DragStuff

If you can help with a few beginner questions, I have installed an Innovate DL-32 in my small block Chevy / Turbo 400 powered Vega. It is a typical mid-10 sec car.

The rpm readings of the Tach and logger don’t seem to jive during the run. I am shifting @ 7300, the logger says 6900 or so. At idle or static rpm’s, they seem to agree. Is the logging interval (84ms) causing this? Which would you believe, the tach or logger?

The car has always had slow response on the oil pressure gauge, and now on the logger as well. I have bled the system, but would imaging that oil drains back after shutdown and the problem returns. The logger and gauge roughly agree on the pressure. Would oil restrictors in the top end of the motor cause this?

Does the wideband reading always look somewhat erratic? The Vega has modular headers; can these joints be pulling air into the system and causing erratic readings?
The AFR seems about right mid 13’s, part throttle and idle around 10.

Lastly, the driveshaft rpm sensor reading seem too low. I think in high gear, it should read engine rpm right? There are 4 magnets on the ring, so it should pulse at the frequency a v8 does. The data I am getting makes no sense.

Sorry for the long-winded post, I’ll learn,

Thanks in advance

Vega High

I haven't played around with data logging that much, but the difference between the driveshaft rpm in high gear and the engine rpm would indicate how much the converter is slipping, you usually express this in percentage. Contact your converter manufacture and see what percentage you should be seeing. This is a good way to see how efficent your converter is, and if it is going away over time, or if it is already junk.

vegahigh wrote:If you can help with a few beginner questions, I have installed an Innovate DL-32 in my small block Chevy / Turbo 400 powered Vega. It is a typical mid-10 sec car.

The rpm readings of the Tach and logger don’t seem to jive during the run. I am shifting @ 7300, the logger says 6900 or so. At idle or static rpm’s, they seem to agree. Is the logging interval (84ms) causing this? Which would you believe, the tach or logger?

The car has always had slow response on the oil pressure gauge, and now on the logger as well. I have bled the system, but would imaging that oil drains back after shutdown and the problem returns. The logger and gauge roughly agree on the pressure. Would oil restrictors in the top end of the motor cause this?

Does the wideband reading always look somewhat erratic? The Vega has modular headers; can these joints be pulling air into the system and causing erratic readings?
The AFR seems about right mid 13’s, part throttle and idle around 10.

Lastly, the driveshaft rpm sensor reading seem too low. I think in high gear, it should read engine rpm right? There are 4 magnets on the ring, so it should pulse at the frequency a v8 does. The data I am getting makes no sense.

Sorry for the long-winded post, I’ll learn,

Thanks in advance

Vega High

Your driveshaft RPM on an Automatic car should be lower than engine RPM due to converter slippage like YTNova said. That can vary a lot but somewhere in the neighborhood of 5 to 10% should be close.

Your logger and tach should be getting the signal at the same source - if they are not agreeing then I would be tempted to believe the logger as it has a much better memory and is not being distracted by driving like a human is.

Where do you have your oil pressure sensor? Slow gauge response is typically due to the size of the line going to the gauge. You shouldn't have to bleed it...

John_Heard wrote:
Where do you have your oil pressure sensor? Slow gauge response is typically due to the size of the line going to the gauge. You shouldn't have to bleed it...

Pressure is pressure. All that air in the line should do is dampen the response of the needle. I have seen small & long lines have a very slow reacting gauge. I like at least a 3/16 ID line to the gauge. I like the gauge to go to zero in the blink of an eye when the engine stops.

Do you have a shift chip or light? If so, and the tach agrees with the it, I would suspect the logger since two other instruments agree.

The O2 readings are seldom completely stable. a variance of .2 to .4 is often the case through a run. Look to see if the varyance is coresponding to RPM. For example, if the readings are typically higher at the top of each gear, this would indicate the need for air bleed adjustments in the carb or map modification in an EFI. Also, you are correct, leaks in the headers before the O2 can cause the sensor to read lean, but typically, during a run, the leaks will leak exhaust out, not suck in air unless the leak is specifically shaped such that the exhaust flow generates a vacuum at the leak.

Assuming you are running an automatic trans, the ratio of engine RPM to Drive RPM in high gear will depend on three things. How much power are you making, how far above stall RPM is the Engine RPM and how efficient is the converter. To determine if the RPM is far enough above stall to get a good reading, look at the Engine RPM and Drive RPM on the graph. If the distance between the two RPM graphs has reached the point where it is no longer getting closer as RPM increases, the converter has reached it peak efficiency, and the ratio reading will indicate efficiency. Reading the ratio before the converter reaches peak efficiency will not give valid values. If the ratio calculation is Engine RPM divided by Drive RPM, the number will be 1.xx, with the xx being the slip, ie, 1.07 means 7% slip. If the calculation is Drive RPM divided by Engine RPM, the number will be 0.xx with the xx being efficiency, ie 0.96 is 96% efficient.

Typically, if you have less than 800 hourspower, a good converter ratio will read less 1.07 (< 7% slip) The best I have seen so far is 3%.

I am using a flying magnet on the pully for the RPM pickup.
Sometimes it wont read anything. A few re-boots usually gets it back but its inconsistant.
Any ideas?

Idle AFR is 10??? What do you have for a carb???? That is way to rich...It should be around 14/16....you may have to put a extension on you collector to get a good reading...