Misfire?

Looking for some input. My '95 recently started misfiring. No CEL but it gradually got worse to where the car is noticeably down on power, the car back fires a bit when at warm idle, stumbles on acceleration esp at low RPM, when I throw it into neutral when cruising the RPM's drop pretty low and the dash lights dim for a split second. I ran some Seafoam in the gas tank and drove around a bit, seemed to help a bit but only for a little while. Also ran Seafoam through the PCV valve and hardly any smoke blew out, seems clean. Car only has 60k miles on it. Am I safe to assume it would be injectors gunked up? Looks like I can have them cleaned/rebuilt for around $150 with a quick turnaround. Or possibly just fuel filter? Any ideas or advice would be appreciated!

SoloNSX said:

Looking for some input. My '95 recently started misfiring. No CEL but it gradually got worse to where the car is noticeably down on power, the car back fires a bit when at warm idle, stumbles on acceleration esp at low RPM, when I throw it into neutral when cruising the RPM's drop pretty low and the dash lights dim for a split second. I ran some Seafoam in the gas tank and drove around a bit, seemed to help a bit but only for a little while. Also ran Seafoam through the PCV valve and hardly any smoke blew out, seems clean. Car only has 60k miles on it. Am I safe to assume it would be injectors gunked up? Looks like I can have them cleaned/rebuilt for around $150 with a quick turnaround. Or possibly just fuel filter? Any ideas or advice would be appreciated!

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You should still check for error messages even with the CEL light is not coming on.
Start there and let us know what you find.

As per JD's comment, check for error codes. Your car is 1995 so the engine should be ODB II?

In the absence of OBDII codes, how do you know you are getting misfires? You say the car back fires. A true back fire occurs through the intake system and is usually indicative of a severe ignition timing or valve timing problem. If you have a fuel mixture problem, that could be responsible for the engine hesitation. Severe fuel mixture problems can result in popping noises coming from the exhaust system. However, I would expect fuel mix problems as bad as what you are describing to trigger mixture out of range errors on the OBD II system.

Diagnose before replacing. If the fuel filter has a lot of time or mileage on it, replacing won't hurt; but, I suggest it would be better to test the fuel pressure first before doing that. Low fuel pressure can cause lean fuel mixtures and poor operation. The problem could be a clogged fuel filter; but, could also be a dying fuel pump or a faulty fuel pressure regulator.

Take a look down your throttle body and see if it needs cleaning (including the various ports in the throttle body). If the throttle body turns out to be dirty, pull out the intake air temp sensor and check it. A dirty throttle body and / or intake air sensor will screw up the fuel mixture. These are low cost actions that do not require the replacement of parts.

Has the engine ever had the valve clearances adjusted? That can cause operating problems; however, valve clearance problems tend to creep up on you rather than show up all of a sudden.

Here's what I've done. I pulled the coils, all 3 of the rear coils had oil residue on them from leaky valve cover gaskets. The fronts were all dry. Rear spark plugs were all nasty. I replaced all the valve cover gaskets, replaced the spark plugs, cleaned the coil packs, put dielectric grease on them, tested all the coil packs and they all test the same and seem to be okay. After all of this, I let the car warm up and took it out. It ran smoother but still having hesitation, stumbling on low rev accel and popping at idle.

I do have a fuel pressure gauge on the fuel filter, which appears to be reading normal. I've ordered a new fuel filter just in case, cheap enough and I don't mind replacing it. Will see if that does anything. Throttle body is clean, I replaced my intake recently, everything was spotless. I even did the Seamfoam through the manifold and there really wasn't any smoke at all, so I'm assuming things are pretty clean inside. As far as I know, engine hasn't had any valve adjustments. Though the motor only has 60k seemingly easy miles on it. I'm going to also fill up the tank with some gas from a different gas station.

I'm sure the oil getting down in the tubes and nasty spark plugs didn't help anything. But I feel like this may be more of a fuel problem. I would have imagined if the coil packs were faulty, the CEL would go on right? Will try new fuel filter and full tank of gas and see what results.

SoloNSX said:

put dielectric grease on them

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Dielectric grease is a non-conductor so you don't want to get any of it on the top of the park plug.
Still suggest you check codes as it helps to know what's stored in there.

BTW what spark plugs are you running?
Is your engine stock?

Based on the pixs of the plugs you removed...you should have a look at this post.

http://www.nsxprime.com/forum/showthread.php/181594-Coil-pack-weather-strip?highlight=Bram

Bram

The photo of the nose of that one coil looks nasty! Its not conclusive that they are the cause of your problem; but, I would be inclined to replace just based upon their visual condition.

If by testing the coils do you mean you did the resistance test as set out in the service manual? If so, that is the most basic of tests and is really just useful for confirming that a coil is totally fried (shorted internally or open circuit). The most common problem resulting from contamination on the coil nose like you have is external flashover on the high voltage terminal. In this case, the high voltage spark current goes to ground through an external path on the coil nose rather than across the gap on the sparkplug - resulting in a misfire. This flashover is caused by insulation failure on the sparkplug insulator nose and the coil resistance test does not detect this problem.

The OBDII ECU monitors the voltage on the coil pack (that third terminal connected to the misfire detection module). The misfire detection circuit can reliably detect a total spark failure event; but, may not be able to differentiate between an external flashover on the sparkplug insulator and the normal flashover on the sparkplug gap. OBDII cars also have a misfire detection system that checks for small rapid fluctuations in crankshaft speed caused by misfires; however, most manufactures filter these signals because really bumpy roads can also cause the same fluctuations resulting in false misfire error codes. So it is possible to have slight ignition misfires and the OBDII not throw a code.

You can try cleaning the coil insulator nose; however, if you have had a number of flashovers it can result in tracking which permanently damages the surface of the nose. Once clean, evidence of tracking can be exceedingly difficult to see; but, it still causes flashover problems. I recall seeing pictures on Prime of somebody who had the coil out of the engine but still connected and with the sparkplug still in the insulator. They were pressing the plug body against the side of the sparkplug well and they had somebody cranking the motor. You could see external flashovers on the nose of the coil. Given how bad your coil nose looks, I would be inclined to replace them and follow Bram's advice on fixing the source of the contamination.

As a heads up, rather than buying three new individual coils, Honda has a coil pack replacement kit that offers a set of six new coils. Do a search on Prime and you should be able to find the part number for this kit. My hazy recollection is that the replacement kit is cheaper than buying 3 coils separately.

As a note, although the photo of the plug tips is indirect, based upon the color and condition of the insulator tips on you sparkplugs that are visible, it doesn't look like you have an obvious fuel mixture problem.

Well, just went out to get some gas with the car and shortly after driving around the CEL finally went on. Need to get a code reader... At least this, like you guys have mentioned, will help steer me in the right direction.

SoloNSX said:

Well, just went out to get some gas with the car and shortly after driving around the CEL finally went on. Need to get a code reader... At least this, like you guys have mentioned, will help steer me in the right direction.

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You can read a lot of codes by shorting the blue service connector in the passenger footwell and turning the key on. CEL/MIL will flash the codes at you long flashes for tens digit and short flashes for ones digit. The codes are in the service manual.

he has a 95 so he could just plug a reader into the obd2 port.......btw this is what happens with 45 series front tires...:wink:

docjohn said:

he has a 95 so he could just plug a reader into the obd2 port.......btw this is what happens with 45 series front tires...:wink:

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Yes a reader is an important tool for these cars but I was suggesting something that might give some useful info before he gets a reader. I think some codes only show up on the service connector (like ABS and power steering?).

The too-big front tires may trigger TCS and but will they trigger the MIL?

Just for the record, I've never had the TCS light come on with these tires. Hell it barely flashed when I went out on an autox run and realized I left it on mid run lol. Grip>tall tires with no ill effect from what I can see.

I just bought a code reader from Amazon. Never needed one before with my other cars..

I'm just busting you for stretching the rules of nsx land....:tongue:

Finally able to pull the code. Cylinder 1 injector circuit open.

Did the codes change in '97? The '97-'05 manual lists 1201 as cylinder 1 misfire related to fuel injector, fuel-injection circuit, ignition system, low compression, or valve clearance. I don't see a code specifically for injector open.

Well the good news is you only have one fault showing and it's a misfire code on cylinder #1 . Try swapping a coil pack from #3 with #1 and see if the code follows. If you get a new code of P1203, you know it's the coli pack and you will only need to replace one of them.

jwmelvin said:

Did the codes change in '97? The '97-'05 manual lists 1201 as cylinder 1 misfire related to fuel injector, fuel-injection circuit, ignition system, low compression, or valve clearance. I don't see a code specifically for injector open.

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Just read from the code booklet provided but yeah that should be the code specifically for this car. I'm pretty sure it's just a faulty injector, esp looking at the spark plugs and thinking about the symptoms when driving. Hope to fix it before this weekend. Should be installing resonated test pipes tomorrow so I definitely want to drive it this weekend lol

SoloNSX said:

Just read from the code booklet provided but yeah that should be the code specifically for this car. I'm pretty sure it's just a faulty injector, esp looking at the spark plugs and thinking about the symptoms when driving. Hope to fix it before this weekend. Should be installing resonated test pipes tomorrow so I definitely want to drive it this weekend lol

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I suggest you try Valhalla's suggestion of switching the ignition coils. Its zero cost and would eliminate the ignition coils as the source of the problem. You want to make sure it isn't the coil before you go fiddling around with the injectors. Much easier to R&R a coil than an injector.

The code is not specific. Starting in 1995 there was a "misfire" detection module added to the car. This code just means misfire, and does not relate specifically to a fuel injector per say. The manual lists the 5 things it could be. Swap the coil for sure.

HTH,
LarryB

In case anyone is interested or for future searches for similar issues, here's an update. Since the code read cylinder 1, I replaced the cylinder 1 injector. Still didn't fix anything. After doing that, I noticed on the cylinder 3 wire harness one of the wires was chewed up and exposed. I thought this may have been the culprit, I repaired the wire and still did not solve the issue. Engine was still misfiring/backfiring between 1.5krpm-3krpm. Decided to replace the other 2 rear injectors and there we go, seems to have solved the problem. I'm not sure which one of the 2 was bad since I replaced both at the same time. But after putting about 70 good spirited miles on it between yesterday and today, I haven't felt a single hiccup. I'll be replacing the front 3 injectors as well. Should have gone with my original feeling of it being one of the injectors..

All said and done, the car runs fine now. In some ways I'm glad this happened as it made me do some necessary repairs that before this I was unaware of.

Awesome that the issue appears fixed.