Bogs for a second and then takes off

[Bearly Flying]

I have the same problem as the OP, ported plenum and IH's, secondary delete.

The car runs very well except for when it is in low throttle positions. ie normal traffic stop and go conditions.

Any periods of light or no throttle positions seem to generate a rich condition and flood the motor.
A decisive hit on the throttle will clear it's throat and all is good until the next lite throttle event.

It's not all that fun when you are in stop and go traffic.

I believe we are flooding the motor at low throttle positions.

[BennieC.]

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.

[Bearly Flying]

I have FIC injectors from Jerry.

Headers and a 3" exhaust, Ported plenum and IH;s, port matched heads. If that helps....

[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.

[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.