this just popped into my head today. i was working on a car at work... and old chrysler and found the ignition module was making the car cut out at certain rpms... so i put a new ingition module on and bam... ran great and customer was happy. so since i never have any time to work on my own car (work 7a.m. to 7p.m., 6 days a week) i was thinking maybe some of you guys could back me on this one... i have an 86 n/a and the will not go past 3800 at all. i replaced the fuel injectors, fuel pump, filter, added grounds everywhere, new computer, new spark plugs, newer coils, newer pressure sensor... and it still falls flat on its face at 3800... when it does this, right at 3800 the sound of the engine changes, like its only running on one rotor or just the leading or trailing plugs or something with the ignition firing.... where is the ignition module located? or are they built in to the coils? what could be breaking up the ignition like that? at least i think thats what its doing, since i replaced all the stuff as listed above....

 

Have you checked the wireing harness from the secondary injectors back to the ecu?

 

yeah harness is all good. i know theres a few other people out there with this problem as i have read their posts before about it. since i have straight pipe (pretty much) exhuast on my car i can hear it alot better when it "falls flat on its face". it sounds like ignition break up. like i said the sound of the motor changes its weird, and since i replaced the computer and secondary injectors and all that its got to be ignition....i know if i take it to the local mazda dealer they could fix it but im not willing to spend like $700 for the them to fix it

 

i believe its cuased by ignition breakup, not the secondaries not firing... i know more people than me are having this problem/?? no body can back me on this?

 

matt..you tried new plug wiires ..never know ..

 

Everything above says you have a secondary injector not firing, particularly when you say "right at 3800 the sound of the engine changes, like its only running on one rotor". With one injector not working that chamber won't fire at all. The mixture will be too lean to ignite and the fuel just gets pumped out the back unburnt.

The fact that the secondaries are supposed to come on right when you say the symptoms start makes this far more likely than ignition. The trailing plugs don't do much for power so if they weren't firing you'd barely notice it. The leading coil is a double-post coil firing both leading plugs at the same time (wasted spark), so if it wasn't working neither of the leading plugs would fire. The engine would feel like it's making only half its normal power, but it would be perfectly smooth. It wouldn't feel like only one rotor was firing and it's very unlikely it would always happen at the same rpm.

I suspect a broken wire. You should check for electrical continuity between the injectors and the ECU. See a wiring diagram for the wire colours.

 

check the harness ground.

 

Yeah I agree with Jason, thinking the problem is the coil and ignition break up at 3800 is barking way way up the wrong tree.

Much much much (much) more likely that your 2ndaries are not working correctly.

And the odds of a Mazda dealer fixing it are like 1000 to 1

 

that's what I said in his last thread but apparently everyone thinks I'm crazy

 

wooof! i was having flashbacks of TFI modules and GM ignition modules going bad when i read the title of this thread.

don't scare me like that!

 

The "ignition modules" are "dumb".
You're barking up the wrong tree.


-Ted

 

On an '86, don't the secondaries crank up based on exhaust back pressure? If you're running straight pipes, then you've probably eliminated back pressure, which normally is a good thing, but now your secondaries don't know they're supposed to fire.

 

^ don't confuse auxilary ports and secondary injectors

 

You're so lost you need a map *and* a GPS tracker...
*sigh*


-Ted

 

excuse me. i need to laugh...

LMAO!!!!

 

Since you work on cars for a living.....................You could pull the vacuum hose off the boost/pressure sensor then back probe one of your secondary injector wires at the ECU (pins 3F or 3H) with a digital meter.

Then rev the engine over 3500rpm. Prior to 3500rpm the voltage will read whatever the alternator puts out. Once over 3500rpm there should be a voltage drop indicating that at least the driver in the ECU is working for that injector (either 3F or 3H).

The above is just a copycat of what is written in the 87FSM in the Fuel Section. Be sure to remove the vacuum hose off the boost sensor prior to doing the above or the secondary injectors won't come on line.

Your car is a candidate for a factory service bulletin that was issued against that year car. The problem traced to a AFM ground problem. So they added/spliced a extra ground to the brown/black ground wire in the BOOST SENSOR PLUG and attached it to the water thermostat housing. Note that virtually all the engine sensors ground wires, are ALL splice together in the Emissions harness and terminate in the ECU at pin 2A. Eventually finding ground on one of the ground wires 3A, 2R, 3G.

 

HAHA... man... alright cool ill check the secondaries again and see what i come up with... it was just a thought about the ignition... cuase it backfires and pops and all kinds of **** when i hit 3800... just sounds like ignition break up... ill find out why the secondaries arent firing soon hopefully. thanks

 

bad *** hailers... thanks man! ill get on that today

 

yeah i knew about the bulletin and already have added a ground from all ground pins on the ecu to where the ecu mounts to the floorboard and spliced in a ground wire from the brown/black wire of the boost/pressure sensor and termintaed it at the waterneck housing... no change at all in what its doing... my guess is that i just happened to coincidentally picked up 2 bad computers... both from junkyards

 

My 86 is having the same exact problem
Falls on its face around 3800 rpm
I just put another motor in becuase my coolant seals were shot,and this one is doing the same thing.
Its driving me nuts.in the next few weeks I am going to try and take it to a dealer and see if they can figure it out---I hate dealers but I have done everything that people have said on here ,with nothing working.

 

Swap the primary fuel injectors with the secondary fuel injectors positions and see if the engine runs like **** if it starts at all?


-Ted

 

That's what I told him in his last thread also. If it starts and runs that means the injectors are fine and most likely the issue is with your wiring to the secondaries.

 

Well nothing wrong with my wirring,I just put a new wirring harness in,along with a friends ecu and nothing--same damn thing--Oh and 4 brand new injectors--not remans.Not much more left.Same problem--no fix.