I have a 1998 6.5 I use for towing. Bone stock. New fuel pump stock replacement. New vacuum pump stock replacement. On hills the turbo cuts out I pull 20 mph only. I'm thinking of going to turbo master on stock tune for now at 5 to 8 pounds boast. Any advice would help.
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6.5 cutting out up hills while towing
- Thread starter AMCTruck
- Start date
What codes are showing?
jrsavoie
Recruit
What do you mean by stock replacement?
Sometimes, brand makes a difference. I only tried a couple parts store / aftermarket lift pumps. They were both crap.
After that I stuck with AC Delco.
A fuel pressure gauge will tell you if your lift pump is keeping up.
Sometimes, brand makes a difference. I only tried a couple parts store / aftermarket lift pumps. They were both crap.
After that I stuck with AC Delco.
A fuel pressure gauge will tell you if your lift pump is keeping up.
Big T
Well-Known Member
P0251 is lift pump, or air in the fuel. I'll let Will L. tell you about clear return line at the IP. Then test fuel pressure at IP. I've gone through this twice on K2500 Suburbans and it was leaky o-ring seal at the fuel sender on the tank. Ended up replacing the feed and return lines, as well as the fuel tank, due to rust. Seal would have done it, but I replaced all to be certain. Also installed Wabro lift pump and pre-filter on the '94 and an Air Dog Raptor on the '99.
Will L.
Well-Known Member
Normally that power loss you describe points to lack of fuel from lift pump.
New parts are not always good parts… having low lift pump pressure not only causes lack of power but wears out the expensive and pain to replace ip (injection pump). Adding a metal T at the fuel inlet for a fuel pressure sensor and permanently mounting fuel pressure gauge where you see it while driving is a worth while investment.
Many people put temporary gauge tapped off the ffm, drain valve, etc but never get correct reading and replace good ip, or sometimes diagnose ip as good when it isn’t. Hence the location and fitting being in metal section not rubber.
ModMafia.com sells a perfect adapter fitting. Not sure if any of the guys here found lower priced sources.
You should never get below 1psi- if so you are doing a lot of damage to the ip.
1psi-7psi will keep it running but ip have a shortened life. 8-14 psi is where it should be from idle to wot towing heavy load.
Replace the 6” long black 1/4” diameter return fuel line, coming out of the top portion of the IP with a clear hose. The best line That I found for this was from fuelline.com. Many people, including myself, I’ve just use the clear to be available from hardware stores sold by the foot. Do you need screw style hose clamps for securing it. The line from the hardware store will last 3 to 5 years before needing replaced, but only takes five minutes and cost about five dollars. Leave the clear line in place permanently. Whenever you have a problem with the system simply look at that line for any contamination or bubbles flowing through it. The bubbles are sign of aeration , most commonly air intrusion before the lift pump. These air bubbles can cause a menagerie of problems.
You absolutely have to ensure there are no bubbles in the line, how do you have proper fuel pressure going into the IP before proceeding with any other repairs. Either one of these two problems or both could absolutely cause all of you listed problems.
New parts are not always good parts… having low lift pump pressure not only causes lack of power but wears out the expensive and pain to replace ip (injection pump). Adding a metal T at the fuel inlet for a fuel pressure sensor and permanently mounting fuel pressure gauge where you see it while driving is a worth while investment.
Many people put temporary gauge tapped off the ffm, drain valve, etc but never get correct reading and replace good ip, or sometimes diagnose ip as good when it isn’t. Hence the location and fitting being in metal section not rubber.
ModMafia.com sells a perfect adapter fitting. Not sure if any of the guys here found lower priced sources.
You should never get below 1psi- if so you are doing a lot of damage to the ip.
1psi-7psi will keep it running but ip have a shortened life. 8-14 psi is where it should be from idle to wot towing heavy load.
Replace the 6” long black 1/4” diameter return fuel line, coming out of the top portion of the IP with a clear hose. The best line That I found for this was from fuelline.com. Many people, including myself, I’ve just use the clear to be available from hardware stores sold by the foot. Do you need screw style hose clamps for securing it. The line from the hardware store will last 3 to 5 years before needing replaced, but only takes five minutes and cost about five dollars. Leave the clear line in place permanently. Whenever you have a problem with the system simply look at that line for any contamination or bubbles flowing through it. The bubbles are sign of aeration , most commonly air intrusion before the lift pump. These air bubbles can cause a menagerie of problems.
You absolutely have to ensure there are no bubbles in the line, how do you have proper fuel pressure going into the IP before proceeding with any other repairs. Either one of these two problems or both could absolutely cause all of you listed problems.
jrsavoie
Recruit
I haven't figured out exactly what else I need to install the fuel pressure gauge. I'm pretty sure I will need more than the 1 T.
Maybe a T before the FFM. Not sure What I need for the T to attach a hose to it.
A plugged tank sock and/or a faulty fuel fill cap will also cause similar issues.
I've never seen an aftermarket fuel fill cap that was the correct part. No matter if it said it was for a diesel or not
Maybe a T before the FFM. Not sure What I need for the T to attach a hose to it.
A plugged tank sock and/or a faulty fuel fill cap will also cause similar issues.
I've never seen an aftermarket fuel fill cap that was the correct part. No matter if it said it was for a diesel or not
jrsavoie
Recruit
8AN Female To 8AN Male Fitting with 1/8" NPT Gauge Sensor Side Port Adapter US | eBay
Application: The 8AN fitting compatible with Oil/ Fuel/ Water/ Fluid with AN-8 Ends. Benefit: The 8AN fitting can ensure positive sealing at a maximum working pressure. Well-Made: The 8AN fitting is made of high quality lightweight 6061-T6 aluminum, the surface is anodized, durable.
www.ebay.com
dbrannon79
I'm getting there!
Found this one on the jungle site. have not looked at the cost for the one that modmafia makes
Will L.
Well-Known Member
Here is a picture of Tads with the fuel pressure sensor inplace.
The wiring harness is different (worse) in hummers. So just reference the fso (fuel shut off solenoid)
In the second picture I put a circle around the adapter fitting and the pressure sensor is to the left of it (facing foreward towards fan)
The links you added are for -8, i think that is 1/2” hose size iirc. -6 is 3/8” and -5 is 5/16.
So if you are keeping the inlet line stock you need -5, and if you have the normal FTB modification you need -6. I don’t know anyone running a ds4 and -8 size inlet.
Double check the sizes- I’ve been wrong before…
The wiring harness is different (worse) in hummers. So just reference the fso (fuel shut off solenoid)
In the second picture I put a circle around the adapter fitting and the pressure sensor is to the left of it (facing foreward towards fan)
The links you added are for -8, i think that is 1/2” hose size iirc. -6 is 3/8” and -5 is 5/16.
So if you are keeping the inlet line stock you need -5, and if you have the normal FTB modification you need -6. I don’t know anyone running a ds4 and -8 size inlet.
Double check the sizes- I’ve been wrong before…
MrMarty51
Well-Known Member
Thank You for reminding Me. Every time I twist off, the fuel tank cap not Me
, I get the sound/feel of either pressure or vacuum. I need to drill the fill cap.Is there a certain position or procedure for drilling the cap. One position better than another ?
I was thinking a hole downwards through the top would work real well but, will it allow water to get into the tank ?
MrMarty51
Well-Known Member
I have never had issues with the engine running on lack of fuel but I dont want a problem too.
jrsavoie
Recruit
On some fuel caps, I was able to gut them with a pair of needle nose pliers.
I forget where exactly I drilled the 1/8" or #30 hole, when I did that.
Seems like I remember it being horizontal, someplace.
At one point I ordered 3 or 4 diesel fuel fill caps and would just pitch to j if they went bad.
I think I still have one left.
MrMarty51
Well-Known Member
Pulled the fuel cap.
Took a peek at it. Appeared to be a check valve in the middle. Give it a blow, locked up. Drew a breath through it, it is vented to let air in and none out.
Guess thats a win/win situation.
Will L.
Well-Known Member
If it builds pressure then it just makes the job of the lift pump easier.
It will not let out the evaporative fumes of the fuel. Then as the tank and fuel cools it would draw vacuum- the one way just allows air in. Also allowing it in as the fuel is consumed and you need air to come in so it doesn’t restrict the lift pump operation.
Absolutely nothing wrong with a little pressure in the fuel tank. Definitely something wrong with vacuum in the fuel tank.
It will not let out the evaporative fumes of the fuel. Then as the tank and fuel cools it would draw vacuum- the one way just allows air in. Also allowing it in as the fuel is consumed and you need air to come in so it doesn’t restrict the lift pump operation.
Absolutely nothing wrong with a little pressure in the fuel tank. Definitely something wrong with vacuum in the fuel tank.
Big T
Well-Known Member
How did this discussion get side tracked to drilling fuel caps? New locking fuel caps by Gates cost $12.00 on Amazon. Just buy a new one.
Paveltolz
Доверяй, но проверяй
Don't drill your fuel caps (where's the 'rolls eyes' emoji?). There's supposed to be some low pressure, aka 'vacuum' in the tank to assist in pulling the return fuel. The cap vent is supposed to keep that pressure difference in check.
ak diesel driver
6.5 driver
IIRC the vacuum is supposed to help with foaming
MrMarty51
Well-Known Member
The OP is having problems with his truck running out of power on a pull. Just thought that throwing out the functions of a fuel cap could help him determine if his fuel cap was creating too much of a vacuum.
Thats all.
Will L.
Well-Known Member
The two things required to be done are the clear line and read actual fuel pressure.
The findings of those results determine the next action.
Someone could bring up left rear tire squeaking and the same action is required- clear line and fuel pressure. Otherwise there is a hundred things that could be on the road of repairing it- aka fire the parts cannon. So the wise move is to buy nothing other than components to complete those tests.
The findings of those results determine the next action.
Someone could bring up left rear tire squeaking and the same action is required- clear line and fuel pressure. Otherwise there is a hundred things that could be on the road of repairing it- aka fire the parts cannon. So the wise move is to buy nothing other than components to complete those tests.