Mystery motor problem, code P1399

I'll start with the basics:
2002 NSX, 6-speed
Stock motor, 42,000 miles
All scheduled maintenance done
Aftermarket exhaust, high-flow cats, K&N filter, otherwise stock
Never had any other problems with the motor before

I go to start the car yesterday after driving her to the grocery store, and suddenly the car feels/sounds/accelerates more like an air-cooled VW beetle than an NSX. Motor is running really rough and it sounds a bit louder. Check engine light flashes any time I push the pedal down more than about 1/3 of the way. NO SMOKE coming out of the tailpipe. I limp the car home (luckily it's only a couple miles to my house) and check the codes. Only one.....P1399.

So, I get on Prime and just about the only thing I can find on this code by itself is a suggestion to clean the EGR valve and the throttle body. I suspected that maybe this would help since I was running the K&N filter and they are known for gunking things up downwind because of the oil. So, I disassembled both and cleaned them as good as I could......there was a thin coating of gunk on everything that cleaned up easily. Looking inside of the intake manifold, things looked fairly clean. So, I reassembled everything, pulled the clock fuse to reset stuff, installed a standard air filter, and it didn't fix a damn thing. Still running like crap, still get the flashing engine light when I push down >1/3 on the gas pedal, and the P1399 code.

This comes completely out of the blue for me. I haven't done anything to the motor in a long time, so there's no recent changes that I can go back an look at. The car had been driven several times in the previous week (and just 20 minutes prior as well), with no issues at all.

Could it be the igniter? There are no other codes other than the 1399, which is confusing based on what other folks typically get. The only other thing I can come up with is that maybe it might be on the fuel delivery side? Would a low fuel pressure (pump going bad or clogged filter) cause this? Any potential of the motor having more serious damage/ issues that this might be a symptom of?

Any help would be greatly appreciated! I really don't want to have to take her to the local dealer. I haven't had my car in to the dealership here yet (SOS is up the road in Phoenix and are who worked on her last, but I don't want to truck the car up there just yet).

Please someone help! Surely someone has seen this before, or may have an idea.

check post #15 here http://www.nsxprime.com/forum/showthread.php/59059-Check-Engine-Light-and-TCS?highlight=cel+p1399

I would replace the main relay.

Thanks to both of you! This gives me a vector to go on.

Update so far:

Looking at the "easy" stuff right now. Pulled the spark plugs, all looks normal. Coil packs all appear to be in working condition and could almost be mistaken for brand new. No rust, no water anywhere. I started the car and did two things......pulled each coil pack at a time off of their spark plug, to see if I could isolate a cylinder that may not be firing. Nope, all cylinders are creating a spark. I also listened to the injectors with a stethoscope to see if one wasn't working the same as the others. Nope, all sounded the same. But the car is still running really rough, code P1399 and a flashing CEL.

Next, I will swap out the main relay and check the fuel pressure since I have the capability to do both. I will also do a local search for an ignition module at a junk yard (as per the thread in the link above) to see if that leads me to any conclusions.

I believe that there may be some main relays floating around the Phoenix owner community that you may be able to borrow for testing

YET ANOTHER good reason to have a group drive to Tucson to hang with ya ; )

Probably not the case, but easy to Check the injectors as well. using a car stethoscope (or a home made one using tubing and a rod) with the car running (and CEL on) listen to each injector. You should here tapping from each one, if one or more is not tapping they are bad or clogged. You can ohm them to while you are checking.

I did check them with the homemade stethoscope idea, but it wasn't with the flashing CEL on. That light doesn't come on until I have the gas pedal pressed down more than about 1/3, and that really only happens under load (ie I'm in gear and driving). The car still runs like crap, though, whether the CEL is on or not.

RedWings, I hesitate to say this because I don't want you to cancel a road trip down here, but I actually do have a spare main relay.

Clogged cats?

Tangoman said:

Clogged cats?

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I wish it were this easy! I pulled the cats earlier, and they are both in perfect condition. The exhaust out the back of the Taitec GTLW seems to be normal, so there's not anything now that would point me in that direction. However, I have gotten a P1410 code with the P1399 the last two times I've started the car, so maybe the EGR valve is the culprit after all based on a single thread I found here on Prime: http://www.nsxprime.com/forum/showt...-Engine-Light-P1607-and-P1410?highlight=P1410 Yep, another rare (for the NSX) code that isn't on the code list in the NSX Wiki.

I'm gonna swap out the main relay just to be sure anyways, since I have the panels off the rear firewall behind the seats right now.

I let the car run for about 45 minutes to see if warming up the motor would change anything. Nope, it sounds and runs just as crappy cold as it does warm.

- - - Updated - - -

Well, it's not the main relay. Swapped it out and no changes. EGR valve perhaps? Wonder if anyone has any ideas before I start spending money.

An EGR failure would be really rare on an NSX, not so in other Hondas where it is quite common. I had a failure on another Honda and solving this Problem was changing the EGR. It has a potentiometer in it and if it's worn out the ECU is getting wrong data. In this Scenario you can clean all air passages but won't cure the Problem.

BUT I highly doubt that a bad EGR would let your engine run like a Beetle.

Regarding the excessive loss of power you describe: fuel delivery in general as you've ruled the ignition System out as you describe (except the igniter unit). P1399 is random misfiring as I've read somewhere (not sure).

Good luck!

I suggest getting a compression or leak down test. You could have a carbon deposit stuck on the valve, causing a misfire code. And you will be able to see if you have a healthy engine.

If you are suspecting this is related to perhaps fuel starvation, check the fuel filter. Many owners forget to do maintenance on this cheap part which does tend to get dirty. One symptom is it cut off your fuel unexpectedly - not fun if you experience it at track out on a no margin-of-error corner.

I had the same problem on my 91 after a washing/detailing weekend in 2004. Turned out that my igniter went goodbye.Replaced and no problems for many years now

If the cel is flashing its probably a misfire issue. Continue to check the ignition componants also check fuel pressure. Have you thought possibly bad gas?

Actually, it totally could be bad gas. It could be the igniter, it could be the fuel filter, it could be just about anything. That's the frustrating part, is trying to diagnose this. Another reason why I'm running the car as much as I can is to see if it "burns through" the bad gas if there is any. I figured that if there was some bad gas, it wouldn't be a whole tank full of it (the water/etc would settle at the bottom of the tank and be out of the system fast?).

I thought that the fuel filter was changed a while back when I got the timing belt/water pump done at SOS, but I'm gonna have to find the receipt to figure that out.

The whole reason why I was looking the EGR route is that the exhaust is noticeably "smellier" than it normally is, almost as if I'm running straight pipes instead of cats. The cats look just fine, though, and there's no smoke coming out of the back. I figured that the EGR might not be working as it should, contributing to the problem. However, I'm not sure if the EGR issue would cause a misfire code. Sigh.

Checking the fuel pressure today, since that's about the only thing I have left to check before I start spending money on replacement parts.

Thanks for the help everyone, by the way!

When you say smellier what do you mean. Usually if the cats blow through or guys that don't run cats will report a more sulphery smell. But even with no cats you shouldn't have that problem. Just be weary last time a friend of mine drove his car with a missfire issue it ended up burnung a valve. Have you had a missshift lately? Possibly a bent valve. Also do a commpression or leakdown test and report results

Rogue MotorSports said:

When you say smellier what do you mean. Usually if the cats blow through or guys that don't run cats will report a more sulphery smell. But even with no cats you shouldn't have that problem. Just be weary last time a friend of mine drove his car with a missfire issue it ended up burnung a valve. Have you had a missshift lately? Possibly a bent valve. Also do a commpression or leakdown test and report results

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It just smells like car exhaust, that's really the only way I can put it. I used to run test pipes on my '91, and the exhaust smells the same as that (but nowhere near as strong).

I have been getting a sporadic P1204, but I thought that was because I got a little air in the fuel line when I put the banjo bolt in that I have the fuel pressure gauge connected to. Speaking of which, the fuel pressure is fine on the outlet side of the fuel filter, so I can eliminate that.

The two most persistent codes are P1399 (always) and P1410 (about 1/2 the time.)

Okay, now you have me scared about the valve. I haven't missed a shift lately, but I did bounce off the limiter about 4 days before I started having the problem. I drove the car four or five times between that and when the motor started running badly, though. Dammit, I really don't want to take her to the dealer, but I can't do a leakdown or compression test on my own.

The 1399 is the random misfire code, and would result in a flashing check engine light. The 1204 is the missfire code for cylinder 4. The p1410 seems to be air pump malfunction. Does the nsx have any type of pump for removing crank case pressure?

I hate to get you nervous about it. How many miles on the motor? Has it ever had a valve lash adjustment? A compression test would be a rather easy check. If you can change your spark plugs you can do a compression check. If you need any assistance feel free to pm me.

Reading over the thread I am thinking your timing belt has jumped a couple of notches. A compression check would be a good thing to do.

The timing belt being out of time could cause those issues. But unless it bent valves compression test wont tell you if its out of time.

Update:
I got the leakdown tester and a compression tester in the mail today. I was "solo" in the garage, so I found that finding TDC for the leakdown was a royal pain in the ass by constantly getting up and looking, then going back under the fender to rotate the flywheel, and so on. Instead, I opted to go the easy route and check the compression. I'm happy to report that the motor is healthy in that regard......all cylinders were between 197 and 202 psi at 2500' elevation. That obviously doesn't mean a thing as far as the timing goes, which I am wondering if there is an easy way to check this? I have a friend with a timing light who can help me tomorrow night.

Viper Driver said:

...That obviously doesn't mean a thing as far as the timing goes, which I am wondering if there is an easy way to check this? I have a friend with a timing light who can help me tomorrow night.

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Well, it means that it's not far off. Checking the timing means dismounting the cyl. head covers.

Update:
Swapped out the exhaust because someone suggested that it might be back pressure from a clog somewhere, no change. Changed the fuel filter, siphoning out a couple of gallons of fuel in the process just to see if it might be bad gas. No change.

Spoke with a local factory-trained NSX tech today, and he thinks that either a coil pack or spark plug is bad, and it manifests itself when any additional power is applied over idle. He said he doubts that it's the timing. I'm still not sure, but swapping out spark plugs and coil packs is still cheaper than cracking the motor open for timing belt repair, and I can do it at home. So, I'm going to try this first before I take her to the shop. Luckily, she can sit in the garage for a while since she's not my daily driver. Still frustrating, though.