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Diagnosing why my Estilo's engine was misfiring & how I got it fixed

6th September 2022, 14:40 by Rahul Nagaraj

Doesn't happen at a cold start, doesn't happen at higher RPMs. However, once it starts happening, the behaviour persists.

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Seeking some advice to get my old Suzuki Estilo F10D fixed. The car is strictly used as a beater and I have no intentions of selling/exchanging it since the running is minimal at about 150-200km a month as a city runabout. Barring this misfiring issue, the car has no other problems whatsoever.

Here's what's wrong. The car has done around 60,000 kilometres, maintained well and serviced in a timely manner with oil changes every year. All servicing has been done at Maruti's authorized service centres. Off late, the car's been giving trouble, as in it'll start to randomly stutter and buck under throttle input at low speeds/low RPMs. The check engine light does not come on.

So let's say I've slowed down at an intersection and the road ahead is clear for me to proceed, I give it gas and it just doesn't respond for a couple of seconds before suddenly surging ahead. This happens only after the car has run for 20-30 minutes in heavy traffic. Have had a couple of near-miss scenarios due to this weird behaviour. Doesn't happen at a cold start, doesn't happen at higher RPMs. However, once it starts happening, the behaviour persists, even when idling in neutral, until the car is shut off and allowed to cool for some time.

Here's what's been done till now in an attempt to fix it.

PCV valve, spark plugs, coils, air filter, fuel filter, fuel lines, O2 sensor- changed.
Fuel pump, sensors like TPS, MAF/MAP- checked by the authorized service centre folks.

The fact that it throws up no error codes/CEL is making things difficult to diagnose. Asked the service centre mechanics to check for vacuum leaks and they dismissed it by saying that wouldn't make the vehicle behave the way it does.

Any leads as to what I should be looking at next would be really appreciated!

So here's a detailed rundown of the messy situation.

I start my car on a warm, sunny day and drive it around in city traffic; all's well for the first 10-15 minutes. Low RPM, high RPM, idling, everything seems alright. Now at some point, I have slowed down to cross a speed breaker or at a traffic signal, and as I downshift and give it gas, there's no response for 2-3 seconds. It's as if the car doesn't know that I'm giving it gas. And then, there's a sudden surge. Now, if I keep the RPMs high enough, the car runs fine. (while guzzling petrol of course).

At this point, the car becomes undrivable in bumper-to-bumper traffic with the constant lag-surge behaviour. Even if I pull over and let the car idle, the car continues to misfire. The exhaust is inconsistent and has a fuel vapour smell to it when it misfires. Shut it off for 30-40 minutes and start it again, it's back to normal until it warms up enough and the cycle repeats.

Here's the work carried out at the authorized service centre (Mandovi Motors):

Throttle body has been cleaned.
Injectors have been cleaned.
Spark plugs replaced multiple times in the past year.
Ignition coils have been checked.
Fuel tank cleaned, fuel pump checked, fuel filter and fuel lines checked/replaced.
Air filter replaced.
TPS/MAF sensors are fine as per the service centre. The O2 sensor had been replaced 5,000 kilometres back.

The main problem with the authorized service centre is that they don't (or can't?) work on the car immediately when the problem occurs. I got a call from them a couple of days back after I had left the car with them, asking me 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, cruising on a 4-laned highway with sparse traffic. They tagged along for a test drive as I drove through city traffic and demonstrated the issue which they acknowledged, but by the time the car gets to the servicing bay, the engine has cooled down enough and the mechanics are clueless again.

1st Update:

It's been a week since I left the car at the service centre but no luck on pinpointing the culprit that's causing the misfire yet. Saw the car parked outside the service centre while passing by the place and the rear seat covers were removed. Guess they're testing the fuel pump again. Ignitors were swapped with another car and they seem to be fine. Hopefully, the issue should be sorted out by this week.

2nd Update:

Been two weeks, so-called the SA for an update. They tried swapping ignition coils but the problem wasn't rectified. The next step will be to swap the throttle body since a senior technician from their head office has suggested they do so and drive around with their scan tool connected, and if it isn't rectified even then, they'll hand the car over to their main branch(Mandovi Motors, Hampankatta, Mangalore).

3rd Update:

The entire throttle body, injection rail and ignitors were swapped with the ones from another car today. The misfiring problem reappeared after a short city drive.

Now they're planning to swap the ECM and check as a last resort.

SOLVED

It was the ECM at fault. Got the fuel pump motor changed and the situation worsened. After fuelling up, the clamps holding the fuel lines failed and the car left behind a trail of petrol on the road much to the bemusement of motorists following behind before stalling right in front of the service centre today! It was towed into the service centre using another car: an Alto and both cars were damaged after they collided while being towed. My car's front bumper has a few scratches from the collision which I didn't bother about since the bumpers are anyway due for a repaint. A make-shift locking mechanism was devised to hold the fuel, line anchored to the tank.

Returned back home and disconnected the ECM and opened it to find a black residue on areas of the inner surface of the metal cover which rest against the ICs. The ICs themselves had some light burn marks as well. Plugged in the ECM without the cover and drove around for a while with the AC blower set to the "feet" position and the car acted normal. Will monitor the behaviour for a month or so before ordering a new ECM.