Ignition Questions...

[CajunKenny]

Over the course of a couple of months, the typical Supra "Idle Bumps" have been increasing and it is also showing up under load. At WOT, it almost feels like a slipping clutch. My clutch is new...

I have tried three different stock coil packs, two igniters, and my plugs and wires are new. One noteworthy thing is that at cold start, there are no idle bumps whatsoever.

About two weeks ago I got a code 14. I know that it is related to the IGf signal and is activated when the TCCS does not see three consecutive "fire" confirmations from the igniter. I cleared the code and it has yet to return.

So, I sourced a set of MK4 2JZGE coils and in doing some troubleshooting to figure out why my COP's would not run the car I found out that the coil for Cylinders 2&5 fire at the 'Key-On' position.

Here are my questions:

1. Is it normal for that coil to fire at the 'Key-On' position?

2. Why does this seem vary between years of manufacturer? (My car is a 91)

3. Why does the coil fire at 'Key-On' position?

Thanks!
-Kenny

 

[Nick M]

You get secondary fire without the car running on cylinder 2 and 5?

 

[CajunKenny]

At 'Key On' 2&5 fire one time. None of the others do.

How I see this is with my spark/coil tester in between the coil and the plug.

EDIT: The coil for 2&5. Just wanted to clarify...

 

[supraguy@aol]

I'm a bit ignorant on this, but is it possible that any wire off the CPS causing a short to another, would cause a misstep in the TDC signal to the igniter?
Might that possibly cause occasional stumbling as well as a code 14?
Again, I'm spitballing, and hope none of the more adept(JJ, IJ) members get pissed at me.

:bowdown:

 

[CajunKenny]

Well, I just got the COP's working tonight. Yay!

I'll drive the car tomorrow and beat on it a bit to see if things have improved at all. However, my idle is still quite bumpy.

Either of those cases should throw a code 14. If there is no improvement with the new COP's, I'll install a spare CPS.

The 'Key-On' firing of 2&5 isn't as strong as when the car is turning over. For what that's worth...

 

[Nick M]

Yeah, Kenny knows how it works. I assume he also has the schematic.

That is strange. I don't know how you do it without the IGt and data a and b signals to turn on the igniter. Data a is on, and data b is off (for 2 and 5), and that comes from the ECU to the igniter. A genuine ECU malfunction. I would like to see JJ's idea also.

I would think about fuel for the bump first. By bump I assume you mean a slight stumble. Unless you mean it goes up quickly or something.

 

[CajunKenny]

Sorry about the terminology. Yeah, the bumps are misses.

No schematic other than what's provided by the TSRM. Is there something else out there?

 

[Nick M]

No schematic other than what's provided by the TSRM. Is there something else out there?

In one of my old school books. It shows data a and b. On the schematic it shows those wires with IGf and IGt. I could scan it, but it is probably on autoshop101 anyway.

On cylinder 1 and 6 it shows a at 0 and b at 1. 3 and 4 are both 0. 2 and 5 is a at 1 and b at 0.

edit: unless 2 and 5 are supposed to fire once at key on. I don't know why they would.

 

[CajunKenny]

Interesting. Now I'm even more lost as to why 2&5 would fire at Key-On.

I'll take a look at autoshop101. Learn something new everyday!

 

[CajunKenny]

Bump...

 

[CajunKenny]

Can anyone confirm that the 2&5 coil firing at 'Key-On' is normal and what the purpose is for that particular coil to fire at that time?

 

[jetjock]

Interesting. I can't offer much Kenny because I never noticed that and no longer have the car to confirm. My guess (and a guess is all it is) would be it's due to either the hardware settling as the system is powered up or from code that is typically programmed into MPU based systems to do "housekeeping" upon power up/reset. Other than that I dunno.

 

[CajunKenny]

Thanks JJ. Well, one thing is for sure....it helped me in figuring out why my car wouldn't run with the new COP's!

Since there are no codes or other seemingly related symptoms, I'll just assume that it is normal operation. I've always noticed a slight arc'ing sound at the 'Key-On' position. That could be it...or a related relay...?

What I'll do is run the same test on a buddy's car the next time one is over.

 

[jetjock]

Yeah, see if happens on other cars. I suspect it's just hardware settling. I have the ECU code, pulled in the late 80s using an MDS and emulator, but never much dug into it.

 

[3p141592654]

The MCU does not handle coil pack selection, that is done by the fail safe ICs in the ECU. The MCU just issues the IGt pulse and checks for corresponding IGf. I have never seen any ignition activity at power-up, but I won't swear it isn't normal since I would typically be looking only at 1&6.