Opinions needed - Performed Optical Bump

[MrMarty51]

A couple of good questions that I am not having enough knowledge to answer.
I dont remember what years of fuel gauges is affected, but, like with My 2000 year truck, the gauge is always slow to respond, the gauge swings lower and fuller and never seems to settle on a position that accurately tell tales how much fuel is actually in the tank.
I do know this, when the needle finally get to that red zone below the 1/4 mark, the tank is empty.
I think there is some write ups about this malady within the forum, I just cant remember what a partial cure might be, unless it is that sender unit that Leroy has in his store.

 

[dbrannon79]

I'm just worried that the last owner may have screwed with something in the cluster that is now sending too much voltage or amperage to the FSU and has turned it into a resistive heater filament not to mention a major fire hazard! if this is the case, with an OE FSU or Leroy's FSU, this screw-up will burn ether one up! If I'm not mistaken, the OE FSU has a ohm range or 0-90 ohms. I may grab a potentiometer and set it to various ohms in that range and see how the gauge reacts and if it doesn't burn the pot up before I attempt to connect any FSU to the harness. I showed the FSU to one of the mechanics at my work and the first thing he said was "good thing it's not gas in that tank"

 

[MrMarty51]

I wonder how a volt meter would react if attached to the sender wire at the tank.
Also, might it be possible that a wire that has potential to become live with 12 volts have rubbed through to contact with the FSU wiring ?
IE, tail light wire etc.

 

[MrMarty51]

I guess that in the above instance, it probably would take out the resistor, or gauge in the dash.

 

[dbrannon79]

@MrMarty51 that is very possible. there is a spot in the harness where a PO tapped into to wire lights to the headache rack. the lights all work, but when they did this they could have probed the wrong wire for a ground! this also may be why the gauge always reads right at 1/2 tank. I will have to pull the loom apart there and check. also put a meter on the FSU connector and function all the lights and watch the meter to see if anything changes.

 

[dbrannon79]

Got home today and was able to check all I could. Never found anything wrong with the FSU wires so I took the chance. Connected the new FSU and turned the key, gauge was responding but was maybe 90 degrees off where when full it was marking at the E and at empty the gauge was pointing at the straight down. I played with the cluster , even tried my donor cluster which wasn’t any better. I finally ended up pulling the needle off the gauge and resetting it like I did to the tach and other gauges. Whoever had this cluster apart must have messed with all the needles. Now on to the tank and lift pump

 

[DieselAmateur]

If the fuel gauge is jumpy and reading all over the place it could also be a problem with the aircore motor in the cluster. The liquid in the gauge unit goes bad giving improper readings. When I bought my truck the fuel gauge didn't work and nothing changed even after dropping the tank and replacing the sending unit. This video does a good job describing the repair. Only problem is that it seems nowadays there's nowhere to get new gauge motors anymore.

 

[dbrannon79]

Well happy Saturday everyone! Finished cleaning up the tank and installed. Installed an inline filter between the tank and the new LP since I removed the sock strainer. Filled about 10 gallons of diesel in the tank and started priming all the air from the lines. Ran to the auto parts to find a 3/8” fitting for the hose on the IP so my hose wasn’t pinched down to the small barb, but no dice. I ended up getting a 1/4” barb for my remote filter and a length of 1/4” hose as a temporary fix until I can order the right fitting for the IP for the 3/8” fuel line.
Primed the LP and watched the pressure... holding at 10psi. Cranked up the engine and pressure dropped to about 3 to 4 psi and stayed while at idle.. revving would drop to 0. My head fell in disbelief

after a little while of staring at the truck, I had a thought about the “top of the line” HarborFreight fuel pressure tester I was using... I disconnected my boost gauge line from the intake and finagled me an inline “T” at the IP inlet and connected the boost gauge there... Well I’ll be dammed, key on psi was 11 and at idle showed a steady 7-1/2 psi. Revving it only dropped to 5psi. Hallelujah! I was happy at least I had made progress!

now there’s fuel pressure, no air in the lines, and a working fuel gauge. I know some of the work could possibly been avoided if I had checked how accurate the cheap Chinese fuel gauge was, but I’ll take it as lesson learned the hard way!

now I just need to put the dash back together and go fill the tank . I did take some time cleaning up the engine compartment while striking up the bbq pit!

 

[Will L.]

progress is always nice.
Waiting to hear on the road running conditions.

 

[MrMarty51]

I’m shopping for an electronic vacuum /boost gauge that dont cost a hundred bucks plus change. Analog units are cheap but I am trying to eliminate the live pressure tube into the cabin.
Thats great progress You made on Your truck.

 

[dbrannon79]

I’m shopping for an electronic vacuum /boost gauge that dont cost a hundred bucks plus change. Analog units are cheap but I am trying to eliminate the live pressure tube into the cabin.
Thats great progress You made on Your truck.

Thanks I couldn’t have done it all without everyone’s help here.

Let me know what you find! I like that idea. It would be nice to keep the analog style with an electric sender. All the newer Kenworth trucks we work on at my job all use electric analog style gauges and I think there made by VDO. I work in the parts department there, I’ll have to check to see if they make one for boost!

 

[dbrannon79]

Didn't do a whole lot Sunday, I did finally moved the PMD seat sink to the front bumper, that was long overdue from lazyness lol.

headed out to work this morning and noticed the fuel pressure on my boost gauge was a little higher at idle showing 9 psi. I think it's because I changed the the hose size to 1/4" until I find the IP fitting for the 3/8" hose. anyway all good news so far. she cranked up better, key on psi was at 11 -12 psi and idle was holding at almost 9 psi. it did fluctuate as I was accelerating but not by a lot. cruising at 65 it stayed right at 5-6 psi and when climbing a small incline the lowest I saw was 4psi briefly. letting off the pedal coasting it jumped right back up to 9.

I still haven't filled the tank yet but I did notice the fuel gauge was moving from 1/4 to 1/8th as I used the brake or accelerated, but I can live with that, at least it works

Thanks again everyone for all the help.

short list of things to do from this is: find a 3/8" fitting for the IP inlet, find an electric fuel pressure gauge and get an EGT gauge installed. Hopefully I won't have any more engine troubles for a while, but Ill give more updates as I drive it more.

 

[DieselAmateur]

Here's a link for the upgraded fitting, the threaded part is 7/16"-20 ORB x 3/8 hose barb. If you wanted to super beef up the fuel supply you can get fittings with the ORB lower and flare/ hydraulic style fittings on the other end too

Amazon.com

www.amazon.com

 

[dbrannon79]

Here's a link for the upgraded fitting, the threaded part is 7/16"-20 ORB x 3/8 hose barb. If you wanted to super beef up the fuel supply you can get fittings with the ORB lower and flare/ hydraulic style fittings on the other end too

Amazon.com

www.amazon.com

Nice!! Thank you placed the order for tomorrows delivery I was already looking at the hydraulic filltings at work and figured out it was #4 o-ring boss but was not having luck getting to the hose barb end!

 

[royunion]

So. A concerned question.... the ground problem I found was the eyelet ground on the frame was off from my own doing about a month ago due to me probing the harness checking the fuel gauge. With that said. The truck apparently has been running all that time without the lift pump working and I didn’t know it.. shame on me. Have I possibly caused irreversible damage to the IP. Also what should the line pressure be from the lift pump with key on and idling.

now I’m headed inside to go kick myself in the A$$ for this mistake

I will be looking into an inexpensive gauge to mount in the cab real soon because of this experience

Well as I read the whole post, I was waiting for the post where you discovered that the lift pump pressure was not good enough.

There are a number of things that matter, but the number one is good presistant high lift pump pressure. The OEM style solenoid pumps do not work at all or for long. When warm up they loose the ability to pump even more. I use the Sure Cure Lift pump solution. It comes with three pumps. One to use, one is a spare, and one is a emergency use one that is a canister style and a fuel pressure regulator that will hold and let 20 psi to be set. By the time it passes through the filter you get 16 to 18 psi at the lift pump under all conditions even wide open throttle. The emergency pump is used for mounting bracket and some hardware., but it is emergency swap use only because it only puts out 4 to 5 psi. You will hear and read that fuel pressure should be 5 psi, but that is MINIMUM psi. Even the Delco EP 158 has a spec of 10 to 12 psi though it won't hold that for long even after new.

I have an electric in cab digital readout that I use rotary switch to switch from vacuum / boost, to fuel pressure at the ip, to fuel pressure pre filter, to transmission line pressure. They all use 0 to 300 psi transducer sensors. The readout is dual display and the other is post turbo exhaust gas temperature (EGT)

It has been five years since the Sure Cure Lift Pump solution went in and recently pressure dropped to 14 at the IP. OK so what I figured I needed to change the filter.

One day it stumble started only the second time in five years. Then again a d shut off. The lift pump is really quiet so much so if the HVAC fan is running I can't hear it. I cut off the fan turned the key on and it sounded weak. Then it started on the fifth try. The next morning no start, and no lift pump sound at all. This is why the Sure Cure Lift Pump Solution comes with a spare. Checked for 12 volts at key on and swapped the lift pump which took 30 minutes, and started it right up. Now it was back to 18 psi at the IP.!!


Since I used to work with a Diesel shop that specialized the Stanadyne pumps, it is important to understand the pump expects about 12 to 18 psi to perform best. At about 10 to 12 psi the return check valve on the top of ip opens to begin to let let fuel return to the tank. The purpose of that is to keep the timing wheel tank full of cool recirculating fuel which supposed to cool the PMD that mounted on the side.

But here is where the problem started where GM wod not listen to Stanadyne that the solenoid lift pump they selected would not work for the DS4. GM did not understand the electronic nature needs 18 psi to work properly for long life. The PMD also called the Fuel Solenoid Driver or FSD is a poor ideal to use Power Transistors ( the two round things on the underside of the PMD) as a voltage regulator switch to drive the the Fuel Solenoid which is on the rear of the IP which is effectively the throttle that is actually pressure controlled. FUEL pressure controlled, and it is kept closed by a spring and assisted open by the Fuel Solenoid which driven by the PMD. The PMD is supposed to to assist only to open the plate more to increase engine speed. When there is low fuel pressure in the IP, two things happen, first there is no fuel to fill the optical sensor tank area to cool the PMD and second the the switching transistors are OVERWORKED trying to keeping the throttle plate open to try and increase engine rpm. This overheats both the PMD and the Fuel Solenoid which also shortens the Fuel Solenoid life also. So this the DS4 death spiral. The PMD relocation is a band aid. Minimum fuel pressure is also contininung the death spiral.

It is all because of the lift pump. The Sure Cure Lift Pump solution has in line axial pumps but the emergency one is a canister motor driven wet pump.

When you put 18 psi at the IP you should notice a light foot on the accelerator will make it take off and it will pull like a gas engine if everything else is right.

It sounds like there are turbo and waste gate issues. The waste gate solenoid or actuator or map sensor may have issues assuming you have good vacuum. An OEM setup will never go over 10 psi. It will open the waste gate using the map sensor and waste gate solenoid. As others have said the wicked wheel will spool pressure faster but a proper system if stock will work with the ecm, timing and fuel input. pressure

I would get a good positive in line true motor driven ift pump that is dependable first. Most of the problems may go away like you realized the lift pump was not working. Also even the OEM solenoid pump from cold start pumps strong and then gets weak when it warms up.

Also my TDC offset is - 1.25 and it ran like crap until I did the key on key off procedure

 

[Will L.]

@royunion
Cool info, 2 items
The 5psi is a maximum figure for mechanical injection pumps like db2, db4.

Everything I found (can’t really remember as Stanadyne class was in the 90’s and I slept too much since then) but I am pretty sure ds4 spec is 8-14 psi. At higher rpm the upper psi will have loss in throttle response. This was shown well by meangreenh1 with his on the fly adjustment system as he could control pressure while driving and saw the results. If you have any docs from Stanandyne showing above 14 is correct, can you post it please?

yeah, the factory pump is junk. It barely did ok with sulfur diesel and only needing 5psi max. Too bad the FASS pumps and such are so pricey.

 

[royunion]

@royunion
Cool info, 2 items
The 5psi is a maximum figure for mechanical injection pumps like db2, db4.

Everything I found (can’t really remember as Stanadyne class was in the 90’s and I slept too much since then) but I am pretty sure ds4 spec is 8-14 psi. At higher rpm the upper psi will have loss in throttle response. This was shown well by meangreenh1 with his on the fly adjustment system as he could control pressure while driving and saw the results. If you have any docs from Stanandyne showing above 14 is correct, can you post it please?

yeah, the factory pump is junk. It barely did ok with sulfur diesel and only needing 5psi max. Too bad the FASS pumps and such are so pricey.

Yes db2 and db4 is where gm's head got stuck. On the db pumps higher pressure changes the timing. Here is a link to the DS4 service manual. At page 1.8 section H it talks about the return fuel circuit duty to limit housing pressure to 5 - 14 psi, and that means the check ball starts to open around 10 psi and is fully open at 14 psi. Inlet line pressure is safe up to 18 psi, and I have seen it as high as 22 before the throttle plate and spring will let it runaway or not be able to idle.

It does not affect timing like on the db pumps. https://bit.ly/2Ua3cii. This is a Google crack through the Stanadyne dealer portal and may stop working at anytime. Or Google "Stanadyne DS4 SERVICE MANUAL". That may be where you got your figures. The Inlet pressure is safe up to 18 psi unless someone has rebuilt it and did not use a dial Indicator on the throttle plate setup or reused the crush ring back there. It idles properly smoothly and strongly at higher Inlet pressure and uses less voltage - which is the fuel solenoid power duty cycle to open the throttle because fuel pressure does it and let's the PMD do as little heavy pulling as possible.

My pmd at idle is barely warm to the touch because it is not doing any of the work that drives the fuel solenoid. On the test bench the pmd gets hot testing at 5 psi and at 18 psi it is cool. The lift pump solution I use was $ 299 and I got three pumps, a regulator that is a pressure plate steady type with a mech gage and swap in hardware complete for the 6.5. No more buzz noise and is really quiet. It took five years for the pump to fail and immediately I have ordered a replacement spare to replace the spare I just used.

 

[dbrannon79]

At page 1.8 section H it talks about the return fuel circuit duty to limit housing pressure to 5 - 14 psi, and that means the check ball starts to open around 10 psi and is fully open at 14 psi.

This is very interesting. I was researching this while testing pressures on my truck. I actually removed the return line fitting from the IP and did a “dirty” test to see what pressure it held at with my air compressor and regulator. It would open up at or around 5 psi and allow air for flow out. I did unscrew the two sections thinking there was a ball and spring but to my surprise the upper section had a crimped metal plate inside with a glass BB, I could blow both ways by mouth on it. The lower section had a small rubber check valve in it that was only allowing a one way flow out of the pump. I wonder if this part is going bad! I ended up reinstalling it on the IP and moved on but still had the curiosity

 

[ak diesel driver]

When the db2 starts to die it will sometimes push junk into that check ball and cause the engine not to run, same as pinching it off will. I've seen guys break the bb out and gut the fitting to get them home. Very temporary fix

 

[dbrannon79]

I wonder since when I pulled the one on my IP apart messing with it and it has a rubber check valve in it that it might be going bad. By me messing with it and reinstalling it maybe had a little to do with bringing fuel pressures back up. I did notice this evening taking a trip into town idle pressure was slowly fluctuating a lb or so but was still up at 7-1/2 to 9 sitting still. I didn’t really think much about it.