6.5 Performance issues

[grader6.5td]

Hey guys, its been a while since my last post, but you were all so helpful in the past I figured I would try again. I have the same pickup, 1995 K2500 Ext Cab, SWB, 4WD, Auto. I had installed an Optimizer 6500 a couple years ago and just moved everything from the old engine to the new one. Pickup has 4" intake, 3" Downpipe and no cat, S54 turbo, heath diesel hd fuel pump, duramax fan set up, and a quadstar multi position tune. It has a lot of other small mods.
I really havent put that many miles on this pickup since the engine swap. I work on a farm and have a company provided pickup. But I started driving this pickup more recently and while it starts and runs seemingly okay, its a bit of a dog. It seemed to me like the old wore out 6.5 ran better, it could actually burn rubber a bit, the new one can keep up with traffic but it doesnt tow great and my friend's stock 6.5 5 speed manual passes me when we were running around on the farm a while back.
I had contacted the guys at quadstar and they gave me several things to check out. I went ahead and did that, and then Michael had me send him a picture of the sticker that came on the back of my engine when I installed it. Turns out I was sold a Naturally Aspirated 6500, even after the seller was given all of my truck information and stuff. I had done a lot of business with the seller prior, so its a disapointment. Its been long enough now that not much can be done about the purchase, but I want to build it right and get it running well. It only gets 15 mpg and egts get higher than i'd like when going between Cheyenne and Laramie climbing the pass. It seemed like this really could be a major part of my issue.
I was told by Michael at Quadstar that the bottom end of the optimizers are the same, so I could go with different heads, or get the turbo precups installed on my existing heads. If I do this, Ill stud it while im in there, and maybe put some cometic head gaskets on while im at it.
Does this sound like a reasonable game plan? Do you guys think that the smaller precups would make that much of a difference in performance on my diesel pickup? Perhaps there are some other things that I need to address before I go tearing down my engine?
Thanks for anyone willing to share some advice!
-Grader

 

[ak diesel driver]

I don't think the precups will be make much if any difference. What's your TDCO? Fuel pressure? Any black smoke? We need more info what all did quadstar have you check?

 

[Will L.]

N/A precups are squares from GEP. Turbo is diamond. You have to really be fighting for top power to find a difference in the two power wise. I had a set of squares machined out to be as big as diamonds that I never installed because I bought a set of p400 heads instead. If you are set on replacing them- hit me up for the set at an ok price.
My thought is more injectors.
N/a injectors are 1850 pop pressure and turbo is 2250 iirc.
But if they are not some chinese set, I would send them of to be reset but instead of the normal +- 150 range, pay extra to have them all adjusted to within 25psi of each other So 12.5+- psi. & that size turbo I am guessing you also have a Qstar tune? If so I would bump the setting to 2350psi.

Definitely go into detail more because something isn’t adding up.

What is fuel pressure measured AT THE IP INLET while running down the road under hard acceleration?

 

[grader6.5td]

I wondered that about the precups, I was having a hard time fathoming how such small size differences would make a difference. Im not really set on replacing them unless it would fix my issue. The pickup doesnt really black smoke bad at all, it black smokes just a bit under the hardest acceleration.
After I did the engine swap I set the TDCO to -.70, my fuel pressure gauge reads off of a sender that screws into the top of the fuel filter housing, it reads around 7-9 psi at an idle, 3-5 psi going down the road and drops to 0-1 psi under hard acceleration. I have noticed the fuel guage does like to fluxuate in pressure, instead of being a constant pressure, even at idle, which admittedly is odd. I had removed the fuel sock, installed a spin on filter before the lift pump and replaced the FFM just a couple months before engine swap as well. But i have yet to find a cause for the fluxuating fuel pressure. There is no air in the system, the vehicle starts great and doesnt have any symptoms of air in the system when running. I have thought that it might be the cheap glowshift guage, or the lift pump itself since its just a dieselsite heath "HD" lift pump.
The injectors were newer Bosch injectors that I swapped from the old engine, and they seemed fine in the prior application, but im not opposed out sending them out to get adjusted. I had bought them brand new 25k miles ago. They had logged 5k on the old engine, and roughly 20k on this new engine. They came from Badger diesel as I recall, likewise with the DS4 injection pump itself.
I run a super 54 turbo, it spools well. Runs around 6 or 7 psi driving at 65 mph. It is set for 15psi max.
Quadstar recommended that I check for boost leaks, exhaust leaks, fuel leaks, check base timing as well as TDCO. I discovered no boost leaks, no exhaust leaks, which seems probable since it spools right up and holds pressure steady.
I will have to T in my mechanical pressure guage at the inlet of the IP to follow up with that request, but I will try to get that rigged up and give you some info.
One last thought I have to this puzzle, is that my quadstar multi-tune has never made sense since i bought it. The tunes dont match the printout they sent me, and when I reached out about it, it never really was resolved. I dont notice much of a difference in any of the tunes other than some of them are thirstier than others and selection number one is high idle, whereas the sticker has it labeled as "stock". One thing I havent tried is putting back in the factory EPROM to see how it would run different, but i know with the super 54 and no vacuum system it would probably throw a fit.
I agree, its not making a ton of sense, but thats why I reached out and will do my best to follow up with these inquiries!

 

[Turbine Doc]

Yes delivered fuel pressure to IP will tell us a Lot, you can have bad fuel and plugged filter at any time, lift pumps known to fail as well. I got bit by weak lift pump myself earlier this summer in May doing some disaster relief volunteer work in NC mountains near Ashville, truck ran like a old whipped dog climbing mountains there, kicked dow to OD to get more spin for boost, then looked over at IP inlet pressure gauge well look at that almost zero psi, I turned on 2nd pump that runs in parallel with the 93 GM lift pump all back to normal, just not enough fuel to climb hills at WOT on 1 pump starting to show its age.

 

[Will L.]

The pulsing you see is from the liftpump- not being a gear driven pump but similar to an actuator ram going back & forth so this will cause pulsing. While it is good to see how bad the pulse is when diagnosing, it is really hard on mechanical gauges & sending units for electrical gauges.

The bleeder atop the ffm is pre-filter. So it is expected you will have a lower pressure post filter.
Often the hose from the ffm to the ip fails first and with the new ethanol fuel that damages the hose from the inside out, you might have amazing flow & pressure through the filter but not into the ip. After seeing this so many times Income to the resolve to have a metal T fitting at the ip inlet so no rubber line is between it and the ip.
As to the pressure- going into a vacuum is insanely damaging to the ip taking much of the life of it away. Having low pressure creates aeration in certain circumstances and can cause fits. Stanandyne teaches 8-14 psi for the ds4.
So towing the heaviest trailer up the steepest hill with foot smashing the floor, you don’t want under 8psi.
Gm set different specifications and remember all they care about is:
1. Sell the truck
2. Make it through warranty without failures
3. Sell a new truck

Remember the linear style lift pump were actually designed for the db style fully mechanical injection pumps that NEVER should exceed 8psi and above 5 pei under hard acceleration can cause issues…


My theory of lack of fuel hence injectors was thinking you got n/a injectors.
Imo address fuel pressure to the ip first. For now keep the normal amount of fuel lube in the fuel, Once this issue is done I would consider bumping it up to help with the ip after running it on low pressure for this time.

 

[MrMarty51]

I have the AirDog lift pump system.
At the port on the LP I have a Glow Shift sending unit screwed into that port.
I also have the JVC No.6 fitting into the IP and the FFM is the feed the beast from Leroy Diesel, a swivel fitting screwed into the inlet fitting of the IP with the 1/8” NPT port for another sending unit. I also have a Glow Shift sender into that port, so, I have pre and post FP sending units and one Glow Shift gauge in a pod on the top of the dash board with a toggle switch to shift to either sending unit.
I dont trust these Glow shift gauge units.
I had the post FFM running on 9 PSI and the pre FFM was holding about 11PSI.
I cranked up the pressure regulator to get the post FFM to closer to 15 PSI and got it to 14 but then the pre FFM is busting up at right below 30 PSI and I just dont know if the regulated pressure is that great to get the post FFM to 14 PSI or if both sending units are faulty.
After getting the pressure to that 14 then after todays 80 mile drive the pressure had dropped to about 9 PSI. I didnt think to switch to the pre FFM sending unit to see what it was reading.