6.5 suburban

[Burnsey94]

I have a big issue with motor ir starts up runs good sometimes a little hard to start then after it warms up it stalls and runs like crap everything pointed to ip so i replaced that and the pmd and it still does the same thing I'm lost can anyone give me Any ideas

[a5150nut]

How's your fuel supply?

Lift pump working?

Fuel filter good?

Have yo used a clear return line to look for air in fuel?

Fuel shut off solinoid working properly?

[racer55]

Anytime you have a temp related problem consider the ECT or coolant temp sending unit.

You also have to tell us what year truck you are working on.

[Burnsey94]

Its a 94 and fuel is good pump is workin good and new filter and bled all air out

[racer55]

I still say the coolant sensor is involved likely,but how was the electronic timing set after the IP replacement?
Who did the TDCO relearn?
What scan tool was used to to command the TDCO relearn?
What is the new TDCO value?
Was a PMD resistor installed in the new PMD or was it part and parcel of the IP?
Are there any trouble codes to report to us to make diagnosis easier?

[DmaxMaverick]

What IP model # was installed before the problem first began? What IP model # did you replace it with? Was the PCM replaced or modified in any way during any of this time? It may be important, being a 1994 model year.

[racer55]

What IP model # was installed before the problem first began? What IP model # did you replace it with? Was the PCM replaced or modified in any way during any of this time? It may be important, being a 1994 model year.

The 5068 IP was only on F vins and mostly 3500's so while unlikely may still be a concern on a burban?

[DmaxMaverick]

The 5068 IP was only on F vins and mostly 3500's so while unlikely may still be a concern on a burban?

It is a factor, if the Suburban is a 2500, or if the wrong pump or PCM is installed. The VIN will indicate which PCM and pump should be installed. It doesn't indicate which is actually installed.

The 1994 VIN "F" pump/PCM is the only year model EFI system that isn't interchangeable with anything else.

Also note, if the PMD resistor isn't present, or is "out of range", it will (eventually, not always immediately) set a DTC and some minor running issues (defaults to preset fueling table). It won't cause a stall, in itself. The diagnostic series runs infrequently, like 50 warming cycles, so it can take a while to actually show up in many cases.

[racer55]

The 50 cycle resistor sampling is OBDII only ASFAIK-no documentation I have ever come across indicates that is also a function with OBD1.

[DmaxMaverick]

Documented or not, that's what it is. I don't know what it is, exactly, but 50 is about right, or close to it, in my experience. I don't think that's the problem here, regardless of how it works. It won't cause a stall, and will always, eventually, cause a DTC, if it's wrong or missing. The only exception would be if the PCM is modified to omit the diagnostic process.

In any case, the resistor doesn't actually DO anything. It is an external, after-assembly calibration adjustment tool. It's value is read periodically, but the resistor has no actual operational function. There are at least a dozen ways Stanadyne could have accomplished this, but this is what they chose. I would have done it much different, if I were the engineer there. I've disassembled a few 6.5's, and had a collection of resistor cards found in the engine valley, all apparently dropped in there by techs (a DIY'er would spend the time to find it, not having another on the shelf to replace it). I had a 1994 2500HD pump replaced once at a dealer (warranty, back when pumps were routinely replaced for PMD failure), and didn't find out for months it had no resistor installed. Found it in the valley.

[phantom309]

I,ve posted before ,.. so its a hands on experience,..
Once and for all,.
Please read and remember,.
The pump on my K2500 'F' engine failed,. no start.
I Replaced it with the 5068 pump from my C3500 hd dually (the motor grenaded)
It works fine,. NO other changes,..
Truck has larger down pipe, no muffler and a very large cone filter for intake air,.a higher pressure lift pump, and a large fuel filter,.

I,m tired of people that have NO hands on experience simply regurgitating internet myths,.and it seems on this forum,. if it's not stock,.it's no good, and it likely won't work.

I have posted numerous times that the engine has much more power than it had stock,.and fuel mileage is good when i i drive it respectfully,.

THE only "problems" i have is if i blast up a hill too hard,(without down shifting) it sets an SES.
The reason for this is i have a screen door spring on the wastegate, and it overboosts and the stock computer doesn't like it,.

The trans shifts a little too soon for my liking because it takes less TPS input to get the fuel it needs,.when towing i shift manually,.and I added a manual lockup switch to help with deceleration, and lockup sooner when the trans is cold,.
I also added a pot resistor to the force motor in the trans and i can increase the shift firmness with a turn of the dial,.

I did NOT use the 5068 chip or ecm,.i have a "bastard" unidentified chip in the spare ECM but i,m not using it,. it really adds lots of fuel, and will rev the motor to 4400 or so,.but the motor is old and i need it for a daily driver,.and i don't need 26psi of boost,

It runs away from any other 6.5 diesel its ever been up against,.and will stay with a stock early duramax,.


Nick

[DmaxMaverick]

Phantom, not sure exactly what you're saying here. To which myth are you referring? Stock (anything) or not, the discussion is about 1994 HD pump and PCM compatibility. Of course, if you replaced your 1994 VIN "F" pump, with another 1994 VIN "F" pump, it would work (or should work), with no problems, regardless of the "chip" installed. That's not in question. The confusion begins when the foggy definition of the 2500's come into the picture. The 7200 GVWR 2500 will/should be VIN "S", while the 8600 GVWR 2500 will/should be VIN "F", but is specific to the pickups. The lines aren't so clear with the Suburbans, but the VIN will/should determine the calibration, and emission equipment (LD or HD), which determines the pump requirement. If it's a California emissions Suburban (and some New England, perhaps), all bets are off. I've seen both, in like-new condition, side by side, with both configurations, and no rhyme or reason for it. If it's a Canada delivered truck, it may be less clear yet, as they weren't bound by US DOT/EPA requirements. It may be specific to actual build/delivery dates, such as a 1994 model with a 1993 build, compared to a later 1994 build. The Duramax trucks saw the same type of emission requirement switch-up in several year models (2004, 2006, 2007).

[phantom309]

The Myth i am referring to is that a 5068 pump needs a dedicated ecm or chip to run it,.
My truck IS a canadian, truck and its an 8600 lb truck with an F engine,
I,m very pleased with the performance of the vehicle,.

As to you bringing in the emissions card to the discussion,. i still don't see how that would make a difference, The IP isn't complicated,. once its energized, and rotatating it pumps fuel,. end of story,.
I fail to see how the ecm could make the motor "run" like crap because it is controlling a different flow rate IP,.driveability shouldn't be an issue.
Over fueling a diesel has to be such a huge percentage over stock before driveability gets noticeable. A rich running diesel just produces more power,. it doesn't run "worse" I know i,ve turned up just about every diesel i have ever owned,. from 5.7 olds diesel to cats cummins and series 60's,.
The "bastard" chip i have was being used in a 1995 suburban ecm that was an S engine,.it runs an F engine with no hassles at all,. it likely has the emissions provisions deleted or turned off,.

I have yet to meet a 6.5 diesel owner that is more concerned with emissions rather than performance and or economy,.;)

[racer55]

How do you say it runs great and then provide a laundry list of half measures and workarounds to deal with issues you have?
Trans not shifting right,overboost-not related to the IP or chip but a self imposed issue ect.

The fact remains that a 5068 IP performs better with a 5068 ECM chip and vice versa-the more common problem is when folks put a 5521 IP into a truck that originally had a 5068,drivability issues do come into play in that instance.

Your real world experience has nothing to do with that situation since you went the other direction.

[DmaxMaverick]

If that's the myth, then I've not heard it. A misunderstanding perhaps, but not a myth. The reality is opposite, actually. It's the chip, not the pump, that's the problem. You can use a 5068 pump on any EFI 6.5. It's the 1994 HD PCM that's unique, not the pump (other than it accommodates the 1994 PCM calibration). 1994 was a first-year release, and whatever the reason was for the issue, it seems they abandoned it by 1995 model year.

If you able to run "any" pump on 1994 HD without issues, then the "chip" programming has been modified to eliminate the issue. Many, if not most aftermarket power chips do this. Kennedy offers a chip for the 1994 "F" that divorces the marriage between the PCM and 5068 pump, but is "stock" otherwise.

Sure, the pump rotates and moves fuel, but that's not where the story ends (or begins, for that matter). The DB pumps work that way, to some degree, but the DS pumps, and the system as a whole, is entirely different. It's ALL about the programming. The pump is a dumb slave with no external mechanical control input. Bad (or no) programming can make an engine run bad, or not at all. In the same manor aftermarket programming helps make more power, it can just the same make an engine run bad, or not start at all. All the mechanical part of the pump does is make the fuel available. It's the electronics that control when (timing) and how much (dwell), according to dozens of factors, all calculated by the program table. The injectors determine the pressure.

[phantom309]

How do you say it runs great and then provide a laundry list of half measures and workarounds to deal with issues you have?
Trans not shifting right,overboost-not related to the IP or chip but a self imposed issue ect.

The fact remains that a 5068 IP performs better with a 5068 ECM chip and vice versa-the more common problem is when folks put a 5521 IP into a truck that originally had a 5068,drivability issues do come into play in that instance.

Your real world experience has nothing to do with that situation since you went the other direction.

A laundry list of half measures and work arounds,.,..??? bit of an exaggeration on your part,....

to describe things more accurately one might say for optimal performance a modified transmission shift point table might be in order and i would agree,.

The waste gate spring is just laziness on my part which i am honest about,.the vacuum pump kaffed,. so i added a spring,.
The other GM8 turbo i have i ground the exhaust side out smoothed things off and welded the gate closed,.it worked for ME,.no it wasn't optimal, but i knew what i was dealing with,and how to drive it,.

The trans shifting a little too early for MY liking because it has more torque ( notice the use of the words A LITTLE)
Under normal driving, its not noticeable,. anyone else that drives the truck never notices,. so perhaps i should say I notice it when tps input is over 50%,.i can improve the performance by holding it a little longer in each gear,.i guess thats my laundry list. If WOT is used the trans shifts at max allowable rpm determined by which ever ecm i,m using,.so wot tables are fine.

My spare ecm is the original 5068 ecm from my dually,.so its obvious it doesn't need a dedicated 5068 ecm to run properly,the trucks' original 5521 ecm is working just fine,..i have installed the 5068 ecm a couple of times with its performance chip,. it does not set over boost codes because of the modified programming,.and i,ve swapped the chip into the 5521 ecm in the truck, no discernible difference, it's just easier and quicker to swap ecm's than chips,.
I,d pretty much say that there's no difference in the ecm's,. just the chips,.

My point being,. that either ecm runs the truck just fine,.because it has more power etc, as i stated i prefer to shift it manually when i,m towing or working the engine hard,.an honest observation which has become a laundry list.

Explain exactly please how swapping a 5068 for a 5521 causes driveability problems,.or conversely where someone inadvertently swapped a 5068 ecm into a truck that had a 5521 IP,.. and what the problems are,. and where i can actually read about the problem(s),. and how it was rectified,.I am curious,.

I believe the OP in this thread has an air in fuel problem,.or possibly a bad ignition switch,. because the symptoms are still consistent even after an IP change,. which brings me back to the reason i posted in the first place,. that in my opinion the wrong IP will make little difference to driveability, but it will make a difference to max power output. As i said it seems to be a favourite possible problem to quote,( the infamous 1994 5068 pump myths). but i,ve yet to see any real world data to back up the claims, but i,d like to.

Nick

[Robyn]

We owned a 94 Burb 2500 (8600gvw) truck from new, and it came with a 5068 IP on it.

The Dahoooley has a 5067 on it, but it's anyone's guess about what it came with.

Missy