How weak the 6.5TD LP really is ???

[Acesneights1]

I was going to tag on one of the other LP threads but didn't want to Hijack.

The Burb started running like crap on the way home today (Yes I know it's a 6.2 but the info to follow will be of more interest to 6.5'ers). It was losing power badly on hills, smoking and felt like if you let off the throttle it would"Catch up".

A little history. I converted the Burb to a Factory 93 6.5TD Elec LP. This is supposed to be "The better" one.

So The burb felt like it was running out of fuel under load. I disconnected the fuel line from the FFM (I have the old square style) and threw it in a jug and turned the key on(NO OPS here). Fuel came out .

Hmm...Hooked a FP Gauge to the effluent side of the FFM. 5lbs at idle. The minute I put the truck in drive and touched the fuel it dropped to zero. Driving down the road under load(Climbing) it went into 10+ inches of vacuum.

Hmm...Here is where TD's wisdom comes in. The Pickup tube had rotted off in the tank so I took the unused bulkhead from the Lemon(Dodge) that came with the Raptor and made a new pickup. However there was no way to put a sock on it.

The aftermarket Pureflow (AIRDOG) Pickups are designed without them. I knew there was some rust floating around in there so I took a Glass Holley inline fuel filter from a gasser and put it in pre LP to grab any big crap.

TD warned me it may clog quickly. He was right. So I removed it and bypassed. Now the truck was running good again under load(so far) but now I noticed the LP pressure was still zero under acceleration except this time, it did not pull a vacuum.

At WOT it was zero. That makes me wonder, if my lowly 135hp DB2 driven 6.2 can pull the stock LP down to Zero at WOT how could this thing possibly feed a 6.5TD...Now the same reasoning that brought TD's FTB to life I had actually done years ago but on a 6.2

The 6.2's have a tiny little supply lline from FF to IP as well. ON that truck I did the experiment on it had the older 6.2 setup with the 2 spin ons. I elimiated the PIA seconday under the manifold , used a better fitting on the IP and ran straight to the primary and used a better spin on filter.

What has my noodle cooking now ...Is the 6.5 LP really that weak or is my 6.2 having starvtion issues due to small supply.

I find it hard to believe since the 6.2 is stock

What will really make this interesting is when I install(now I have the motivation) my nice new Autometer Full sweep on the CUCV which is runnig a 100GPH Raptor and see if the same thing happens..That will tell alot.

 

[Turbine Doc]

Kenny one of my "to-do" projects is to come up with a FTB inlet fitting on the DB2, you look at the inlet of that and it is more orifice restricted than the DS4 is was, the DB2 is more robust complexity wise no driver issues, or solenoid head/armature issues, but there is no way a DB2 can out pump a DS4, if it could don't you think Bill would have it on the LSR.

 

[Acesneights1]

It's been about 10 yrs since I owned that Brown K20 in my album but I know it was no big deal to swap that fitting on the IP. I think I used something from an Autoparts store and wrapped teflon tape around it and screwed it in. I'll work on it tommorow. I have 3 dead DB2's on my bench right now and a Parker store that can get every fitting known to man. Now when you say you are working on something , do you mean "Just the inlet fitting that the hose attaches to" ? or actually doing something to the bulkhead(for lack of better term) at the IP ?

 

[Acesneights1]

Also is there any difference in that fitting from the DB2's I have on my bench(All 6.2 ones, don't know the #s) and a 4911 ?

 

[6.2 turbo]

A 1/4 compression union will fit with the nut and feral removed,this worked untill I broke it off trying to remove the hose,I then drilled and tapped the inlet to 1/8 pipe.

 

[Turbine Doc]

Kenny look at the restriction of the inlet fitting itself on the IP, 1/8" maybe 3/16" I'm guessing, I never got to point of threading it out of the IP to see what would be required to open it up, too many other irons in the fire to worry over a DB2 at the present moment.

IMO as with the 6.5 FTB diameter into the IP should be no less than ID of the line at the tank all way to IP. Since I've never had a DB2 apart what I don't know if the inlet needs to be necked down to be a flow control regulation, since no solenoid driven control head on a mech IP to regulate flow requirements across the board.

Possibly Stanadyne set it for a metered flow of X at all rpms. I just don't know enough to be fully committed to a full opening of the inlet fitting. maybe it will be a good thing, or a failure.

 

[midniteplowboyy]

Sounds like you have other problems Kenny, either bad lift pump, a restriction or it aint a 93 lift pump. What brand LP is it?

On my 92 and 93 with A/C delco lift pumps, I have the IP and filter housings drilled/tapped to 1/4" pipe with 3/8" barbs/hose. The 93, with fuel stroke screw cranked all the way, IIRC it will only drop to around 5psi @full throttle and cruise is around 10psi, Autometer 15psi gauge. If I remember I'll check full throttle pressure today.

Here's a pic of the before and after filter housing fitting. http://www.thetruckstop.us/forum/picture.php?albumid=656&pictureid=5873

Cant find a pic of the modded IP inlet. The IP transfer pump housing is some real hard steel, best to have some good tooling or have a machine shop drill and tap it for you, your tap will be about trash when your done, atleast drill bits are easy to sharpen. If you dont believe its hard steel, try scratching it. But without drilling the IP out, IMO, there would be no gain to modding the fuel filter housing and hose to a bigger size.

On a side note, I gained a couple psi from changing the filter housing screen, even though the old one was cleaned/blowed out a few months earlier. Maybe the old screen had years of residue built up on it making the mesh smaller, I dont know.

 

[iamdave0887]

I've got a 93 HO lp on my blazer. Engine off ~11-12 psi. Engine idling ~8 psi. That's with a stock(as far as i'm aware) J code IP.

I have a gauge i want to put on at some point to see what my WOT fuel pressure is, but i have to figure out my engine issue first.

I think you have other problems Kenny.

 

[Acesneights1]

Gonna change the Fule filter today. It can't be the pick as that is aftermarket and wide open. Maybe the LP is on its way out. It's only 3 months old if that. I got it from Advance Auto for a 93. BTW Truck is running fine today. gotta figure out what I could use inline with low rest for a pre LP sceen.
I think it's Matt's Fault. He was over not too long ago and I think his truck has a LP fungus that infected mine...:rofl:

 

[Burning oil]

I would start with the basics. Blow out the lines. How much volume does the LP pump. Check for air leaks before LP............

 

[buddy]

A more restricted fuel line and IP inlet would make it a lot easier for the LP to maintain pressure. Doing the FTB and opening up the line puts more mass in front of the LP and allows IP to pass more through it making it harder to maintain high fuel line pressure.

Also what can cause the problem is if your return line is not regulated correctly. If the return fitting is allowing too much flow, not enough restriction, then you wont be able to hold pressure on the inlet as it will just pass a lot of fuel through the IP.

 

[Acesneights1]

Fuel lines including PU are new and I sight glasses it. No air.

 

[ireburb]

I can't explain the stock LP issue either but I tried two 93 version lift pumps with no success and could only get 6psi at idle and 0 psi at WOT.

I now have 10-11 psi at idle and 6 at WOT but I am using a Mallory 110GPH fuel pump to get this pressure.

So either the 93 version lift pump is weak or maybe I got 2 bad pumps from the auto parts store.

Whatever the reason, my fuel pressure issues are now fixed thanks to the Mallory fuel pump.

 

[buddy]

Could be the return is not being regulated properly, so inlet cant maintain pressure.

You can get a real high power LP, and unrestrict the return path so you circulate a lot more fuel but still maintain inlet pressure. Then you would keep the IP as cool as possible.

 

[Acesneights1]

Could be, I strognly suspect the IP I got was a Dud.

 

[midniteplowboyy]

Did a few tests in the 93. 0-80mph full throttle run, pressure dropped to around 3.5psi @3500rpm and came back up with each shift, pressure was 4.5psi @3000rpm @80mph. I should have been watching my other gauges though, looked over and pyro was setting @1400ºF and coolant temp was @230ºF.

Hot idle is 11-11.5psi.
Cruise @70-75mph 1800-1900rpm is 9.25-10psi.
Fuel pressure readings taken @ IP inlet Autometer gauge.

This is on a DB-2 not DS-4 guys, I think the DB-2's dont return as much fuel since some fuel pressure is used for part of the advance control and is more restricted than the DS-4's which as far as I know dont use housing pressure for advance being all electrically controlled.

Kenny, does your cold advance work, just thinking maybe somebody left part of the housing pressure regulator out or stuck open, dumping the fuel as fast as it gets it. Have you checked voltage @ lift pump?

 

[iamdave0887]

Did a few tests in the 93. 0-80mph full throttle run, pressure dropped to around 3.5psi @3500rpm and came back up with each shift, pressure was 4.5psi @3000rpm @80mph. I should have been watching my other gauges though, looked over and pyro was setting @1400ºF and coolant temp was @230ºF.

Hot idle is 11-11.5psi.
Cruise @70-75mph 1800-1900rpm is 9.25-10psi.
Fuel pressure readings taken @ IP inlet Autometer gauge.

This is on a DB-2 not DS-4 guys, I think the DB-2's dont return as much fuel since some fuel pressure is used for part of the advance control and is more restricted than the DS-4's which as far as I know dont use housing pressure for advance being all electrically controlled.

Kenny, does your cold advance work, just thinking maybe somebody left part of the housing pressure regulator out or stuck open, dumping the fuel as fast as it gets it. Have you checked voltage @ lift pump?

I'm guessing this is the the stock 93 HO LP? My 93 HO LP on my blazer puts out 8 psi at idle, ~11 with engine off. engine temp doesn't seem to matter. The thing that bugs me is the second i shut the engine off the fuel pressure starts to drop and goes to 0 within 2 minutes. I used to hold pressure for a bit. Now it doesn't, yet i have no leaks. Does your fuel pressure just drop right off within a minute or two of shutting the truck down? I'm wondering if that little valve in the top of the IP that lets fuel into the return system is stuck open?

 

[Matt Bachand]

Gonna change the Fule filter today. It can't be the pick as that is aftermarket and wide open. Maybe the LP is on its way out. It's only 3 months old if that. I got it from Advance Auto for a 93. BTW Truck is running fine today. gotta figure out what I could use inline with low rest for a pre LP sceen.
I think it's Matt's Fault. He was over not too long ago and I think his truck has a LP fungus that infected mine...:rofl:

):h

LOL Kenny! Well your damn cloud followed me home... In fact I moved in the rain 2 weekends ago... Half my shit is still wet! Now we are even. Take that damn cloud away now, or at least teach me how to use the suicide smiley! :thumbsup::thumbsup:h):h

 

[midniteplowboyy]

I'm guessing this is the the stock 93 HO LP? My 93 HO LP on my blazer puts out 8 psi at idle, ~11 with engine off. engine temp doesn't seem to matter. The thing that bugs me is the second i shut the engine off the fuel pressure starts to drop and goes to 0 within 2 minutes. I used to hold pressure for a bit. Now it doesn't, yet i have no leaks. Does your fuel pressure just drop right off within a minute or two of shutting the truck down? I'm wondering if that little valve in the top of the IP that lets fuel into the return system is stuck open?

Yea, its a 92-93 AC/delco 6.5 lift pump. Mine drops to around 5psi pretty quick after you shut it off(couple minutes), still has around 3psi after setting all night, takes prolly 24hrs to drop completely to zero.

I wouldn't worry about it as long as you always got some fuel pressure available to charge the transfer pump in the IP when you hammer on it. Does your cold advance work?

What brand is your lift pump? I tried some Carters, but they didn't seem to last as long, dont have any pressures on them though, quit using them years ago.

 

[iamdave0887]

Yea, its a 92-93 AC/delco 6.5 lift pump. Mine drops to around 5psi pretty quick after you shut it off(couple minutes), still has around 3psi after setting all night, takes prolly 24hrs to drop completely to zero.

I wouldn't worry about it as long as you always got some fuel pressure available to charge the transfer pump in the IP when you hammer on it. Does your cold advance work?

What brand is your lift pump? I tried some Carters, but they didn't seem to last as long, dont have any pressures on them though, quit using them years ago.

I believe it's an Airtex 93 HO LP.

I'm going to have to check that little valve on the top of the IP. My pressure just vanishes in under 5 minutes, yet i see no leaks. It fires right up after a few turns due to the Duraterms(extra glow time and it catches in a 1/2 a turn) so i know i'm not having a drainback issue or air in the system. Only other place the pressure can go, if not on the ground via a leak, is back into the tank.