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Chevy/GMC 6.2L and 6.5L Discussion of Chevy and GMC Trucks with 6.2L and 6.5L Diesel Engines

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  #1  
Old 07-13-2013, 08:50 AM
ThomasKammermann's Avatar
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Default 6.5L Turbo - Mobilehome - Lift pump Voltage

Hello everybody, I new here, have a or have not a problem with the lift pump voltage.

As I have ever and ever again had shut-offs of the engine, mostly going uphills, I have investigated this for over 2 years now.

(as well as no-start due no Diesel injected and other issues like under ceratin load SES lamp going on)

So far i found and solved:

The PMD was replaced by a DTech relocation-kit including new DTech PMD.
But unfortunately it was forgotten to take out the resistor of the original Standadyne-PDM and to put it in the new DTech PMD.
That i have just done now.

As the lift-pump does pump (I took off Dieselhose directly at inlet of Injectionpump and ran Lift-pump with booster) i checked then the voltage going to the pump while engine is running (soldered 2 wires onto lift-pump power supply cabel, after the plug, layed cabel till driverseat, connected multimeter) and found that the lift-pump only gets 7,3 Volt.

Then I soldered another wire to lift-pump relay directly to see if there is more (as I understand while cranking this relay supplys the voltage to lift-pump; when running Oil-Pressure-Switch supplys voltage to lift-pump) > it's the same, 7,3 Volts.

Now I am sitting here and are wondering: how can that be?

Can anyone understand this or has a idea how to approach further?

thanks in advance

Thomas
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  #2  
Old 07-13-2013, 09:31 PM
racer55's Avatar
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Corrosion in the circuit?

Burnt contacts in the OPS causing high resistance?

The LP voltage should be battery voltage when running so 14.5v or so from charging system.

Also AC Delco ONLY for OPS replacement-aftermarket OPS are often bad out of the box.

Google "OPS relay mod" for long term reliability.
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  #3  
Old 07-15-2013, 01:13 AM
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Thank you for swift help Diesel Wrench :-)

Now that I now that also the lift-pump lust get the max. Alternator-chargin voltage during running of the engine i know what to hunt for.

So i will go and hunt from approx. Wednesday on this "whatever-source-of-voltage-drop"

Thank you indeed Diesel Wrench. Have a nice weekend

---AutoMerged DoublePost---

Meanwhile i found "the answer to my desires" >

Engh Motors - USB-to-ALDL Interface Cable

:-)

I have just yesterday placed a order.

Then I will install a Laptop as "Boardcomputer" and then I will have great fun learning this Software and technology, reading out all the sensors.

What I will do as well is checking all the ground's; the one going from the Batt. - to tha Chassis (just below the cooler) i redid already, the next at the back end of the motor i found already, the others i will need to search for.

Last edited by ThomasKammermann; 07-15-2013 at 01:13 AM.. Reason: Automerged Doublepost
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  #4  
Old 07-21-2013, 11:26 AM
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Instead of swapping the OPS, you can add a lift pump relay - recomended - you can do both, but I would definitely add a relay to be triggered by the OPS - oil pressure switch.
I have 2 vehicles running with bad OPS's. With the relay, the OPS only needs to send out enough voltage to trigger the relay. Then you run a fused wire to feed the power to and from the relay.

Google "dual lift pump relay upgrade".

You should find a schematic by Buddy on some threads. I do not know if the schematic is on this forum. But it would be a good add. IMHO, it's a must do for any vehicle that came stock with the LP running off the OPS.

Since you already have the prestart lift pump relay, you only would need to add one relay as apposed to the dual relay upgrade.

You can show full voltage to the lift pump and still not have it work when sourcing off of the OPS for power. You can have full voltage but the OPS switch sometime will not carry enough amps to run the lift pump. It's easier to diagnose in your case since you are showing low voltage.

As with the OPS use only an AC Delco lift pump if going with an OEM style pump. Get a lift pump for a 1993 - they are supposed to have a little higher flow.
The aftermarket lift pumps do not have a great track record for longevity
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  #5  
Old 07-22-2013, 08:32 AM
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Hello jrsvoie,

Thank you for forwarding informations, I do appreciate your advice very much.

After reading true hundreds if not tousends of pages i found so many unlocigal non-corresponding informations about the matter "which Lift Pump for a 1995?" and "which PMD-Resistor number to be used?" that I really have been confused.

For sure I came to the conlusion:

If LP must be replaced it is - from the technical point of view - very wise to use a ACDelco Lift pump.
My findings where that the originally intsalled ACDelco Lift Pump is a Model EB309; so next I have to find out the ACDelco type for a 1993 > jrsavoie do you have any information about the ACDelco Model for a 1993?

As I have shown in the youtube videos I did take out the original Resistor from the original PMD. Most interesstingly it was a Resistor number 6.
Up to my limited understanding of the functioning/influence of this Resistor it is so that it can be used to kind-of "fine calibrate"/"adapt" the supplyed ammount of Diesel to the InjectionPump in accordance with the vehicels main-use (for example towing; snow pushing . . . ) and the Area the vehicle is mostly driven in (for example Flatlands like the Salt Desert in Utah compared to hilly Areas like for example San Bernardino Los Angeles).
As this Mobilehome has always been in Switzerland since 1995 i would have expected to find a Resistor number 9 installed as overehere it is rather hilly Area.
So I am a bit confused now of this.

Furthermore i am facing the challenge that I have to do ANY and ALL work OUTSIDE at any weather with extremly limited space (Switzerland is a very very very very little and a narrow Country, finding somewhere only a parkingsspace is a constant challenge - even to find a fuel station where i can - without bloking all traffic - fill the 226 Liters Diesel is a challenge).
However, so far I managed during the last winter to undertake lot's of repairs/maintenance/modifications (we had a loooooong winter, temparaturs to minus 18 degrees here) somehow.
So all and everything takes overhere a little longer while for me to do.

The diagnostis software/cable should arrive this week, the widening of the parkingspace I should have finished by then too, then I can repark, level that Baby and continue my investigations.

jrsavoie thank you again for your support
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  #6  
Old 07-23-2013, 09:09 AM
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Ok the 93 AC Delco LP is the best flow/pressure available for a 6.5td stock replacement LP.

The PMD resistor calibrates IP output to a common baseline,all IP's are not created equal and some fine tuning is required at build/rebuild time to equalize the fuel they meter out.

The resistor has nothing to do with hills or flatlands or how the vehicle will be used.
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  #7  
Old 07-29-2013, 11:31 AM
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Thanks Racer55 for your explanations; helped me understanding things better.

Meanwhile i have received and connected GMTDScan.
I have permenantly "49 - Service Throttle Soon Lamp circuit fault"

The engine started and was running OK (no driving) since the installation of the missing PMD-Resistor.

Everytime i started the engine i have noted it in order too see what happens after 50 starts.
Today now i went on to check further on the chassis-grounds.
The one on the leftbside motorblock i redid (0,0 Ohms now) annother one in the P30-chassis-extension as well) Both I have filmed and out to my youtube-channel (channel name: thomas kammermann).

Meanwhile 50 starts have taken place > engine starts no more again (no diesel coming on injectior).

This might be a coincidence or not, i do not know.

However, first i think i should get rid of this "49 - Service Throttle Soon Lamp circuit fault"

Each time I delete this Error withnthe GMTDScan Software it comes back immeadeatly - no matter if engine is running or not (ignition is on).

I appreciate every single idea-of-further-approach - so far i found only this chassis-to-motorblock flatband-woven ground cable (see youtube video) - is there annother one.
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  #8  
Old 07-29-2013, 01:37 PM
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On the regular trucks the rear passenger side of the engine just behind the intake manifold there should be a stud holding a water block off plate-it should have 3 ground wires from the harness fastened to it,2 on 1 ring terminal and 1 with it's own ring.

Your truck may be different but the grounds should still be fastened to the block somewhere close to the harness.

The STS light code could just be a blown bulb in the instrument cluster?

You can force a resistor relearn with scan tech by doing a timeset command.
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  #9  
Old 07-29-2013, 02:22 PM
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Thank you racer55 for your ongoing support; I appreciate it very much, thank you.

I will tomorrow search for the mentioned 3 wires on the passenger side, rear end of engine (towards automatic transmission).

I redid later on today the ground connection of the ground wire coming from the IP solenoid going which is connected ontop of the IP-casing.

If I understud you you correct you say it could as well be the light bulb "Service Engine soon" which is blown causing the 49?

If have just now re-checked the SES light on the Cluster > the light/lamp is actually lighting up when "Glow plugs" is performed ("no-Belt" - "Park" - "Service Engine Soon" - "Glow Plugs" are ON during Glow Plugs-period).

Do I need the full version with license of scan tech to do a timeset command?

THank you again and Best regards

Thomas
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  #10  
Old 07-29-2013, 04:58 PM
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As far as I know you do need the full version of scantech to do TDCO relearn but I am unsure if timeset will work in the free version?

You miss-understand me about what light may be burnt out-there should be a service throttle soon light in the dash,and if it is burnt out it could be the cause of the code?
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