Hi,I have a stickshift 5 speed 1999 Suzuki Grand Vitara 2.5.
For the last 50,000 it has had slight hesitation on initial acceleration, noticed in 1st/2nd gear.
Recently this has become worse and the service engine soon or check engine light (can't remember which wording) has come on. I can feel the engine running rougher at higher speeds now.

I discovered its diagnostic code, P0304

I've replaced the spark plugs with no change in the problem.

I know it could mean a number of things, but the symptoms most likely typically point to one thing that  many people will have been through before (could be wrong!).

What is typically wrong when this is occurring?
If a part(s) is needed - What part(s) is needed? Where's the part located? Easy repair? and a rough cost for part (Suzuki only or aftermarket)?

Thanks!!!!

also, on this P0304 Cylinder 4 misfire,

How can I tell what cylinder 4 is on this V6 engine.
Is it Driver's side front, middle, rear or
Passenger side front, middle rear?

Thanks

when you pull the coil packs from the engine pull the rubber boot off the coil pack you will notice a contact spring in the boot, look in the coil pack at the contact point of the spring you will see a screw head clean all the corrosion off the screw heads to get better contact and see if that works

There's nothing in the coil packs that'll give a shock / stores a charge?

and these coil to plug boots simply pull off the coil?

Thanks again!

Well, I'm going out to look at it regardless. Hopefully in a few hours we'll know if it helps.

charge or spark it still has to transfer to plug through spring in boot
It has fixed plenty to know it works

did you clear the codes ?

I didn't get shocked.

I had the check engine light a few times.
The first time I cleared it.
The second time, it appeared to clear itself.
The last time I cleared it.
The hesitation seems/ed to vary. Sometimes little to none and other times bad.

When you say that you'll post the results in a couple of hours, you know that something's going to go wrong.
I lost one of the 2 screws to the ignition coil cover in the engine. Couldn't find it anywhere.
After an hour I jacked up the car and not long after I found it had been caught by the A/C lines, but hidden under the EVAP Canister, so I couldn't see it from above. But I found it!!!!

So I ended up just cleaning the ignition coils on the passenger side, with the #4 cylinder.
I used a Dremel tool with the small round stiff wire brush, and used it to clean the 3 other contacts on the ignition coil too.
I ran some emery paper over the end of the spring.
I'd prefer to clean that screw manually, so I'll have to think of some other tool or tool I can make to do it.

I gave it a test drive, but I'll do the other 3 cylinders tomorrow and report back.

FYI
Position of cylinders on a V6 2.5 (aka. H25) engine.
From the oil cap (front) to the windscreen (aka. USA driver side front to back) = 1, 3, 5
The other side (aka. USA passenger side) - 2, 4, 6

also, for anyone new to these ignition coils just over the spark plugs. What you would think of as the ignition wire part of this (as on the older cars) only 5" long between the rectangular Ignition coil and plug. It's called a boot. Just twist it and pull at the same time and it'll come off the ignition coil.

I cleaned the other bank of cylinders' ignition coils.
I think I did a better job, using a Dremel tool brush instead of wire brush, and I cleaned the 3 metal connectors (where the wiring harness connector snaps on) with a small file.
The screw area seemed to hold the dust/debris, so I used an art brush with stiff bristles and it seemed to clean it all up nicely.

I decided to redo the 1st bank of cylinders to get them into the same shape.
I also moved the #4 cylinder coil to the front (the #2 cylinder), just in case I get a diagnostic code again, to see if it moves to this cylinder.

Today's test drive seemed to produce smooth acceleration.
Only when it is under extreme load at the start of gear #2, just for a second, it hesitates.
I don't know if this is just because Gear #1 didn't have enough speed for gear #2 to take over? I feel that it should have handled it anyway.
Possibly, I still haven't cleaned them well enough yet?

I'll report back again after driving it for a few weeks to make sure the acceleration stays this way, and it wasn't just a good day.

I also need to figure out a good tool to manually clean/polish those screw heads thoroughly - any ideas?, and I need to do a better job cleaning the end of the spring (which could be the problem).

To my eyes coil to boot connection really seems to be a weak link. Are their aftermarket performance replacement or improvement boots that provide a much better connection?

The car's been running good since this, so many thanks to LowRangeWilliam. It's a pity I can't send him a slice of chocolate cake through the internet wires....
Seevral months later - the minor hesitation is beginning to appear again. You can hear it missing every now and again while it's idling.

I didn't feel like I had cleaned the spring and screw well enough. What do you you use to get to the screw in the ignition coil pack, to clean it with? Do you do anything to clean the end of the spring?

Also. Even when I'd cleaned it - there was a slight misfire. Cleaning the connection, as we've discussed, is the 1st thing you would do if it was misfiring, but what would be the next thing you would look at if it wasn't this connection that was causing the problem?

The car's been running good since this, so many thanks to LowRangeWilliam. It's a pity I can't send him a slice of chocolate cake through the internet wires....

Over by his avatar click on [Applaud - helped me].
It won't taste as good as cake, but should be appreciated.

Ha ha, I suspected there'd be suggestions on how to get cake thru copper wire....
Ah, so that's what the [applaud] thing is for - I just noticed it the other day - thanks.