Hey all,

Been having trouble with my car for a while now. The behavior I'm seeing makes me think I have some sort of ECU/tune/wiring problem, but it could be a number of other things. Here's what I'm seeing:

1. The car won't idle from a cold start. Fire it up, it revs to about 1500 then dies.
2. If I fire it up and then hold the RPMs at ~2k, it will run. The AFR is between 17-21 (per the gauge) when this is happening
3. At this point, if I rev the car and then get off the gas, or if I just let off the throttle, RPMs drop to ~400 and the car will die if I don't give it gas again
4. Once warmed up, the car (usually) gets to a point where it will idle on its own at ~900 RPM with the throttle closed. AFRs hold at 16-16.5
5. At all points, the exhaust smells very rich
6. Occasionally the car will will settle down and idle at 14.5, but I haven't figured out what causes it to do this
7. The last time I drove/raced the car, whether the engine was warm or cold when I started the car seemed to have no effect on whether it would idle properly or not. Sometimes I would start the car warm and it wouldn't idle. Other times it would fire up and idle right away from cold
8. When on track, the car had no power until 5k RPM, and then all of a sudden I would get full power from 5k to redline. This happened consistently at the same RPM (can't remember if it was 5k or 5500 though)

I checked all the wiring for the ECU and wideband, and didn't find any loose connections. I did find some scorch marks on the wiring harness though (note the brown marks on the glue):



Seems like there could be multiple problems here. Anyone have suggestions on how to troubleshoot this? I'm a complete tuning and MS noob, so simple explanations are appreciated.

Specs: Brain-built MSPNP, MTX-L wideband, tuned by a local dyno tuner Apr 2015. No new engine mods to the car since then, and the motor has about 19 hrs of track time since the ECU install.

 

Yeah, car needs tuning, nothing special from what you're describing. Check your ASE and WUE for starters.

 

Interesting... I had been thinking that there was some issue with the tune, but wasn't thinking that would be the only thing. I will check those parameters tonight - can you give me a rough idea of where they should be? Or do I just need to mess with them until it behaves better?

 

Post your tune, maybe a log of the car and your set-up.
And yeah, I've seen better wiring, but did it work fine and then suddenly started having these problems?

 

Tune and datalog attached. The log is a cold start with me managing the throttle until it can finally idle on its own. As far as setup, it's an N/A 99 motor with just bolt-ons and the Brain-built MS. The wiring has always been a little touchy. When I first installed the harness from Braineack, the AFRs would go haywire if you poked on the wires in the connector. That's why I added the potting you see in the pictures. The car was running OK for a while, but recently the idle and power issues popped up.

One thing I notice from the datalogs is that the MAT readings look screwy. It's reading 307F before I even start the car for the first time. That doesn't seem right?

 

Your VE table needs some work, car is lean.
Looking at your idle settings, have you observed the indicator for cl idle?Is it entering cl idle?
Since you are also using Idle Ve with cl activation, it might not be working.
Your rpmdot threshold activation is too tight, try bigger numbers, your idle valve works 20-99%?I doubt that, find your min,max.
Initial value table seems a bit off also.
Try these, then check your wiring again.

 

Thanks; appreciate all the help so far. I don't know what half of this stuff means, but I'll do some learning and then try to dial some of this in better.

To answer your question, I have definitely seen it enter CL idle when warm, not sure about from cold starts or during warmup. I will check it again tonight.

You're not concerned about the MAT readings? I poked around on the wire harness a bit more, and now the output is pegged at 70F, and doesn't seem to change whether the car is on or off, etc.

 

Now that you mention it, if your iat readings were this high, if you go to your iat correction table you ll find out that it's pulling 25.4% of fuel with that reading.
Plus a whole lot of timing from the spark correction table.
Steady 70F reading=default reading when no iat connected, you know what this means
Zero-out your MAT air density table(make all values 100%) and your MAT based spark retard(make all values 0)and see what happens, then fix your iat connection.
Finally, tune the car with 1-2 Cells on MAT Correction having 100%(The temps at which you will tune), then more fuel for colder (over 100%) and less for hotter(under 100%)

 

So I did as you suggested, and with the MAT tables zeroed out, the car fired up and idled normally. Seems like this is the problem!

The thing is, the IAT is doing something strange. If I have the IAT sensor plugged in, TS shows the air temp as 70F, just like if the IAT was not connected. But, if I unplug the the IAT, I get a reading of 115F (which was actually pretty close to the temperature in the garage...). This was pretty repeatable - the air temp reading would swing between 70F and 115F depending on whether the sensor is unplugged or not. I also tried plugging in the OEM IAT sensor - same result. The air temp reading goes straight to 70F as soon as I plug it in.

This is making me think there is a wiring problem somewhere, not a sensor problem. I'm thinking it must either be at the ECU harness connection, or in the MS itself. If I measure the resistance across the two pins of the IAT connector (with the IAT unplugged), am I measuring the bias resistance of the IAT circuit?

I also read a thread on rennlist about a guy who fixed a similar problem (70F IAT reading) just by flashing the firmware on his MS. Thinking about trying that too, since it doesn't seem like an issue with the sensor itself.

 

Are your themistor calibration values correct for your Intake Air temp sensor? Go into Tools/Unlock Calibrations and then Calibrate Thermistor tables. What values do you have there? Are you running a GM IAT sensor? When you changed back to the stock IAT sensor did you change the thermistor calibration to match?

 

I believe they are correct. I am running the GM IAT sensor - I selected the "GM" option in the thermistor table menu (I'll double check when I get home). When I switched back to the stock IAT, I didn't update the cal table. I figured it wasn't worth it since I got the exact same 70F reading (i.e. not connected) as I did with the GM IAT.

 

Here's my IAT settings in TS:


That should be correct, right?

 

Yep.

 

Last night I measured the harness at the IAT connector, with the IAT disconnected. I thought I read somewhere (can't find it now, argh) that one of the pins should measure 5V to engine block ground with the car keyed on. I measured 0V on one pin, and about 0.2V on the other. This sounds to me like there's either a short in the harness somewhere, or there's something wrong internal to the MS. Does that make sense?

I also measured about 8-9 k-ohm between the two pins (with the vehicle power keyed off). Shouldn't it be closer to the 2.5k bias resistor value? The IAT itself measures about 1600 ohm across the pins, so it's reading about right at ambient temp (it's hot here... ).

 

Those thermistor values don't match what's on the MSPNP page.

 

I'm using the GM IAT - looks like the values you posted are for the OEM IAT. I could switch back and see if that makes a difference, but based on my earlier post, I think it's still going to read 70F as soon as I connect the OEM IAT.

 

Sorry, the pasted image got cut off prior to the GM values. This is what they show for the GM IAT. The top value of ~100k ohms in your cal table is really going to throw off your values for any temp under 30C. That said, no 5V output coming from the MS is going to cause the sensor values to be way off as well. One of the pins on the plug going to the IAT should have 5V on it.

 

Interesting, thanks. Which page did you find those on?

I'll double-check the voltage measurement when I get home next week. One of the pins should be 5V to engine block ground, correct? I was picking up ground from the screw on the top/front of the IM. Is there a better place to reference it? I have no idea where the ECU is grounded with the factory harness.

Can I check the voltage at the harness as well? Should I be checking the "5V REF Main - 26" (Pin 21) to ground, in the diagram below?

 

5v reference is used for TPS which appears to be working. I'd say the output from the MS is fine. You should have voltage at the IAT sensor though.

 

Ground your sensors to 3C/3F