How to prevent the FSD from collapsing?

[GMC 2500]

How many are there, who have looked in to that problems?
Many have tryed.
Most of them come up with the solution to re locate the FSD.
Some with good results and some bad.
Some day they are going to collapse at the good place too.

Ok, but why are they collapsing?
There must be a reason for that?

The reason are so simple, you will have problem to accept it.

Last summer we started a test.
That was after I had open up an 94 DS IP
I looked at the system in the IP

What caught my attention, was the Transfer Pump.
Or the weakness in that TP.
Compare to the TP in a mechanical BD IP

The test are not done.
We will continue the test next summer.
Then we have plans to add more truck to the test.

We also gain good MPG and performance in the trusks

So for those of you who like to read the test.
Here it is.

The test (http://www.v8dieseltech.net/gm65td/main_e.htm)

[sailun]

Sounds logical. Nice work.

When are we going to see some results with a better lift pump in place ?

What kind of MPG gains are you seeing ?

Thanks for your testing.

[65TD]

Not to disregard your findings, but what about when the engine is shut down?

The heat in the engine bay will rise to the point of being to hot for the PMD. If it is relocated away from engine heat this will not occur.

I guess what I'm saying is the PMD is known to work fine and last longest out of the engine bay on a suitable heat sink. So why not use that method?:confused:

[GMC 2500]

Yes, we are going to relocate the FSD.
In the summer we also going to run 1 or 2 trucks in normal mode.
FSD at IP
To see if they can take the heat with rebuilded fuel system.

Hope to have new lift pump

[65TD]

You are using a Carter pump?

Do you have the part number?

So from what you have seen the IP is able to produce more power than before and now the fuel pump is limiting the power.

[sailun]

I'm wondering how you know you are sucking the IP dry, and why you didn't replace the lift pump first, before increasing the volume of fuel available to the IP ?

What guage(s) did you use to monitor the fuel pressure ? Do you have part numbers ?

Did you address any of the known issues of the OPS/LP, such as adding the relay to bypass the OPS ?

I'm not criticizing your work, as I have no practical knowledge of this topic, other than what I read here at TDP. I am very interested in seeing where this goes.

Have any of the other experienced power junkies out here run through this aspect of the fuel system ? I'm thinking that anyone who has increased their fueling rates should have run up against this limitation.

Is this another example of GM cost-engineering to the point of inadequacy ?

[65TD]

Nothing wrong with the stock system as it was according to a fuel pressure gauge.

Adding all of the popular mods that give more power will stress the fuel supply to the limit and beyond.

Some people have seen that the stock pump supplied more fuel to the IP with the larger lines. Fuel pressure went up at the IP by enlarging the feed to the IP.

Some people upgrade to Duramax lift pumps, some use two OEM lift pumps, some use other variations.

[DmaxMaverick]

.........Some people upgrade to Duramax lift pumps, some use two OEM lift pumps, some use other variations.

Which Duramax lift pumps? Aftermarket? The Duramax has no lift pump. The exception is the vans, but it is only engaged during startup (for priming, due to filter location). The Duramax fuel system is suction from the tank to the HP pump.

[moondoggie]

Good Day!

[FONT=Verdana]Bravo

[TurboDiverArt]

Confused a little here. I'm no fluid dynamics expert but wouldn't increasing the size of the line between the LP and the IP increase flow but lower pressure, all things being equal? Unless I guess if the IP was sucking the tube try with the stock size and what you're actually seeing is less of a decrease in pressure when the IP takes a fuel sample to step the pressure up on. Typically I would think that the pressure would drop while the flow would increase by increasing the feel line assuming the tank line is also staying stock.

Art.

[65TD]

http://www.lagunaspeed.com/uploads/images/1676__orig.jpg

[sailun]

I'm no expert in this topic, but did have a similar situation on one of my boats.
A restriction in the line between tank and filter would not allow enough fuel to pass in full-throttle conditions. This condition resulted in Racor being sucked half-empty, (and engine dying) with resulting vacuum so strong I could not remove the lid to service.

So maybe:

There is more fuel VOLUME available to the IP, to be pressurized and injected, hence increased power, until the fuel FILTER is sucked dry on the long hills. This may be what he refers to as "sucking the IP dry". IP is probably fighting a vacuum of undetermined strength at this point. (Maybe this is why he sees 0 PSI on the pressure guage ?)

Then lift pump begins to catch up with demand after lifting the pedal.

During normal light-medium load conditions, IP again has more volume available to pressurize, and LP is keeping up with demand, and is providing 5 PSI to help the IP.

As Art suggested. sounds very likely that tank outlet, lines, fittings, LP capability and LP-to-filter line restrict the amount of fuel that the IP is allowed to pump.

So, how much fuel could the IP pump(both inject, and circulate), if it was given fat pipes, and twice the fuel pressure coming into it ? And shouldn't it waste less energy (HP) and generate less heat and vibes doing so ?

And wouldn't that cool the PMD that much better?

How much fuel could the LP pump, with larger fittings and lines ?

I think we need some FI engineers to weigh in on this.

I would also think that people in the Pull-Offs, and people who tow uphill alot would have run into this starvation issue, if there is indeed an issue. Or, you need to lift your foot, to cool down EGT's ?

I dunno, this is all speculation, based upon my limited experience.

Let me know if this don't make sense, or if there's really no issue here.

I just gave blood, so my brain is down a pint.

[GMC 2500]

Confused a little here. I'm no fluid dynamics expert but wouldn't increasing the size of the line between the LP and the IP increase flow but lower pressure, all things being equal? Unless I guess if the IP was sucking the tube try with the stock size and what you're actually seeing is less of a decrease in pressure when the IP takes a fuel sample to step the pressure up on. Typically I would think that the pressure would drop while the flow would increase by increasing the feel line assuming the tank line is also staying stock.

Art.

You are correct.
When you open up the fuel line, pressure will drop.
We are looking for more fuel, not the pressure.
We open up the fuel line from the filter house to the IP

When the owner ask the engine for max power.
The pressure drop to 0 psi.
OK. so we open up for more fuel.
The engine give out more power and the pressure are still down to 0 psi.
And then the engine hesitate.
That are an indication.
The IP Needs more fuel.

As the owner said.
Never have he had power like he have now.
But we need to give the IP more fuel.

But the problems are.
We can

[markelectric]

I think I have read this before. Replace the GM with dodge, swap ds for VP44 and VIOLA , same discussion......

Seems this is exactly the presumed cure for problems on the Cummins. Since owning the Cummins I have been wondering of this exact senario.

Any other 6.5/5.9 combo owners thoughts?

[sailun]

65TD, do you have a link for that FASS pump ? I keep running into too many junk websites that reference, but don't actually list that pump.

Is anyone using anything like this ?

[65TD]

The one in the picture above can be found at various places..

Laguna Speed
US Diesel Parts

It's pretty high priced.


Look at the lift pump at Kennedy Diesel for a Duramax, it's a lot cheaper and will work just as good. He also has a 6.5 harness for that pump.

http://www.kennedydiesel.com/images/kdliftpump_tn1.gif


If that don't cut it get a jigger pump and some fire hose. :)

[d350diesel]

A Walbro 393 fuel pump with a bypass valve after the filter would work wonders here. With the regulation after the filter, the filter no longer acts as a false load. You would have at least 40 gph at whatever pressure you set the bypass valve for flowing past the injection pump inlet at all times. No need for the big line with this setup. Opening the ports in the pump inlet is still a good idea, though. When the weather warms up I plan to implement this on my Suburban. My Dodge has a Walbro 391 (same type of pump, higher volume) plumbed as I describe. The fuel pressure gauge is now boring - and that's a good thing. ;)

[d]

DB4 low fuel pressure = poor performance
VP44 low fuel pressure = need a new VP44
Brain low pressure (Sailun) = poor performance; even lower pressure = need a new brain.
I wounder why the dodge injector pump is more sensitive to lower fuel pressure. From what I have read the dodge pump is greatly improved with a FASS or a Wallbro. A 6.5 GM diesel should benefit as well

[sailun]

Thanks, guys.

Another inadequate GM system to throw money at.

[65TD]

I am currently using the stock lift pump system and filter system.

I have more than enough pressure for normal operation.

[sailun]

65TD, that was one of my points, too. "Is there really an issue here ?"

None of the heavy pullers here have weighed in, saying that they are starving for fuel. I would think that there would be a lot of posts and articles, if there was a known problem.

[ol9465er]

Gents...

I have found this very interesting as I have been the route, original FSD, then Sol-d, but then replaced IP so have FSD again with Sol-D as backup. I have also installed the OPS relay for the FP - but I am still worrying about the next time it may act-up. I will follow this thread.

Just a question though as I have not looked into this, is there any thoughts that the fuel suction lines or tank pickup may be contributing to the problem from constricting or plugging. Has anyone had experience with this?

Thanks,

[65TD]

Fuel sock is a major problem. One of the main causes of fuel issues that you would not fix by changing parts, only improve it until the new lift pump starts to weaken a bit.

Also the fuel cap has been a problem.

Many people put on a gas cap and the fuel tank is not allowed to breath properly. Then they might gut the valve from the cap causing another problem with contamination when water and growth builds up due to an open tank.

That's about the time the sock filter in the tank gets clogged up.

Running low on fuel makes it worse because of the hot fuel. Heat promotes growth in the tank. Factor in the lack of additives to deter the growth and build up of water and next thing you know you need a 150 gph fuel pump to ride down the road.


On the other hand plenty of people with the heavy duty replacement oem pump towing heavy RV's and 5th wheels and reach a point where they back off the throttle for high EGT or ECT without any fuel issue.