I have a 2007 GMC 3500HD 4WD Crew Cab SLT with a 6.6 Diesel Duramax Engine. Changed the fuel filter the other day and when I tried to start it, it turned over extremely slow for a couple of cranks and then started fine....like a nearly dead battery or for whatever reason, struggling to turn over...but then it started fine. Drove it around, no problems. Parked it over night, started fine in the morning. Then drove for about 1 mile and parked it for 3 hours and went to start it and it did the same slow crank, but then started. It has been doing this ever since randomly. Took it to a GMC dealer who thought problem was starter. Put new starter on it and it still did the same thing. Dealer tested batteries (both only 6-months old)...even tried one new battery and still did the same thing. Dealer has started searching for bad connections but so far nothing. I am looking for ideas...particularly strange that this started with first attempt at starting after changing fuel filter. Help.
6.6 Diesel Cranks Hard Randomly
- Thread starter sgarwood
- Start date
Or check all of its connections yourself. Sounds like a loose contact point.
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Mine did that too, I found that the bracket that ties the two batteries together to ground was loose. If it's like the LLY, there is a jumper cable ground point on the end of the bracket on the driver side near the battery. A single bolt attaches it to the motor. Tightened it and problem fixed!
I had a failing Optima battery and my truck would do this too. Sometimes would just click. Go out, wiggle the cables and slap the batteries around, and it would crank great. Two new batteries fixed it.
Like was said, check the connections yourself, and ensure the cable ends are clean and corrosion free. This really sounds like an electrical issue.
Since it started after the fuel filter, I would be suspect of the passenger side battery and cables, as those are what would get bumped during a filter change.
Like was said, check the connections yourself, and ensure the cable ends are clean and corrosion free. This really sounds like an electrical issue.
Since it started after the fuel filter, I would be suspect of the passenger side battery and cables, as those are what would get bumped during a filter change.
To all that responded, thanks for the suggestions. Truck is still at the dealer who has tested batteries and even tried a new one. Dealer claims they did find one poor ground and fixed that too. I will print out your suggestions and take them to the dealer on Monday. Just one question I still have dealing with the fuel filter change....since it was first time I changed this filter myself, I research on YouTube to make sure I knew how to do it. To make certain I knew where the primer pump was, the very first thing I did was pushed on it a couple of times to convince myself that was the pump...I also confirmed I found the bleed screw. So my questions is this, if there was some water in the old filter but not enough to trigger the warning light or cause engine to run poorly, could I have pumped water into the engine when I pushed the primer a couple of times? Remember, I did this prior to removing the old filter. If I did pump some water into the engine, what damage could this have caused? Another mechanic said I could have a bad head gasket allowing some engine coolant to enter a cylinder and if that cylinder happens to be in the compression stroke when the engine is turned off, the next time the engine is started, it will struggle to turn over. What do you think?
The primer is perfectly safe to use. If your filter was 100% full of water, maybe you could've forced some through, but that's basically impossible.
I think the hard starting is unrelated to the fuel filter.
When your truck does start hard, does it smoke white for a while afterwards? Because when I had a cracked head and was leaking coolant into the cylinder, it would smoke for a while after startup.
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I think the hard starting is unrelated to the fuel filter.
When your truck does start hard, does it smoke white for a while afterwards? Because when I had a cracked head and was leaking coolant into the cylinder, it would smoke for a while after startup.
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I didn't notice any smoke but admit I didn't specifically look for any. I did look for bubbling in coolant tank which I was told would happen if head gasket was bad. I found no bubbles. GMC dealer service department hopefully looked for this too but they seemed convinced it is a mysterious electrical problem. Frustrating for sure now that dealer service department has more than 2-days of labor into this and still has no idea what the problem is. All they know for certain is that a new starter and 1 new battery didn't solve the problem.
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You need to get your truck away from that dealer, they are just shotgunning the problem, changing stuff to see if anything works. You will have nothing but a big bill and some new stuff you didn't even need! Take it to a competent shop or different dealer. better yet, try cleaning all the ground points yourself and using a multimeter to check for voltage drops across grounds and +12V cables. There are a bunch of utube vids on how to do this stuff. Dealer should know you NEVER just replace one battery on these trucks, even if one LOOKS good. Better for you to learn than spending good money for their "tech" to learn on your truck...!!!
I agree with ALLY Fox.
Some one need's to check for voltage drops across all the cables. If they get corrosion inside them this can increase the resistance and cause the hard start issue you describe.
All the connections need to be clean and shiny on the mating surface so they make good contact.
As mentioned you can't replace just 1 battery since they run in parallel.
Some one need's to check for voltage drops across all the cables. If they get corrosion inside them this can increase the resistance and cause the hard start issue you describe.
All the connections need to be clean and shiny on the mating surface so they make good contact.
As mentioned you can't replace just 1 battery since they run in parallel.
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The batteries actually run in parallel. Series it would be OK to replace just one. But because they are hooked in parallel (both positives are tied together), if one has a bad cell, the good one will drain into the bad one, shortening the life of the good one in the process.
If they were series (positive to negative), it would be 24 volts, like the military Hummer and stuff.
If they were series (positive to negative), it would be 24 volts, like the military Hummer and stuff.
Check the voltage drop on the positive cables. Ground cables. Cable going to the starter. Will need a dvom that has a min max feature and a fast response time
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Well guys...truck is fixed! Turns out the UBEC (underwood bus electrical center) was the problem. Dealer never experienced this issue. They contacted GM who told dealer mechanic to check it and how to check it and apparently that was the problem. Dealer supposedly waived many hours of their time charging me for a total of 5.5 hours of labor after having truck for 5 and a half days. Total bill came to $940 of which the part (UBEC) was around $280.
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Never heard of an entire underhood fuse block failing intermittently unless it's been damaged or splashed with salt water. The 175 A fuse can fail occasionally and a faulty "ignition" switch can mimic a bad fuse block and drive you crazy. Glad (hope) that fixed your problem, my hat's off to that dealer for making things right for you.