Where's the boost?

[Thewespaul]

That’s good, stripped fuel screws isn’t fun. Have you adjusted anything else or just the fuel screw? The fuel screw is just a small part of the big picture for tuning one of these, make sure your throttle cable isn’t keeping you from wot. A lot of times you need to put a big crescent on the throttle bracket to bend it away from pump to get it back in range. I had a customer that had performance issues with his truck and I let him time his truck with my meter. He said it got a lot better mileage after timing it, but it didn’t change the power. The next day he cracked it all the way as advanced as he could and he said it ran better than it ever had, even though it was a half an inch from where it was at 8*. I went out to look at the truck and the only reason he had more power was because the pump was further from the intake and was getting more throttle throw.

 

[Thewespaul]

I can get you the correct rebuild kit with the 360 thrust bearing upgrade.

 

[DrCharles]

The only thing I've tried so far is the fuel screw.

I have read your DB2 Tuning Guide on here... do I really need to do more adjustments to run 10 psi boost? Most every article I've seen on the factory turbo setup says that a couple of flats is all the increase that should be needed. Or is that only if running 6 psi? Is that the stock boost level?

I can try the minimax adjustment too, since even if my turbo is worn and not producing enough boost (or a leak is preventing it from doing so), I have not yet reached an excessive fuel setting at which I can blow black smoke...

Will check tomorrow to see if the fuel is wide-open with the pedal floored. Thanks for the tip.

Looks like the turbo is a TC4305 and kits are readily available. I'd rather rebuild the turbo than spring for a new IP!

 

[Thewespaul]

It varies with how worn your pump is, some trucks will make ten without any adjustment. 7-8.5 psi is what you see stock, that’s what the wastegate is set to open depending on your altitude. If you have the torque screw make sure to adjust that as well, it could be limiting your metering valve travel and nullifying your fuel screw adjustment. For the turbo rebuild kit, be sure youre getting the right kit, there’s 3 different shaft seals for these turbos, two compressor housing o rings and two different sets of hardware. Russ sells rebuild kits too

 

[DrCharles]

I was reading this thread (on the torque screw) and now I'm more confused than ever...
https://www.oilburners.net/threads/torque-screw.38325/

Some people say it does nothing above 1100 rpm. Near the end of the thread there's a comment that on the NA trucks it's seated against the jam nut, but on the turbo trucks the screw is backed out. I will see if mine has one, and try adjusting it since I think I've turned the fuel screw enough.

 

[Macrobb]

I was reading this thread (on the torque screw) and now I'm more confused than ever...
https://www.oilburners.net/threads/torque-screw.38325/

Some people say it does nothing above 1100 rpm. Near the end of the thread there's a comment that on the NA trucks it's seated against the jam nut, but on the turbo trucks the screw is backed out. I will see if mine has one, and try adjusting it since I think I've turned the fuel screw enough.

I have played around with it, and what it actually does is limit metering valve travel - how much "total fuel" can be pushed when the governor/pedal requests "more fuel".
I found it to have a much bigger limiting impact at the upper end - cutting peak fueling off drastically.

With a Banks kit on 92 and totally maxed fuel screw, I ran it on the dyno. 150RWHP. Wondered why the numbers were so low, found that screw, backed it off, and ran again. Same dyno, 2 hours later. 200RWHP.

That's a 33% power improvement from a single screw.

Oh, and before I adjusted it, I would get black smoke flooring it at idle(as expected), and nothing at the high end(which makes sense).
Now, well, it makes good power, still cleans up to a light haze or less, maxes out the 15 PSI Banks gauge(wastegate disconnected) and produces plenty of power.

 

[The_Josh_Bear]

@Thewespaul makes an excellent point, if the bushing on the throttle cable fell off or just for some reason the full swing isn't there your 2 extra flats mean nothing and that matches your description so far. With the engine off reach down behind the go pedal and pull up on the cable, see if you can get any more pull out of it!

Edit: plus that test can be done in any weather or light condition!

 

[DrCharles]

That's an interesting case report. Thanks!

I'm not sure if my pump has a torque screw (may or may not be the original), but will definitely look tomorrow...

I did some light reading this evening http://radionerds.com/images/f/f4/Stanadyne_db2_operation_and_instructions_manuals.pdf


Keeping fingers crossed, I really don't want to buy a pump just yet... and I won't waste money on a parts-store "rebuild" either.

Weather forecast is for 57F tomorrow

 

[Macrobb]

That's an interesting case report. Thanks!

I'm not sure if my pump has a torque screw (may or may not be the original), but will definitely look tomorrow...

I did some light reading this evening http://radionerds.com/images/f/f4/Stanadyne_db2_operation_and_instructions_manuals.pdf


Keeping fingers crossed, I really don't want to buy a pump just yet... and I won't waste money on a parts-store "rebuild" either.

Weather forecast is for 57F tomorrow

I'm very doubtful you can have an IP worn enough to not provide higher end performance/fueling, while still being startable. Realistically, the most leakage is going to happen at hot startup, so if the truck starts, it's not going to be worn that way.

It's much more likely you:
1. have a fuel supply issue(partial clog of supply line from tank)
2. Have a fuel pump issue(I don't trust duralift pumps to be able to provide fueling at WOT. My dad's certainly cant).
3. Have a filter issue(fuel filter clogged, or input IP screen clogged somehow).

Those would be the next candidates to me, once you figure out the torque screw.

 

[DrCharles]

That's reassuring Truck starts fine when hot. In fact I'm considering modifying the GP controller to avoid afterglowing when warm, since it doesn't seem to need it and changing GP's is even more of a PITA now that I have a turbo.

The tanks, showerheads, FSV, and fuel lines are all less than a year old and a couple thousand miles. Ditto the Facet 40285 and the Wix fuel filter. The bowl & screen on the Facet looks clear.

The Stanadyne manual says that as long as you have at least 0-5 psi (i.e. no vacuum) at the transfer pump inlet, that's enough. I will check the fuel pressure at the filter head (and make sure the vacuum "filter clogged" switch actually works. The panel light does). I didn't even think of the IP inlet screen

 

[Macrobb]

The Stanadyne manual says that as long as you have at least 0-5 psi (i.e. no vacuum) at the transfer pump inlet, that's enough. I will check the fuel pressure at the filter head (and make sure the vacuum "filter clogged" switch actually works. The panel light does). I didn't even think of the IP inlet screen

Personal experience says that they are right...ish. 0 psi or 5 psi is fine for running. 5 psi at idle, 0 at WOT... not so much. The varying pressure changes your timing(lower pressures ends up retarding it a bit). If you have a consistent pressure(whatever it may be), you can adjust the base timing to compensate.

 

[sjwelds]

Sealing washer under the head of the bolt that holds the snail to the intake?

 

[DrCharles]

Found the torque screw. The locknut (two 3/8" flat sides) is a major PITA with the airbox in place but it can be done. I backed it out two full turns. Now I see a moderate gray cloud of smoke when I floor it below 2000 rpm which goes away as the turbo spools up. On the back road I got 6.5, almost 7 psi. Before it was 5.5 at best.

So, now I have enough fuel to make smoke. Now to start chasing exhaust and possibly boost leaks! I'm headed for town to get a proper (and removable) connection to the downpipe made. Then I can listen for exhaust-side leaks. But as mentioned yesterday, no obvious soot marks found. It definitely will not make boost in neutral, up to 3000 rpm. Still a sign of exhaust leak?

Edited to add: Accelerator pedal does open the lever to the stop.

 

[hacked89]

Found the torque screw. The locknut (two 3/8" flat sides) is a major PITA with the airbox in place but it can be done. I backed it out two full turns. Now I see a moderate gray cloud of smoke when I floor it below 2000 rpm which goes away as the turbo spools up. On the back road I got 6.5, almost 7 psi. Before it was 5.5 at best.

So, now I have enough fuel to make smoke. Now to start chasing exhaust and possibly boost leaks! I'm headed for town to get a proper (and removable) connection to the downpipe made. Then I can listen for exhaust-side leaks. But as mentioned yesterday, no obvious soot marks found. It definitely will not make boost in neutral, up to 3000 rpm. Still a sign of exhaust leak?

Edited to add: Accelerator pedal does open the lever to the stop.

An exhaust leak, or even running no exhaust, should not have the effect of less boost or not building boost in neutral. Overly restrictive exhausts and back pressure can actually lower boost numbers.

So low boost is obstructions such as intake or exhaust side, leaks before the exhaust, or you have an issue with the components inside the turbo and its creating drag when it's in neutral. And when you are under heavy load its overcoming the drag coefficient to a degree.


Sent from my SM-G955U using Tapatalk

 

[DrCharles]

Thanks, I am aware of that Your definition of "exhaust" apparently differs from mine - which is, anywhere between the manifolds and the end of the tailpipe. So that includes leaks in the piping upstream of the turbine, of course!

Meanwhile, more data. I'm actually overfueled now for the amount of boost I can make, since it will smoke in 4th and 5th when floored, even at 7 psi boost and 2500+ rpm (and 1100F on the pyro passing through 80 mph!).

The connection from the downpipe is now quiet. The shop guy looked for soot at all the connections also, and couldn't find any. We started the engine (no visible puff up front) and put a board over the end of the tailpipe. No audible leaks. I will try one more run with the wastegate wired shut just to make absolutely sure it's not opening prematurely, even with the rod shortened three turns.

I'm thinking you're right about the turbo being in need of a rebuild. The Garrett catalog shows .0065 max clearance for all the smaller T3/4 models. So that's close to .013 back-and-forth radial play, and I know mine has quite a bit more than that (although it did not show any evidence of scraping the housings).

Any recommendations for inexpensive upgrades while I'm in there with a bearing/seal kit?