36 replies to this topic

[High Chair]

I'm getting 23.5 at WOT according to the ECU.  Is 28-28.5 what the ECU is supposed to think, or do I add the 4-5 degrees of additional advance, in which case it looks about right now?

If you are reading the data from the ECU it will read 23.5. When you take it to the dyno have somebody stand outside with a timing light as you do a pull. You should see 28 or 28.5 total timing rock solid. If it is there is nothing wrong with the timing. However, while you are on the dyno make sure the butterflies snap open at roughly 5500. They should open and not float around. I have had the check valve go bad more than once and will certainly cause low TQ. 

[fw87]

Both of my 99s do the exact same thing however there is nothing wrong with them. Solid at 15 and as soon as it reaches 180 F the timing is reduced by 8/10 degrees as it switches maps.  If you put the car on a dyno and check it at WOT you will see the total timing is rock solid at 28/28.5 right where it should be. You can change all of the parts you want but you will not get it to stop doing it. I actually changed everything in my car (everything including all wiring) and it still does it. That is when it was suggested to take it to the dyno. The car make the same HP/TQ as the rest and the timing is right where it should be under a load all the way to read line. I never looked for a resistor as Drago suggested and that might stop it but under power it makes no difference. By the way I had multiple engine people look at it and all said they had never seen anything like it. That includes Ti-Speed and Jeff over at Auto Technics yet I have two cars that do the exact same thing and both with new Ti-Speed engines

 

 

Is there a solution to this or is it not a big deal. With a OBD Scangauge mine does the same thing but the map switch happens at 175 F. Timing goes from 10 (ECU Timing) to 0 with a noticeable change in engine tone (at idle). At WOT timing is correct at 23 on OBD reader. 

[Mark]

I chased this problem on one of my cars for months. I never solved it and I still don't understand why this car pulled timing when others did not. Many hours and dollars spent to no avail. In the end the car ran like a beast and dynoed quite well so we just ran it. 

[fw87]

I was able to chase this problem down to the neutral switch on the transmission. With the neutral switch not connected the computer stays in open loop at idle and causes the map change to 0* timing at 175.

 

Also fixed the low idle stumbling issues after a rev as I THINK the ICV only works when it knows the car is neutral?

[FTodaro]

I was able to chase this problem down to the neutral switch on the transmission. With the neutral switch not connected the computer stays in open loop at idle and causes the map change to 0* timing at 175.

 

Also fixed the low idle stumbling issues after a rev as I THINK the ICV only works when it knows the car is neutral?

Are you talking about the Big square switch on the top of the clutch pedal or the smaller one, mid pedal on the clutch? I had the hunt at low RPM problem and I cut that lower switch to solve it.

[ChrisA]

I think the neutral switch is the one that sit on top of the transmission.

[ECOBRAP]

My 99 has started falling on its face (yet pulls fine on the dyno), and feels like it is yanking timing when on track.

 

Surprised to see this thread resulted in a neutral safety switch, which I thought was only a necessity on NB2 cars. Mine is currently not hooked up to anything on my 99.

 

Any comments on this switch on top of the trans for NB1 vs NB2?

 

I am also going to be looking into the ECU water temp sensor on the back of the head...

[Steve Scheifler]

If you haven’t solved it by next outing you might want to get an OBDII scanner that can record. Slow data rate but adequate to spot something big like this. You should be able to track timing, temps, fuel trims etc. Odd that you can’t reproduce it on a dyno though. Is it consistent once it starts happening or more intermittent like a bad connection being bounced around? Are you already monitoring AFR?

[ECOBRAP]

I bought an OBD2 module that will connect to my phone (arrives today), and I will try to find an app that can log the data. Would be nice to confirm if it is indeed pulling timing or if the problem is elsewhere i.e. brake drag.

 

As for AFR, on track it looked fine (13.6 exiting a corner in the lower RPM range, and gets down to 12.0 at max RPM). However, after the race on the cool down lap and/or in the pits, the car would start to sputter, and AFR was locked at 10.0. Didn't sputter during the race, only after, which is making me consider water temp sensor as the engine bay starts to heatsoak after the race?

 

But back to the NB neutral switch, does anyone know if this matters on NB1?

[ECOBRAP]

Update:

 

Got OBD2 live telemetry.

 

ECT's looked normal, 160 through 190 water temp just idling in my garage.

 

Ignition timing was the unusual one to me. From what I understand, even though the slotted timing wheel pushes ignition timing to 15 degrees, the ECU is still interpreting it as factory 10 degrees.

 

So from OBD2, the ECU should read a steady 10 degrees at idle.

 

I saw that for a while, but then the timing dropped to only 2-3 degrees advanced. Is it normal for the ECU to cut timing at idle when the car is warmed up?

 

The other weird thing is that when I brought the rpm's up (likely around 4,000, not much load), the ECU saw timing advance to 35. And again, that doesn't include the extra 5 degrees from the timing wheel, so that is more like 40 degrees advanced in the real world?

 

Any insight appreciated...

 

 

 

 

Also worth noting: scanner showed "closed loop using O2" even on initial startup. Also showed some voltage from first O2 sensor (downpipe), but no voltage from second O2 sensor (mounted in trunk)

[chris haldeman]

Everything you have seen is normal.

[ECOBRAP]

Thx.

 

After a bit more investigation today, and side-by-side comparison with a known fast 99 SM, found a couple things.

 

1.

 

When full throttle, the OBD2 scanner shows the ECU is only seeing 86-88% throttle. The throttle body is wide open, cable is fine and also tried manually twisting throttle body. No change.

 

If I take the TPS off the throttle body, and use a flathead screwdriver to manually turn the potentiometer inside the TPS, it does register 100% throttle at the ECU.

 

Swapped TPS, throttle body, and ECU - no cigar.

 

I did notice the throttle body has "BP4W" engraved/stamped on it, but my ECU (and spare ECU that I tested) is a "BP5R". Is there anything to this? Different ECU's require different throttle bodies? (I find this hard to believe but figure worth asking). The reference Spec Miata that I was using had a BP4W throttle body and BP4Y ECU, and had no problem registering 100% throttle at the ECU. Unfortunately I didn't get the chance to try that car's ECU in my own car, got sick of the upside-down-under-the-dash work...

 

I was also told the 88% TPS did not matter, which would make sense if the air flow sensor controlled the A/F ratio. But in that case, what is the point of the TPS in the first place? I assume the TPS is an instantaneous tune change when quickly getting on/off throttle, then the air flow sensor takes over when it gets the information it needs. Considering the car did fine on the dyno, yet seemed slow directly after a shift or throttle application, does this mean I am headed in the right direction?

 

 

2. 

 

My car was showing some voltage variance (0.1-0.7 volts) at the O2 sensor, while idling.

 

The reference car had 0 volts at the O2 sensor, and actually never left open-loop on the scanner (mine said "closed-loop using O2 sensor"). I don't think the front O2 sensor was even hooked up on the reference car.

 

Curious as to what the O2 sensor actually does on these cars?

 

 

 

Sorry for the ramble, any insight appreciated.

[Steve Scheifler]

Sounds like you may be closing in on it with the TPS, except for the fact that swapping parts didn’t change anything. Hmmm...

Your O2 is working correctly. The narrow-band ones flip between a few tenths of a volt (leaner than stoichiometric) and roughly 1 volt, too rich, adding then reducing fuel “hunting” continuously either side of 14.7:1.

[chris haldeman]

Inspect air intake tube to verify it isn’t going soft.
Had a car a few weeks ago arrive with a similar complaint.
On the dyno a 4th gear pull showed consistent good numbers. Did a 3rd fear pull then upshifted and it choked.
My dad was observing under the hood to verify proper operation of the vics system and noticed the tube suck shut for a moment

[ECOBRAP]

Intake Tube (TB to MAF) is fine, VICS system appears operational (opens at around 5k RPM).

 

Data logging system showed ignition timing, fuel flow rate, MAF readings all normal. Only difference in data sets was that my car is using O2 sensor, and fuel trim adjustments are taking place (up to 5%). Reference car has no O2 sensor functioning, and therefore no fuel trim adjustments.

 

As for the TPS only reading 88%, this is where it got weird. I swapped TPS, throttle body, and ECU with no change. Then we measured voltages at the sensor. Both cars identical (0.5V at closed throttle, 3.7V at full throttle, input voltage 4.99V). Totally stumped why mine registers differently on the OBD2 scanner.

[ECOBRAP]

Just an update, my issue ended up being a Knock Sensor, car finally threw a code through OBD2.