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Max PSI for a DS4 IP?

J

JayTheCPA

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Question: Is there a recommended 4 psi limit for the DS4?


Background: Wanted to push my shop on getting / learning how to get injector balance flows for the Burb and they drove over to the local Stanadyne dealer whom had better computer equipment. The Stanadyne dealer was not able to get injector balance flows either, but did notice that the idle fuel pressure (measured just prior to the IP) was ~13 psi (as reported by my Edge) and commented that the recommended max was 4 psi; over that and it could mess with the optic sensor.

If there is a recommended max of 4 psi, should we look into a regulated system?

Edit: Title should read DS4, and will appreciate a Mod fixing it.
 
As I understand it, 11-12 PSI is about as high as you want to push one to avoid an overpressure situation in the rotor head. Even stock they run more than 4 psi. I know mine ran 5-6 at idle with a bone stock 150K mile lift pump in it.
 
I think I read the return fuel fitting in the housing has a pressure release / check valve that opens at something like 16 psi. So excessive pressure should bleed off.

I haven't heard any short life of Optic sensor from high inlet fuel pressure.

The DB pumps have a low psi input limit as it effects housing pressure and timing. Bet that was convoluted and mixed up story repeated with the optic sensor as reasoning.

DB pumps don't have the stepper motor for timing control correct? I think that is why a little more housing pressure is not a problem for DS pumps the stepper motor can control timing independent of rpm forces.

I get more than 4 psi with GM lift pump at various times.

A fuel pressure regulator and accumulator for rock steady fuel pressure and supply would be nice but not sure if would increase any performance or reliability.
 
I ran a 15-17 PSI Mallory racing pump on mine for awhile. The DS4's only issue is blowing the shaft seal with too much inlet (lift pump) pressure. The newer part number Walbro lift pumps have higher pressure.

The DB2's reference housing pressure for timing and that is set by the rotatory pump in the nose and it's pressure regulator is also in the nose and referenced to the inlet. Thus higher inlet pressure affects timing. So use the older 5-7PSI Walbro pump on them.

So this shop is completely out of line. It should be 4 PSI MINIMUM!
 
Yep 4psi min under moderate load, should have a min of 9 psi at idle and up to 13-15 is great. Engine will thank you for it.
 
THEFERMANATOR said:
As I understand it, 11-12 PSI is about as high as you want to push one to avoid an overpressure situation in the rotor head. Even stock they run more than 4 psi. I know mine ran 5-6 at idle with a bone stock 150K mile lift pump in it.
Click to expand...
That was the word I got when I mentioned my fuel pressure was pushing 16psi, turn it down! 8-10 max.
 
Ah, so while the local dealer was not exactly correct, he was not exactly incorrect either.

Does it matter that the idle psi is as high of 13 and then drops to 10 and under during any load? Or just start looking at figuring out how to bleed-off above 10 psi under any scenario?
 
I decided to break the 'guy-rule' and reached out to Stanadyne. Will post-up the response after I clarify a detail.

Short version is that it looks like the local dealer is nearly on target and a regulated system is in order.
 
Looking forward to info. I quit trying to organize my post but here is what I was working on.

Not to split hairs just to keep my understanding accurate. I don't THINK there are any air pockets or voids in the IP.

Its a closed system that does use the input fuel pressure to reference or baseline internal regulation pressures through a rotary vane transfer pump. The pump also has through put and relieved at something like ~ 16 psi??? I will try and measure the return relief check valve mechanism. But that is probably more an end cycle area and not really the limiter except for seal pressures?

Liquid is not compressible. Pressure vs volume is extremely related.

The plungers and rotor can only fill to a finite point no more. There can form vacuum forces that don't allow the plungers to stroke their full movement if enough fuel is not there on the fill stroke (probably applicable to describe as not filling). The plungers are a positive displacement pump on output but not necessarily filled chambers as a vane pump can have more slippage than a piston pump.

There are fill, spill, and injection strokes of the plungers flow. I think there are accumulators that are spring biased/balanced to I think the inlet pressure and?or housing pressure related to the fill stroke. I assume there has to be a give and take somewhere or something would hydrolock or vacuum lock with large forces.

So wondering about the accumulator spring forces?
 
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Surely GM would not design a lift pump that was too strong! :facepalm:

It will be interesting to see what Stanadyne shares and says since further distance from GM.
 
Got the follow up response.

The DS4 wants 5 psi (with a tolerance of +/- 0.5) at the inlet whether idle or WOT.

The question I posed was regarding GM's 6.5L turbo diesel using a DS4 IP (and whether ULSD compliant made a difference) purchased in 2014. Also stated that my system was observed with 13 psi at idle. So while GM may have used one spec, we now have the supplier's response to a targeted question.


Am impressed with Stanadyne as I posed the question via their web portal yesterday afternoon and received response (and follow-up response) via E-mail today.


Any thoughts toward a regulated system . . .?
 
If someone were to put on a regulator and test at intervals, you would know the different effects of it. I can't imagine there's not a few people here that played with it, I did on db2. 6 was my magic number on that truck. Less and I would loose power climbing big hills, more messed up timing.

They state 5 psi. Ok, is that why the engineers planned everything on, or did they do in house testing to determine it? What I mean is, any of us that played with injector pop pressures learned the factory level did good, but increased pressure worked better for both mpg and power. The mfr's, even different brands, will still say factory specs because they have to in order to maintain "oem spec" level.

They have to come up with a pressure and a variable to that pressure, doesn't mean it is the best pressure in real world application for end user. Factory turbo is what GM will say is the thing to use. Real world proves otherwise.
 
I once pondered about it with a regulator after the filter and thought an accumulator/expansion tank would be ideal too. I googled a bit but never found a good accumulator/expansion tank.

I think the regulator part would be relatively easy. Do we need the accumulator probably not necessary just would help hold that +/- 0.5 psi. Maybe a larger diameter hose would help flex a bit or add a dead end Tee with P trap and air pocket to function as an expansion tank????
 
I'd like to know where he got his info (Stanadyne guy)? Was he looking at DB2 manual? 5 psi is not the # I have seen in Stanadynes own service manuals!
To much real world driving and reports that 5psi is to low and 9-13 is perfect.
 
Will L. said:
If someone were to put on a regulator and test at intervals, . . . I can't imagine there's not a few people here that played with it, I did on db2. 6 was my magic number on that truck. Less and I would loose power climbing big hills, more messed up timing.
Click to expand...

(Just asking) Was the 6 psi constant-ish to WOT, or did it tail-off?

One regret I have at the moment is not data logging last Summer when I climbed through the Appalachians with the RV in tow. Was more focused on keeping temperatures and RPM's under control and did not look at the fuel psi. Might do a pull in a few weeks up a shorter and slightly flatter hill to see what the fuel psi's do at WOT with a load.


Burning oil said:
I'd like to know where he got his info (Stanadyne guy)? Was he looking at DB2 manual? 5 psi is not the # I have seen in Stanadynes own service manuals!
Click to expand...

I did ask for either a response to the question or direction to a URL to look it up myself. Got the response via E-mail.


So at the moment am still coming up with reconciliation differences where the community is firm on one set of numbers yet the manufacturer and (at least one) dealer / rebuilder is using another spec.

IIRC, suttlebutt is that 2 psi at WOT with a Walboro lift pump is sufficient to maintain power (especially presuming a FTB mod), so why wouldn't ~5 work?
 
If you start with 5psi most likely you will go to a vac condition at WOT.
Can you buy a regulator, do FTB or other considerations? Yes, but not necessary for 95% of 6.5ers IMO.
 
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