Hi,
Greetings everyone, I am new here and I need help diagnosing an issue with my Honda during cranking

Year: 2017
Type: GK7 - Indian version.
Mileage: 7000 km
Engine: L12B4 1.2 l

The issue is - the car hesitates a little during cranking on cold starts. (By cold start, I mean the ECT and ambient temperature are close to each other, the weather is tropical over here and temperature rarely go below 15 deg c). The tachometer pauses for a bit while crossing 700 rpm mark. Sometime it is just like a fraction of a second and sometimes it is very prominent.

Check out the video

here

But here is the catch, this does not occur on every cold start, I could not figure out what makes it do this and cannot say for certain when it would occur again (it did this on 62 of 113 cold starts in the past year). Cranking speed is normal and have had the battery checked to be ok too.

Things I have observed so far
- The time for which this pause occurs varies with every other cold start
- The hesitation does not depend on how far the car was driven in the previous drive cycle, happens on the next cold start after both a 1 mile trip and a 100 mile trip.
- The hesitation does not happen when the car is started after it had been parked for over 3 or 4 days in a row
- The subsequent starts are all good as long as the engine is warm.

Things I have tried to do differently
- I have let the key stay in “On” position until the fuel pump prime completes and shuts off and then cranked it – it still happens
- I have tried cranking immediately after turning to “on” position – it still happens

I have been observing this for over a year but couldn’t figure it out. There has been no DTC. Even though this is nothing major it has been a nuisance.

Sorry for a long post and thanks for any help you can offer

 

I'm no expert, but that seems pretty normal to me. Especially if you're not having any symptoms. Got to remember that you're making lots of heavy metal pieces go from no movement, to over 1000 rpm, with tiny explosions. It's not always going to speed up at the exact same rate. Could also just be a delay in the display, as I doubt our tachometer has a direct physical link to the engine.

 

Agreed on the fact that inertia plays a role at startup. But what doesn't add up is, the issue does not show up when cranking after the vehicle had been parked for a while (as mentioned earlier).

BTW I am certain that it is not a tach delay, as you can hear the engine pausing briefly at that particular moment. I am not sure if it is audible in the video.

And thanks for the response, cheers.

 

Interesting! Certainly paying attention to details, arent we? Excellent job isolating the fault by the way.

Now then, is the engine otherwise in good health? When dealing with something so goofy it may be a good idea to start with the basics. You know and love 'em, air fuel and spark!
This likely wont be a quick fix so much as a slow progress resolution that would quickly become overbearing/overcomplicated/risky if rushed.

Starting with simple stuff,

• inspect the air filter/map sensor
• throttle body and sensors for dirt and grime.
• Next up, spark pluuuugs. Pull and inspect plugs/coils
• after that run a test light inbetween the coil and plug for each cylinder when the fault is expected.
• Fuel pressure is next. Youll need to hook up a pressure gauge to the rails and once again try to isolate the fault.
• If thats okay, pull and clean/test injectors (this can be done by removing them and making jumper wires to connect them one at a time to the battery. A foot or two of wire, little quick disconnect on one side, ring terminal to fit the car battery terminal on the other side.
• When powered you can see the spray pattern, repeatedly if you pour a little fuel or fuel cleaner in the top of em. You want complete atomization (mist) + immediate response..

Oh, and consider the viscosity and quality of the engine oil you're using, as well as the quality of your fuel. I'm not familiar with your country's fuel, let alone the 1.2L engine.
Back to the oil though, another possible area of cautious inspection would be to go through drained oil to check for cross contamination/metal particulate/plastic-like pieces.

I cant recommend taking it slow enough. Its too easy to fall "down the rabbit hole" as it were, and wind up creating/imposing new faults/swapping out perfectly healthy sensors.

 

Okay. let me go about this one by one:
Now then, is the engine otherwise in good health? - Yes it is, power delivery is good, the MID right now says 12.7 kmpl (~30 mpg) for Trip meter at 1300 kms - mostly driven in city conditions with stop-go traffic. (10% ethanol 91 RON gasoline)
inspect the air filter/map sensor - Air filter was replaced in March, no change with the old and new. MAP seems to be accurate, had it verified with data scan tool, it is equal to BARO at KOEO and is steady around 28 kPA (BARO-101kPA) at KOER after warm up
throttle body and sensors for dirt and grime. - Throttle body is pretty clean
Next up, spark pluuuugs. Pull and inspect plugs/coils - Plugs were replaced last June, actually had a dead miss (P0304) on Cylinder-4 due to a carbon particle bridging the spark plug gap, so had all four spark plugs replaced back then with genuine Honda-NGK BKR6E-11. During this had the coils inspected no visual damage.

Beyond this it is uncharted territory to me,
Fuel injectors - havent touched the injectors. I believe the intake manifold needs to come off to pull the fuel rail and I am not sure if i can do it at home. From what i have observed the idle quality and power delivery is good. Is there anything else to look for in drivability with respect to injectors? (BTW injectors are Bosch EV-14 Part no. 0 280 158 306)
Fuel pressure - I guess a T-adaptor is required to check it, so may be i can get this checked at the dealer next time i visit

 

Since we are troubleshooting an unusual and rather small fault we must be certain that nothing we touch on gets overlooked. At your convenience I'd like to see a current image of all four spark plugs.
Carbon build-up on the electrode is definitely something we must figure out before going any farther.

Here is some information I was able to find regarding this issue, it should be useful for you:

Carbon fouled

Black, dry soot on the electrodes and insulator tip indicates a carbon-fouled plug. This can be caused by a dirty air filter, excessive driving at low speeds, too rich of a fuel/air mixture or idling your vehicle for too long. Your mechanic can offer you advice on what type of spark plug to buy to replace the damaged plug, but you may want to consider switching to a “hotter” spark plug (the higher the spark plug number, the hotter the plug).

https://www.championautoparts.com/Pa...ark-plugs.html

What is Heat Range?

Heat range is the speed at which a spark plug can transfer heat from the firing tip to the cylinder head water jacket and into the cooling system. Choosing the right heat range is crucial for high performance engines. If the heat range is too cold, the spark plug will be unable to properly self-clean by burning off carbon deposits.

If it the heat range is too hot, your engine could experience detonation, pre-ignition, or power loss. Most spark plug manufacturers recommend that the tip temperature remain between 500° C and 850° C.

Heat ranges are designated by each spark plug manufacturer with a number. In broad terms, spark plugs are often referred to as “hot plugs” or “cold plugs.” A cold plug has a shorter insulator nose length—the distance from tip to spark plug shell—and transfers heat rapidly from its firing tip to the cylinder head water jacket.
Cold plugs are ideal for high rpm engines, forced induction applications, and other instances where the engine produces high operating temperatures. Conversely, hot plugs are good for applications that operate mainly at low rpms. Because they have a longer insulator nose length, heat is transferred from the firing tip to the cooling system at slower pace. This keeps the spark plug temperature high, which allows the plug to self clean and prevent fouling.

Unfortunately, heat range numbers are not universal—each brand has its own method for assigning heat ranges. You’ll need to talk with your sales rep or consult with the manufacturer to find the best heat range for your application and spark plug brand. Be prepared to supply some basic vehicle information, including any modifications you’ve made.

https://www.enginebuildermag.com/201...ug-heat-range/

I think that there is a chance you may need a "hotter" spark plug, but that will be decided later on
Identifying exactly which spark plug you should try requires that I know the part number of the one you had that became obstructed.

Oh, your English is great by the way!