Random drop outs and misfires - Miata Turbo Forum - Turbo Kitten is watching you test compression.

thedguy · **Random drop outs and misfires**

I've searched and I think I might know what it is, but not 100%

I have what feels like a grounding issue on my 91 1.6 with an MS2 (bought second hand and supposedly built by Braineack), 460cc rx7 injectors. The problems at WOT became (obviously) more noticeable after throwing an SC at the engine but I've had this issue since day one.

I cleaned up all my chassis/engine grounds, even did the one in the trunk that bolts up next to the battery. Still hasn't solved it. My adapter harness had 1 spare GND lead not soldered to anything so I went ahead and ran a 14g wire from it directly to the battery. STill didn't solve it.

The problem comes on at WOT as well as part throttle (though less common) and many times as an idle droop. If it happens at idle it tends to happen at the worst time and leave me stuck in an intersection until I can get the motor to recover or die and start up again with some luck.

I've got logs of the Idle dropping out:

And here is a WOT situation. When it happens it's just a quick hickup and then I get a misfire when it recovers

Only thing I haven't done is try running a power lead from the battery to the ecu. I've tried turning on the noise filters as well.

I have read there is a small capacitor that could be related to the issue.

Any help is appreciated,
Dustin

timk · 09-22-2011, 02:26 AM

I don't know if you are thinking of the 4/2 CAS decoder on the MS1? It was fixed with a capacitor:
http://www.msextra.com/viewtopic.php?t=26727

I don't think this applies to MS2 though?

***Braineack*** · 09-22-2011, 08:59 AM

post the log, I'm not sure I see in those screen captures what you are describing.

thedguy · 09-22-2011, 12:59 PM

http://www.miataturbo.net/attachment...1&d=1316710551

http://www.miataturbo.net/attachment...1&d=1316710551

The first one is just a trip down the road, at about the 253 mark is where 1 of the hiccups happen.

On the 2nd log near the beginning is it happening at idle. You can see my stabbing the throttle a few times to try and get the engine to recover and you'll notice the RPM's drop to about 400.

I've had at least 1 person suggest I have a problem with the 5v line, possibly the tps is shorting out (going to check my harness for shorts here in a few).

Thanks,
Dustin

thedguy · 09-22-2011, 02:36 PM

Well this should show how much a tard I am. I didn't put any marks in the logs.
Here's a fresh log from with markers just after the events.

There marker "012" shows a good one of the event. A lot of the other ones are softer. I noticed it completely drops the RPM signal and even triggers cranking mode and ASE.

Am I just having misfire issues that are screwing with the ecu? I've never had a problem like this so I'm a bit out of my realm.

http://www.miataturbo.net/attachment...1&d=1316716540

Thanks,
Dustin

**Joe Perez** · 09-22-2011, 03:16 PM

Quote:
	Originally Posted by thedguy I have read there is a small capacitor that could be related to the issue.

I haven't yet downloaded the log file (I don't have MLV on this computer) but based on the pictures you posted, I don't think this is it.

The "cap mod" fixed a problem related to noise on the cam sensor line. But when that happens, you would see it in the log in the form of a very sharp spike or dip in computed RPM. I'm not seeing that here.

thedguy · 09-22-2011, 05:18 PM

Thanks Joe.

Looking at the log some more, it's appearing that I'm losing tach signal. I'm not sure that is a symptom or the problem though.

Interestingly my updated log doesn't show the TPS ever dropping out like before

**Joe Perez** · 09-23-2011, 01:01 AM

Quote:
	Originally Posted by thedguy Looking at the log some more, it's appearing that I'm losing tach signal. I'm not sure that is a symptom or the problem though.

If the RPM is spiking or dropping in the log, that's pretty much a guarantee that you have a problem on one of the CAS wires, most likely noise. I'm not seeing it in the pictures, can you point me to a timestamp in a log?

If this is the case, it's entirely possible that the bypass cap on the CMP line will ameliorate the problem.

thedguy · 09-23-2011, 01:23 AM

Quote:
	Originally Posted by Joe Perez If the RPM is spiking or dropping in the log, that's pretty much a guarantee that you have a problem on one of the CAS wires, most likely noise. I'm not seeing it in the pictures, can you point me to a timestamp in a log? If this is the case, it's entirely possible that the bypass cap on the CMP line will ameliorate the problem.

on the most recent log posted, it's just before marker 012, time stamp 529.

A similar event is at time stamp 218, just before marker 5

I noticed it triggered a lost sync (code 38?) and it even shows a the ecu went into cranking mode for a moment.

thedguy · 09-23-2011, 03:21 PM

My igniter went bad.

threw one in the car from the junkyard and the small hiccups went away, and I've only had 1 noticeable one since changing it.