Things that cause an Early Rev limit. - Too soon Junior

[dan10101]

Other that the standard fuel cut rev limiter, what are some things/sensors that can cause an earlier than expected rev limit? The dyno sheet that came with the car shows it revving to 6800 but it cuts out at 5200 in 1st gear.

Coolant Sensor - engine thinks it's cold. (my OBDII says it 190) Are there 2 coolant sensors?
VSS - Speed says it's too fast when it isn't
Gear based speed limiter (same as above?)

Here's what I'm working on.
2004 LS6 crammed into a Porsche 914 4 speed manual.
2001 Camaro 411 ECM.
Speed Density Tune, (no MAF)

[stew86MCSS396]

Idk if it has anything to do with this. I like to wind out that first gear but I don't own anything that has a 3.06 1st gear.
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?7967-7427-4L60E-1st-Gear-Fuel-Cut-Off

[dan10101]

That's the kind of thing I'm looking for. Thanks...

But with my trans being a manual 1978 Porsche transaxle, I don't know how the computer would know how fast I'm going. Sure I have a speedometer, but I'm pretty sure it's analog. Still, I'll look for that in the computer to see what it says. It makes the most sense. Maybe it calculates it based on gear ratios and rpm.

[1project2many]

Vehicle speed is generally one of the values which can trigger the ecm to cut fuel. If the vehicle speed is reported incorrectly then you may need to increase the maximum speed allowed in the calibration. The maximum speed allowed is 255mph so if the reported speed is dramatically off you may have to find a way to change the speed signal so it is reported correctly.

[dan10101]

Thanks, I need to research how the speedo is driven, maybe they are tapping into it somehow.
I still suspect that a sensor/sender is causing this problem since it all worked at one time.

[1project2many]

I still suspect that a sensor/sender is causing this problem since it all worked at one time.


Hmmm... has it ever worked for you? Is it possible the speed sensor was disconnected for the dyno run?

[dan10101]

I've had it all apart since I bought it a year ago. One item I rewired was a sensor to the transaxle located just above the half shaft. Not sure if it's a speed sensor or a backup light sender. It's possible I reversed the wires which may be the whole problem. (however, the speedo still works...)

[dan10101]

14523
This is the sensor in question.
I'll be checking that wiring tomorrow..

[dan10101]

Hmmm... has it ever worked for you? Is it possible the speed sensor was disconnected for the dyno run?
I never answered this. The answer is ... For me, I don't know, for the previous owner, yes.
So back to me checking my wiring 'fix'....

[1project2many]

If you can get information about the Porsche signal it may be easier to figure out what's going on. The signal type (a/c or d/c pulse) and the number of pulses per mile or per driveshaft revolution are the keys to understanding what's happening.

[dan10101]

If you can get information about the Porsche signal it may be easier to figure out what's going on. The signal type (a/c or d/c pulse) and the number of pulses per mile or per driveshaft revolution are the keys to understanding what's happening.

Here's what I know. There are 8 magnets on a wheel in the Diff/transaxle that this sensor reads. It switches from 0-70ohms as the wheel rolls. That part is working. I also found out that switching the wires makes no difference.
I'm trying to find out if it is AC or DC. It is a Porsche design from 1976 or earlier if that is any clue.

[1project2many]

There are 8 magnets on a wheel in the Diff/transaxle that this sensor reads.

The sensor appears to produce a 12V square wave signal. I'm having trouble confirming but one forum discussion mentions eight pulses per tire revolution. If so, calculating the pulses per mile is a matter of determining tire rotations per mile then multiplying by eight. After confirming the pulses per mile that the sensor produces the next step to me would be to check the calibration to see what values are programmed.

[dan10101]

I figured that the next step would be to get into to computer to see what's going on. I spent the day reading and writing junkyard PCMs and getting familiar with the process. Unfortunately, when I got to the one that counted, I wouldn't read because it it locked. Probably with HP Tuners.

I know it was tuned by a Corvette shop in Manchester Ct called J and M Motorsports. Unfortunately they are closed as of a couple years ago. It runs good, and I know they didn't set the main rev limiter to 5200 rpm. But something is causing the limit.

So I have all these computers. Anyone have a Speed Density TunerPro tune for a 5.7 running about 500 crank hp? I know it won't be right for my purpose, but anything close will get me 1/2 way there.

[1project2many]

Is this helpful?
https://www.youtube.com/watch?edufilter=NULL&v=oGeMK6LvQck

Edit: Lotsa "not nice" forum reviews on J&M.

[dan10101]

Actually that is. I got that from someone else yesterday as well.

Well, assuming I can break into it. Has anyone had experience reading HP tune file with something like TunerPro?

Interesting about J&M. That was before my time with this car. And even if they were open it's 3000 miles away. I'm actually happy with the tune, just not the RPM. I got a new O2 sensor for my wideband yesterday, so todays job is to see if I can make that old LM1 tick again. Then see how far off I really am if any.