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Hello. This has been bugging me for some time now. Occasionally, when I rev the engine, as if I was taking off from a stop or when someone asks me to rev it, I get a lean spike and a stumble around 1200-1500 RPMs as the engine is revving upwards. I have a video of what's happening. I am wondering if there is a way to tune this out. I have a 1985 Corvette with the '870 ECU.
Hello. This has been bugging me for some time now. Occasionally, when I rev the engine, as if I was taking off from a stop or when someone asks me to rev it, I get a lean spike and a stumble around 1200-1500 RPMs as the engine is revving upwards. I have a video of what's happening. I am wondering if there is a way to tune this out. I have a 1985 Corvette with the '870 ECU.
Increase your acceleration enrichment by adding more fuel at very limited throttle movements.
Another item to look at is when you are commanding WOT AFR and timing? Set the WOT activation lower like 25% after 1500 RPM so the car automatically commands a richer AFR. This can cover up a difficult to tune out acceleration enrichment condition. The 1985 computers are the most difficult to tune this out of (In my opinion)
Increase your acceleration enrichment by adding more fuel at very limited throttle movements.
Another item to look at is when you are commanding WOT AFR and timing? Set the WOT activation lower like 25% after 1500 RPM so the car automatically commands a richer AFR. This can cover up a difficult to tune out acceleration enrichment condition. The 1985 computers are the most difficult to tune this out of (In my opinion)
How do I add more acceleration enrichment at very limited throttle movements?
Also P.E. comes on at 50% TPS.
In the video I only pushed the pedal down about 1/4 of an inch.
And this stumble only happens if I'm under 1000 RPMs. If I hold it at 2000 RPMs for instance, and give it more gas it will never stumble.
How do I add more acceleration enrichment at very limited throttle movements?
Also P.E. comes on at 50% TPS.
In the video I only pushed the pedal down about 1/4 of an inch.
And this stumble only happens if I'm under 1000 RPMs. If I hold it at 2000 RPMs for instance, and give it more gas it will never stumble.
Thanks.
At lower RPM you need a bigger fuel charge to eliminate the stumble when you snap the throttle. I have attached a screen shot of your scalers and tables that effect acceleration enrichment. What you need to study is the temperature that you are having this problem at and the throttle position (which is related to LV8 and change in LV8, use a scanner to look at LV8) to determine where the problem is occurring and then adjust those tables to solve the problem.
-My thoughts are have power enrich occur before 50% throttle (use the scanner with engine off but key on to see how far you are pushing the throttle down when this problem occurs, set the power enrichment to come on before that throttle position)
-Use the scanner (engine running) to see how warm the car is when the problem occurs and adjust the LV8 vs. temperature factor larger so more fuel is added in at the effect temperature range.
-Use the scanner (engine running) to see how much the lV8 factor changes during this throttle transition and adjust the LV8 factor vs. Delta LV8 table to a larger factor so more fuel is added in at throttle transition.
-Look at tables and possible lower the min LV8 delta change and throttle change to lower numbers to allow acceleration enrichment to occur with less throttle change.
Good luck, with some playing and careful thought you can solve this issue.
At lower RPM you need a bigger fuel charge to eliminate the stumble when you snap the throttle. I have attached a screen shot of your scalers and tables that effect acceleration enrichment. What you need to study is the temperature that you are having this problem at and the throttle position (which is related to LV8 and change in LV8, use a scanner to look at LV8) to determine where the problem is occurring and then adjust those tables to solve the problem.
-My thoughts are have power enrich occur before 50% throttle (use the scanner with engine off but key on to see how far you are pushing the throttle down when this problem occurs, set the power enrichment to come on before that throttle position)
-Use the scanner (engine running) to see how warm the car is when the problem occurs and adjust the LV8 vs. temperature factor larger so more fuel is added in at the effect temperature range.
-Use the scanner (engine running) to see how much the lV8 factor changes during this throttle transition and adjust the LV8 factor vs. Delta LV8 table to a larger factor so more fuel is added in at throttle transition.
-Look at tables and possible lower the min LV8 delta change and throttle change to lower numbers to allow acceleration enrichment to occur with less throttle change.
Good luck, with some playing and careful thought you can solve this issue.
Is there supposed to be a different TPS percentage for the Positive Threshold and Negative Threshold, or can they both be the same number?
Is there supposed to be a different TPS percentage for the Positive Threshold and Negative Threshold, or can they both be the same number?
They can be different or the same (it is not related to positive threshold), the negative means if you back off on the throttle this amount the acceleration enrichment will turn off.
How fast the additional acceleration fuel is taken away. The faster the decay rate the quicker the additional fuel is pulled out, so the car does not go to rich. As shown the warmer the car the quicker the fuel gets pulled out.
Okay I was not able to tune it out with the LV8 tables.
I was able to tune it out by setting the Positive TPS Threshold and the Negative TPS Threshold both to 0. But as a side effect, the AFR now goes to 9:1 during acceleration.
Okay I was not able to tune it out with the LV8 tables.
I was able to tune it out by setting the Positive TPS Threshold and the Negative TPS Threshold both to 0. But as a side effect, the AFR now goes to 9:1 during acceleration.
Play with the settings, i do not agree with zero on the tps threshold, try 10. Also play with the scale factors for load value, that is what determines how much fuel is added. Double them and see what happens and then make educated changes based on the results.
I have it set to 1.17% positive and negative. If I set it any higher than that it bogs down or hesitates.
Danial, play with the multiplier vs. coolant temp table or the multiplier vs. LV8 table to see if you can tune this out without setting the LV8 threshold table at 1.17. I believe that is too low since what this means is any time the LV8 (Load value) of the engine increases by 1.17 or more the car will go into acceleration enrichment. This means as you cruise down the road and make minor gas peddle changes the car will be dumping in additional acceleration fuel which will be costing you gas mileage. Try to set the LV8 table to 10 and then increase the coolant temperature multipliers and/or LV8 multipliers to cover up the lean transition that you see. This way you can still get good gas mileage and good acceleration. Don't be afraid to make large changes in these tables to see what happens and then adjust accordingly. As shown in the stock vette tune once the engine hits 80 C almost all acceleration fuel is eliminated, add some back in and see what happens.
04-14-2015, 01:32 PM
How to tune out stumbles on revs?
