I've been battling a misfire in cylinder two. I've gone over everything I can think of. I started at the sticks themselves:
checked spark plug #2, was highly corroded, replaced. No change
I checked the ignitor sticks. all 4 of them have 2 ohms. No variation.
I swapped sticks between cylinders 1&2, no change.
Checked all grounds from all the ignitor connectors, through the harness, to ground. Consistently good.
I checked continuity of the trigger wires to the module. Consistently good.
checked voltage to each stick while firing at the molex connector- all four cylinders have 2.6vdc.
I have continuity, voltage, and ground. Why the #### wont this thing fire on cylinder 2?!?
for reference- 1997 miata, has denso Honda cbr sticks, VAG ignition module, and the Miata ecu controls that.
before anyone comes in to wag their head - yes. I know that's not an ideal setup, but it has been working for the last two years that way, I just need this thing to run long enough until my other setup arrives.
the only thing I can think of is the ecu isn't triggering number 2, BUT, cylinders 2&3 trigger together, and 1&4. And the idle only changes when I Unclick cylinder 2's connector!
here's a wiring diagram, although the COPs I'm using are 2 wire, not four. Instead, the the Miata ecu sends signal and voltage to the module, the module then sends the signal to the cop and ground returns through the module, and then the ground.
Leakdown and compression check. If those come back good, then lose your mind...
Or check the injectors.
You have checked spark. Fuel and compression are equally important.
Maybe I missed it but how do you know you don't have spark? A misfire could be fuel or compression related. Something like a broken rocker arm can cause misfire-like symptoms. Bad injector?
^ I guess we were typing at the same time, lol^
It reeks of fuel out the tail pipe when I let it run for a bit. CEL also confirmed p0302. Misfire cyl 2.
Yup. Fuel.
Ive also seen ignition modules fail in VERY strange ways.
In reply to Dusterbd13-michael :
So I bought two new modules, just in case. Installed, no change.
I think the next thing to do would be to pull the stick and plug out of cylinder 2, attach a wire from spark plug to ground and observe the arcing.
On some vehicles the ecu is measuring crankshaft acceleration at given points. Longtube headers or a cam can often throw a code for misfire. Just because it's throwing a code for misfire does not automatically mean it's ignition related. Try swapping injectors around, pull the valve cover and confirm everything is where it should be, if that checks out do a compression test.
A broken cam follower on the intake side would not open the valve so you're not getting any air to compress which would just dump fuel out the exhaust. I've been down this road with a SR20.
Could injector 2 be stuck open?
Just to clarify, occasionally fires normally, occasionally doesn't fire normally, occasionally sputters but never really fires, or is a totally dead cylinder?
Matthew
No, I took the car for a long drive after changing the belts. I was running the piss out of the car and came up a hill, noticed a sudden drop in power, CEL blinking. Pulled off, used my scanner. Limp home. Here I am. It misses non stop, never gets better.
Unbolt the coils. Fire the engine. Lift the coils one at a time till you can hear the spark snapping. If you have one not snapping, exchange it for one with a running cylinder. Problem moves? Coil. Problem doesn't move? Elsewhere. Buy a self powered led test light. Backprobe stuff.
All four snapping? Get a stethescope and listen to all four injectors. All four clicking? If not, get out your new self powered led test light again.
All four with spark, and all four with injector? Unplug all four coils, crank the engine and listen to the cadence. Rhythmic? Chuf-chuf-chuf-chuf, not chuf-chuf-whee-chuf?
All you need is compression, spark and fuel.
Do we know of a way to verify the Ecu is doing its part? I can measure 12v, but not sure how I would measure if it is triggering.
as you can see, the brown/ylw supplies trigger to 1&4. the brown supplies 2&3. Do I need an oscilloscope?
I will be doing many checks when I get home (checking for physical spark, injectors, compression)
In reply to _ :
A self powered test light will do a whole lot of basic signal diagnosis.
In reply to Streetwiseguy :
I've already done the basics. Now we are onto the harder. I need to know where to connect to so I don't blow fuses/meters/ecus.
a test light doesn't do a whole lot except let you know the amount of voltage is present to light it. I do electrical diagnostics ALL. DAY. LONG.
give me the info I need and my very expensive multimeter does the rest.
Sounds like it! If you have a good meter and even basic knowledge, this should be easy. A 2 channel scope would clear it up even quicker.
A self powered LED test light is a very different animal. Have you ever heard of a noid light? You can do the same thing with an LED test light.
http://www.amazon.com/OTC-3631-Heavy-Duty-Logic-Tester/dp/B001GZH1C8?ref_=fsclp_pl_dp_1
Hook the two cables up to power and ground on the battery. One LED will light up green to confirm you have power. Touch the probe to the positive battery post, and the second LED should light up green. Touch to ground, and it lights up red. Note- I might have the colors mixed up. Thats why you test it at the battery.
Now, since its a high impedance tool, you can backprobe just about anything without fear of killing drivers or something.
Figure out how to access the back side of the wire connector. Sewing T pins work well if everything is too well sealed up.
http://www.amazon.com/Pieces-Stainless-Steel-T-Pins-1-5inch/dp/B0777PCHJM/ref=sr_1_1?crid=1VSUXC7P5GQ0P&keywords=tee+pins&qid=1578084472&sprefix=tee+pins%2Caps%2C210&sr=8-1
Key on, engine running, you will have constant power on one connector on each coil and injector. On the other wire, you will have power through the coil pulled to ground to fire the coil or injector. You will be able to see the led become green/red/green/red etc. If it stays green, you are missing the trigger signal from whatever is driving the coil or injector. If its never green, you have an open winding in the coil or injector. The injector will get progressively more red as you increase rpm and duty cycle. The coil will stay the same, or close to it.
If you find you are missing a signal, head to whatever is supposed to be driving it, and see whether you have a signal there, if yes, you have a wire problem. If no, you have a problem in the driver, or in the trigger that runs the driver, and that might need the involvement of a smart guy so you don't wear out your parts cannon.
A very expensive multi meter can do a similar thing by watching AC voltage, but its not as obvious as an LED. A scope would be ideal, but expensive.
_ said:
In reply to Streetwiseguy :
I've already done the basics. Now we are onto the harder. I need to know where to connect to so I don't blow fuses/meters/ecus.
a test light doesn't do a whole lot except let you know the amount of voltage is present to light it. I do electrical diagnostics ALL. DAY. LONG.
give me the info I need and my very expensive multimeter does the rest.
Sounds to me like you've done 1/3 of the basics and are prematurely moving on to the "harder stuff." You also sound awfully dismissive of the advice that you're asking for. Plenty of info can be had from a test light. But I think you're getting ahead of yourself.
In reply to dculberson :
You are correct. I've ruled out the most basic. The rest comes tonight. But if someone with intimate knowledge of a '97 Ecu could tell me what I should measure at the trigger points I wouldn't have to post back here to ask that very same question, again. Due to the nature of this E36 M3 hole ignition setup, we have no way of knowing whether the Ecu is the culprit.
we know we have power.
We know we have continuity.
We know we have ground.
we know the module is not faulty
we know the igniter sticks are good
All that's possibly missing is trigger. Injector (though the heinous fuel smell leads me elsewhere), or compression (which will be done tonight.)
06HHR
Dork
1/3/20 4:28 p.m.
In reply to _ :
Before you go any further, you should check the injector for #2. They will stick open, and what you describe (raw fuel smell out the exhaust, corroded spark plug) sure sounds like one. A noid light is the easy button for this but Streetwise described the procedure if you can't get one. Posters are wondering if you are a troll because you are constantly ignoring their advice. Slow down and cover all the basics before loading the parts cannon again.
A stuck open injector will fill the cylinder with fuel and hydraulic the rod in that cylinder so i strongly suggest you check the injector(s).
In reply to 06HHR :
Very good advice. Thank you for your patience with me. That goes to everyone as well.
Fuel injector would be the best issue at this point. With as many miles as are on this motor, I am not looking forward to the compression and leak down test. Those will likely confirm what I already suspect
