Help me diagnose this problem


I was not having this issue when tuning the engine. It seemed to show up later on. I just got the injectors back today cleaned and flow tested from RC.

 

Seems like an ignition issue. Fouled plugs, weak spark, bad plug wires, bad/weak ignition coil, poor power to ignition coils, poor grounds, etc.
Had a similar thing happening to my car at WOT, it was poorly wired ignition coils. Now it's fixed and the car needs to be retuned because it's too lean.

 

Thank you.

I was going to go through the ignition system next. I also don't have a working tachometer ever since the new rebuild, which also points to the coils.. so I'm glad you said that haha.

 

The coils get their ground from being mounted to the fender so make sure you have a tight and clean ground for the trailing coil.

 

It would be helpful to know what ECU you're running and general info about your build (still wasted spark, coil dwell settings?, porting?) but the first question should be: what's your O2 sensor reading look like during breakup?

 

Stock ecu with safc fuel tuner. I richened it up in the higher rpm's because I wanted to be safe, it's reading in the mid 10's at those rpm's. And as the title says it's a mildly streetported motor.

 

Sounds like too much fuel, especially at low loads. You only need to be in the low-mid 11's while under boost, otherwise you should be much higher. Try backing off the fuel under 1 psi 'load' and see what happens. Note that, while you should figure out why you're tach is dead, the trailing spark is insignificant to how well your engine runs, it mainly just fires to bun-off emissions.

 

It's not cutting out because of the fuel. I was in the mid 11's and I just richened it up after I ran into this issue just to be on the safe side. Will be diagnosing the coils/spark tm.

 

It is if it's fouling the plugs. That can be a combination of too much fuel and weak spark. Pull the plugs out and look at them, check resistances on the plug wires too.
How old are the spark plugs you're running and what are they?

 

Fair enough, but that's new info. Was your tach working when you tuned it? Just seems odd that the ignition is problematic with the stock ECU. I've seen old plug wires cause high RPM breakup.

And I agree that inspecting the plugs is an easy diagnostic check. Wet, worn, black?

 

trailing tacho dead = trailing coil malfunction = likely it is stuck on t2 and wasting that spark

lost count now of how many times i have seen it .. even on MT/LT stock coil setups
engine breaks up on mild boost

it will cost engines


-disconnect trailing coil entirely and i bet the miss disappears -

 

I tried as bumpstart suggested, and unplugged the trailing coil pack. I had all sorts of backfiring with just the leading coil pack connected.

 

just to be sure .. you had only the leading coil operating ( coil pack at front of car )

and it ran worse than when it does with the trailing connected.. yet have a faulty tacho ?
( which points at the trailing coil not working.. or worse. not flopping )

have you tried some decent plugs and wires yet ?

 

yes

yes

when I unplugged the trailing coil, it didn't seem to affect idle at all. once I started trying to rev it it started backfiring.

The plugs and wires I have are decent. I replaced the wires not super long ago, I wanna say within the past year but maybe more than that. I guess in that amount of time they could have failed. I'll take them off and inspect them as well as the plugs, which i replaced even sooner than the wires. If I can find some used coil packs in the meantime I'll probably order them as well.

 

. Something's seriously amiss (beyond plugs and wires) if disconnecting the trailing coils has much effect at all. Seems like your coils are miswired somehow (?) or your timing is off (CAS stabbed wrong, although that doesn't explain the tach).

 

I was just about to say, I've already checked my cas..twice. Is it possible that both coil packs are malfunctioning?

 

Presumably the SAFC uses an ignition input for RPM. Consider how you wired it.

 

Correct, but the safc has been wired for about a year now. I'll definitely check the wiring on it though in case something happened.

 

Okay somebody help me out here because I'm a complete noob when it comes to wiring.




If I measure the voltage between the two pins on this connector, should it read 12+vdc? Or does it not work that way. lol.

 

Coil grounds to the chassis. One of those pins should read 12v constant with ign on, the other is the trigger signal.

Check your wires for continuity, they should all match. Check all the plugs too.

 

OKAY so some weird test results

I checked to make sure I was getting full voltage to both coil packs..I was
I checked the ground at the fenders right where both packs mount..ground was good

I grabbed two used coil packs said to be taken from a running car.

Then I tested each lead for spark with each combination of the old/new coil packs (16 tests) by plugging each lead into a spark plug one by one and setting it on ground and watching for spark as I turned the motor over.

These were the results:

Old Leading Old Trailing - All leads sparked
Old Leading New Trailing - All leads except Trailing #2 sparked
New Leading Old Trailing - All leads sparked
New Leading New Trailing - All leads except Trailing #2 sparked

The other thing I noticed that in all scenarios, the trailing spark was much stronger in appearance than the leading spark.

Does this tell anybody anything? From the results all it really looks like is the new trailing coil pack I bought is half dead.



*edit* and because I know someone is going to ask, when I had no spark on trailing #2, I tested it again with a different spark plug wire to make sure it wasn't the wire at fault.

 

If you look in the FSM (wiring diagram) where it lists the ECU pinouts you will see there are three readings related to the trailing coil. One of them is the select signal and it chooses whether to fire the front rotor or the rear rotor. The wire's voltage varies from 5 volts to 0 volts. When it reads one value it fires a certain rotor and when the other value appears the other rotor is then fired. W/the plug pulled the select wire, w/key to on, will show one of the values. As the main pulley is rotated, achieved by rotating the alternator pulley, the value then will change.

Select signal Brown/Yellow wire (pin 1J) 4.4 volts w/key to on and 2.2 volts while idling
Timing signal Blue/Yellow wire (pin 1G) 0 volts w/key to on and .8 volts while idling
Feedback signal Blue/Green wire (pin1V) less than 2 volts w/key to on and 1.4 volts while idling

 

But does that explain why it only happened using one of the coil packs?

 

Okay just did a little more testing with it. I hooked up two spark plugs this time. I noticed that the leading plugs would both spark at the same time...that can't be right can it? They should alternate.

So I get two more plugs, I have all four hooked up and grounded to the top of my tmic so I can see them all, and notice that as the trailing plugs alternate correctly (are sparking once during the compression stroke at each rotor), the leading plugs are actually sparking together on both compression strokes.

So as one rotor fires while in compression, the other one is firing pretty much right on the apex seal, right? Which could definitely cause some pre-ignition problems as the spark is retarded under high rpm's and boost i believe. The chamber would ignite just after the apex seal passes the spark plugs, as it is beginning its compression stroke.

I believe this is my problem. If anyone has some insight into how the hell this happened or wants to tell me I'm wrong, please chime in!

 

Both leading plugs are supposed to fire at the very same time and it's called wasted spark. If they did not do this then there would be something wrong.