full os bump

[luke22494]

i tried a full os bump on my 94 a couple weeks ago and i drove it a couple miles like that. when i got back to the house my truck was loping. would a full os bump cause any problems with anything at all

 

[ak diesel driver]

yes

 

[luke22494]

i turned it back that same day but what problems would it cause

 

[ak diesel driver]

lopey idle, touchy throttle, etc, a good tune is the best way to go

 

[THEFERMANATOR]

lopey idle, touchy throttle, etc, a good tune is the best way to go

Don't forget if it's an automatic it can also slip the trans pretty badly. When you do the bump, you only go maybe 1 MILLIMETER which is not very much.

 

[buddy]

I suspect it would make it difficult shifting into gears, and could stall out the truck, because what youre doing is making the PCM think it is injecting almost no fuel so it cannot balance it at idle very well.

 

[THEFERMANATOR]

I know I went pretty far with mine(about 2 MM's), and it shifted into gear fine. It idled a little rough though, would lope occasionally, and teh trans shifted like a slip and slide. Only kept it bumped for a few days because of how badly it shifted.

 

[Slim Shady]

If you are interested in doing the optic bump right, pm me and I will tell you how to set it correctly ( well at least to where it works fairly well) then you can further play with it on another note. Need a scanner to do it correctly.

 

[buddy]

I was thinking more along the lines of a manual trans feathering it into first gear. The problem with an automatic is that tranny pressure is throttle percentage dependent so if using less pedal and getting more fuel its not operating like intended for tranny pressure.

As suggested, an aftermarket PCM program is a better investment.

 

[Slim Shady]

It can be made to work fairly well, most just don't set the bump correctly, to much of anything isn't good. It is nice to play with, especially if you go the other way and play around a little as well with different configurations. Nice learning event.

 

[luke22494]

i have a 5 speed and i noticed the touchy pedal but is there any way to make the pedal less touchy but still keep the lope. it would prolly be better to have a switchable chip to go back and forth with as far as driveability is concerned

 

[buddy]

If you like the lope, then it can be implemented in software a lot better than messing with the hardware. Just not something I would recommend subjecting your IP, PMD and engine to all the time.

 

[Slim Shady]

Actually you can adjust the bump to get rid of all most all off the problems it may cause at idle.I would suggest not going below 4 MM cubed at idle this generally leaves enough room for the computer to compensate for most idle irregularities. yet every truck is different based on how your pump was set up and how worn it is.

I have actually played with a reverse optic bump. Some interesting things these mechanical DS 4 with electronic control.

 

[ak diesel driver]

Actually you can adjust the bump to get rid of all most all off the problems it may cause at idle.I would suggest not going below 4 MM cubed at idle this generally leaves enough room for the computer to compensate for most idle irregularities. yet every truck is different based on how your pump was set up and how worn it is.

I have actually played with a reverse optic bump. Some interesting things these mechanical DS 4 with electronic control.

what's to be gained by a reverse bump?

 

[Chevy3500]

Ive never hear of this before, whats the purpose, what is to gain from this and where can i learn more.

 

[buddy]

The purpose is to fool the PCM into not knowing how to accurately gauge its fuel rate commanding, so that you get more fueling off the line. Its not necessary as it could just be programmed to do that. And it has other consequences, that its not really worth messing with. The reverse bump would make the PCM think its injecting more fuel than it is, so depending on your timing curve could put you at higher advance. And messing with fuel rates will mess with tranny pressures and boost if using the vacuum control.

 

[Chevy3500]

are their any bad consequences , i have a manual tranny and have the hx40wii turbo.

 

[buddy]

The bad consequences is what has been discussed in this thread

 

[Chevy3500]

Where can i find out how to do this with pictures and how can you tell how many mm