40 replies to this topic

[Duane Polsley]

With the runoffs here and gone, It appears that several cars including some top notch teams and drivers had the dreaded missfire. Has anyone figured out exactly what the cause is. It's sad to see that all the effort, time and money spent just to get to the runoffs goes down the drain when this happens.

Should the rules be changed so that whatever causes it can be repaired permanently ? I know it starts with the cam sensor and/or the crank sensor along with the engine harness. Has anyone figured out a fix ?

 

Dewey~

[Michael Colangelo]

Is this primarily a 99+ issue?

[Duane Polsley]

AS far as I know it's only on the 99+ and maybe in the engine harness.

[MPR22]

Bill Agha is looking into having a new engine harness manufactured to help with the issue. It should be identicle to the Mazda stock harness just newer. I'm sure he will post something if he gets this project on track.

[ChrisA]

I had the misfire at hi-rpm. It killed a weekend at the Glen after a 7-hr tow. I checked everything and replaced the cam & crank sensors and the coil, but the misfire remained. When I got home I ordered some new spark plug wires, although I didn't believe the Magnecors were the problem. After I pulled them I noticed inside 2 of the coil-end boots that the terminals were very sooted. Enough so that it was probably the cause for my mis-fire or at least the continuation of it after replacing the coil. The problem, knock-wood, hasn't returned. What I think happened was the coil was failing and became heated enough to burn the dielectric grease I used on the terminals. I'll never use that stuff again, because while it's good for preventing corrosion on the connections, it is bad for actual electric connection. Since a dielectrics function is to act as an insulating electrical barrier. Sad thing on my weekend, replacing the wire was the only thing I didn't try and I had an old set of NGK wires in my track box. 

[Keith Andrews]

Maybe it has something to do with The Glen 

 

[Todd Green]

You do realize that Bench Racer has little voodoo dolls of all the 99 cars and is just randomly sticking pins in them, no?

[Keith Novak]

I don’t think there is “a” solution to misfire problems as there are multiple potential causes. Sensors, pinched wires, loose or bad grounds, bad connectors, etc. can all cause the problem in any year car.  The more times parts are replaced, the more opportunities for something to get damaged in the process.  I've had a few of the issues above on occasion.  I've had a plug wire (Magnacor as well) separate from the connection to the coil inside the boot.  I think I have a gremlin now because my car acts like it fuel starves but only in one specific corner after a series of tight downhill turns with lots of fuel that may be something loose somewhere.  They can be a bugger to diagnose because they're often intermittent and can be caused by so many things.

 

[Bench Racer]

You do realize that Bench Racer has little voodoo dolls of all the 99 cars and is just randomly sticking pins in them, no?

Only if they have an issue below 5,500 rpm would it be Bench Racer's handy work. Don't want to start any $hit with the 99's about above 6,000 rpm's because then the 99's would sticken pins in their 1.6 dolls.

[Jim Drago]

I took the time to cut open Craigs harness from one end to the other. I never felt the need to do this, since we had plenty, we would just change the harnes when needed. In short, this harness is a patched up POS! There are no less than 16 different splices and crimps in this harness. I hate to say, but we will start disassembling each harness before each build and soldering ALL of these crimps and joints.

Of the three wires going to the cam position sensor the power wire is spliced 1 feed into 6 wires and crimped together. The ground is joined with two other grounds (3 into 1) then that one is joined in a crappy plastic junction box of six more grounds. I will post some pictures of all the splices and crimps.. NONE are done by us, all as the harness was delivered.


here are a few pictures.. look for orange circles..  
We are going to solder all of these from here forward before installing, looks like fun

[AW33COM]

^ Would a brand new harness fix this?

[Jim Drago]

^ Would a brand new harness fix this?

It is not available new, but I imagine a new one would last quite awhile before having the same issues. I did not find anything obviously "loose" in any of teh crimps related to cam or crank sensor BTW

[DrDomm]

Are you allowed to run a "modified" harness?  "Repaired"?

[Joe (dad) Jordan]

After struggling through 2 weekends, which happened to be 2 of the most important races of the year with our 1.6 can we officially have a rule that allows us to wire our spec miata's without the factory wiring harness?  My understanding is it's illegal to do so.  I could be wrong, but these misfires from wiring harnesses older than my driver are killing us...rant over...

 

We replaced the following: kill switch, alternator, tps sensor and wiring, cam sensor and wiring.  (then tried wiring directly too sensor), air flow meter, fuel pump, fuel filter, injectors, ecu, tried to buy a new engine harness...not available....  still not solved.....

 

On too next year!

[Joe (dad) Jordan]

Bill Agha is looking into having a new engine harness manufactured to help with the issue. It should be identicle to the Mazda stock harness just newer. I'm sure he will post something if he gets this project on track.

Bill please help the 1.6's too if you get this figured out.  You have your first customer ready to go!

[Derrick Ambrose]

After struggling through 2 weekends, which happened to be 2 of the most important races of the year with our 1.6 can we officially have a rule that allows us to wire our spec miata's without the factory wiring harness?  My understanding is it's illegal to do so.  I could be wrong, but these misfires from wiring harnesses older than my driver are killing us...rant over...

 

We replaced the following: kill switch, alternator, tps sensor and wiring, cam sensor and wiring.  (then tried wiring directly too sensor), air flow meter, fuel pump, fuel filter, injectors, ecu, tried to buy a new engine harness...not available....  still not solved.....

 

On too next year!

 

You left out going from one end of the car to the other checking all of the grounds and power connections!  That was fun

 

-Derrick

[AW33COM]

Those splices and crimps in the picture above are done by someone else than Mazda, which does not explain the same misfiring problem across multiple cars.   Unless they came from the same shop, which I doubt.   

[Jim Drago]

Those splices and crimps in the picture above are done by someone else than Mazda, which does not explain the same misfiring problem across multiple cars.   Unless they came from the same shop, which I doubt.   

 

Joe, do you have a video of your 1.6 misfiring?

I doubt Mazda makes the harness, but those are 100% certainity in every 99/00 miata harness. It is definitely not something done post production. They came off the assembly line that way.  

[AW33COM]

those are 100% certainity in every 99/00 miata harness.

 

Did not know that.  I have never seen a splice like that unless home shop production.  Even Lucas Electronics would not do that. 

Scary, I wonder if my 1.6 has that kind of work hiding somewhere. 

[Jim Drago]

Did not know that.  I have never seen a splice like that unless home shop production.  Even Lucas Electronics would not do that. 

Scary, I wonder if my 1.6 has that kind of work hiding somewhere. 

It does for sure