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Opinions needed - Performed Optical Bump

dbrannon79

dbrannon79

I'm getting there!
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Seguin, TX
Hello all, I have recently been comparing my truck to others who run a 6.5 with a similar stock setup and noticed that my truck seemed to be lacking power. I had noticed from the beginning that it doesn't have the power to break the tires loose on dry pavement much less barley able to do it in wet conditions. At first I really didn't think much about it since I know it's a heavy really long wheel base crew cab 1 ton pickup, plus I have 265-75 tires on it. But being as it is, even with having 4.10 gears with the 4L80E trans, I've had several friends tell me that it should have more power than it does unless the motor is just worn out (low compression) or having some kind of fueling or timing issue. This got me thinking about the age, mileage, and how it runs (smooth vs rough, missing ect.. ) even with 280k miles on the clock. Currently it has no miss and never skips a beat, idles smooth as if nothing is wrong, so I started doing a lot of reading on forums looking to see if there were some simple things I could check for or try in the hopes that the motor is not worn out. I don't have access to a diesel compression tester so checking the compression is out if the question until I can get my hands on one. while reading, I ran across several threads talking about the "optical bump" that from what I understand is advancing the timing slightly (compensating for minor timing chain wear) and changing the "pre-fueling" time for the injector pump. each thread I read had various results with some even reporting 20+ hp increase running like a scalded ape! so I decided to try it, thinking "what have I got to loose".

before I did the bump I connected GMTDscan and took a snapshot of the PCM readings, also did one after. doing the bump, I moved the optical sensor adjustment in the direction of the passenger side fender guesstimating 1mm (marked it's position before hand) and slapped everything back together. As for my results, I haven't really taken it out on the open road yet but just a quick trip through town I noticed a smoother idle (thought it was smooth before) and seemed to have slightly better pickup response from a traffic light (couldn't go too fast, 30mph limit in town). The engine didn't seem any louder than before, it may have been slightly quieter! anyway I have attached the before and the after PCM snapshots for the you guys to have a look through to see if readings look good or can be better. After my drive through town noticing the slight differences, I'm thinking that the timing may have or is still slightly retarded and I simply brought it closer to where it should be.

on a side note, I have not even attempted to try the TDC relearn. Frankly I'm scared to do it thinking it will make things worse!

let me know your opinions and suggestions, any help is greatly appreciated
 

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  • Snapshot Before.pdf
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  • Snapshot After.pdf
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TDC offset is -0.62, that could be advanced up slightly and it would increase performance a little. It will also increase injector rattle a little too.
I am running Mine at -1.43 and it seems to run a lot better than it did when it was at -0.56.
Others with better info and more knowledge should chime in. Might be a little while, with this being Memorial time.
 
WarWagon said:
No reason to put up with a truck that can't brake stand smoke it's tires! Although smoking the tires with a loaded trailer in reverse is a little more excitement than most want when it starts to walk sideways. I had to back up in 4x4 in case I hung up on the driveway curb.


Would you like to know more?

:woot:
Click to expand...
I giggle and laugh like My grandson with a big salmon on the line, evertime I see a video of that truck and how it run. 👍😹😹😹
 
MrMarty51 said:
TDC offset is -0.62, that could be advanced up slightly and it would increase performance a little. It will also increase injector rattle a little too.
I am running Mine at -1.43 and it seems to run a lot better than it did when it was at -0.56.
Others with better info and more knowledge should chime in. Might be a little while, with this being Memorial time.
Click to expand...

in the TDC offset, I'm assuming that I'd have to turn the IP slightly to adjust that correct? To be honest the way my truck drives reminds me of my dads old 1/2 ton 91 Chevy step side that had a 6 banger 4.3L it could move around good but didn't really have the balls to do things. the 6.5 I think is a 396L engine which puts it somewhere between a 350 and a 454 but I feel like a 305 small block in this same size pickup body could out do mine! if that makes any sense. Granted I know the 6.5 isn't a power house.
 
It's a diesel. Size vs. a gas engine gets you nowhere. Turbo's really make a small diesel able to murder a big displacement NA gas engine.

The original NA 6.2 was a 305 equivalent. The 6.5TD (6.5 is merely a punched out 6.2) is 200 HP and 400 TQ. That's gas 350 HP, say 1995, but less tq. The 4.3L had 161 HP "please shoot me now" TBI versions in 1993, but, a 200 HP 1994+. The "All blow and no go" of GM's mediocre engines for this era was specifically humiliating for the gutless 454's. The things that had to be done to wake them up.

The 6.5L doesn't have the HP at low RPM to back up the torque. Then at RPM it hits a wall with GM's slapped together parts for airflow. You should check for a restrictive fender snorkel as a Bic lighter could plug it. I forget what year GM quit choking their engines with that factory part.

You are chasing crumbs on the floor if you want power. The turbo is the biggest thing holding you back followed by the airflow abortion for the intake and exhaust. The video is a big turbo - some now have variable turbos strapped to this engine. Then you can throw some fuel at it to light the tires off. (If smoking the tires is all you want just throw fuel at it in a tune.)
 
I admit I havn't done anything with the factory air cleaner. I was hoping those snapshots would show if everything was up to par or if something was out of adjustment especially since everything is still mostly factory
 
Optical sensors bumps are the old way of doing things. Now the same thing can be achieved with tuning. If you want more power get a tune from Quadstar, that will get you in the 100cc fuel range (70cc is stock) pair that with a hx35 and you should be close to 275hp at the wheels.
 
Exactly what Rockabillyrat said.
Imagine if you played with the bump and the timing many times. The could add and subtract fuel with adjustments. Then play with the mixture of all that many times and took notes to figure out what is the best for where. Also learned where damage occurs, and can avoid that. That is tuning.
Talk to him, explain miles and power you want. Risk you are willing to take and so forth.

Getting a better turbo on there is so much of a change. @WarWagon Do you still have your ATT? MrMarty was in the right track for this as an option for being low cost. Used turbo- many people are super afraid to install a used turbo- why? You have how many miles on your gm turbo now? Probably WAY less than any used one you would get. Then turn around and sell your turbo depending on what you pay you might break even on the turbo cost.

Yes improvements on air intake helps, but more people do that just because it is doable from junkyard- which so is turbo btw...
If the air intake is too small- you could do a fast test on a non windy day. Running without an airfilter for a 1 minute test isn’t going to destroy an engine. Drive out of the town to where you can get on freeway/ hiway. Pull over, remove filter and 0-60 it. Then pull over put it back in and 0-60 it on way back home. If it is a massive difference, like 1.5 seconds then yes consider improving it. Otherwise no.

Going with a SMALL bump in tune and larger turbo won’t kill the engine sooner, because the better breathing turbo takes load off the engine and your normal driving will have you using less throttle to do what you normally do- unless you are a foot to the floor everytime guy. Even with a little more fueling the bigger turbo should also help mpg, again unless you are foot to floor all the time.
 
It's already been said, but I'll reiterate, if you want more power, you have to increase both fuel and air. Only way to increase fuel on the electronic IP is a tune. Quadstar has a great reputation for tuning if you want to go that route. You're fortunate in having the OBD1 where you can have multiple EPROM chips or several switchable tunes in one

Turbo upgrade will also give more power and improve health of engine. There's many options out there that will have to be configured with your tune if you end up going that route. A Team Turbo, Holset 35, 40, or 35/40, Peninsular Turbo are a few upgrades that come to mind

Also at 280k you're probably due for a timing chain. IF this is the case consider going to a DB2 mechanical injection pump, easy to do with the front timing cover off. On a DB2 you have a little more control over the fuel output as there's a fuel screw on the IP that provides small adjustments in fuel output, something not possible on a DS4. You're also fortunate that if your 95 still has the single stat it will make the DB2 conversion easier, as the throttle bracket for the DB2 was designed for the single stat setup and wont require modification like folks have to do on the dual stat setup

Granted how large your truck is nothing will make it take off like a hot rod, but as you'll see there's many aftermarket things that can be done to wake up the engine, just up to you how much you want to pay to play
 
Is this truck a daily driver or a loaded towing rig? Tunes and "easy" stuff without a turbo change will wake it up unloaded. Loaded using a truck as a pickup is my POV. I disagree with @DieselAmateur as some on here like @n8in8or 6.5L Tahoe will run doorhandles down the 1/4 mile track with a Corvette LS2 powered Trailblazer SS. The Yank stall converter hit hard without a lot of fuel thrown at it.

The factory air filter system is ok except for the snorkel in the fender. A upgrade is a later year K47 Diesel round air filter assembly. The gas engine K47 is different and not what you want.

Does it still have the engine killing 6 blade fan? :eek: and crud covered origonal fan clutch that won't work when you need it? 210 is the max ECT temperature you want to run at. Over 210 you need to reduce throttle, pull over, etc. The 9 blade fan, now Dorman offers it, or a Duramax fan both backed by a low temp Kennedy Diesel fan clutch is the best easy way to go. A spin on NEW High Output water pump also helps. (You convert the water pump and fan clutch to a spin on. The 6 blade 6 bolt fan is pure garbage.) Also remove the engine oil cooler and clean the mat of trash off the condenser that builds up behind it.

Loaded like it's a pickup towing power:

www.maxxtorque.com

The 6.5L Diesel Factory Equipped Asthma Attack

Online Diesel Community featuring news and articles on 6.2L, 6.5L and Duramax GM diesel engines, Ford Powerstroke, Chevy Cruise, lubrication and more.
www.maxxtorque.com www.maxxtorque.com
 
Everything under the hood is still factory GM except for the PMD remote mount, OPS relay mod, and now the Optic bump which I think just made the timing closer to where it should be rather than an actual advancement. Has the steel 6 blade bolt on fan. I use it as a daily driver unloaded. Only weight it carries is the steel headache rack with steel bed rails and a 62 gallon auxiliary fuel tank in the bed. I know I made my original post sound like I want to burn rubber at every stop but honestly I’m usually the slowpoke that everyone hates on the road lol. I’ve just noticed some tell tail signs that the truck just doesn’t have power it should have

I’m sure it’s due already for a timing chain and probably some other major maintenance. The most recent thing that I noticed was our last trip to the coast while just arriving there it began to act like someone just reached over and turned the key off at random. I knew the PMD was dieing, lucky I had the cheapo PMD that came with the mount kit with me. After I swapped it all was back to normal but I just didn’t feel the same power as before. I know I need to cough up the money to get another OEM one but I’m still cringing at spending $300+ for the little black box! Plus I have never heard of a working PMD doing that so I’ve convinced myself that I’m crazy for thinking it would.
 
PMD can do many a strange thing, working or not.
I went with the uprated grey box Stanadyne unit and the adaptor harness and have had zero issues since.
I also pack along two spare black box units for the just in case.
I also built my own turbo master boost controller. It cut my MPGs by about one so I delved in and did the necessary repairs and upgrades to the vacuum controlled unit. I also pack and extra boost solenoid valve and the boost sensor mounted to the top of the intake. If either of those would not fix the boost issues and, I am out on the road, then, the turbo master it will be. It is packed along for one of those just in case items.
 
I still have the old one it was the grey box Stanadyne. I could connect it back and see if anything is different, the truck still ran fine when I swapped it out. Only randomly died after a 2 1/2 hour drive. What really got me was the what these things are designed, the two components that produce the heat doesn’t even touch the heatsink. I do a lot of fiddling with electronics and have been very tempted to tear it apart seeing what’s inside but that’s for another later adventure
 
Yeah, you and about 10,000 other guys all started down the road of seeing whats up with the pmd. I probably heard or read 100 people that swore up and down they were going to build a better unit.
Just not worth the time and hassle.

Get 2 mounted onto heat sink(s) next to each other. The working one you have and a new one with lifetime warranty from Leroy. Get a spare plug and fill it with silicone in the back, or buy that already made from Mod Mafia since they bought out blue hummer.
Drive it now off the new one, have the other as back up. One day when the new one dies (they all eventually die), plug in the other right next to it and be in your way. This is especially nice in emergencies, freeway traffic, horrible weather, etc. Then when youget home, remove and ship the bad one off for warranty replacement. When the new lifetime one gets back, drive on it again, and put the sealed plug back in the old unit.
 
I would verify lift pump PSI with the "loss of power". Engine running and bring RPM up to 2500 to make sure PSI doesn't fall off to 0. Plugged tank sock etc.

Testing the vac system, as it holds the turbo WG closed, say if you get black smoke now. Old bad connectors on the vac hoses appear common failure points. Vac pump INOP...

As you are just DD then a tune will wake it up enough.
 

Guts of a PMD

So while I was waiting for the oil to drain on an air compressor I building up I decided it was as good a time as any to disassemble a PMD. There was actually a little more to it than I thought there would be. Fairly complicated circut board with chips. The resistors we all see are actually...
www.thetruckstop.us
 
ak diesel driver said:

Guts of a PMD

So while I was waiting for the oil to drain on an air compressor I building up I decided it was as good a time as any to disassemble a PMD. There was actually a little more to it than I thought there would be. Fairly complicated circut board with chips. The resistors we all see are actually...
www.thetruckstop.us
Click to expand...
It seems that someone in here may have made a thread about replacing the faulty components in the PMD. Seems they replaced them two round things with two hold down screws and got them working again.
It seems he had a bear of a time getting enough sealer removed to get to the connectors and getting tje solder melted and them two units removed.
 
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