If you found this page you more than likely are having issues with "hesitation and bogging" during throttle application in a Miata. This is somewhat of a common problem for this generation of Miata. My problems were primarily below 4000 rpm, and after the engine had warmed upwards. Throttle response was seemingly normal across all rpm ranges with a cold engine. With a warm engine and above 4000 rpm the acceleration seemed normal.  A warm engine is indicated by the O2 sensor sensing a warm frazzle manifold. The troubleshooting I've washed here is specific to a 1.8L 1995 Miata, you may apply what I've done here for your application.

This may have been a trouble that has been stewing for awhile but became such an issue at Hallett this past summer that I had to solve information technology.

Video of the event with a warm engine [Note the misfires, VERY bad news, indicates a VERY lean condition and can damage the engine]:

The simple "golden dominion" with any debugging is start with what is nearly elementary and to the lowest degree expensive and work your way up. Retrieve, the internal combustion engine is simply an air pump and needs i). air, ii). fuel and iii). spark, or ignition, to role. Go along that in mind during any troubleshooting of engine issues.

The Haynes manual describes these steps, in order, to tackle "Hesitation and stumble during acceleration":

  • Ignition timing
  • Ignition arrangement non operating properly
  • Muddy or chock-full fuel injectors
  • Depression fuel force per unit area

Below is the guild of troubleshooting that I went through to solve my issue and may aid you solve yours:

MAF (Mass Air Flow) Sensor

From prior feel I know issues with the MAF (Mass Air Flow) can cause SERIOUS issues with acceleration. [Note: I was at Autobahn Country Club most Joliet, IL a few years agone and ran across the FIA rumble strips pretty aggressively on corner go out and jarred the piping connecting the air inlet to the throttle torso loose. I immediately went offline, struggled back to the paddock and discovered the consequence when I opened the hood]. And then bank check all of your connections and vacuum hoses and make sure they are tight from the air box to the throttle body.

You may besides attempt cleaning the MAF by putting it in a large GLAD handbag with booze and shake the bag to completely glaze the MAF. Remove and be sure to let COMPLETELY DRY before re-installing otherwise you lot may damage the internal electrical components if y'all try and start the car earlier dry. I let mine sit outside on a dry summer night all night and re-installed the following afternoon after returning home from work.

TPS (Throttle Position Sensor)

I wanted to await at the TSP because a guy in my paddock had an acceleration issue last season, and his issue was a bad TPS.

The throttle position sensor is located just to the right of the throttle body inlet. This sensor tells the ECU (Engine Control Unit) the position of the throttle plate. The ECU uses this data to calculate the amount of air flow to the engine and the corporeality of fuel to exist injected for the required ratio of air-fuel mixture.

From the image below, Pins A & B are the variable resistor that changes equally throttle is applied, and Pins C & D are the idle switch.

Use an ohmmeter across pins A & B, the resistance should subtract linearly every bit the throttle is opened. For me, I had iii.26k Ohm at idle and decreased linearly to 1.06k Ohm at WOT (Wide Open Throttle).

Pins C & D should bear witness a  short (continuity between C & D) in static position, or idle position. Pins C & D should and so evidence an open (no continuity between C & D) when rotated off idle position.

The TPS tested equally skillful.

1995 Miata TPS, Pin out

Ignition Arrangement

It should be noted the ignition col is the nearly expensive part in all the troubleshooting I was doing, and then I was putting that off for final.

Pull the spark plugs and compare against the film of analyzing spark plugs in most maintenance manuals. For me the spark plugs checked out, although well-nigh had a slight ash deposit indicating a rich mixture. [Confusing to me considering the misfires indicated a lean condition].

I knew the spark plug wires were skilful considering I had but replaced them earlier in the twelvemonth with MSD screw whorl wires.

O2 Sensor

The O2 sensor is located on the drivers side simply off the exhaust heat shield. There is a hog tail wire leading from the O2 sensor and connected at the main engine wire harness near the upper office of the rear of the engine by the ignition whorl. Wait for the engine to warm upward. This normally occurs inside 2 minutes with the engine started from cold, and can be observed by a noticeable drop in rpm at idle. With the engine warmed upward disconnect the pig tail wire of the O2 sensor from the main engine wire harness. Repeatedly and quickly apply large amount of throttle. If throttle response is normal, replace the O2 sensor. For me, I still had the  "bogging" and misfires. And so the O2 sensor was not the consequence.

Fuel Pump

As I was troubleshooting I recalled the only thing in the stuff that I was checking that had changed within the past year was the fuel pump. I installed a new fuel pump last year. And so I began to investigate the fuel system thinking I may accept a bad unit of measurement. Seems unlikely, merely I'll check.

Connect a fuel pressure guess (About $60 at your local auto parts shop) to the high force per unit area fuel line. The high pressure fuel line is the rearmost of the ii metal lines (passenger side of engine), pictured.

1995 Miata, fuel lines

Pictured below is the force per unit area I read off the fuel pressure level gauge. The Haynes manual states between 32-38 psi is normal, at idle. Yous can check the maximum output of the fuel pump past crimping the return line with a pair of pliers and observe the pressure level. If information technology does not increase the problem is either the fuel pump, fuel filter or fuel feed line. Not stated in Haynes,, you tin eliminate the fuel filter or fuel feed line every bit the problem by connecting the fuel pressure gauge right off the fuel pump coming out of the tank. I did and observed simply nigh the aforementioned 20 psi as pictured below. Bingo! At present I'grand getting somewhere!

Denso makes the function for Mazda so I got on Google and searched for the part. [The fuel pump that I replaced last yr I bought at a local machine parts store and was made in Mexico]. I recommend, in retrospect, going correct to the source. This car goes on runway so I am looking for performance. I found a certified Denso part online for around $100. You local Mazda guy will ask around $400 for the same role. A 300% markup for spare parts past the manufacturer is non uncommon. What would we do without Google?

low fule pressure

The office arrived [Made in Japan! Yea!!!] and I installed, including new high pressure pocket-size safety hose connecting pump to the sending unit of measurement. The one I pulled off was a little cracked (after less than a year being in the tank).

Pictured below is the new pressure number I saw at the fuel line in the engine bay. 35-36 psi is correct in the sugariness spot! Video beneath is how the engine at present sounds with new fuel pump!

Miata, normal fuel pressure

Summary

This is what worked for me. When I researched this issue online, I constitute other things that fixed the event for other people, and other issues that were similar simply not the same. I wanted to post what worked for me in hopes information technology may help someone else. Over again, start most simple (like spark plugs, MAF connections) and least expensive, and piece of work your fashion upwards. Good luck! In that location is cipher similar the Eureka moment! and the feeling of solving the issue!

[I stated "seemingly" in the showtime paragraph when discussing throttle response, because I did know at the time that I had a fuel pump just capable of producing 20 psi, which was OK with the engine cold and using the difficult coded AFM (Air Fuel Mixture) in the ECU of 14.seven:1. I may take had this consequence for sometime, and what I thought was normal, actually was not].