Bogs for a second and then takes off

[Marc Haibeck]

Hi Bennie,

I resolved the problem that I was having with the car that was bogging or stumbling under light loads.

This is what I was seeing in the scan data. When the engine would bog the short term fuel trim would go down to about 90. As if the the fueling was really rich. Then the oxygen sensor voltage would then go to less than 50 mv. This would close the fuel injector and I would see 17 to 20:1 AFR on my wideband oxygen sensor.

If the calibration was set to open loop the car would drive perfectly so the fuel table was correct. I eliminated the problem by replacing the oxygen sensors. New sensors respond quickly to fueling anomalies and don't get stuck down at less than 50 mv when responding to a rich AFR.

[XfireZ51]

Marc,

You may recall I was chasing an issue w my O2 sensors earlier this year. Particularly the pass. side. On a scan, I would see a string of 0's for the voltage, which thee ECM would interpret as running lean. If that condition remained long enough, it would throw the LEARN function OFF and default back into Open Loop.
W a bit of accelerator, things would come back. You wouldn't feel any difference as it did that, but for purposes of tuning it would throw things off.
Some other tuners I communicated with suggested that AC O2 sensors were more consistent than the Bosch so I got two of them off Amazon. Voila!
No zeros, no open/closed loop flipping, no going into and out of learn.
However, I can't say that I experienced the bog others are sensing. I do see that on closed throttle decel, my WB will sometimes spike to 17 or 18:1 AFR.
I wonder if that's not the injector shutting down due to a too small pulse width being commanded, which brings up the issue of the injector offset. Another tuner using the ACCELs in a different motor saw the same thing happening

[Marc Haibeck]

Dominic,

I installed Bosch 13077 (similar to the OE sensor) and then the oxygen sensor performance was excellent. They solved the bogging problem.

In general, I think that the control system is not very good at fuel corrections that are greater than -10%. Then maybe it overshoots the adjustment and goes too lean. In the future when encountering the lean out problem, I'm going to adjust the AFR into the 13.2 to 16.1 range with my wideband and with the system in open loop. Then go to closed loop and make fine adjustments.

I have seen the deceleration trims in the 90's on some cars. I too think that it could be a fuel injector low flow limitation. Excellent oxygen sensors will help there too.

[XfireZ51]

Marc,

Interesting observations. Let me suggest you try the AC O2 sensor at some point. My experience and that of some others suggests it's more consistent and reliable. I have used the Bosch for a long time but more recently have found that for some reason performance deteriorates over time.
I wonder if the use of headers, creating a longer travel path for the exhaust, affects the accuracy of the Bosch.

Some questions:

1. Has your experience been w both exhaust setups or just the stock manifolds?
2.Is it coincidence that the "defective" sensor seems to be the one I have a harness extension on?
3.O2 voltage is small and the extra resistance doesn't work well w the signal from the Bosch??
4. If you still have the logs of those scans, what is the PW when you see the AFR spiking lean?
I'm assuming you're zeroing out the secondary injector delay on your secondary delete calibration.

[WVZR-1]

Originally Posted by XfireZ51

2.Is it coincidence that the "defective" sensor seems to be the one I have a harness extension on?

It very well might not be a coincidence. I'd think the quality of the components quite important. How long is the extension?

[XfireZ51]

Originally Posted by WVZR-1

It very well might not be a coincidence. I'd think the quality of the components quite important. How long is the extension?

I use the wiring and connectors from used O2 sensors so my extension adds about 9" in length. Just thinking out loud if there is any correlation to which side of the motor the defective sensor is usually found. Also, if it happens w motors using headers (the reason for the extension) as opposed to stock manifold motors.
Given the very low signal strength used for the O2 sensor, perhaps the Bosch O2 is marginal in those situations. Or perhaps it works fine at first but then deteriorates over time.
The O2 sensor I am now using is the AC AFS-74. It looks more like a Denso sensor than the Bosch. When I logged the ACs v the Bosch , the ACs seemed to tell a bit of a different story re: BLMs. Motor appeared to be running leaner than I had observed before. Another observation is that the motor does not drop in and out of C/L. Once there, it stayed in C/L.

[Marc Haibeck]

Dominic,
Your question 1. I find that oxygen sensor performance is better on OE manifolds. The OE manifolds are designed to jet each of the four cylinders across the sensor. With headers usually only two cylinders are in the sensors path.
Q 2 and 3. Extending the oxygen sensor cable has no effect on the sensors voltage to the ECM. Voltage drop is determined by resistance x current. Ohm's law. The sensors's current is so low that if the cable was lengthened by three feet the voltage drop would only be a millivolt or two. An insignificant loss. Adding tape or sealer to an extension cable can cause problems. The sensor gets its reference air through the connectors. Only use crimp connectors.
Q 4. I have a nice scan of the fueling going falsely rich on deceleration. At 2300 rpm the throttle was closed. The FI pulse width is 3.2 ms, then the sensor goes to 898 mv, very rich. The sensor stays at about 880 mv for two seconds. Meanwhile, the FI pulse is ramping down to 2.0 ms. Then the sensor snaps quickly to lean. About one second later everything is normal with a FI pulse os 3.2 ms. The new sensor switches faster from rich to lean, without running down the FI pulse to the point to where the engine misfires.
I always set the secondary throttle opening delay to zero, even though it doesn't matter if the secondary throttles are not present. The delay is for the opening of the ports, not the fuel.

[Johnny5]

"It appears that Z owners that is having the problem have in commons are: 1) the secondaries eliminated
2) Haibeck chip

How about the injectors. What injectors do you have currently installed. I have talked to Marc in regards to this concern and he has 2 1990 that are doing the same thing as well. He suspecting injectors. I'm going to data log and check the car out this weekend. Will let you know what I find out. We can make some changes to the fuel trim if need be."

I have a 1991 (27k miles) that is all stock so I did not delete the secondaries or have a chip. (The secondaries won't open up either) it currently has the stock injectors as well and I noticed my car bogs or surges when cold too! I'll see if it does this after changing the injectors. I just ordered the obd2 to obd1 conversion so i can see if I get any codes from my scanner.

[StickWalker]

I have new injectors from FIC that I installed this spring and maybe have 1000 miles on them now.

[secondchance]

Originally Posted by Johnny5

"It appears that Z owners that is having the problem have in commons are: 1) the secondaries eliminated
2) Haibeck chip

How about the injectors. What injectors do you have currently installed. I have talked to Marc in regards to this concern and he has 2 1990 that are doing the same thing as well. He suspecting injectors. I'm going to data log and check the car out this weekend. Will let you know what I find out. We can make some changes to the fuel trim if need be."

I have a 1991 (27k miles) that is all stock so I did not delete the secondaries or have a chip. (The secondaries won't open up either) it currently has the stock injectors as well and I noticed my car bogs or surges when cold too! I'll see if it does this after changing the injectors. I just ordered the obd2 to obd1 conversion so i can see if I get any codes from my scanner.

Assumption that secondary removal and Heibeck chip causes stumble is not true. I had my secondaries removed and run Heibeck chip. I had stumbling problem but the issue turned out to be O2 sensors. Replacement of O2 sensors fixed the problem. After another couple of months stumbling returned. This time the cause was TPS going bad. MAP sensor going bad will cause the car to stumble also. Bear in mind that our cars are 20 plus years old resulting in some sensors giving up the ghost.

Done correctly, secondary removal and Heibeck chip to run both injectors are worthwhile modification.

In your situation, with OEM injectors, I'll bet your injectors are failing. I've seen enough ZR-1s with OEM injector failures.