Hi guys I was wondering if someone has experience with the situation I am in. Driving home from work today all of a sudden the car developed a miss fire during partial throttle (If I put my foot down more it clears) and it miss fires at idle as well sounds like it has a big cam kind of miss fire (if I tap the gas at idle the miss fire clears). The check engine light did not turn on however I did cycle the OBD1 jumper and the traction control light gave two codes: # 31 A/T FI Signal B and # 51 Rear VTEC Solenoid Valve. I am tempted to drive the car further hoping the check engine light comes on so I could get more information but I am not that interested in driving around on a miss fire.How can I diagnose things like coil packs, sensors, air leaks, plugs etc to determine what is causing the issue and what is not? I am not new to engines but new to NSX's as this is my first one is there anything common that could cause this? It is a relativity stock 1991 5 speed nsx with 178,000 miles on the engine no oil consumption, no coolant consumption, and good compression results 4,000 miles ago (everything was within 20 psi). With aftermarket headers, stock cats, and an aftermarket exhaust. Does anyone have any suggestions on what could be causing the miss fire, or where to start?
Missfire with fault codes 31 & 51 / 91 nsx, 5 speed
- Thread starter Toddp
- Start date
Those descriptions are for error codes read on the MIL not the TCS light. If the TCS light is showing the codes, the TCS 3-1 code is a problem with the fuel injection ECU or the TCS control unit and the TCS 5-1 code is abnormal fail safe relay. I don't think you would be getting 31 on the MIL unless you have a secret automatic transmission!
If you really do have a misfire, I think the early NSX ECU has to go through 3 bouts of misfire before it will light the MIL; however, if you have 1 or 2 stored events, I think you should be able to retrieve them even if the MIL is not lit up. Check the fuel section of the service manual for a better explanation. If you don't have any stored misfire codes, you likely (not a guarantee) do not have a misfire problem. Your TCS may be doing funny things.
Pull and record (don't just erase) all the stored codes on the TCS and ECU and then reset everything and see if the problem re appears. You may be in for some TCS diagnosis. Do the drive-ability issues go away if you turn the TCS off?
I have been around a couple of NSXs (including mine) and they all seem to have a very pronounced thump at idle, particularly noticeable when the engine is cold. I find that it is more noticeable from inside the car and is not all that noticeable listening outside. This thumping does not seem to manifest itself as a noticeable change in engine speed on the tach and it is present over a very limited range of operation (definitely disappears if you rev it a bit). I don't know whether it is an oddity of fuel mix under those particular conditions or an artifact of the 90 deg V6 engine with the resultant uneven firing pattern. The first time I noticed it I thought I had lost a big end bearing. That was seven years ago and it continues to run fine. Don't mistake that sound for misfire.
If you really do have a misfire, I think the early NSX ECU has to go through 3 bouts of misfire before it will light the MIL; however, if you have 1 or 2 stored events, I think you should be able to retrieve them even if the MIL is not lit up. Check the fuel section of the service manual for a better explanation. If you don't have any stored misfire codes, you likely (not a guarantee) do not have a misfire problem. Your TCS may be doing funny things.
Pull and record (don't just erase) all the stored codes on the TCS and ECU and then reset everything and see if the problem re appears. You may be in for some TCS diagnosis. Do the drive-ability issues go away if you turn the TCS off?
I have been around a couple of NSXs (including mine) and they all seem to have a very pronounced thump at idle, particularly noticeable when the engine is cold. I find that it is more noticeable from inside the car and is not all that noticeable listening outside. This thumping does not seem to manifest itself as a noticeable change in engine speed on the tach and it is present over a very limited range of operation (definitely disappears if you rev it a bit). I don't know whether it is an oddity of fuel mix under those particular conditions or an artifact of the 90 deg V6 engine with the resultant uneven firing pattern. The first time I noticed it I thought I had lost a big end bearing. That was seven years ago and it continues to run fine. Don't mistake that sound for misfire.
Last edited:
Okay thanks for the info, Just so I know When the check engine light flashes, and the tcs light flashes they throw different codes from one another? I did drive around today with the traction control off, and still noticed the hesitation. Everything you mentioned makes a lot of sense that my car may not be miss firing, so Ill look at it as more of a hesitation as I put my foot on the gas rather than a miss fire.Now that I think about it I just put a set of wheels on my car two weeks ago; I searched around before buying them to get the proper size but maybe I mess up. Lets say I did get the wrong size wheels and tires how would the car act with the traction control going against my wheel size? My fronts are 18x8.5+45 with a 215/40/17 tire and my rears are 18x9.5+35 with a 265/35/18 tire, is there a possibility that size and setup has something to do with causing this hesitation?
I have an OBD II, so no direct experience with the pre OBD II cars. My take on the instructions in the service manual is that triggering the service check connector will cause display of stored codes in the ECU, ABS and TCS and EPS (I think). I assume, reading between the lines in the manual, that if you have errors in multiple devices, the codes will all start displaying at the same time. The codes displayed on each light would be specific to that device. Error code 31 on the ECU is not the same as 3-1 on the TCS.Increasing the rolling radius mismatch can trigger TCS operation; but, should not trigger TCS error codes. Error codes are an indication of a problem with the TCS system, not operation of the system. The tolerance to mismatch changes year by year so I can't comment on whether or not you created a problem for yourself. However, if the mismatch is triggering TCS action turning the TCS off should eliminate the retarding effect that the TCS has on the throttle. If you are still getting hesitation with the TCS off, something else is happening. You will need to do a little research in the service manual - I don't even know what the function of the TCS fail safe relay is.
So After resetting the ECU with pulling the clock fuse, the car has been running as it should. Hopefully it is something as simple as that, but I will keep an eye on it and if not dig into the traction control system and see if my new set of wheels could also be causing it. Thanks for the info.
Give it a week of driving and then use the service check connector again to see if there are any stored codes that have shown up since you did the reset. If nothing shows up, then life is probably good - sit out in the deck in the sunshine and reward yourself with a beer!
Similar threads
