Scanner quits logging when rev limit hits?

[RonSSnova]

Hi,

I'm having a unique issue.
2 weeks ago while drag racing, the car began hitting the rev limiter on the 1-2 shift. A4 C5 Vette.
The trans shifted, but the scanner quit taking data.
I reloaded the tune, and all was well.

The next week, the trans would not shift 2-3, hit the limiter, and once again the scanner quit taking data.

I've been on the limiter before with no issues.

The scanner quits right at the shift point, before it hits the rev limit.

Any ideas? This is rather puzzling, and it doesn't do it all the time.

Shift point is 6600, rev limit is set to 7000.

Ron

[Pekka_Perkeles]

I've been in a somewhat similar situation, but in dyno. Logging just stops before redline. I never figured out if it was a physical problem with USB, OBD2 or RS232 interfaces. It just didn't do it anymore after couple of pulls.

[RonSSnova]

I plan to start looking at all the chassis grounds. The C5 has a lot. And the connections at the transmission.

I wish it would fix itself......

[frans96ss]

Anything on this?

[planethax]

I would start by logging Standalone to eliminate the Usb and or laptop.

[jimmyblue]

There's other threads of a similar nature. My gut feel, and
I've seen this occasionally on my car, is that something
"gets lost" when there is a lot of PCM "extra activity" and
maybe the link reacts badly to a dropped or not-sent-on-
cue packet.

Solutions, I got nuthin'.

[Tick]

Got a 98 c4 with an a4 trans. It has seemingly hit the rev limiter on two pulls at 6600 rpms and two pulls at 6800 rpms. The limiter and all other cuttoff settings were set to 7400 rpms on the last pull but the car still hit a limiter of some sort at 6800... When it hits this mystery limiter the data log stops like clock work every time. It is almost like the pcm is just loosing power or ground.

Another thing that looks pretty strange is the map sensors readings. They seem to jump around pretty wildly during wot. Anywhere from 88 kpa to 100 kpa. I know the sensor should be in place good because we just installed the intake manifold. The sensor reads fine and the car drives great at part throttle.

[blownbluez06]

I've seen one tuner (that I respect) claim changing plug wires solved the problem for him on the dyno. That would make me think it was a EMI issue. We all know grounds on these cars are an issue, which could easily contribute to the cause, if it's not the cause itself.

[Tick]

This morning I cleaned all the grounds to the frame rails in the engine bay. I cleaned the grounds under both kick panels inside the car. After doing this, the car would shut off as soon as the tires would roll. It would rev great in park, but as soon as it went into gear and started to roll it would shut off. I un hooked the speed sensor and then it would continue to run while rolling up to a point....when I suppose it would go into reduced power mode.

I then changed the pcm for a spare one I have and it would then run in gear while rolling. With that accomplished I expected the car to run better and rev to the actual limiter but it did not. The car still shuts off at 6600-6800 every time.

I installed the wires from another car which runs fine and this one still has the issue.

[Tick]

I also made a few pulls maf only (all previous runs were SD) and the problem remains. We made an SD pull with the inlet to the throttle removed so we could watch the throttle plate to see if it were doing something goofy (even tho it shows 100% tps throughout the entire run). It remained steady until the mystery limiter hits.

This car has TFS 220's, our custom cam, a FAST 92, and a 90mm LS2 tb and its only making around 420 rwhp which is pretty horrible for the combo...

[Tick]

So the car shut off at 2 mph first thing today with the original pcm. I swapped the pcm and it didn't shut off. I swapped the original back in to confirm and it shut off again. I then put the replacement back in and it shut off again!?

I went into the tune and set the column lock to disabled and the fail fuel cut to 256 mph and now it doesn't shut off at 2 mph.... but there was never a "service column lock message" or "pull key and wait 10 seconds" like I've seen so many times.... Even with that fail fuel cut raised to 256 it still shuts off at 6800 rpms though. I set security to "none".

[blownbluez06]

So the car shut off at 2 mph first thing today with the original pcm. I swapped the pcm and it didn't shut off. I swapped the original back in to confirm and it shut off again. I then put the replacement back in and it shut off again!?

I went into the tune and set the column lock to disabled and the fail fuel cut to 256 mph and now it doesn't shut off at 2 mph.... but there was never a "service column lock message" or "pull key and wait 10 seconds" like I've seen so many times.... Even with that fail fuel cut raised to 256 it still shuts off at 6800 rpms though. I set security to "none".

I'm inclined to bet if you tied an O-scope to the OBDII interface wires, you'd see some noise.

[Tick]

I'm inclined to bet if you tied an O-scope to the OBDII interface wires, you'd see some noise.

Forgive my ignorance, but which wires? The noise on the obdII interface wires would cause the vehicle to hit a rev limiter pre-maturely or cause column lock issues without a diagnostic message or code?

If there is noise, what is the fix? This car is a 60,000 mile un-molested pace car edition vette that other than a set of headers has never been touched before our head and cam install. I'm not sure what to do at this point....I was able to produce the mystery limiter on the street at 6300 rpms once with quick acceleration in 1st gear and the logged stopped of course.

[Tick]

Another thread that went no where: http://www.hptuners.com/forum/showth...re+rev+limiter

[blownbluez06]

Forgive my ignorance, but which wires? The noise on the obdII interface wires would cause the vehicle to hit a rev limiter pre-maturely or cause column lock issues without a diagnostic message or code?

If there is noise, what is the fix? This car is a 60,000 mile un-molested pace car edition vette that other than a set of headers has never been touched before our head and cam install. I'm not sure what to do at this point....I was able to produce the mystery limiter on the street at 6300 rpms once with quick acceleration in 1st gear and the logged stopped of course.

I'm bad about scanning when I read sometimes. I didn't read the entire thing, but noise is the effect and not the cause and I would expect the cause in this case to be from a defective/broken circuit inside the PCM causing something on the ground side to float. I might be looking for noise for the HPT module signing off during a pull, but there's got to be a better test to determine what's going on to cause the remaining issues. I might put a meter across each ground with the meter set on volts and look for any significant voltage, which would reflect a diminished ground.

[Tick]

I'm bad about scanning when I read sometimes. I didn't read the entire thing, but noise is the effect and not the cause and I would expect the cause in this case to be from a defective/broken circuit inside the PCM causing something on the ground side to float. I might be looking for noise for the HPT module signing off during a pull, but there's got to be a better test to determine what's going on to cause the remaining issues. I might put a meter across each ground with the meter set on volts and look for any significant voltage, which would reflect a diminished ground.

A different pcm has been tested.