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I have a twin 340lph fuel setup with check valves. Since a few months ago, it takes considerably longer for the car to fire and run upon cranking. It used to start up perfectly at one point. But not so much anymore. When I turn the electronics on, I see the fuel pressure gauge prime to 58 psi immediately. Withing 30 seconds, it is down to 45 psi and slowly dropping. Is this the result of bad check valves? My system has two.
I have a twin 340lph fuel setup with check valves. Since a few months ago, it takes considerably longer for the car to fire and run upon cranking. It used to start up perfectly at one point. But not so much anymore. When I turn the electronics on, I see the fuel pressure gauge prime to 58 psi immediately. Withing 30 seconds, it is down to 45 psi and slowly dropping. Is this the result of bad check valves? My system has two.
At 45 psi the car should start up fine.
Check for leaking fuel injectors? When it does finally start up are you smelling unburnt fuel?
It will crank for about 5 or 6 seconds. Sometimes, I'll hear a pop and a stumble and then it will finally fire up. Sometimes, I'll turn the electronics on then off about 3-4 times first. This will ensure that it cranks for about 4-5 seconds and fire up. Occasionally, it will take 2 attempts to start the car. It always starts, and runs fine after it starts.
Sounds like the ecm is not getting a signal to turn the ignition on.
I thought about this, but if this were the case, it wouldn't start at all...
I was getting a P0340, P0341 code after installing my new motor. That turned out to be a wiring problem that was corrected. This began shortly after my car threw the blower belt and overheated. There was no damage but immediately after the incident, the car started up perfectly and ran perfectly. A few days later, the hard cranking began. This occurred last December. The car has since been dyno'd twice and makes shy of 900. It behaves nicely on the street.
My research showed that some C6 cars needed a case relearn after getting this code. As this began after installing my new 416, is a case relearn necessary?
0340/0341 are cam sensor DTC's...a failing cam sensor can cause "longer than usual" crank times !!...what wiring issues did you find ??...the sensor is a 3 wire Hall Effect sensor...I'd look at replacing the CAM sensor with an OEM if the wiring is good...don't use an aftermarket one !!....and it's called a "crankshaft variation relearn"...can be done with any bi-directional scan tool !!
0340/0341 are cam sensor DTC's...a failing cam sensor can cause "longer than usual" crank times !!...what wiring issues did you find ??...the sensor is a 3 wire Hall Effect sensor...I'd look at replacing the CAM sensor with an OEM if the wiring is good...don't use an aftermarket one !!....and it's called a "crankshaft variation relearn"...can be done with any bi-directional scan tool !!
I bought 2 different cam sensors online and replaced it. When I replaced the motor, I was getting this code, so I bought the new pigtail and sensor from GM. I took the car to Redline Motorsports and the tuned it and got it running perfectly. The code remained however ..I took the car back for a retune, and that when Redline found that the wires in the pigtail were mixed up. They corrected it but the codes came back. I'm not sure what to do next.
YES !!...anytime a motor is replaced you have to do the crank relearn...the crank sensor provides misfire info to the PCM...you can also get "phantom misfires"...flashing MIL but no actual misfires felt...as far as the 0340/0341 I would find a shop that can scope the cam and crank sensor too...my LS1 is a 24X crank and a 1X cam...below is my cam and crank signals taken with my scope...you have to make sure that you are getting the full amplitude (12 volts) on both and they line up correctly...the red signal is my 1X and the blue is the 24X...making sure they line up correctly is imperitive...as you can see the crank signals have wider and thinner "on-off" times !!
..we call it a "cam and crank variation" !!!...I believe your engine is a 58X and a 4X !!
YES !!...anytime a motor is replaced you have to do the crank relearn...the crank sensor provides misfire info to the PCM...you can also get "phantom misfires"...flashing MIL but no actual misfires felt...as far as the 0340/0341 I would find a shop that can scope the cam and crank sensor too...my LS1 is a 24X crank and a 1X cam...below is my cam and crank signals taken with my scope...you have to make sure that you are getting the full amplitude (12 volts) on both and they line up correctly...the red signal is my 1X and the blue is the 24X...making sure they line up correctly is imperitive...as you can see the crank signals have wider and thinner "on-off" times !!
..we call it a "cam and crank variation" !!!...I believe your engine is a 58X and a 4X !!
That is really good info. Would the lack of a crank relearn cause this issue?
I doubt it !!..I may want to check the wiring again...enclosed is a good video on testing !! ...you should have 12 volts on the orange wire, the brown wire is the signal back to the PCM, and the pink/black is low reference (ground) !!
I bought 2 different cam sensors online and replaced it. When I replaced the motor, I was getting this code, so I bought the new pigtail and sensor from GM. I took the car to Redline Motorsports and the tuned it and got it running perfectly. The code remained however ..I took the car back for a retune, and that when Redline found that the wires in the pigtail were mixed up. They corrected it but the codes came back. I'm not sure what to do next.
We are well aware of a crank relearn process. This car has had an issue since the day it was brought here for calibration. Its an intermittent issue that comes and goes. If it required a crank relearn the DTC would not go away until it was done. Car was successfully calibrated with no DTC and drove fine....then randomly starts acting up. Its also possible there is a problem with the cam gear. Car was brought here with a built motor by others.
We recalibrated your car 2-3 weeks ago, after a pulley change, in which you spoke to Rich and had no issues. Rich received an e mail from you this morning that you just had the issue. If it was a "hard" issue it would of been there from jump. We are more then willingly to continue looking at it only as long as we know if there is an issue brought to our attention. We have also seen issues with bad E38 controllers that can randomly drop input functions as this.
Keep us posted...
Last edited by Redline Motorsports; Oct 24, 2019 at 01:51 PM.
I doubt it !!..I may want to check the wiring again...enclosed is a good video on testing !! ...you should have 12 volts on the orange wire, the brown wire is the signal back to the PCM, and the pink/black is low reference (ground) !!
Thanks for that. I have a voltmeter and will check this out when I have some time!
Originally Posted by Redline Motorsports
We are well aware of a crank relearn process. This car has had an issue since the day it was brought here for calibration. Its an intermittent issue that comes and goes. If it required a crank relearn the DTC would not go away until it was done. Car was successfully calibrated with no DTC and drove fine....then randomly starts acting up. Its also possible there is a problem with the cam gear. Car was brought here with a built motor by others.
We recalibrated your car 2-3 weeks ago, after a pulley change, in which you spoke to Rich and had no issues. Rich received an e mail from you this morning that you just had the issue. If it was a "hard" issue it would of been there from jump. We are more then willingly to continue looking at it only as long as we know if there is an issue brought to our attention. We have also seen issues with bad E38 controllers that can randomly drop input functions as this.
Keep us posted...
Thanks for replying. I told Rich, this issue is the only thing holding this car back from being perfect. I'd like to get it resolved. I am going to troubleshoot a bit more and if I can't figure it out, I will bring it back to Redline to have your team take a look at it. By bad E38 Controllers, you are talking about the PCM?
Last edited by slow goat; Oct 24, 2019 at 06:34 PM.
I had a very similar problem with my '07. Same fuel test results as yours. Finally took her to dealer for diagnosis and they agreed with my diagnosis that there was a $2.50 nylon anti-drainback check valve in driver's side fuel pump that had gone south. $1600 later she runs like new! To verify it is your check valve (in your case 2 ea.). hold in on the bottom of your start button until the dashboard lights up. During this 2 seconds you should hear your fuel pump prime the fuel line. Now hit the start button. Does she fire right up instantly, or is there still a 3 sec. or more pause? If she starts up instantly that is a telltale sign that your check valve is leaking, allowing fuel to leave the line and drain back into the tank (thus causing pressure loss). Your 3 sec. or so lag is due to your pump having to re-pressurize your fuel line. Once min. start pressure is reached (about 2-3 sec. on an empty line), that's when she fires! And yes, just like yours, once started she ran just fine. Good luck with this and please report back. By the way I did extensive on-line research about this problem (before I got it fixed) and yours is the only other problem like this that I could find.
I had a very similar problem with my '07. Same fuel test results as yours. Finally took her to dealer for diagnosis and they agreed with my diagnosis that there was a $2.50 nylon anti-drainback check valve in driver's side fuel pump that had gone south. $1600 later she runs like new! To verify it is your check valve (in your case 2 ea.). hold in on the bottom of your start button until the dashboard lights up. During this 2 seconds you should hear your fuel pump prime the fuel line. Now hit the start button. Does she fire right up instantly, or is there still a 3 sec. or more pause? If she starts up instantly that is a telltale sign that your check valve is leaking, allowing fuel to leave the line and drain back into the tank (thus causing pressure loss). Your 3 sec. or so lag is due to your pump having to re-pressurize your fuel line. Once min. start pressure is reached (about 2-3 sec. on an empty line), that's when she fires! And yes, just like yours, once started she ran just fine. Good luck with this and please report back. By the way I did extensive on-line research about this problem (before I got it fixed) and yours is the only other problem like this that I could find.
Good info there. I think it's worth it for me to rule them out. I'll pick some up off of jegs.
Bad check valves?
