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Anybody else running a DB2 4911 on a 6.2 ?

12K views 71 replies 12 participants last post by  acesneights1 
#1 ·
I have had 2 4911's in a row now on my 6.2 and both had to be set retarded about 1/16" to the pass side of the base timing mark. I am sure the timing chain and IP gear are timed correctly. Could it be the 4911 has a different base timing mark ?
Truck starts right up hot or cold but I have never in the many many IP job s I have done seen one run set there. In fact most 6.2 probably wouldn't even start.
 
#2 ·
I know it's been mentioned before (& sorry for derailing your topic) but where exactly do we find the pump info? I know it'll be on the pump itself, just wondering where to look.

Btw.....that CUCV of your's is older than dirt. Props on keeping it going for so long. :thumb:
 
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#6 · (Edited)
i have a 4911 on my 6.2. I have my timing marks aligned between engine and pump, but I know my pump is still advanced. I had to disconnect my cold advance otherwise it wouldn't start worth a crap. With the cold advance disconnected it starts fine tho. But im not sure about retarding it as I get good mileage (18-20 normally, once got 21 on a tank)
 
#7 ·
I'll 2nd usually covered in gunk
 
#9 ·
Interesting...I gotta dig an old 6.5 timing case cover out of my shed and see if it's stamped in the same spot.
 
#11 ·
I'll keep this simple cause it's not that simple...

If you took 5 IP's and put them on the same motor and timed it by the advance leaver method, I'd be surprised if 1 of them was in the same spot as another cause it's a relationship of head and rotor, injectors, governor settings....

Ha hah ha 1886... CUCV's woulda made a big difference to that misunderstanding...
 
#12 · (Edited)
what are you running for lift pump pressure? what injectors do you have in it, N/A 6.2l, or turbo popped ones? both of these things can play a lot with initial timing. You have a timing meter, what is the truck timed at (luminosity or pulse probe)?
 
#14 · (Edited)
The base timing for the 6.2 and 6.5 is basically the same. Other words they both start to fire at the same place, so the timing mark remains virtually in the same spot. There are a bunch of different timing differences as to where it is marked on the housing but most don't vary more than 1 degree. Now here is where it gets tricky. If you bump the fuel up the start of injection gets bumped up also. So a pump that has been turned up will actually start injecting fuel early BUT only at wide open throttle.

Base timing can also be altered by the use of incorrect parts in the advance.

So when you crank it up, the IP will advance the timing a few degrees once it is running.Typically you can push the light load advance lever in with a long screw driver and the engine die back just a small amount because the timing is going back to base. If the engine has no change in running the advance is not working. A drastic change in engine performance would would lead you to believe the IP has to much advance at Idle.

So in your case I would push the lever in. If it really falls on it's face then the IP has to much advance.

Try finding that info on the net.
 
#15 ·
#16 ·
Could it be the 4911 has a different base timing mark ?
Diesel place always has the best info here. I was referring to the question at hand. On the different base timing points of the 6.2 and 6.5.

Hopefully my condensed method of checking the light load advance is still helpful.
 
#17 ·
Hey, I am still at a standstill with this thing to the point where I am just disgusted with the truck. Honestly I have no idea what's wrong with it and I have worked on a lot of them.
To answer the questions posed:
I am running short style 6.5 Injs
I am running about 7 psi fuel pressure at idle dropping to 4-5 at wot.
I am using 6.2 inj lines.
I changed the ip with a reman and the problem actually got worse. Now it still falls on it's face about 2000 or so(guessing) rpms but now smokes(black coal) when I take off or hit a hill. I can punch it on the highway and no coal but if I hit a steep grade she rolls coal. Truck has less power than my bone stock M1009. It feels like it's de fueling past 2000 or so RPM but note I say defueling, not starving for fuel. Like some sort of governor is cutting it back past a certain point. When this happens I watch the boost fall off as well(no coal).
It starts fine hot or cold and idles smooth. Other than it being a slug it runs smooth through it's entire range. No missing shaking skips etc.
I was sure a fresh reman IP was gonna solve this but it didn't. I have to run the IP about 1/16 inch to the pass side of the base mark on the case which in all my years I have never seen on a 6.xx.
Honestly I am out of ideas with this truck. If I had the money I would put a Cummins in it . I am ready to rip the turbo off and put a stock 6.2 IP back on because honestly it ran better. All this trouble started when I messed with it. I have not tried the luminosity probe yet. I am going to cut thefuel back on hte 4911 to try and get rid of the coal but the IP shjop said the IP was set to stock specs for a 6.5.
I am running 6.2 NA heads.
Motor has 450 psi on every cyl.Done with a Snap on tester.
The truck runs good, just has no power and falls on it's face when you accelerate but like it's being governed somehow.As the rpms climb the boost climbs and then all of a sudden feels like it just hit some sort of governor and the boost starts falling off. I had a GM4 on it and also repplaced that with a GM8. No difference other than sligthly slower spooling. I have the waste gate cranked shut and the best I can get for boost is about 13 psi under load on the highway. I really just want to dump this thing. I have no idea what is wrong with it but it has taught me a valuable lesson . 6.2s are ok when you leave them stock and keep expectations of power low. When you start screwing with them, it's gets costly and the results are not worth it. I could have done 2 cummins swaps for what I have into this POS.
 
#21 ·
I put a turbo and a 4911 on...:confuzeld

I should have left the truck alone. I just finished reading your cummins swap thread because I'm ready to do the same or dump the truck. I would go NV4500 though. Sucks because I have a 1st gen GM specific NV.
 
#19 ·
Just throwing out a wild card.

Exhaust restriction?
 
#20 ·
Any ideas are welcome. I have 5 inch ex no muffler.
 
#22 ·
Only other thing I can think of is restricted intake, you kept the same intake between turbo swaps? That or sh!tty rebuilt injectors
 
#25 ·
Where did you get those IP's cause bad running higher RPMs sounds like they are NFG....

Your at a cross roads and your gona have to make the next choice....
 
#30 · (Edited)
Two different places and the first IP came of another motor I had and worked fine on it. In fact it worked so good the crank snapped:clap:.
It doesnt run bad at high RPM's, just feels like I hit a brick wall and just when it's about to take off it just does nothing. It's like I'm on the floor with the throttle but feels like I'm not. The boost starts dropping. No smoke.
It feels like it's de fueling gradually.
I looked at my M1008 cucv thread here and the pic I posted is crystal clear. The timing chain is lined up.
http://www.dieselplace.com/forum/6596169-post189.html
 
#26 ·
I don't think I responded, but I run a DB2 4911 on my turbo'd 6.2L. It was built by DieselPro and does great. I am often bounce off the governor in Low, 1, & 2, not sure if it is set high enough (or even adjustable). It may be that I just have a heavy foot combined with the NV4500. It tells me when to shift!
 
#29 · (Edited)
Did you have to set the pump to the left of the base mark on the cover ?
Also did you use 6.2 lines or 6.5 ?
 
#27 ·
Just for grins and giggles. Take the return line off the IP and blow air back to the tank. Is the line free and clear? ( Do this with the tank cap off please.)

Any chance we can get a video of this problem?
 
#28 ·
I'll try to have someone follow me and also I'll make a good vid while I'm driving.
 
#32 ·
I will tomorrow. I am taking it to work.
 
#33 ·
The only other thing I can think of is maybe the base mark is stamped different on a 6.5 but I never found the 6.5 old cover to compare.
 
#34 ·
ok here are some quick ones I did this morning. One is when I accelerate in 3 rd it gets to a point then just doesn't go anymore and you can see the boost dropping.
Second it pushing in the advance lever. 1st time I did it it changed a little but then after that not at all.
Also a pic of the timing marks.
Do I retard it even more or is something wrong with the IP ?

https://youtu.be/sJsQSvzHimM


https://youtu.be/rJbdplRgnNI
 

Attachments

#35 ·
What is your inlet fuel pressure to your IP?
 
#36 ·
7-8 idle 4-5 wot. My gauge is t'd in at the inlet. I also took the cover off the old IP and the screen was spotless.
 
#37 ·
Spoke with Metro inj again. He thinks I am running the wrong injs and lines. He said the 6.5 lines are bigger and also I am using 6.2 short injs. He said I should run 6.5 injs.
The problem I have with that is how many people have put a Banks on a 6.2 with the stock lines and long 6.2 injs and run fine. he also said the gov on the 6.2 IP will go 300 more rpms than the 4911 which might be the brick wall I'm hitting.
 
#38 ·
He said air time on the 6.2 is zero and on the 6.5 -1.5 and that might be why I am retarded on my base marks because that equates to 3 degree of difference ???
I'm lost.
 
#39 ·
Well anyone who knows me from being on this forum for the last 8 yrs knows that I have the (insert expletive) luck and that nothing for me is ever a simple problem. That is why I took the picture of the timing gears because I knew something like this would happen and I would tear the motor down for nothing and even with that picture I was planning on yanking the timing case cover off this weekend anyway...until I saw this...

https://youtu.be/2Q7qBnGFuUM

Metro diesel is telling me I have take the IP off and bring it back to them and I didn't like his attitude like implying I must have done this...I am so pissed right now. Why does this **** happen to me ? Is it God testing me ?
Can't I just tighten it back up on the truck ? I know people have done throttle shaft seals without pulling the IP.
 
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#46 ·
Kenny, if I see that correctly, all it is, is the ramp for the advance lever is loose. It is as simple as tightening it up with a torx wrench (usually a torx). Set it up, with the throttle at its idle stop, and bring the ramp to the point, just before it begins moving the lever. It is just cast aluminium, and can break easily if over-tightened. Hopefully this is the problem. If it is cracked, the ramp (rocker lever cam plate) is interchangeable from any DB2831 series pumps. Part#29122. This would explain a lot of things with your timing, as the lever is there to bleed off some of the pressure acting on the advance piston, to retard (or limit over-advancing) some what as rpm's increase.

as for the injectors and lines being different, they are in the sense that the 6.2l N/A spec lines are actually a bigger I.D diameter than 6.5l lines( we have measured all the lines that have been used through the years, no one else has to date proven otherwise) and the injectors, well, the 6.2l 253 nozzles actually are bigger than any other used( we have measured ID of every injector nozzle style ever used in these engines as well), including "marine" ones, the only difference being the marines use a stubbier needle than all others( while the ID of the nozzle is the same as the 304's), giving more low RPM fueling potential, other than that its the difference of pop pressures, and physical appearance, IE long and short.... sounds like metro diesel would hate us when we told them they were crooks... LOL... they are taking you for a ride....:shake:
 
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