Of course y'all know that I'm slowly trying to figgure all this out (although I'm still somewhat confused about my cold start problem, but that's neither here nor there for now). Anyway, my guini pig is my '88 Blazer (350TBI, 700R4 combo) with 3:42 gears and 33" tires.

The chip that a nameless source burnt for me (learned my leson there!) has a slight knock (by the knock counts thru ALDL) but nothing that I can hear unless I run regular gas. Anyway, I acquired a set (well two actually) of 4:10 gears that a friend (who is very experienced at installing gears) will install for beer labor.

Now after all this build up, the question of the evening is.....how will this (gear change) effect the knock counts that I am seeing? As always...TIA.

 

It'll probably move them lower in the MPH range, as the engine will reach that particular rev range faster, but other than that I can't see how it'd make much difference. Changing any single thing will affect lots of other things, and often in unpredictable ways. It's hard to anticipate those effects.

You may have to push the engine a little harder to get knock as the deeper gears will give the engine more mechanical advantage over the weight of the truck and therefore reduce the load on the engine at a given rate of acceleration.....but that's just a theory I pulled out my ****.

 

The difference is simple. Your knocking will just be slightly reduced in the lowest gears but still there. It depends on what is causing your knocking. My engine will tolerate 6 degrees more timing EVERYWHERE in 1st gear, 3-4 more in 2nd than in 3rd and 4th. When I remove the timing to keep the engine from pinging in 3rd gear my car gets soft off the line . Source code or a patch would help me but I've learned to balance it but I hate compromises .
As for your rich cold start, it's all in the code to start and then to lite off the cat as quickly as possible. I'm actually suprised GM ran so much timing on choke as they did. I think it's because they didn't want to run a TON of unburned fuel past the o2 sensor but I can't be sure of that.
Just adjust your open loop vs CTS table to lean out the cold starts, that's how you do it.

 

Just adjust your open loop vs CTS table to lean out the cold starts, that's how you do it.


Sorry to sound so dumb, but what peramiter in the $42 ECU (7747 bin) do I need to adjust. I've been studying everything in the ECU, but the only thing that even looks remotely like it would do the trick is the "Cold AFR vs VAC kpa (added to AFR vs Temp). Is the area that I need to adjust? Thanks

 

You just said it yourself. Adjust the AFR vs Temp table which is added to the Cold AFR vs Vac table. They're added together so say the AFR vs temp lookup is 10 and the Cold AFR vs Vac table has 2.2, the open loop AFR for that manifold pressure and temp is going to be 12.2 . Keep in mind that the open loop AFR tables are still looking at the main VE tables to calculate fuel so if your BLMs are really low or high at idle when warmed up and in closed loop then you've got a VE problem, not an open loop AFR problem.

 

Thanks that really helped. :hail: My C/L BLMs at a warm idle are hanging around the 130 mark. I've noticed that sometimes during a long deceleration the BLMs can rise into the mid 130s, but drop right back to around 128 as soon as I touch the throttle. Is this normal? Im my readings I've come across a paramiter that I think has to do with deceleration. I can't think of it right now, but I'll try to look it up tomorrow evening if I don't have to work to late.

 

If you're BLMs are in the 130's I'd say you're a tad lean. If that's the case, then leaning out the AFR vs temp should help a lot. I noticed that stock TBI's are usually SUPER rich from the factory. I'm suprised they don't smell like raw fuel they're so rich. Then again with the reversed logic in the IAT all of that might be compensated for. Kind of like compensating for things using unorthadox ways.... that's GM for ya .