Need BLM advice

[jameslleary]

I am trying to help a buddy in a stock 88 GMc truck deal with the 108 blm issue as well. all sensors are new Ac Delco, and engine is mechanically sound. Seems to be a big problem with TBI.

[EagleMark]

Dave, the 10% AE in MAP and TPS sure did the trick for the throttle off idle hesitation. Now the only issue I'm having is a closed throttle in gear at speed to open throttle jerk. Would that be more AE MAP or more AE TPS related? I'm guessing MAP?

Expalin more on what throttle jerk is?

10% is not much, for instance Vortec heads swap needs like 200%!

To help you decide what it needs you need to understand the difference of TPS AE and MAP AE. AE-TPS is for when the throttle blade moves, that's it, very short like millaseconds. AE-MAP finishes off the transition and is much longer, like 2-3 seconds.

Mark, I still have the lean surge in open loop after start up even after adjusting the table to 14.0:1 in any cell 14 or higher with no success. Then I remapped the table even richer and only gained a rich condition on a dead cold engine. Which then after some warm up, still open loop, turn back into a lean surge. When I does enter closed loop the idle settles but BLM is 140 or higher around 150 degrees F coolant temp. The BLM will return to 128 or close after engine is fully warm at 190-200 degrees but it takes driving the truck to get that tempature.

I'm thinking I should revert the Open Loop AFR table to stock, then possible fool with my timing table some more. Maybe I just have too much advance and thats causing the surge? Or maybe there is a coolant temp bias I need to look at?

Yes if the change did not help always revert back.

Did we ever see a data log after warmed up and driven, then idle in drive and park for a minute? What I'm getting at is IAC count to be as low as possible.

It could be a spark timing issue! You have increased spark correct? Sometimes when spark advance is more on the performance side it has enough spark for cold conditions, then you have to much Cold Spark added on top of that!

Do a data log of the cold start issue and post it with your current bin and we can take a look at how much spark is going on through this issue.

I am trying to help a buddy in a stock 88 GMc truck deal with the 108 blm issue as well. all sensors are new Ac Delco, and engine is mechanically sound. Seems to be a big problem with TBI.

Only when it's rich! The 108 is bottomed out so it can't do anymore, this is always an issue at idle with aftermarket cams. But could be to much fuel pressure? Or a vacuum leak! EGR stuck slightly open? IAC count to high... meaning not enough air mixing with fuel over the throttle blades and it drips causing a wet (wetter then normal) intake.

Where you been?

[brian617]

First log is cold start albeit 70* ambient temps today with plenty of humidity. Note that when I spent the day tuning my BLMs it was a cooler 55* day with alot less humidity. May need to remork fuel map again for some balance.

Second log is a short drive with engine already at max coolant temp and then some idle time.

I reverted my Open Loop AFR table back to stock, and took some timing out of the idle cells before I logged, along with a little more AE which seemed to help the closed throttle to open throttle at speed jerk.

[EagleMark]

The warm log idle shows a low IAC count 13 which is good. I don't think you could do better.

One thing you have done and I don't see a need for it with this cam is set base timing to 4.2* This also advances injector timing. If you don't have a reason or want to try, I would go back to 0* base timing. Also change it in bin.

Since your learning great and still eager! I'm going to do this a little differant. I made some changes to your bin, open it and use the compare feature and load the old bin. Then go to tools and Difference tool and find what I did and try to explain why I did it! You'll also have to check and see if it helped... I'm not sure it is the cause but will soon find out!

You got headers on this? Stock exhaust?

[brian617]

One thing you have done and I don't see a need for it with this cam is set base timing to 4.2* This also advances injector timing. If you don't have a reason or want to try, I would go back to 0* base timing. Also change it in bin.

I can certainly try it, only reason I have it set like that is the cam is ground 4* advanced and I thought it would work well together.

Since your learning great and still eager! I'm going to do this a little differant. I made some changes to your bin, open it and use the compare feature and load the old bin. Then go to tools and Difference tool and find what I did and try to explain why I did it! You'll also have to check and see if it helped... I'm not sure it is the cause but will soon find out!

Much appreciated, will give a good look over!

You got headers on this? Stock exhaust?

I have a very unique set up for exhaust. Stock manifolds mated to a 96-98 3/4 ton factory dual 2-3/4'' no cats into 02 model 3/4 ton dual inlet dual outlet muffler then it Y's into a 3-1/2'' single out. I think it moves air well without any noise.

[EagleMark]

How far from stock location did the O2 sensors move?

[brian617]

The stock o2 for my truck was in the left manifold just before the collector. Now I have a heated o2 in the right side pipe just 2'' down from the collector and my wideband in the left pipe same location. These are the stock locations for the upstream o2's on a 96-97 Vortec truck.

[brian617]

Here is a picture off Google image.

[brian617]

Since your learning great and still eager! I'm going to do this a little differant. I made some changes to your bin, open it and use the compare feature and load the old bin. Then go to tools and Difference tool and find what I did and try to explain why I did it! You'll also have to check and see if it helped... I'm not sure it is the cause but will soon find out!

First, I see you smoothed out the Idle VE map

Second, Looks like you reduced the Startup Spark vs Temperature meaning less cold advance.

Third, Idle Overspeed Retard/Advance vs RPM Error were reduced to calm the swinging advance at idle.

Forth, and i'm not sure why you did this, but you zero'd out negative advance in the 104* Celsius (219*F) row in the CTS Spark Advance Compensation vs Vacuum vs Temperature.

[brian617]

This mornings cold start still surging but not the o2 or wideband readings of lean like yesterday. The other thing I think is crazy with my current Idle VE map, the BLM at 158* F is 136 and thats shortly after closed loop. Then when I drive to work with the coolant temp around 194* F the BLM is back to 124.

Is there a specific table for that bias? And is that what I need to work on first?

[EagleMark]

Your good!

First, I see you smoothed out the Idle VE map

When I was using data tracing I saw during the lean surge it was jumping from the flatter idle area up a big slope. So smoothing it out should be a help. Still may need work there in tuning the VE.

Second, Looks like you reduced the Startup Spark vs Temperature meaning less cold advance.

Yes because you've added much swpark to stock table and with this adder could be to much, causing mis fire, surge etc...

Third, Idle Overspeed Retard/Advance vs RPM Error were reduced to calm the swinging advance at idle.

Right! Idle is controlled by spark but sometimes it can be to much and constantly over-undershoot. Not so much stock motor but cams and such do cause issues.

Forth, and i'm not sure why you did this, but you zero'd out negative advance in the 104* Celsius (219*F) row in the CTS Spark Advance Compensation vs Vacuum vs Temperature.

Data tracing found some missing spark advance and it was bumping into row before this so I zeroed it out.

That was before I noticed the Base setting timing bias which explained the missing timing!

[brian617]

Data tracing found some missing spark advance and it was bumping into row before this so I zeroed it out.

That was before I noticed the Base setting timing bias which explained the missing timing!

Can you explain this more, I did notice the increase of advance at cruise and light throttle on the way to work this morning. It was an improvement for sure.

[jameslleary]

Expalin more on what throttle jerk is?

10% is not much, for instance Vortec heads swap needs like 200%!

To help you decide what it needs you need to understand the difference of TPS AE and MAP AE. AE-TPS is for when the throttle blade moves, that's it, very short like millaseconds. AE-MAP finishes off the transition and is much longer, like 2-3 seconds.

Yes if the change did not help always revert back.

Did we ever see a data log after warmed up and driven, then idle in drive and park for a minute? What I'm getting at is IAC count to be as low as possible.

It could be a spark timing issue! You have increased spark correct? Sometimes when spark advance is more on the performance side it has enough spark for cold conditions, then you have to much Cold Spark added on top of that!

Do a data log of the cold start issue and post it with your current bin and we can take a look at how much spark is going on through this issue.

Only when it's rich! The 108 is bottomed out so it can't do anymore, this is always an issue at idle with aftermarket cams. But could be to much fuel pressure? Or a vacuum leak! EGR stuck slightly open? IAC count to high... meaning not enough air mixing with fuel over the throttle blades and it drips causing a wet (wetter then normal) intake.

Where you been?

My burb is dead in the water up in humboldt county. trans seal failed, and roasted my barely 2 year old trans rebuild. wifey has had it, and wont trust it, even with a new trans.

[EagleMark]

Can you explain this more, I did notice the increase of advance at cruise and light throttle on the way to work this morning. It was an improvement for sure.

Depending on engine temp the "CTS Spark Advance Compensation vs. Vacuum vs. Temperature" can add or subtract spark. Using the Data Trace feature during playback of a log you can see exactly where you are. In this case the line above where timing starts to pull from heat, but remember the cells are interpolated so it was getting some, not all.

I saw in your spark advance table around 21*, but only 15-16 showing in data lists. But now I believe this is from the base timing at distributor set to 4.x, your distributor set to 4.x so it's there. But my adx file did not have the extra timing built into the Conversion, it is set to 0*.

[brian617]

Depending on engine temp the "CTS Spark Advance Compensation vs. Vacuum vs. Temperature" can add or subtract spark. Using the Data Trace feature during playback of a log you can see exactly where you are. In this case the line above where timing starts to pull from heat, but remember the cells are interpolated so it was getting some, not all.

I saw in your spark advance table around 21*, but only 15-16 showing in data lists. But now I believe this is from the base timing at distributor set to 4.x, your distributor set to 4.x so it's there. But my adx file did not have the extra timing built into the Conversion, it is set to 0*.

Ok the light bulb came on finally I plan on setting it back to zero* next chance I get so I can better understand whats going on. A lot to digest so it would just be better if i'm seeing actual data right now.

Thanks Mark