph and boost when it's very cold and quite a bit above sea level

altitude means lower atmospheric pressure ie air is less dense, so less oxygen, less fuel hence less power. On the plus side -slightly less drag.

But we have a turbo so can pump up the pressure to whatever the engine can handle, and the lost power is restored. There will appear to be more boost but this is because the atmospheric pressure is lower to start with.

Now because the ambient temperature is low the intercooler can reduce the temperature of the charge, therby making it denser, so for the same pressure you get more oxygen and can add more fuel and hence get more power.

In addition the cold charge and increased fuel octane mean that the pressure can be increased further before it is limited by knock. Again more power

[lotusflasherman]

Would the extra power from the turbo you experinced in Austria also have anything to do with the cold and increase in altitude as well as the OMV 101 ?
I always seem to experience better oomph and boost when it's very cold and quite a bit above sea level

It was summer, very warm and altitude about 500m on the main roads in the valleys. High altitude reduces power in NA because air is less dense but turbo and MAP sensor does a good job to compensate for normal running at altitude. Though max' available power would still be down. Next tank of fuel had to be 'regular 98' and I noticed the difference so started topping up or filling up with 101 whenever I saw it.

It's cold dense air that gives the oomph. Cold air is heavier because the same molecules occupy less space and the stoichiometric ratio is 15:1 by weight, i.e. 15 grams of air requires 1 gram of fuel, so cold air being heavier, the fuel intake is heavier and the power output greater.

A car engine is really a gas expansion engine. It's all about taking in cold air and heating it up quickly via a fuel mix to make it expand and push the pistons down and still works according to Boyles Law, formulated in 1662, known as the First Gas Law, and the Second Gas Law by Charles in 1787. Around 'standard temperature and pressure' air expands by 1/492 of it's volume for every 1°F rise in temperature. (Sorry, was still using old units when I did Thermodynamics at college. That will be 1/273.3r for every 1°C according to my phone).

So as much air, as cold as possible, going into an engine as hot as possible is what is wanted. The charge takes heat out of the engine and starts expanding and producing work before the spark initiates combustion and the fuel continues the process. Practicalities are compressed air fuel mixture at high temperature is prone to detonation, as exploited by Rudolph Diesel, so the Octane rating is a guide to how that is delayed. Interesting to note that the higher the octane rating the less flammable is the petrol...

Not sure that's helping Stef with her flat spots... but it's useful to know the theory.

Edit - with Simon. Didn't see the post but we're 'singing the same tune'...

[Simon_P]

so the Octane rating is a guide to how that is delayed. Interesting to note that the higher the octane rating the less flammable is the petrol...

I don't think that is correct - Octane rating is a measure of to resistance to pinking. at the bottom of the sacle is n- heptane (0 octane) and the top of the scale iso-octane (100 octane) so iso-octane is more resistant to pinking than n-Heptane.

Flammability of a fuel is defined by its flash point which is due to the volatile part evaporating enough at lower temperature - iso-octane has a flash point of 10 oF whereas n-Heptane has a flash point of 25 oF so iso-octane has a higher octane rating and is more flammable. Petrol on the other hand has an octane rating of 95/101 but needs to ignite easily so has a flash point of -45 oF. (clearly I have had to look up all these numbers )

The important part to octane rating is the temperature at which the fuel spontaneously ignites ie burns uncontrollably. If we link this back to the gas law PV=nRT then for a lower spontaneous T and an instantaneously fixed V, P will rise in an uncontrolled manner. ie pinking

Now back to the application in our engine. A higher octane allows a higher instantaneous pressure. Since the mixture is burning in a controlled manner at greater pressure, you can have a higher compression ratio or more boost or advanced ignition, thereby getting more bang for your buck.

The MPG of a fuel is also related to its calorific value, and this is where we are being conned as ethanol is an octane booster but has a lower calorific value.

An interesting discussion (for me anyway) and I'm happy to be corrected.

How are you getting on Stef?!