Engine Misfire under Acceleration

[Mike Y]

Hi
First drive of my Elan S2 in a number of years (been laid up in my warm garage) and straight away on pulling away I started to get a misfire. It is OK at steady RPM but does not like anything but the lightest acceleration. I straight away thought maybe the coil packs are showing their age but just wanted to check if there is any easy way to find out what the problem is. Would Elan Scan be able to trace the problem without replacing perfectly OK parts until curing the problem.

Cheers Mike

[John_W]

Mike,
Élanscan won't identify a coil pack problem.
I would suspect the HES. Maybe have a look at the static timing marks and see how steady they are. If they're fluttery I would change the HES before the coils. It will be cheaper and easier to do so, if you're going to change something to see if it makes a difference.
John

[Peter_W]

...First drive of my Elan S2 in a number of years

If you haven't already, put some new gas in the tank (it loses its stability after a few months).

[HJ2]

I would start with a wastegate wiggle
http://wikilec.9600.org/index.php/Relea ... _wastegate

[Peter_W]

“Gasoline tends to lose oxidation and deteriorate after 4-6 months of non-use and will be for the most part useless after 1 year. While it certainly will still ignite and burn, the octane content for any engines usability is severely diminished…”

[steve matthews]

This just recently happen to me. It turned out to be the plug wire jumping to ground.
Did not find it until I pulled the cover on the plugs and saw it.
Idle was fine but on acceleration the miss was not to be unnoticed.
Steve -w- new Kingsborn leads

[Mike Y]

Thanks for the replies.

I will check the plug leads (What are HES?). The fuel was virtually out so I put £15 of fresh in the tank.

Cheers Mike

[Brit-Car-Nut]

HES is the Hall Effect Sensor in the CAS. Lotus PArt Number A100E0102S. They are on the Aftersale list for £18.28 + VAT. You can get them at ANY Lotus Dealer for that price. No need for special orders anymore.

[Mike Y]

Would the HES throw up a fault code?

Cheers Mike

[John_W]

Mike,
HES is indeed the HAll Effect Sensor which lives in the Cam Angle Sensor unit. As Brit-Car-Nut says above, they're cheap enough to buy a spare anyway.

If faulty, it should show a code 41, however there have been people on here saying that sometimes other codes can be caused by HES failure. When mine started misfiring under load, there were no fault codes, so I changed the coils. No difference. I changed the HES and the problem was gone.

Codes are here or here, and how to change the HES is here.

All the other suggestions above are also valid, so start with the cheapest first.

Good luck,
John

[tweetdriver63]

I have just noticed mine doing this today after the car sat for four days. The day before I went out of town, it was definitely not doing it, because I did a couple of full throttle accelerations -- just in a mood I guess. Anyway, oddly enough, the car ran beautifully for the last two weeks despite sitting for four months while I was overseas.

I also had this happen once before and found that the pipe to the intake plenum wasn't well seated and was therefore leaking air pressure under demand. (I'm going to check this one again to see if it's doing the same thing this time.)

[max-walls]

Hi,

No doubt a lot of potential causes, but after trying everything to solve the same problem, I changed the coil packs - instant cure!

Regards,

Max

[Mike Y]

Ok I replaced the coil packs for new NGK units. The misfire if anything is worse it happens at idle now the car does not need to be under load. The leads are Magnicore and were not long on the car before I bought it 7 years ago. The cars will be lucky if it has done 1500 miles since. I think I will try the HES next cheapest option???

Any further thoughts?

Cheers Mike

[chrisP]

Hi Mike
I would check the magnicor leads - both ends of them. I had a set on my car a few years ago and found that the terminal came loose from the actual lead. In one case leaving it in the coil pack.
Regards
Chris

[Peter_W]

Back to the gas - in addition to going bad, when sitting for long periods (years in this case) it will create varnish that can clog fuel lines, filter, and injectors - I'd try adding the best fuel system cleaner you can get and add to a fresh tank of gas.

[Mike Y]

The car has fresh petrol in and the leads end fittings are fine. I have ordered a new Cam Angle Sensor (HES). Please be aware although the car has not been used on the road for some years the car has regularly had its engine run up to temperature and driven up and down my street (Which is a private development.

Cheers Mike

[Mike Y]

Hi

OK new HES of CAS fitted today. The old one was indeed damaged one of the locating lugs had broken off and the sensor was rubbing on the metal spinning tab. I thought great this is the problem but I was wrong. Still have the misfire at idle without putting any load on the engine. I was thinking next cheapest option spark plugs then leads??

I drawn towards it being an ignition problem as replacing the coil packs has made the problem more evident.

Any thoughts?

Cheers Mike

[Mike Y]

Hi

OK new HES of CAS fitted today. The old one was indeed damaged one of the locating lugs had broken off and the sensor was rubbing on the metal spinning tab. I thought great this is the problem but I was wrong. Still have the misfire at idle without putting any load on the engine. I was thinking next cheapest option spark plugs then leads??

I am drawn towards it being an ignition problem as replacing the coil packs has made the problem more evident.

Any thoughts?

Cheers Mike