need help: 6.5 problems
#22
04-24-2012, 10:00 AM
Diesel Wrench
Reference Material: Lift Pump/OPS
Here’s another one for the newbie’s out there.
After frequenting the boards for awhile, you’ll notice there seems to be a few things that come around, and around, and around again. One of those things is the Lift Pump, official title: Fuel Lift Pump. So, what is a lift pump, and why does it lift fuel? The lift pump is an in-line fuel pump mounted on the frame rail under the driver’s seat. This is a small electric pump that “helps” bring fuel out of the tank and up to the injection pump. This is to help prevent the expensive injection pump from having to “suck” it’s own fuel all the way up from the tank, which it can do, but can cause damage to itself and it's driver module - more on that in another section*.
Now, that’s pretty straight forward isn’t it? So, why so much fuss about a lift pump anyway? Only because it causes so many issues* when it’s not working.
Will my truck run without the lift pump? Yes it will. How well? Well, to some it will be very noticeable when it’s not working. Some may not even notice.
If I don’t notice that my lift pump isn’t working, I’m okay right? Not exactly. That means that your expensive injection pump is doing all the work in the fuel system. This is NOT a desirable thing. Plus you are setting yourself up for problems*.
How can I tell if my lift pump is working? Do the famous “lift pump test.” How do you accomplish this highly scientific experiment you ask? Very simple. Pop the hood - you’re half way there. Find on the front top of the engine the thermostat housing. You should see a little T-handle valve standing proud there in front of you. (If you have a van, you’ll have a schrader valve down deep behind the oil fill) That T-valve is calling your name saying “turn me.” Pay attention, ‘cause there’s a hose on the end of the T-valve. That hose should have diesel fuel come out of it when the engine is idling and you open the T-valve. When you open the T-valve and the engine is idling, and no fuel comes out, you’ll hear your engine cough, sputter, and die within 30 seconds. If it doesn’t cough, sputter and die with the T-valve open and no fuel coming out, something is plugged up in your fuel system between the fuel filter cannister and the t-valve, perhaps even inside the fuel filter cannister.
If the engine does die, it has emptied the fuel cannister and run out of fuel, so you will need to close the T-valve, then troubleshoot and repair the lift pump system, as follows in the text below.
Now, if you get a continuous stream of fuel out the hose, then close the T-valve and open the plastic air-bleed valve on the top of the metal filter cap - if fuel spurts out there, then congratulations! You are the proud owner of a working lift pump. Not everyone is as blessed as you are at this moment. If you're not, keep reading.
To those not as blessed, pickup reading here. You must determine why you have no fuel supply coming to your injection pump. There are two main culprits to the demise of a lift pump. Either it’s out to lunch, or it’s in the morgue. See, one means it still might work, the other means it’s dead. How do you tell? Check to see if it has power.
First, find the lift pump under the truck. With the engine idling along, pull the plug for the lift pump. You can either use a test light, or a meter to see if you have voltage at the pins. Make sure you get a good connection, otherwise you may condemn the wrong thing. Sometimes it is difficult to get a probe to meet up with the pins inside the plug, so make double sure you’ve got it.
If you have voltage, *chances* are you have a dead lift pump. Not always, but could be a dead lift pump. You may have voltage present under a "no load" condition. This means that voltage may be present when the lift pump is not attached to the circuit, but once the lift pump is connected, the load exceeds the amount of power the circuit can provide because the OPS contacts are creating a high resistance.
Now, if you don’t have voltage, you’ll have to verify upstream from there why there is no voltage present. What is upstream? The infamous OPS (Oil Pressure Switch), or fuse.
What does the OPS have to do with the lift pump? Doesn’t sound right does it to have oil pressure tied to fuel does it? Well, some think that it is a fail safe that in case your engine ever lost oil pressure, it would shut off the lift pump so that engine would stall. Guess what? If you read a little bit ahead of this paragraph, you’ll find 'dat ain’t so'. The real reason why this circuit even exists is because of an accident. In case you should be in a wreck, the last thing you would need is to have your lift pump going to town pumping out that precious, expensive, fuel all over the accident scene. After all, should you be bleeding and having a thumpin’ head - the last thing you’ll be thinking is “Hey, I just paid $3.50 a gallon for that, somebody get a shop-vac!”
Why would the OPS not allow my lift pump to work? Well, from time to time, or shall we say in the corporate world, from dime to dime, some decisions get made. Some for the good, and some for the good of the keepers of the money. The OPS has a set of contacts inside to power the lift pump. This set of contacts are not heavy enough to carry the pathetic amount of current to the lift pump. Sad, I know, but true. So, what ends up happening is your lift pump works fine, but the OPS gets smoked, and then it quits. You think the pump is bad, but it’s not.
Can I just eliminate the OPS? Well, be careful, it is a safety device in some people’s eyes, and to the rest of us, a pain in the rump. Eyes, rump, pick your part. Anyway. If you just “jump past” the OPS, then your pump will run all the time. Not just all the time, but ALL THE TIME. Christmas and Easter included. It will stop when your batteries are dead. Because, while you are grocery shopping, that pump is running. While you are down for a long winter’s nap, it’s pumping. Doesn’t matter if the key is on or off, it’s pumping.
You can make up another circuit and repower it some other way, but be careful how you do it. Some methods have kept the truck running after the ignition is shut off and keys in pocket.
Back to our little friend the lift pump.
The lift pump may fail in a variety of different ways. It may fail “open” meaning that the coil driving the pump no longer has continuity. It may fail mechanically where it is just frozen and nothing moves. It may even (not as often) fail to pump. This means, it makes noise, but doesn’t actually pump.
Does the lift pump make noise? Yes it does. The model year of your truck will determine if your lift pump is powered during the Wait To Start period. That’s the time where that light is on before actually starting your engine. '96-up OBD2 models pre-run the lift pump during WTS and during START, '94-'95 OBD1 models pre-run the lift pump only during START.
The lift pump is characterized by a kind of “purring” noise heard beneath the truck. That noise is quickly drowned out by the engine, once started. When you shut your engine off, you will hear that pump run briefly, maybe only a quick second or two. If you shut your engine off when cold, you will hear the pump run much longer, sometimes up to 30 seconds or more.
A loud clacking noise would indicate no fuel from the tank, or the lift pump is failing or failed - it will run without pumping fuel when the one-way valve(s) fail.
A faint purring or vibration when touching the lp body indicates it is running, but the internal valve-shuttle armature is stuck due to mechanical failure.
So what kind of problems will it cause if the lift pump isn’t working? Many. It will cause all sorts of fuel related issues*. It can be some of the following:
°Stumbling
°Hard Starting
°Lack of Power
°DTC (Diagnostic Trouble Codes) on the Computer
°Stalling
There are be other* issues too, but these seem to be a very (un)popular list.
Where do I get one of these? Some of our site vendors, or any of the popular auto parts stores, or the dealership. More often than not, the auto parts store is a good bet for Ineeditrightnow.
Ask for the version for the '93 6.5TD truck - it is a direct-fit HD replacement that will supply increased fuel pressure and volume to the Inj Pump, which is a good improvement for the '94-up EFI trucks.
FYI: don't mention that you have a '94-up truck, or you will just confuse the parts guy\gal - just describe your truck and drivetrain as a '93.
The ACDelco or Delphi lift pumps are the best replacement, which you can get from O'Reilley's or NAPA , and some of the site vendors, such as Heath Diesel.
Also FYI: the parts-guy\gal may call it a fuel pump.
Are they difficult to change? No - loosen the tubing-fitting nuts on either end, remove and reinstall. Now, if it were only really that easy. Let’s get real here, no camera out-takes…. You’ll end up getting a Diesel bath. You see, depending upon how much fuel is in your tank, there will be fuel that wants to come out of the fuel line. Be ready, because your chances of a date after changing that lift pump dwindle a bunch, unless they are really into the smell of a Diesel cologne. J
After the successful fuel lift system repair you will need to refill the fuel filter cannister - after opening the air-bleed valve, which is the plastic nut on the very top of the metal cap, power up the lift pump, then close the air bleed when the bubbles stop and fuel begins spurting out - if you still get no fuel, you likely have a stopped-up fuel filter - no need to tell you what to do in that event, right?
FYI: after successful fuel flow out the air-bleed, the engine may take a while to restart and run as the Inj Pump begins to draw fuel from the filter, fills internally, then starts pump-up to 1900psi injection pressures.
This is at least enough to get you started on your lift pump journey.
Here’s another one for the newbie’s out there.
After frequenting the boards for awhile, you’ll notice there seems to be a few things that come around, and around, and around again. One of those things is the Lift Pump, official title: Fuel Lift Pump. So, what is a lift pump, and why does it lift fuel? The lift pump is an in-line fuel pump mounted on the frame rail under the driver’s seat. This is a small electric pump that “helps” bring fuel out of the tank and up to the injection pump. This is to help prevent the expensive injection pump from having to “suck” it’s own fuel all the way up from the tank, which it can do, but can cause damage to itself and it's driver module - more on that in another section*.
Now, that’s pretty straight forward isn’t it? So, why so much fuss about a lift pump anyway? Only because it causes so many issues* when it’s not working.
Will my truck run without the lift pump? Yes it will. How well? Well, to some it will be very noticeable when it’s not working. Some may not even notice.
If I don’t notice that my lift pump isn’t working, I’m okay right? Not exactly. That means that your expensive injection pump is doing all the work in the fuel system. This is NOT a desirable thing. Plus you are setting yourself up for problems*.
How can I tell if my lift pump is working? Do the famous “lift pump test.” How do you accomplish this highly scientific experiment you ask? Very simple. Pop the hood - you’re half way there. Find on the front top of the engine the thermostat housing. You should see a little T-handle valve standing proud there in front of you. (If you have a van, you’ll have a schrader valve down deep behind the oil fill) That T-valve is calling your name saying “turn me.” Pay attention, ‘cause there’s a hose on the end of the T-valve. That hose should have diesel fuel come out of it when the engine is idling and you open the T-valve. When you open the T-valve and the engine is idling, and no fuel comes out, you’ll hear your engine cough, sputter, and die within 30 seconds. If it doesn’t cough, sputter and die with the T-valve open and no fuel coming out, something is plugged up in your fuel system between the fuel filter cannister and the t-valve, perhaps even inside the fuel filter cannister.
If the engine does die, it has emptied the fuel cannister and run out of fuel, so you will need to close the T-valve, then troubleshoot and repair the lift pump system, as follows in the text below.
Now, if you get a continuous stream of fuel out the hose, then close the T-valve and open the plastic air-bleed valve on the top of the metal filter cap - if fuel spurts out there, then congratulations! You are the proud owner of a working lift pump. Not everyone is as blessed as you are at this moment. If you're not, keep reading.
To those not as blessed, pickup reading here. You must determine why you have no fuel supply coming to your injection pump. There are two main culprits to the demise of a lift pump. Either it’s out to lunch, or it’s in the morgue. See, one means it still might work, the other means it’s dead. How do you tell? Check to see if it has power.
First, find the lift pump under the truck. With the engine idling along, pull the plug for the lift pump. You can either use a test light, or a meter to see if you have voltage at the pins. Make sure you get a good connection, otherwise you may condemn the wrong thing. Sometimes it is difficult to get a probe to meet up with the pins inside the plug, so make double sure you’ve got it.
If you have voltage, *chances* are you have a dead lift pump. Not always, but could be a dead lift pump. You may have voltage present under a "no load" condition. This means that voltage may be present when the lift pump is not attached to the circuit, but once the lift pump is connected, the load exceeds the amount of power the circuit can provide because the OPS contacts are creating a high resistance.
Now, if you don’t have voltage, you’ll have to verify upstream from there why there is no voltage present. What is upstream? The infamous OPS (Oil Pressure Switch), or fuse.
What does the OPS have to do with the lift pump? Doesn’t sound right does it to have oil pressure tied to fuel does it? Well, some think that it is a fail safe that in case your engine ever lost oil pressure, it would shut off the lift pump so that engine would stall. Guess what? If you read a little bit ahead of this paragraph, you’ll find 'dat ain’t so'. The real reason why this circuit even exists is because of an accident. In case you should be in a wreck, the last thing you would need is to have your lift pump going to town pumping out that precious, expensive, fuel all over the accident scene. After all, should you be bleeding and having a thumpin’ head - the last thing you’ll be thinking is “Hey, I just paid $3.50 a gallon for that, somebody get a shop-vac!”
Why would the OPS not allow my lift pump to work? Well, from time to time, or shall we say in the corporate world, from dime to dime, some decisions get made. Some for the good, and some for the good of the keepers of the money. The OPS has a set of contacts inside to power the lift pump. This set of contacts are not heavy enough to carry the pathetic amount of current to the lift pump. Sad, I know, but true. So, what ends up happening is your lift pump works fine, but the OPS gets smoked, and then it quits. You think the pump is bad, but it’s not.
Can I just eliminate the OPS? Well, be careful, it is a safety device in some people’s eyes, and to the rest of us, a pain in the rump. Eyes, rump, pick your part. Anyway. If you just “jump past” the OPS, then your pump will run all the time. Not just all the time, but ALL THE TIME. Christmas and Easter included. It will stop when your batteries are dead. Because, while you are grocery shopping, that pump is running. While you are down for a long winter’s nap, it’s pumping. Doesn’t matter if the key is on or off, it’s pumping.
You can make up another circuit and repower it some other way, but be careful how you do it. Some methods have kept the truck running after the ignition is shut off and keys in pocket.
Back to our little friend the lift pump.
The lift pump may fail in a variety of different ways. It may fail “open” meaning that the coil driving the pump no longer has continuity. It may fail mechanically where it is just frozen and nothing moves. It may even (not as often) fail to pump. This means, it makes noise, but doesn’t actually pump.
Does the lift pump make noise? Yes it does. The model year of your truck will determine if your lift pump is powered during the Wait To Start period. That’s the time where that light is on before actually starting your engine. '96-up OBD2 models pre-run the lift pump during WTS and during START, '94-'95 OBD1 models pre-run the lift pump only during START.
The lift pump is characterized by a kind of “purring” noise heard beneath the truck. That noise is quickly drowned out by the engine, once started. When you shut your engine off, you will hear that pump run briefly, maybe only a quick second or two. If you shut your engine off when cold, you will hear the pump run much longer, sometimes up to 30 seconds or more.
A loud clacking noise would indicate no fuel from the tank, or the lift pump is failing or failed - it will run without pumping fuel when the one-way valve(s) fail.
A faint purring or vibration when touching the lp body indicates it is running, but the internal valve-shuttle armature is stuck due to mechanical failure.
So what kind of problems will it cause if the lift pump isn’t working? Many. It will cause all sorts of fuel related issues*. It can be some of the following:
°Stumbling
°Hard Starting
°Lack of Power
°DTC (Diagnostic Trouble Codes) on the Computer
°Stalling
There are be other* issues too, but these seem to be a very (un)popular list.
Where do I get one of these? Some of our site vendors, or any of the popular auto parts stores, or the dealership. More often than not, the auto parts store is a good bet for Ineeditrightnow.
Ask for the version for the '93 6.5TD truck - it is a direct-fit HD replacement that will supply increased fuel pressure and volume to the Inj Pump, which is a good improvement for the '94-up EFI trucks.
FYI: don't mention that you have a '94-up truck, or you will just confuse the parts guy\gal - just describe your truck and drivetrain as a '93.
The ACDelco or Delphi lift pumps are the best replacement, which you can get from O'Reilley's or NAPA , and some of the site vendors, such as Heath Diesel.
Also FYI: the parts-guy\gal may call it a fuel pump.
Are they difficult to change? No - loosen the tubing-fitting nuts on either end, remove and reinstall. Now, if it were only really that easy. Let’s get real here, no camera out-takes…. You’ll end up getting a Diesel bath. You see, depending upon how much fuel is in your tank, there will be fuel that wants to come out of the fuel line. Be ready, because your chances of a date after changing that lift pump dwindle a bunch, unless they are really into the smell of a Diesel cologne. J
After the successful fuel lift system repair you will need to refill the fuel filter cannister - after opening the air-bleed valve, which is the plastic nut on the very top of the metal cap, power up the lift pump, then close the air bleed when the bubbles stop and fuel begins spurting out - if you still get no fuel, you likely have a stopped-up fuel filter - no need to tell you what to do in that event, right?
FYI: after successful fuel flow out the air-bleed, the engine may take a while to restart and run as the Inj Pump begins to draw fuel from the filter, fills internally, then starts pump-up to 1900psi injection pressures.
This is at least enough to get you started on your lift pump journey.
#23
04-24-2012, 01:17 PM
Join Date: Apr 2012
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#25
04-25-2012, 03:22 AM
To clean up a couple unanswered questions:
The tps is part of the app (throttle pedal). There's redundancy built into the app, there's 3 sensors. Failure of one sensor limits engine speed, failure of two further limits speed, failure of 3 results in idle speed only. Failure of any one sensor sets the truck into "limp mode" ie: limited engine speed. Each will set a code.
There have been pmd runaways. I personally know of one gent who had it happen to him. Haven't heard of any since the most recent pmd redesign.
It is unlikely to FSO solenoid will "stick", failure is a more likely condition. It fails closed, there is a spring that forces the pintle on to it's seat. You can pull it out and remove the pintle from the rod end if it is suspect. If the truck runs, replace the solenoid. I had one fail on my truck. When it fails, you won't even get a kick from the truck. It's dead in the water...
I can't remember the year of you truck, but odbi and obdII power the lift pump differently. ObdI powers the lift pump directly from the ops and this is too high a current draw for the contacts in the switch. It is easily handled by using a 40a relay to power the lift pump and simply have the ops trigger the relay. Obii powers the lift pump through both the ops and PCM. The ops doesn't tend to burn out on obdII trucks.
Sent from my iPhone using Tapatalk
The tps is part of the app (throttle pedal). There's redundancy built into the app, there's 3 sensors. Failure of one sensor limits engine speed, failure of two further limits speed, failure of 3 results in idle speed only. Failure of any one sensor sets the truck into "limp mode" ie: limited engine speed. Each will set a code.
There have been pmd runaways. I personally know of one gent who had it happen to him. Haven't heard of any since the most recent pmd redesign.
It is unlikely to FSO solenoid will "stick", failure is a more likely condition. It fails closed, there is a spring that forces the pintle on to it's seat. You can pull it out and remove the pintle from the rod end if it is suspect. If the truck runs, replace the solenoid. I had one fail on my truck. When it fails, you won't even get a kick from the truck. It's dead in the water...
I can't remember the year of you truck, but odbi and obdII power the lift pump differently. ObdI powers the lift pump directly from the ops and this is too high a current draw for the contacts in the switch. It is easily handled by using a 40a relay to power the lift pump and simply have the ops trigger the relay. Obii powers the lift pump through both the ops and PCM. The ops doesn't tend to burn out on obdII trucks.
Sent from my iPhone using Tapatalk
Last edited by great white; 04-25-2012 at 03:39 AM.
#26
06-19-2012, 09:41 PM
Join Date: Apr 2012
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update
Ok. so i got my engine going. wound up replacing my 94' 5068 oddball injector pump with a newer 98 model pump which requires a prom replacement which i got from Kennedy Diesel. that did not fix my no-start problem so i continued trouble shooting with the awesome assistance from you guys, and determined that the problem had to be my pmd or computer. i replaced both, but the real problem was pmd. i had 4 bad ones. of course none of them were new, but the newest one that works is a brand new Dorman with a life time warranty from oreilly's.
By the way, if anyone has a 94' model with that oddball IP, i suggest doing what i did, and upgrading to a newer one. i don't know if it was just that the pump was old, or if the 5068 is just that inferior, but my engine starts much faster now, and seems to have better throttle response.
However, i'm still having tranny limp mode issues. (see original post)
I have replaced both internal and external harnesses. mainly because the internal had a slight leak, and i couldn't live with it.
i have checked resistance on all the solenoids except the pressure control solenoid, and i didn't do that one, because it has 3 terminals, and i did not know which ones to read through, and could not find what the resistance values for it should be anyway. the shift solenoids looked good on the ohms readings.
also, torque converter feels like its operating correctly. just cant get 1st gear or OD.
i have a pressure control solenoid (or switch - not sure what the correct term is) on order.
some questions i have are - can the shift solenoids be faulty even if the resistance looks good?
Is there something i have missed according to this post and the previous ones?
if i'm shifting good from 2 to 3, and tc is locking in 3rd, how likely is it that i have a mechanical/hydraulic problem? or is it more likely that it's still something electrical/electronic.
gettin really tired of taking the tranny pan off,
but i really don't want to have to buy a whole new tranny either.
thanks,
John
By the way, if anyone has a 94' model with that oddball IP, i suggest doing what i did, and upgrading to a newer one. i don't know if it was just that the pump was old, or if the 5068 is just that inferior, but my engine starts much faster now, and seems to have better throttle response.
However, i'm still having tranny limp mode issues. (see original post)
I have replaced both internal and external harnesses. mainly because the internal had a slight leak, and i couldn't live with it.
i have checked resistance on all the solenoids except the pressure control solenoid, and i didn't do that one, because it has 3 terminals, and i did not know which ones to read through, and could not find what the resistance values for it should be anyway. the shift solenoids looked good on the ohms readings.
also, torque converter feels like its operating correctly. just cant get 1st gear or OD.
i have a pressure control solenoid (or switch - not sure what the correct term is) on order.
some questions i have are - can the shift solenoids be faulty even if the resistance looks good?
Is there something i have missed according to this post and the previous ones?
if i'm shifting good from 2 to 3, and tc is locking in 3rd, how likely is it that i have a mechanical/hydraulic problem? or is it more likely that it's still something electrical/electronic.
gettin really tired of taking the tranny pan off,
but i really don't want to have to buy a whole new tranny either.thanks,
John
#27
10-22-2012, 07:29 AM
Wow, interseting reading...
I'm heading to Phoenix Wednesday to buy a barely running '94 Suburban. Owner says it was running great at 264k, and it died, and will only start/run in limp mode w the Optical Sensor disconnected. No difference with the filter bypassed.
So, I bot and had shipped a good used IP from a junk '94, 5068 too, and it should arrive just before I arrive by plane.
I read that I should scribe the PO position, which I will be sure too before I remove it. What fasteners hold on the OS? I will have to buy tools when I get there. I didn't ask the owner if he checked for any codes, but from reading here, sounds like I should check the oil pressure switch and lift pump and crank position sensor. I got the IP just in case the OS doesn't fix the no run/limp issue.
Pictured is my '95 6.5, also from Phoenix. I was putting on a DS144 alternator, the modified bracket in my hand
I'm heading to Phoenix Wednesday to buy a barely running '94 Suburban. Owner says it was running great at 264k, and it died, and will only start/run in limp mode w the Optical Sensor disconnected. No difference with the filter bypassed.
So, I bot and had shipped a good used IP from a junk '94, 5068 too, and it should arrive just before I arrive by plane.
I read that I should scribe the PO position, which I will be sure too before I remove it. What fasteners hold on the OS? I will have to buy tools when I get there. I didn't ask the owner if he checked for any codes, but from reading here, sounds like I should check the oil pressure switch and lift pump and crank position sensor. I got the IP just in case the OS doesn't fix the no run/limp issue.
Pictured is my '95 6.5, also from Phoenix. I was putting on a DS144 alternator, the modified bracket in my hand
Last edited by CORVAIRWILD; 10-22-2012 at 07:49 AM.
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