Diagnose why my Estilo’s engine was misfiring and how I fixed it

Does not occur on cold start, does not occur at higher rpms. However, once this starts happening, the behavior persists.

BHPian kevz22 recently shared this with other enthusiasts.

I hope you’re doing well.

I am looking for advice on how to repair my old Suzuki Estilo F10D. The car is strictly used as a beater and I have no intention of selling/trading it as running is minimal at around 150-200km per month as an urban runabout. Other than this misfire issue, the car has no other issues.

Here’s what’s wrong. The car has driven around 60,000 kilometres, well maintained and timely serviced with oil changes every year. All servicing has been performed at authorized Maruti service centers. Late the car gave problems as it will start to randomly stutter and lean under the throttle at low speeds/low revs. The check engine light does not come on.

So let’s say I slowed down at an intersection and the road is clear for me to continue, I give it gas and it just doesn’t respond for a few seconds before suddenly moving forward. This only happens after the car has been driven for 20-30 minutes in heavy traffic. I’ve had a few near-miss scenarios due to this odd behavior. Does not occur on cold start, does not occur at higher rpms. However, once this starts to happen, the behavior persists, even at neutral idle, until the car is turned off and allowed to cool for a while.

Here is what has been done so far to try to fix it.

  • PCV valve, spark plugs, coils, air filter, fuel filter, fuel lines, O2 sensor – changed.
  • Fuel pump, sensors such as TPS, MAF/MAP – checked by authorized service center people.

The fact that it doesn’t throw any error codes/CELs makes it hard to diagnose. I asked the mechanics at the service center to check for vacuum leaks and they dismissed it saying it wouldn’t make the vehicle behave the way it does.

Any leads on what I should watch next would be really appreciated!

So here is a detailed look at the messy situation.

I start my car on a hot, sunny day and drive it through city traffic; everything is fine for the first 10-15 minutes. Low revs, high revs, idle, everything seems fine. Now at some point I’ve slowed down for a speed breaker or at a traffic light, and when I downshift and give it gas, there’s no response for 2-3 seconds. It’s like the car doesn’t know I’m giving it gas. And then there is a sudden surge. Now if I keep the RPMs high enough the car runs fine. (while consuming gasoline of course).

At this point, the car becomes undriveable in bumper-to-bumper traffic with the constant lag-surge behavior. Even if I pull over and let the car idle, the car continues to misfire. The exhaust is inconsistent and smells of fuel vapor when it misfires. Turn it off for 30-40 minutes and restart it, it returns to normal until it warms up enough and the cycle repeats.

Here is the work done at the authorized service center (Mandovi Motors):

  1. The throttle body has been cleaned.
  2. The injectors have been cleaned.
  3. Spark plugs replaced several times in the last year.
  4. Ignition coils have been checked.
  5. Fuel tank cleaned, fuel pump checked, fuel filter and fuel lines checked/replaced.
  6. Air filter replaced.
  7. TPS/MAF sensors are ok according to the service center. The O2 sensor had been replaced 5,000 kilometers ago.

The main problem with the authorized service center is that they do not intervene (or cannot?) immediately intervene on the car when the problem arises. I received a call from them a few days after leaving the car with them, wondering what exactly the problem was since they couldn’t find anything wrong with it. Well, obviously they wouldn’t since their test drives were on a cold engine, navigating a 4-lane highway with sparse traffic. They took me for a test drive while I drove through city traffic and demonstrated the problem which they recognized but by the time the car got to the service bay the engine had cooled down enough and the mechanics were again distraught.

1st update:

It’s been a week since I left the car at the service center, but I have yet to be able to identify the culprit that caused the misfire. Saw the car parked outside the service center passing through the plaza and the rear seat covers removed. I guess they are testing the fuel pump again. The igniters were swapped with another car and they seem to be fine. Hopefully the problem should be fixed by this week.

2nd update:

For two weeks, supposedly the SA for an update. They tried to swap the ignition coils but the problem was not solved. Next step will be to swap out the throttle body since a senior tech at their HQ suggested they do that and drive with their scan tool hooked up, and if that isn’t fixed even then they will put the car to their main branch (Mandovi Motors, Hampankatta, Mangalore).

3rd update:

The entire throttle body, fuel rail and distributors were swapped with those from another car today. The misfire problem reappeared after a short drive around town.

Now they plan to swap the ECM and check as a last resort.

RESOLVED

It was the ECM that was at fault. I changed the fuel pump motor and the situation got worse. After refueling the clamps holding the fuel lines broke off and the car left a trail of petrol on the road much to the chagrin of motorists following it before stalling just outside the service center today! It was towed to the service center using another car: an Alto and both cars were damaged after colliding during towing. The front bumper of my car has a few scratches from the collision which I didn’t care about as the bumpers need to be repainted anyway. A makeshift locking mechanism was designed to keep the fuel line anchored to the tank.

Back home, disconnect the ECM and open it to find black residue on the areas of the inside surface of the metal cover that rest against the ICs. The ICs themselves also showed slight burn marks. Plugged in the ECM without the cover and drove for a while with the AC fan set to the “feet” position and the car acted normal. Will monitor behavior for about a month before ordering a new ECM.

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