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What is an optical bump?

B

Big Josh

Dieselholic
Messages
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Location
Lawton,Ok
Hey guys and gals. I was looking through some old posts and saw optic bump or optical bump on some of the members sigs. What is it?
 
Just trying to ask a simple question thats all. I put optical bump in the search engine and came up with a thread talking about doing it or not doing it because Bill Heath said it was a no, no. SO just trying to find out what It is not to inconvenience anyone.
 
Short story long is the DS-4 injection pump uses an optical sensor that reads a disc inside the pump to measure timing and fuel being delivered. Many have moved the optic sensor inside the injection pump which fools the ECM into giving it more fuel and timing as the otpic sensor is no longer reading actual numbers since it has been moved from it's calibrated position. This is a cheap way to add fuel on an electronically injected engine, but it has MAJOR drawbacks as well. It can and WILL royally screw up the idle if you go too far, or have a high numbered resistor in the FSD. It WILL give you a touchy throttle that is hard to drive in town. It will also make the engine surge while the cruise is on if your not careful. Also it can burn a tranny up in an instant(been there done that, got the tranny to prove it). By injecting more fuel than the ECM thinks it is the torque numbers WILL be off, and the trans will be running at low line pressures do to it.

The all round best way to get the added fuel and timing is with programming, either via a chip for 94-95 or flash on 96-00. This eliminates all of the drawbacks and will let the ECM command the extra fuel in a safe manner.
 
Most people advance the timing up a little (physically turning the pump) bit for the desired throttle response without losing PMC's ability to control idle and maintain all the above points mentioned above.

Everything comes with drawback though. When the computer advances everything for really cold startups, add that to the physical advancement which the puter doesn't know about, makes for a loud noisy cold starts... Search for TDC0 and GMCTD....

GMCTD's posts are very informative about this.
 
Bottom line is that optic bump and timing offsets are 'poor man's' way to try and increase power. To really do power safely, proceed as follows:

1) Open air intake and exhaust
2) Put in gauges - EGT, Boost, and Tranny temp are a good set. DO NOT PROCEED UNLESS YOU HAVE GAUGES, or you can't know what's going on. Learn what safe maximums are.
3) Cooling system upgrades if needed. Most people think that Heath Diesel approach is very sound.
4) Manual Wastegate. Some build their own.
5) HD Lift Pump, "Feed the Beast" mod, maybe a fuel gauge.
6) Reprogrammed Chips.

Have fun!

-Rob :)
 
Big Josh said:
Just trying to ask a simple question thats all. I put optical bump in the search engine and came up with a thread talking about doing it or not doing it because Bill Heath said it was a no, no. SO just trying to find out what It is not to inconvenience anyone.
Click to expand...

No inconvience, just laughing that's all. This was beat to death on the old site.:thumbsup:
Lot's of differening opinions on it, that's all. Controversial issue.
 
Okay well I guess I opened up an old can of worms. (sorry bout that) but thanks for the info guys. This 6.5 rookie is gonna stick to tried and true performance mods.
 
I prefer bump, engine response feels more sensitive. Also when you do bump, you need to adjust pump mechanically more advance (~1mm) cause tdc offset will be different when tdc learn is done (like -1.5 => -0.5).
With tdscan tech it's easy to play :smile5:
 
Big Josh said:
Okay well I guess I opened up an old can of worms. (sorry bout that) but thanks for the info guys. This 6.5 rookie is gonna stick to tried and true performance mods.
Click to expand...

Do not feel bad, their is nothing better than opening a old can of worms. Just be sure to hold your nose when you do. You never know what kind of stink will follow the opening. ):h

It is probably good that we have our own info and now future links on this subject for future DTR members! :thumbsup:
 
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