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Discussion Starter · #1 ·
Hi guys,
I started my truck , a 2005 2500HD Duramax LLY to warm it up after a few days. It started right up with no hesitation. I went to get in after a few minutes and it died. I cranked but it wouldn't start. and it's been 5 days now. Here's the list of things I checked and I know:
1. Batteries are fully charged and I have a charger running constantly to make sure.
2. Filter is new (changed twice) and filter head and pump bulb are in good order and rock hard after 2 pumps. No visible fuel leak anywhere and no air in the low system.
3. FRP Fuel rail Pressure shows above 15000 PSI cranking (assuming rail pressure is good).
4. RPM shows about 130 RPM while cranking (assuming crank sensor is good)
5. FICM Fuel Injector Control Module wirings are in good order, no cuts or breaks and both big connectors receive ignition 12v and both have grounds.
6. Injectors 2 & 7 are both ice picked and connected.
7. All fuses and relays are in working order.
8. I disconnected the FPR fuel pressure regulator and still no start.
9. There was never a RPM surge before.
10. there are no codes at all. If I keep cranking it until it cuts off the power after 30 seconds, I managed to get it to throw two codes: P0611 and P0090 but never both at the same time. And the P0090 was probably because i disconnected the FPR.
To me it sounds electrical. We have air, fuel, timing (I hope) and compression. It doesn't even sound like that it want to start, no fumes anywhere and the exhaust is bone dry. I broke down and sprayed diesel fuel with spray bottle down the intake and she seems to want to fire up, so that tells me that the injectors are not opening up. The fuel pressure is plenty so it has to be electrical.
Please help as this is a farm work truck and the animals are going hungry. I'm stuck down in South America for Covid-19and there are no AutoZones that I can throw parts at it. I have a OBDII scanner, no TECH 2 or fancy things but do have a fully stocked shop here.
 

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Did you install AC/Delco Fuel Filters or Aftermarket? Aftermarket filters tend to allow have bad seals and allow air to enter the fuel system.
Did you Individually Load Test the batteries? A Load test is different from a voltage test and will check the battery cells and their ability to spin the engine over fast enough..
When you pump up the filter head primer and let it sit for 30+ minutes, does the primer button go soft?
 

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Discussion Starter · #3 ·
The filter head is not the original GM, as I couldn't find that style of filter down here so I replaced the entire thing with a new unit from SCANIA 18 wheeler truck. Much bigger filter and parts are available. it primes just fine and I disassembled it and checked everything, it doesn't lose prime. It has no fuel heater but again this is a tropical country so I never had a problem with that. The batteries are brand spanking new, I just replaced them last week- YUASA 850CCA X two of them. The engine cranks pretty fast.
 

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The filter head is not the original GM, as I couldn't find that style of filter down here so I replaced the entire thing with a new unit from SCANIA 18 wheeler truck. Much bigger filter and parts are available. it primes just fine and I disassembled it and checked everything, it doesn't lose prime. It has no fuel heater but again this is a tropical country so I never had a problem with that. The batteries are brand spanking new, I just replaced them last week- YUASA 850CCA X two of them. The engine cranks pretty fast.
Inspect your complete engine harness. Look for any rubbed through wire insulation, rodent damage, corrosion, broken wires, Pin connectors are clean and straight.
Give the harness a few shakes and see if things change during attempted starts.
Inspect the fuse block wires for any damage as well
 

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Discussion Starter · #5 ·
I took the fuse block off today a d didn't see anything. tomorrow I'll tear into every loom and will check everything. What voltage should I have at the injector connectors? Two wire goes to each one, assuming one is high voltage pulse and the other ground?
 

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I took the fuse block off today a d didn't see anything. tomorrow I'll tear into every loom and will check everything. What voltage should I have at the injector connectors? Two wire goes to each one, assuming one is high voltage pulse and the other ground?
It should be around 20 volts, engine at at an idle and up to approx.93 volts to compensate for engine loads and RPM .
The FICM energizes each fuel injector by grounding the command circuit between the FICM and the Injector
 

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Discussion Starter · #7 ·
So there should always be a positive 20v or so available with key on at every injector? Sorry I'm not used to electronic injections, all my diesel engines are direct injections and as long as I have compression fuel and air they fire.
 

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So there should always be a positive 20v or so available with key on at every injector? Sorry I'm not used to electronic injections, all my diesel engines are direct injections and as long as I have compression fuel and air they fire.
Sorry about that, you should see approx. 48v from the FICM with engine cranking to start
 

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Discussion Starter · #9 · (Edited)
Thank you. Looking over the wiring diagram, it's my understanding that each injector has two wires, one is a constant positive shared by all (split in two banks), which is an orange wire connected to Pin 3 of the FICM for left bank and Red/White wire connected to Pin 118 for righ bank and both are marked IGN. Then there are 8 command wires going to each injectors. I'll disconnect the FICM and will check with test light connected to battery positive from the connectors to see if any of these wires are shorted to the ground until they reach the injectors plug.

Then I'll check continuity between all the command wires to see if they're shorted to each other. Am i going in the right direction or complicating my life?

I'm attaching the pin-out reading of the FCIM here for the next poor soul who'd find this post and hope it helps them out.

636761
636762
 

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While you're in there, shake, shake shake, that wiring harness. Many times there is an undiscovered problem because of a broken wire inside the insulation that makes some contact, some of the time, but not all the time.
 

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Discussion Starter · #12 ·
Will do, thank you. I just wanna eliminate the harness issues before I throw a new FICM at it. But to be honest I think it's the FICM because when i started the truck I didn't move it an inch and it just shut off by itself. But again, it's my experience with this truck that every time I thought the worst, it was always wiring issues. The transmission used to do all kinds of weird things until I found the shorted wires and it's going strong for 3 years trouble free, I really hope this is the case too.
 

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shirazdrum
Quick questions....Did the truck originally start remotely, then cut off when you inserted the key ?
Are you reading the codes with a generic code reader or was it a GM dealership reading them ?
 

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Discussion Starter · #14 ·
I started the truck with the key. There are no GM dealers down here, most GM vehicles that are sold here only for export market. This truck is the only one of it's kind down here and I'm it's only certified mechanic. The codes are from my generic OBDII scanner. the P0611 was a pending code and I never saw it again.
 

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If you have a spare key, try it.
I had something similar happen to me last year, but I was driving down the road when the motor died.
I checked it with my generic code reader but nothing showed up. It cranked fine and had fuel pressure. After checking the wiring, batteries and regulator, I gave up and had it towed to a local garage that had a Tech2 unit.
They called me 10 minutes later and asked me to bring a spare key. When I got there, they showed me that it was showing a security code issue and they suspected the chip in my key had an issue. I handed them the spare and the damn thing started right up. They didn't charge me anything, but we had a good laugh at modern technology. They also told me that most code readers will NOT show all the OBD codes.
 

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Discussion Starter · #16 ·
I tried it with my spare key just now, still nothing. It's a base model and the key is a plain old key. I bought 10 gallons of fresh fuel last night just in case the tank is low but the gauge shows 3/4 but it's lied before. If nothing, it will have more fuel behind the pump. I'll report back shortly.
 

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Discussion Starter · #17 ·
Ok, I checked every single connection, every wire, and nothing. There are no codes whatsoever. The tank is full, FRP is above 12000, it has compression,... I have no idea help me out please.
 

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Discussion Starter · #18 ·
UPDATE: I measured orange wire connected to Pin 3 of the FICM for left bank and Red/White wire connected to Pin 118 for right bank. these two wires are supposed to take ignition voltage to each injector. According to OkDually, they should be at 48v give or take. They measure 3.5V and 4.8V respectively with switch on, and cranking, no difference. This is my problem i'm guessing.
 

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Discussion Starter · #19 ·
I hope someone is reading these. I cut the orange and Red/Light-Green wires right after the FICM plug. With ignition on; Coming out of the the FICM, the orange has nothing which If i'm reading the diagram correctly it should be the positive high voltage for the injectors, and the Red/LT-G wire that should be the command wire (negative) has 7v+ on it.

To complicate it a little more, the rest of the orange wire and Red/L-G wire that supposedly go to the injector solenoid #1 both have 12V positive! they should have nothing. Unless someone has an insight, I'm gonna take the FICM apart and look for burnt out components. There's fuel that goes through the unit and i have no idea where, I would really like to have it open while on the truck and spray it down with Freeze Spray and see if i can find something that's over heating. Any electronic Guru around here?
 

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Here is a posting about the proper voltages by engine model Voltage
and here is some pertinent info from that thread that may allow you to understand what is happening:
Injector Operation LB7/LLY( prior to 2006)

The FICM uses two drivers to control each injector.The High Side Driver(HSD) delivers 93 volts updated to 97 volts to the B+ side of the injector.Each HSD powers four of the eight injectors,Connector C1,terminal3,powers injectors1,4,6,and 7(Bank 1). Connector C2,terminal 118 powers injectors 2,3,5,and 8 (Bank 2).

Bank 1 is on the right side of the engine.The firing order is 1-2-7-8-4-5-6-3.

The Low Side Driver,(LSD) grounds the injector to turn it On.There is one LSD for each injector.

A peak-hold strategy is used to open the injectors.It requires up to 20 amps to open the injector and 12-15 amps to hold it open.

If a circuit fault occurs for a single injector, a P0201-P0208 DTC will set.In addition, A DTC will set for the bank that contains the injector.
A fault on bank 1 (1,4,6,7) will set a P1261 and fault on bank 2(2,3,5,8) will set a P1262.

Another link: Duramax Fuel System for Dummies
I am a master tech and formal expert on this site. I have 04…
 
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