Weird ignition timing/TPS happenings (SleeperZ or anyone)

[Guest bastaad525]

Not sure why I decided to mess with this again today...

 

I went to check the timing, just for the heck of it. One thing I didn't even think to do was let the car warm up... just started the car cold and started checking. Here's what I observed....

 

At first, the timing was way advanced, somewhere around 25 degrees. After about three minutes, the car suddenly 'switched' (by the way the temp was still all the way down at the bottom of the gauge), the idle dropped down about 200-300rpm, and the timing dropped down to about 14 degrees BTDC. Now, at this time, the TPS was disconnected, it has been for a week or so now, and I remembered that you want it connected when doing the timing so I reconnected it. Before connecting it I revved the engine a few times to see if the timing was advancing with it disconnected, and it was, advances normally, exactly the way I'd expect it to. Immediately after reconnecting it, the idle jumped back up that 200-300rpm, and the timing jumped back up to about 20 degrees. Start to apply pressure on the throttle, and the instant the TPS goes open, you can HEAR this clicking noise, like a switch flipping, the engine bogs or coughs for a split second, and the timing immediately drops back down about 6 degrees, and then starts to rev normally as I apply more throttle, and the timing advances normally. With the TPS disconnected again, the idle eventually will come back up the 200-300 rpm to where it's supposed to be, after the car warms up. Also, with it disconnected, if I rev the engine the timing does exactly what it's supposed to do, it doesn't drop down before starting to advance, and there is NO bog or sputter, just smooth acceleration. And no clicking noise. For what it's worth, I have had the TPS tested and adjusted by a Z only shop.

 

Now, what I want to know, is what on earth is happening here? Why does the timing retard about 6 degrees as soon as the TPS goes open? Why does the thing seem to choke or hesitate, like it takes a moment to figure out what to do, when the TPS goes open? After warming up, the idle doesn't change much at all if I connect or disconnect the TPS, other than the fact that it will idle smoother and misfire less with it connected.

 

Now, for anyone that might remember, there was another experiment I had tried, kinda opposite to this one. A while ago I got this crazy idea to disconnect the TPS, but then to stick a jumper wire in the end of the connector, effectively tricking the ECU into thinking the TPS was ALWAYS in the idle position. When I do this, the slight misfire that is otherwise almost always present, clears up almost completely. I checked the timing like this, and even though the ECU SHOULD think the motor is staying at idle, the timing DOES advance as the engine is revved (Sleeper I've been meaning to mention this part to you for a while but keep forgetting), and the motor has no problem revving (I would have though the ECU wouldn't supply enough fuel to rev, thinking the engine was idling, but apparently it does). As a matter of fact, the car just ran MUCH better in general with the TPS bridged like this. The downside? Ping when on boost above 4000rpm. So needless to say I didn't leave it like that Anyways dont pay too much attention to this paragraph... I'm more concerned with why the car does what it does when everything is connected the way it's supposed to be.

 

Additional info... I'm running with the O2 disconnected, though if I connect it I get the exact same results. The only thing I notice is that when I connect it that the idle gets more rough... as a matter of fact the motor just runs more roughly in general. I've also tried three different head temp sensors, to no effect. Pretty much all the components of my ignition system are new. The knock sensor is disconnected. AFM was tested and working fine. TPS was tested and showed to be working fine. I've tried 3 different ECU's and no effect. I've cleaned all electrical connections like 50 times.

 

Now... mind you the car runs okay with the TPS disconnected, so this is more an issue of WANTING to know what the problem is and wanting to fix it, rather than NEEDING to fix it. The only thing the car does that bothers me, is exibit a mild misfire, at idle and all throughout the rev range. It's always done this. The exhaust smells too rich but when I pull the plugs and look at them they all look good, except for the #1 which is slightly rich, I think it's a faulty injector. I would blame the injector for the slight miss, but keep in mind when the TPS is in the closed position it clears up. Oh and one other thing, the misfire is NOT present at ALL, after the car warms up slightly it vanishes completely... idles so smoothly you almost dont know it's running! But then when the car warms up completely it comes back, and if it warms up even more, like after getting off the freeway, it will get worse and worse... then clear up as it cools back down a bit, etc., etc.... really really odd. This also didn't change after I changed the head temp sensor.... This car is so odd I swear!

 

Okay guys, fire away with those ideas!

[SleeperZ]

Interesting. Confronted with that data, I'd be tempted to swap ECUs to see if they both react the same to the TPS and initial timing. It almost seems you may have a fault in an input signal inside the ECU possibly causing some noise. Either the temp sensor or the TPS. Of course, check all the electrical connections for broken or fraying wires, etc...

 

Interesting about how the timing curves are different for idle mode and cruising mode. I didn't expect to hear the timing changes much with RPM under idle.

 

 

WOOOOOOO!!! My 2000th post!

[Guest bastaad525]

Yeah I've tried running 3 different ECU's and it doesn't change. I suspect the wiring too... I've gone over it a couple times but really am dreading digging into it to see what's really up... I am <..> this close to just getting a whole other wiring harness and trying it, though I know I shouldn't... I just dont want to have to take the current one apart and go wire by wire.

[cygnusx1]

I can't answer your question fully but my 2002 WRX idles bumpy and so does my turbo Z. In the WRX forums people attribute the rough idle to low engine compression. I wonder if that is true and would that apply to our turbo Z's....

 

 

As far as yout TPS switch and O2 sensor. I would confirm they are working properly, by the book, and then make sure their signals are getting to the ECU connector. I recently learned that just because the conector has snapped into the ECU socket, it dosen't mean the signal is getting there....

 

If you know you dont have any vacuum leaks, check your idle mixture screw in the AFM. Sometimes adjusting that screw richer or leaner will help the engine come off idle without that momentary bog. It is almost like the accelerator pump effect on a carburetor.

 

The bog after idle contact open> the timing going back 6, could all be ECU functions that are meant to keep the motor from stalling. The ticking could either be the injectors dumping extra fuel to keep it alive OR it could be the oil pressure dropping due to the engine bog and deflating the hydraulic lifters (if you have those)....

 

It sounds like your timing is being controlled by the ECU which is good.

 

Dave C.

[Organdonor]

Bastaad, I don't know if this may be your problem, but when I had similar symptoms as you are experiencing, it turned out to be a broken wire feeding the injector (#5 for me) same as what your #1 is doing. I would check the first one foot of wiring leading from the injector itself. With the heat thats generated from the exhaust manifold this portion of wiring tends to become brittle and easily broken with handling.