I'm tracking down the cause for a misfire. I've checked my ignition and fuel systems as best I can and didn't find anything abnormal.
I performed a log today and noticed that the tps voltage drops below .67 volts on occasion, I've seen as low as .12 volts. Much of the time, when this happens many of the other readings are weird, temp, blm, int, rpm, voltage, etc. I'm still going through the logs for more info.
Is this a sign of a bad TPS? Should it ever drop so low under any circumstances in normal operation?

 

I forget the exact figures, but normal closed throttle TPS reading should be approx .5V, and WOT voltage should be 4.5V.

 

Also, TPS is slotted, so it can be adjusted to acheive the .5V if it's still good.

 

I normally have .67. It's been that way since I did my first log about a year ago, before I was experiencing this problem.

 

time for a new tps .12 is way low

 

Sounds more like a grounding problem if all readings go south at the same time.
Clean the back of the cylinder head where the main grounds are connected. Check others for good connections as well.

 

I think JP is right, your TPS voltage fallout is a result not cause.
Also,
Check for a corresponding glitch in battery volts.

 

Good thought. I will check the grounds. The battery voltage is another that reads weird when this happens. In one instance I remember it showed just over 16 volts.

When I get the weird readings though, it's only in tunerpro that I see it. The car's gauges are reading normally all the time.

Oddly enough, I replaced the muffler on Sunday and after all the drives and idling yesterday, logging data, checking ignition, and fuel systems, it seems to have cleared up. I drove to a friend's house which is about 16 miles away last night and I did not notice a misfire. My old muffler had something rattling around. It's making me wonder if a partially blocked muffler could have been throwing the computer off enough to cause the misfire.

 

I've been driving it the past few days. Since replacing the muffler,the problem does seem improved but I do still notice it on hard acceleration.

I haven't done anything more than analyze the logs over the past few days. I haven't checked grounds so don't get on me about that just yet.
For one of my logs, I got on the interstate so that I can maintain a steady speed and tps position. Something I notice is that the coolant temperature jumps from 203 to 252 and the INT drops by nearly half. It is only after this occurs that my TPS voltage and rpm drop, also by half. When the temperature returns to normal, so does everything else. Note that I only see the rpm drop in the software on my laptop. I do not see this on my dash. The same goes for the coolant temperature.

 

I wonder if it is just bad data that is being received. Along the lines of the data logger losing sync with the data stream.

Does how the engine is running change at the same time the data does?

RBob.

 

That is what I'm wondering.
No, it does not seem to affect the car at all when this happens. Of course, I'm driving so I can't watch it the whole time but in one instance, I was looking at it while cruising at a steady speed and saw the TPS voltage drop from .86 to .43. When that happened, I did not notice any difference in the way the car was behaving.

 

On the way to work, I performed a bit of a test. I plugged the ALDL cable in without using the laptop. The car runs worse with the cable plugged in. I had noticed this Sunday during the logging but I chalked it up to the misfire situation getting worse. It didn't do this in the past and I've changed nothing since I last used it.

 

Make sure that the ALDL cable isn't putting a 10K resistor between terminals A & B on the ALDL connector. That will change how the ECM runs the engine.

RBob.

 

That's what it was. I'm a newb at all this. I thought I had to leave the resistor in place but it turns out it's only needed to start the data stream. I removed it after connecting and it no longer changes he way it runs.
I guess this makes my previous logs null and void.
I did make a new one on the way from work. I'll look at it shortly.

 

My TPS seems to be gone, too.... 5V and ground is ok.
Diacom/ALDL and VOM shows 0.29-0.33 VDC when turning the tps (adjustable one). the weird thing is that I tried another one and got the same results.

could this be a wiring problem? (signal wire grounded or sth like that? )

Maybe this is the cause for my car's problems at the moment (starts and immediately dies).

edit: problem solved (bad memcal / ostrich not hooked up correctly)

 

My plug wires were old so I replaced them, it was time, and my misfire is fixed.

For the mopst part, everything seems to be normal now. I still have instances where readings just drop off. I think it is loosing connection now and then.

 

One other thing to check is your charging system. If it is having issues it will reflect into the data stream and logs.