Stock 05M6 had intermittent start now no start
09-28-2018, 03:39 PM
#1
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Stock 05M6 had intermittent start now no start
My 05M6 started developing an intermittent start problem about a month and a half ago. It would start fine in the morning and when started after a short down period. If it sat for 45 minutes or so it was a 50/50 possibility of it starting. The first couple of times it would catch but run rough at 200-300 rpm before dying. It has been sitting for three days and it would not start when I tried to start it today. The battery is only 6 months old and the crank is strong. It is a bare stock LS2.
09-28-2018, 04:23 PM
#2
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Hey Ben !!...your a Corvette owner so you really shouldn't be calling yourself "Old" !!...LOL !!...C5 owner here but no drive ability issues going on in my forum today. Any way of getting a scan tool hooked up to look at some data PIDS or maybe see if there are any DTC's present ??...HARD to make a accurate diagnosis without some testing involved. Any issues of starting when the car is cold/hot I'm thinking maybe an ECT sensor. The engine might think it's still cold after the engine is warm so it's getting that "extra" fuel when restarting...that could be giving you that rough idle you speak of... running rich. would be nice to look at those fuel trims !!
Last edited by C5 Diag; 09-28-2018 at 04:25 PM.
09-28-2018, 05:18 PM
#3
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Hey Ben !!...your a Corvette owner so you really shouldn't be calling yourself "Old" !!...LOL !!...C5 owner here but no drive ability issues going on in my forum today. Any way of getting a scan tool hooked up to look at some data PIDS or maybe see if there are any DTC's present ??...HARD to make a accurate diagnosis without some testing involved. Any issues of starting when the car is cold/hot I'm thinking maybe an ECT sensor. The engine might think it's still cold after the engine is warm so it's getting that "extra" fuel when restarting...that could be giving you that rough idle you speak of... running rich. would be nice to look at those fuel trims !!
09-28-2018, 05:25 PM
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72 ??...you’re young !!...how about this...unplug the MAF sensor and see if it will start...it WILL throw a CEL but it’s because of the unplugged MAF...the car will run off the MAP sensor (speed density)....just see if that works...for now anyway !!
09-28-2018, 07:09 PM
#5
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I went out to see if it would start about a half an hour ago. I've read in another thread about hitting the start button without depressing the clutch. Did it and heard the fuel pump cycle. Pushed in the clutch, pressed start button again and car started. Apparently there is a fuel pressure loss. Leaking injector or pump backflow valve?
09-28-2018, 07:30 PM
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I went out to see if it would start about a half an hour ago. I've read in another thread about hitting the start button without depressing the clutch. Did it and heard the fuel pump cycle. Pushed in the clutch, pressed start button again and car started. Apparently there is a fuel pressure loss. Leaking injector or pump backflow valve?
09-30-2018, 03:08 PM
#7
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Yes !!...pump has a 2 second prime. Only way to check fuel pressure is with gauge at fuel rail. You’d have to pressurize the rail and see if pressure holds...don’t know numbers for C6 for pressure drop...if pressure drops there can be a few places where you can be losing pressure in fuel system. If you get to that point give me a holler !!!
It started fine about two hours ago when I made a run to the grocery store and fired right up when I left the store. What can cause an intermittent crank but not starting condition?
09-30-2018, 03:48 PM
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Well the only things we would be looking for is spark and fuel. Unless you can do some testing when it’s not starting you’d only be guessing and that can start adding up as far as replacing parts is concerned !!
09-30-2018, 04:31 PM
#9
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You're correct. Throwing parts at an intermittent problem is a hit and miss proposition that can get very expensive. I don't see how the spark or fuel would be that intermittent.
09-30-2018, 04:50 PM
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I just helped someone on this forum this week that was having a no crank no start condition...we shot some propane into the engine to see if it was fuel delivery...no good !!...checked spark and no spark...MMM ??...had 12 volts to the coil but we checked for ground with test light connected to battery POSITIVE...no ground !!...I believe that the C6 has the same ground as does the C5...G107 I believe is the number and it’s on the back of the left cylinder head...now someone correct me if I’m wrong...OP couldn’t find it...the threads were there in the head but no ground wire and bolt !!...I suggested just connect a piece of wire from engine ground to the ground wire at the harness connectors on both sides...BOOM, the car fired up...check for a bad ground as far as ignition goes...now as far as the pump it’s not about holding pressure but the pump operation being intermittent !!...a few times on other cars just got the pump to start working smacking in the fuel tank while cranking !!
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Old Ben (09-30-2018)
09-30-2018, 05:17 PM
#11
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I just helped someone on this forum this week that was having a no crank no start condition...we shot some propane into the engine to see if it was fuel delivery...no good !!...checked spark and no spark...MMM ??...had 12 volts to the coil but we checked for ground with test light connected to battery POSITIVE...no ground !!...I believe that the C6 has the same ground as does the C5...G107 I believe is the number and it’s on the back of the left cylinder head...now someone correct me if I’m wrong...OP couldn’t find it...the threads were there in the head but no ground wire and bolt !!...I suggested just connect a piece of wire from engine ground to the ground wire at the harness connectors on both sides...BOOM, the car fired up...check for a bad ground as far as ignition goes...now as far as the pump it’s not about holding pressure but the pump operation being intermittent !!...a few times on other cars just got the pump to start working smacking in the fuel tank while cranking !!
09-30-2018, 05:23 PM
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09-30-2018, 06:02 PM
#13
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And also thinking about the fuel pump relay...maybe that’s going bad...on the C5 you can swap out the fuel pump relay with the horn relay to troubleshoot...can look at that too...maybe swap out the relays and see if it comes back...just a thought...maybe try that...no money involved !!
Last edited by Old Ben; 09-30-2018 at 06:03 PM.
10-01-2018, 05:14 PM
#14
Instructor
It's your fuse box. I have an 05 with 63k and I went through the same stuff. You can hit the fuel pump relay down and it will start, Mine would either just just turn over and no fire or would barely run and crap out.
10-01-2018, 05:54 PM
#15
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Thanks for you reply. Will be checking the fuse along with the relay.
10-01-2018, 05:59 PM
#16
Instructor
It's the box under the hood. 05 are notorious for this happening. You can hit the fuel pump relay down and it will work for awhile. Then you will need to do it over and over again. I was stranded until I finally figured out what it was. I carried tools around with me.
11-06-2018, 03:01 PM
#17
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Did the swapping of relays when it would not start and it would start right up. Been doing that for the last month.
I'm sort of reluctant to taking apart the fuse box so would putting dielectric grease on the relay tabs solve the intermittent contact problem?
I'm sort of reluctant to taking apart the fuse box so would putting dielectric grease on the relay tabs solve the intermittent contact problem?
11-06-2018, 03:19 PM
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Last edited by C5 Diag; 11-06-2018 at 04:41 PM.
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Qshiplover (02-17-2020)
11-06-2018, 03:26 PM
#19
Race Director
Usually if the fuel relay is a problem you'll see a dark burn mark on top from overheating.
11-06-2018, 04:09 PM
#20
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Buddy, Hope this video helps...you might have to do this !!...I think you can do this...not too difficult...now when it doesn't start it's either pin 87 or 30 of the fuel pump relay that's not making a good contact in the fuse box ...or can even be the ground side of the 12v feed circuits...one is your control side feed and the other is the load side feed...can't remember which is which...if you want to check this yourself I can maybe do a short Youtube video for you !!
https://www.youtube.com/watch?v=M3-vK06PaXQ&t=376s
https://www.youtube.com/watch?v=M3-vK06PaXQ&t=376s
Last edited by Old Ben; 11-06-2018 at 04:17 PM.