Car running rough during acceleration - LotusTalk - The Lotus Cars Community
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post #1 of 112 (permalink) Old 10-02-2014, 05:00 AM Thread Starter
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Car running rough during acceleration

My 2009 Elise seems to be running rough. This has been gradually getting worse in the past 2 months.

At full highway speed (120 km/hr or 75 mph) the engine seems smooth and the car revs at about 3600 rpm.

But between about 80 km/hr and 100 km/hr while reving at about 3000 rpm there is some roughness. At first I thought it might be due to a tire imbalance or maybe bad shocks but I am tending to think it is the engine.

I tried a few things and none seem to make much difference.

1) Fuel cleaner product
2) Water remover product
3) Octane boost product
4) New spark plugs
5) Octane 94 grade instead of 91
6) Tried PetroCanada instead of Shell

I would not mind taking it to the dealer but I don't think the problem is bad enough yet that they would be certain to observe and fix it.

Note that I did change my air filter about a year ago so I doubt that I'd need to replace that now.
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post #2 of 112 (permalink) Old 10-02-2014, 05:46 AM
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How did the old plugs look?

Did you slather dielectric grease all over the "sleeves" and how did they look?

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post #3 of 112 (permalink) Old 10-02-2014, 07:07 AM
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Fuel filter?

Apexes are a lot like relationships. So tough to get right, so easy to see where they went wrong.

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post #4 of 112 (permalink) Old 10-02-2014, 07:22 AM Thread Starter
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Quote:
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How did the old plugs look?

Did you slather dielectric grease all over the "sleeves" and how did they look?
The old plugs were only about a year old. They didn't look like the problem.

But since I had purchased new ones + dielectric grease I put in the new ones + the grease. I didn't notice any difference.

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post #5 of 112 (permalink) Old 10-02-2014, 07:24 AM Thread Starter
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Fuel filter?
On my vintage 1980 Toyota cars I would change the fuel filter. I've heard that you cannot do that on an Elise without dropping the fuel tank. Is that true?

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post #6 of 112 (permalink) Old 10-02-2014, 04:17 PM
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Try turning off your Atrac.
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post #7 of 112 (permalink) Old 10-02-2014, 09:17 PM
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What did you set the plug gap to?

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post #8 of 112 (permalink) Old 10-02-2014, 09:57 PM
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I had similar issues and it turned out to be my coil packs.

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post #9 of 112 (permalink) Old 10-02-2014, 10:19 PM
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I agree on coil packs if the gaps were checked and set correctly. A plug with a tight gap could give the same issue.

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post #10 of 112 (permalink) Old 10-03-2014, 04:35 AM Thread Starter
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I used NGK plugs as shown. The plugs shown are what I removed but I put in a new set of the same part number. The packaging said to NOT adjust the gap.

If this turned out to be the coils I'd be very happy.

How much do coils run? Is that something I can buy at the dealer?

How often would coils go bad? My car is a daily driver with 115,000 km and 5 years under its belt.
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post #11 of 112 (permalink) Old 11-04-2014, 06:10 AM Thread Starter
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I replaced all four coils a few weeks ago. That did seem to make the car smoother at all speeds. The stumble at 80-100 km/hr is also less but still does happen.

I think I will try cleaning the MAF sensor next.

After that I'll try to clean the throttle body.

Regarding the coils, I did see a brownish mark on the outside of each coil in the area near the spark plug.

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post #12 of 112 (permalink) Old 12-08-2014, 08:38 AM Thread Starter
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I have an update on the car.

Replacing the 4 coils and then driving the car for several weeks has greatly improved the car.

There still is a minor roughness between 80 and 100 km/hr but it is perhaps just 10% of what I had noticed originally.

I'm not planning to clean anything else until the spring. I might clean the throttle at that time.

Is the throttle cleaning easy to do? I have a "drive by wire" 2009 Elise.

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post #13 of 112 (permalink) Old 12-08-2014, 08:19 PM
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Throttle body cleaning is easy, but your lingering symptom sure sounds like a bad alternator which isn't strange for 116,000 km. Take a voltage test at the battery while the car is running. If the voltage is 13-14, the alternator's still good. If it shows 12 (the same as battery), then it's time for a new alternator.
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post #14 of 112 (permalink) Old 12-09-2014, 07:23 AM Thread Starter
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Quote:
Originally Posted by +TSRAGR View Post
Throttle body cleaning is easy, but your lingering symptom sure sounds like a bad alternator which isn't strange for 116,000 km. Take a voltage test at the battery while the car is running. If the voltage is 13-14, the alternator's still good. If it shows 12 (the same as battery), then it's time for a new alternator.
Thanks, I'll try that.

Could you explain how the weak alternator would cause this symptom, I'm curious.

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post #15 of 112 (permalink) Old 12-09-2014, 07:51 AM
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^ Sure. There's more electrical demand when under acceleration compared to steady RPMs, so the alternator spins faster to fulfill this demand. A bad alternator will not be able to generate the higher voltage and the motor will often hesitate/stumble as a result of the lower voltage being supplied.
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post #16 of 112 (permalink) Old 12-09-2014, 08:52 AM Thread Starter
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Quote:
Originally Posted by +TSRAGR View Post
^ Sure. There's more electrical demand when under acceleration compared to steady RPMs, so the alternator spins faster to fulfill this demand. A bad alternator will not be able to generate the higher voltage and the motor will often hesitate/stumble as a result of the lower voltage being supplied.
Much appreciated, thanks.

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post #17 of 112 (permalink) Old 12-09-2014, 09:58 AM
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I like your explanation, except for this:

Quote:
Originally Posted by +TSRAGR View Post
...compared to steady RPMs, so the alternator spins faster to fulfill this demand.
I'm trying to picture how the alternator speed can be different from engine speed, since it's belt driven? Or did you meant to say this differently?

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post #18 of 112 (permalink) Old 12-09-2014, 12:27 PM
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Quote:
Originally Posted by +TSRAGR View Post
^ Sure. There's more electrical demand when under acceleration compared to steady RPMs, so the alternator spins faster to fulfill this demand. A bad alternator will not be able to generate the higher voltage and the motor will often hesitate/stumble as a result of the lower voltage being supplied.
Interesting. But, assuming a below par alternator hasn't charged the battery, wouldn't the latter make up for this?

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post #19 of 112 (permalink) Old 12-09-2014, 06:14 PM
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Quote:
Or did you meant to say this differently?
Yes, bad wording!
Quote:
Interesting. But, assuming a below par alternator hasn't charged the battery, wouldn't the latter make up for this?
Yes and no. Momentary (split second) voltage supply disruptions can occur before the battery (ideally fully charged) supplements the voltage deficit from the faulty alternator, but the bad alternator will breed a bad battery over time.

Ever notice your headlights dim briefly when you shift into neutral from higher RPMs? The voltage production briefly fell below the voltage demand before the alternator or battery supplemented the deficit. Heck, my 1-yr old Jeep even does this! In David's case, a voltage supply error at mid-range RPMs could be causing his roughness. It's a quick and easy test with the multimeter, but who knows...I'm probably way off!
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post #20 of 112 (permalink) Old 12-13-2014, 12:50 PM Thread Starter
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I tested the battery / alternator at the battery terminals. Mileage is about 122,000 km.

1) Car off (overnight) - 12.0 V
2) Idle at 800 rpm - 13.6 V
3) Rev at 1500 rpm - 13.6 V
4) Rev at 2500 rpm - 13.7 V
5) Car off (for 1 min) - 12.8 V

From what I've read on the forum, this seems to indicate that the alternator is OK.

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