bucking

[93Cobra#2771]

My spark tables are all stock - has always had the issue since day one. It got A LOT better after I dinked around with the ProM transfer curve, but still hasn't been totally fixed.

I have simply been too lazy/busy to do any more tuning on it. I have some ideas on what to try, though.

[QWKSNKE]

Originally Posted by 86GT

I put my spark table back to stock and the problem went away. I am going to do some testing to find out what caused it.

Any updates?

It is very annoying. I believe my timing tables are still stock unless the file has gotten corrupted.

[86GT]

My Spark tables are what caused mine. I also left my accel tables alone but raised the global accel multiplier to 1.2.

My bucking is gone but I do have a tad lean tip in. I have 90GT's tune and I am trying to figure out what he did.

[93Cobra#2771]

My timing tables are from an A9L - made no difference, bucked the same...

[86GT]

I only saw the bucking when I changed the spark tables in the mid range and they did not match one another.

These tables are inter twined depending on load. This is hard to put into words but the EEC uses three different tables depending on FN125. If your load is hovering at this cross over point, defined by FN125, and the two tables that are drastically different at this point then the bucking will occur.

I hope that makes sense.

I used the X3Z spark tables and then only messed with the loads above 100%

[Italian LX]

Originally Posted by 86GT

I only saw the bucking when I changed the spark tables in the mid range and they did not match one another.

These tables are inter twined depending on load. This is hard to put into words but the EEC uses three different tables depending on FN125. If your load is hovering at this cross over point, defined by FN125, and the two tables that are drastically different at this point then the bucking will occur.

I hope that makes sense.

I used the X3Z spark tables and then only messed with the loads above 100%

I remember checking the three spark tables you are refering to and thety are all at the stock settings on Lee's tune.

[86GT]

Chances are the spark is not the issue. If I remember correctley you stated the only difference was the MAF and injectors. If this is still true then it has to be the MAF.

What is spark, fuel, MAFV and TP at the bucking range?

[QWKSNKE]

Do you think that I may have a bad MAF.

Italian will have to answer your question Clint. He currently has my car and laptop so I can't look it up

[Italian LX]

Originally Posted by QWKSNKE

Do you think that I may have a bad MAF.

Italian will have to answer your question Clint. He currently has my car and laptop so I can't look it up

Yeah, I've been offline typing up a response.

[Italian LX]

Originally Posted by 86GT

What is spark, fuel, MAFV and TP at the bucking range?

Let’s see if I can give some more information on the problem…. maybe some of this will enlighten other on what is going on.

One thing that happens in addition to the bucking is a weird surge while increasing the engine speed (while the car isn’t moving). I’m thinking this is directly related to what’s causing the bucking while the car is cruising, so I will explain what I have experienced:

The car idles great at around 900RPM. However, if you run the motor up to 1500 it will start a surge that runs up and down a few hundred RPM at about 100 cycles per second. The datalog shows the MAF voltage bouncing back and forth over about a .3 volt range and the pulse widths bounce between .8 and 1.8ms. Also, the timing is up around 37.5 to 42.75* during the surging. It seems to me like something is causing a slight surge and then it starts a cycle.

Jonathan and I had both mentioned that maybe the BOV may be not opening properly and is causing some surging across the MAF that starts the cycle.


As far as the rest of the tune goes, the car feels really good under acceleration and we now have the KAMRF’s staying relatively close to 1.000. There seems to be no bucking as long as the vacuum is below 14 in-hg… but anything above that and you’re very prone to a bumpy ride.