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has anybody seen this before ? Every morning (winter or summer) when I start the Vette (2007 base model, 6.0) it cranks for some seconds before it starts. If I then turn it off an on again, it starts right up. Leaving it parked for some hours after driving - same error again.
I have no DTC´s in the Tech2. Cranksensor and Camsensor have been replaced, both are AC Delco Genuine parts with the hologram stickers, no difference. I enclose a short video....
Thanks in advance and greetings from frosty Germany.
You're back !!...First thing is let the car sit overnight and with your Tech 2 the ECT and IAT should be within 5 degrees (3 C) of each other and also the outside air temp....I would next check fuel pressure so you need a fuel pressure gauge...command the fuel pump on with the scan tool a few times and the pressure should be 55-62 psi...then shut the fuel pump off...the pressure should decrease to no less than 51 psi after 5 minutes...you can also see if you get an RPM reading with the Tech 2 during cranking to see if you are getting a crank sensor signal....that is a rather long crank…did you ever get that relay issue resolved ??
yes I am back. Life got in the way of my Corvette endeavours, but now I hope I can spend more time with the C6 (and C4) again.
Thanks for you fast reply, I will check what you described, Might take a few days to borrow a fuel pressure gauge from my neighbour.
As for the relay, I installed a really bad solution. First I had a switch in the glovebox to turn on the relay manually. And Off when parking. Very cumbersome, and sometimes I forgot to do it alltogether. After a while I had the idea to take power from the heated seat fuse in the footwell which incidentally gets power when the start button is turned on and loses power when the car is turned off. So I put that to the relay side after checking that the power draw is somewhat minimal (Below 1 amp I seem to remember) Voila - car starts and turns off as usual. I still see it as a temporary solution, but it is really hard to find anybody here in Germany who can properly diagnose (or even program a new) module for that car as it is as exotic as a Ferrari over here. This summer I will disassemble the whole thing again and check if there is perhaps a broken cable coming from that module behind the right fenderwell to the fusebox. I am not 100% sure I checked the correct cables last time.
yes I am back. Life got in the way of my Corvette endeavours, but now I hope I can spend more time with the C6 (and C4) again.
Thanks for you fast reply, I will check what you described, Might take a few days to borrow a fuel pressure gauge from my neighbour.
As for the relay, I installed a really bad solution. First I had a switch in the glovebox to turn on the relay manually. And Off when parking. Very cumbersome, and sometimes I forgot to do it alltogether. After a while I had the idea to take power from the heated seat fuse in the footwell which incidentally gets power when the start button is turned on and loses power when the car is turned off. So I put that to the relay side after checking that the power draw is somewhat minimal (Below 1 amp I seem to remember) Voila - car starts and turns off as usual. I still see it as a temporary solution, but it is really hard to find anybody here in Germany who can properly diagnose (or even program a new) module for that car as it is as exotic as a Ferrari over here. This summer I will disassemble the whole thing again and check if there is perhaps a broken cable coming from that module behind the right fenderwell to the fusebox. I am not 100% sure I checked the correct cables last time.
OK, sounds good…we can address that relay issue again once this starting issue is fixed….I’d have to reread what was done with the relay…don’t remember if it was a power or control side issue.
It was relay 44 Powertrain ignition 1 in the underhood fusebox
btw, the long cranking started long before the relay 44 modification, so I would rule that out as a culprit.
Last edited by C4Oliver; Feb 20, 2025 at 12:43 PM.
If it was the “Ignition 1 Relay control circuit (terminal 59 C1 connector) at the ECM was that checked??…could just be a broken wire between the relay and the ECM…if you back probe that terminal with test light connected to B+ it should light when pressing the start button…may be a bad ECM driver which means a bad ECM…let me research and see if there are any inputs that will ground that circuit.
I looked up my documentation of what I did last summer when she didn´t want to start at all. I pulled off the right front wheel and inner fender and got to the connector of the ECM. Probed continuity between ECM 59 (black/White) to fuse block F14 of relay 44 - checked out good. Thats when I established first the power switch and later on the heated seat fuse solution......
There seem to be 3 people in whole Germany who can change and re-learn a new ECM, so that was and is no option...
Bought the car 2 years ago for 21K € and invested about 12K € since then. In retrospective I should have forked out more money when buying it, but that ship has sailed...... still love that car very much
Checked ECT (9 °C), IAT (11 °C) and Ambient Air Temp (5°C), so that checked out OK. Then checked RPM display in the Tech2 while cranking (around 140 RPM until it fired) - So Crank Sensor does it´s work. Then, fuel pressure : it jumps to 54 psi when turning on the fuel pump, but goes back to zero immediatialy afterwards. It´s the damn anti-drain back valve in the fuelpump assembly which is practically new ! Did the following check : pressed the startbutton without depressing the clutchpedal, fuel pump pumps for some seconds, car doesn´t try to crank. Then depressed the clutchpedal directly afterwards and started the car - started right up. I would say, this is proof for the bad anti-drain back valve.
Told this to my trusty mechanic - he suggested putting in an external anti-drain back valve. What do you think, could this be a thing to do ?
Anyway, many things, I was worrying about the coldstart problem nearly a year and always thought it was a bad sensor......
Greetings from Germany
Oliver
Last edited by C4Oliver; Feb 21, 2025 at 12:30 PM.
The anti-drain back valve and check valve are one in the same. I think you know that but just putting it out there to clarify. I would do the new fuel pump module, it's much easier and a cleaner install. And you know it will work. Putting in your own check valve will only keep pressure on the fuel line forward of where your land the valve. Everything before the valve will have no pressure. So the question now becomes where can you fit the valve in the system and can the fuel pump pressurize the line fast enough to maintain pressure at start-up? I'm thinking no, only because the have 35 years experience in fluid mechanics as a Mechanical Engr.
I would still want to check that an injector is not leaking before confirming that the check valve is bad…there are 2 ways to check but I use my Mityvac and pump 15 psi into the fuel rail and see if it bleeds down as shown below on a C5 I did last year…you may be able to pick up the 2 hoses with shut off valves on them and this is the OEM tooling from Kent Moore who supplies GM with this type of equipment..you can make this yourself with some fuel lines and shut off valves with the 3/8 and 5/16 fuel fittings.
Oh no, replacing the fuel pump again will kill my mechanic and my wallet...... I wish it would be on my C4, so easy to reach, but on the C6 it's a nightmare.
i will try and find the hoses for the leakdown test, somebody must have them around here......
For now I am perfectly happy with the 2times start button pressing, wish I had tried that earlier but I was so fixated on the Sensors.....
I would still want to check that an injector is not leaking before confirming tgst the check valve is bad…there are 2 ways to check but I use my Mityvac and pump 15 psi into the fuel rail and see if it bleeds down as shown below on a C5 I did last year…you may be able to pick up the 2 hoses with shut off valves on them and this is the OEM tooling from Kent Moore who supplies GM with this type of equipment..you can make this yourself with some fuel lines and shut off valves with the 3/8 and 5/16 fuel fittings.
One would expect low STFT and LTFT if it were an injector leaking, correct?
One would expect low STFT and LTFT if it were an injector leaking, correct?
If the car sits overnight the fuel probably has evaporated and if not raw unburned fuel would not be picked up by the O2 sensors anyway to affect fuel trims...if you had no spark in the combustion chamber for instance you would have a lean mixture and not a rich one as people may think.
If the car sits overnight the fuel probably has evaporated and if not raw unburned fuel would not be picked up by the O2 sensors anyway to affect fuel trims...if you had no spark in the combustion chamber for instance you would have a lean mixture and not a rich one as people may think.
My thinking was: if the engine was running, a leaking injector would cause a rich fuel mixture, the upstream O2 sensor would see that and start pulling fuel from the base map in order to lean out the mixture. Or is it not that sensitive?
Long cranking time on coldstart
