Misfire, need help!!!

Hey everyone, I could use some help.... here's the backstory:

A month or two ago I went to accelerate in a tall gear at low rpms (gently, just driving normally) and the car jerked on acceleration. I figured I was just out of the powerband and the engine didn't like it and thought nothing of it.

A few weeks ago when accelerating at 1/3 throttle or more the car starts to jerk like it's cutting power and the CEL flashes. Thought it might be bad gas, filled up with a fresh tank and suddenly get CEL and TCS light solid on (not flashing anymore) and the hesitation/jerkiness/cut power happens all the time at anything over about 1/3 throttle. There's also a soft thumping sound when idling and the engine is vibrating more. However, the thumping sound and vibrations are not consistent and would switch between the thumping and running perfectly smoothly every few seconds. There's absolutely no consistency.

Codes are p1201
p1203
p1204
p0300

Which are misfires and random multiple cylinder misfire.

Engine has about 67k miles, I pulled cyl4 plug and it looked worn but not bad. Listening to the injectors they seem to skip steps. It would be click click click silence click click click silence with no patterns and no consistency. All of the affected injectors seem to miss but not consistently (none of them are fully off). There's no fuel smell in the exhaust but there's something different in the smell (noticed it after I put in a bottle of techron, don't know if its the fuel cleaner or something else). All injectors tested fine electronically, all in the same range (my mechanic friend did the test so I don't remember the exact values). Coils I believe tested well also.

Here's a video of it running, note the thumping that is best heard from the exhaust:


When driving at anything over 3k rpms and not using a lot of throttle everything feels perfectly fine. Only on more acceleration the car starts to jerk and seem like its cutting power. I can keep driving it to get the fuel cleaner through the system but I'm worried that to keep driving in this condition is hurting the engine. Any advice before I start replacing injectors/plugs and fuel filter? Would prefer to not just throw parts at it blindly

Your symptoms sound like mine when my igniter failed.
The thumping was a dead cylinder.

I would put in a new set of spark plugs if one of them looks worn.

http://www.ngksparkplugs.com/part_finder/car_truck_suv/results.asp

Here are some options for plugs, $50-$100 for a set of six.

Brad

Thanks for the link. I do plan to do plugs soon but would like to figure out the cause of the injectors missing too. I did check the connections at the igniter and they were all good, is there a way to test if the igniter is going bad?

crazyukrainian said:

Thanks for the link. I do plan to do plugs soon but would like to figure out the cause of the injectors missing too. I did check the connections at the igniter and they were all good, is there a way to test if the igniter is going bad?

Click to expand...

Not that I'm aware of. If you have someone local that could swap one out with you, that would be the cheapest option. I believe that a new igniter is going for over $400 so it's a pretty expensive option to eliminate. Ask me how I know....

1201, 1203 and 1204 are cylinder 1, 3 and 4 misfires. The 2000 NSX service manual does not list 0300 as a code. Is that something that you got out of a code reader?

The ignitor is a pretty simple device. It consists of 6 power transistors in a heat sink which are used to switch the ignition coils. Power transistors tend to be operational or not operational. They rarely have a partially operational mode, although, it is possible for one transistor in the module to fail causing misfire on one cylinder while all the other cylinders continue to operate. In such case, the misfire should show up on only one cylinder. It would be odd for 3 transistors to fail at once. Also, you said that above 3000 RPM and part throttle, the engine runs fine. If you had multiple failed transistors, the engine would barely run at all. However, it is possible that a bad connection to the ignitor could be causing a random problem on multiple cylinders. Make sure that the connector is properly seated. When you do your checking, make sure that you do not confuse the ignitor with the misfire detection module. They look the same. The ignitor is over by the throttle body.

I would pull your ignition coils and have a look at the long 'nose' that extends down to the plug. Look for tracking on the nose which is an indication that the insulation on the nose is failing and allowing flashover to ground rather than firing the plug. If you have any signs of moisture or other contamination on the nose of the coil, clean it off. If you have signs of tracking, I would consider replacement of the coils. You can get a super deal on a 6 pack of the 3 terminal (OBDII) coils for under $120 (less than the cost of one coil!) if you know the right part #. Kaz did a recent post where he provided the part number for the 'ignition kit'.

If this problem emerged some time after you did some engine cleaning or after a really heavy rainstorm, I would be giving the coils a close examination.

One more thought. After clearing your codes, switch one of the coils on a cylinder that is getting a misfire code with one of the coils on a cylinder that does not have a misfire code. If the misfire code follows the coil, then you know that the coil is the source of the problem. If the misfire code stays with the cylinder, then the problem is not with the coil.

If the misfire was due to spark, wouldn't there then be a fuel smell in the exhaust? I will try moving coils around when I get a chance, but I have not driven it in rain since over a year ago and haven't washed it in months either (see how dirty the car is in the video? :redface

If the ignition on one or more cylinders had failed completely, you would notice gas in the exhaust; however, complete ignition failure, especially on three cylinders would likely result in a non operating engine. A severe non operation condition like that would also likely trigger an AFR out of range error if you did manage to get the engine to operate.

Misfires due to coil flashover to ground will likely be random and more likely to occur at high throttle openings where nobody is out back doing a sniff test. You said that the misfires only occurred above 1/3 throttle opening so I don't expect that you would smell anything at idle!

I just picked up the coil pack set its part# 06300-PR7-305

Old Guy said:

You said that the misfires only occurred above 1/3 throttle opening so I don't expect that you would smell anything at idle!

Click to expand...

The hesitation only occurs above 1/3 throttle but it seems to misfire most at idle (hence the thumping in the video) or I can't tell if its misfiring or not above idle until there's hesitation that can easily be felt. When it hesitates it's clear there's a problem happening, but with low loads and low throttle the car drives normally so I can't tell if anything is happening. At idle you feel the extra vibration.

Could it be the speed sensor? Here's an old thread:

http://www.nsxprime.com/forum/showt...le-for-a-wild-guess?highlight=nm speed sensor

Those are easy to test - check it out before shelling out the dough for igniter / coils / etc.

If you were getting multiple cylinder misfires at idle I think you would see the engine shaking. Your engine did not look like there was a lot of vibration. Your engine does seem a little noisy; however, that may be more due to the fact that I don't stick my head as close to the engine as your cell phone.

If you clear the trouble codes, do the codes reappear immediately on restart with the engine idling or do they only reappear when the engine is under load? If they reappear at idle, then your erratic noise could be due to misfire at idle.

I offer up the coil switch test because it is a no cost test. If the misfire codes stay with the cylinder, then it is not the coil and could be something more expensive.

Test and diagnose first, then replace parts.

It does shake more when it's misfiring but only a little bit and isn't noticeable in the video.

I looked at codes again today and there were no new ones. I cleared all of them and went for a long but relaxed drive. And amazingly today was the first time that I saw an NSX in the wild while driving mine!!!! Anyway I specifically drove slowly to avoid the hesitation and when I came back there was only one pending code for one of the cylinders (no CEL yet). It's been about 150 miles since I put in the techron and the thumping happens less though the misfire is still there, BUT I noticed a new issue that I didn't notice before

At 1500 rpm it vibrates a LOT. Revving the engine gives vibrations when it revs up past that mark AND also when rpms drop past that mark. Keeping the rpms at 1500 makes the whole car shake very consistently. Could this be the sign of a vacuum leak as well? I didn't notice this when driving, only when revving the car while stopped.... but with the bumpy roads around here I probably wouldn't notice that while driving anyway.

Did you eliminate the coils as the source of your misfire?

Update after barely having any time to do anything: ran a bottle of techron injector cleaner through the engine and a tank of gas, now onto a fresh tank of different gas (to try to rule out a bad batch of gas)

Ever since I put in the techron, I only get a code on cyl 3. Everything else is exactly as before, still intermittent and both at idle and high loads, but only one cylinder. Is it possible that the issue is in the fuel rail?

My plan is to replace the fuel filter soon anyway, but should I clean the cyl3 injector? Replace it? Replace all 6 injectors?

Seems to me like you'd want to focus on cylinder 3.