Hi,
I have only had my car for about a month and a half, and I haven't driven it much so far. This means I have just now started learning it's quirks and habits.

First a little bit of background. The car is a 2004 CE coupe with a 6 speed. It was already modded when I bought it, but it seems like most of the mods are what I would want to do myself to a stock car. While it does have a full exhaust system with long tube headers and a vararam cold air intake, the most notable mod seems to be the cammed LS2 short block with LS3 ported and polished heads and intake. PO stated that it had dynoed 452 at the wheels.

About a week ago, I went out to find the battery had died, so I put it on a charger and brought it back to life. No problem. But since then, it seems like the engine doesn't want to fire quickly when I crank it. The starter cranks strong, and everything else seems to work right, but it wants to crank for 5 to 10 seconds before it ever fires. Any ideas on what to start looking for? I have a bone stock 5.3 in my Suburban, but this is my first hot rod LS. Used to be you'd check your points, put a timing light on it, and check the float levels in the carb, and you could get that small block to fire off at the flick of the key.

 

Pull the codes.

Delete the codes, run the car and see what comes up as Current.

Check fuel pressure at the rail after turning the ignition key on but not to start for 3 or 4 seconds.

Report back.

 

Sometimes a failing cam or crank sensor can cause this…look at your Tach while cranking and if it doesn’t appear to move it may be the crank sensor…a scope would be needed to accurately diagnose this !!

 

You might try two or three key off back on cycles, let the gauges sweep and indicators turn off, if this helps then low fuel pressure is the cause of the long crank, no pun intended problem.

 

I put my brand new fuel pressure gauge on the rail and as soon as I turned the key I learned immediately why the instructions said to tighten the line to the gauge with a wrench. I got a fine mist of 93 octane all over the engine bay. So I got the suggested wrench and snugged up the connection. Afterwards I turned the key on again and the fuel pressure instantly went to 60 psi. It dropped to 50 as soon as the pump shut off. I was just paranoid/smart enough to know not to crank the engine since the alternator is now baptized with the aforementioned fine mist of 93 octane. I'll let it rest and evaporate overnight.

 

Update, about 5 hours later I looked at the gauge again and it has bled down to zero. I'm beginning to think leaky injector. I have not reset the codes since running it last, but the DIC shows no codes for PCM. I will fire it up with the gauge on it tomorrow and see what it does when running.

 

That don't matter on start up. If it pumps to 55 to 60 psi with in 2 sec it should start right away. Mine has been bleeding down for the past 10yrs. But once i turn the key it shoots to 60 before 2 seconds. Since it has no effect on starting, thats why i left it alone.

 

Normally the pressure shouldn’t drop more than 5 psi in a minute…there are a few components that can cause this and a leaky injector is one of them..you have the redesigned fuel system (RPO code FFS) and the other things that may cause this such as a leaky one way check valve is located as part of the fuel pump module…to check for a leaky injector without having to pull the fuel rail is to buy a GM male and female fuel line fitting and a shut off valve from Home Depot and with some 3/8”

fuel hose…you would hook this up between the fuel line and fuel rail and then pressurize the fuel system and then close the shut off valve…if fuel pressure holds it’s not an injector !!

 

Went out to the car this afternoon after the rain stopped. It dropped to about 50 degrees by the time I went out. With the gauge still on from yesterday, I turned the key on, and it popped up to 60 psi before I cranked it. I didn't touch the gas pedal as I cranked it. It spun over for about 4 long seconds before it fired, but it did give one little sputter after cranking for about a second. Once it fired it ran fine with no touching the accelerator pedal. It idled and sounded good. The fuel pressure stayed at 60 the whole time it was running. I let it warm up to operating temperature, and the condensation burned out of the exhaust. I revved it a few times and then shut it off. After that I pulled the codes on the DIC. The only code in the whole car is TCS C1242 H C. Still no PCM codes.

 

The fact that fuel pressure is up as soon as the key is turned on points to something else as helga203 indicates.

You have not confirmed that the tach is indicating cranking when you are attempting a start as C5 Diag suggested-
"Sometimes a failing cam or crank sensor can cause this…look at your Tach while cranking and if it doesn’t appear to move it may be the crank sensor…a scope would be needed to accurately diagnose this !!"

 

I am confused does a cam or crank sensor not just fail causing a complete no start condition, why would it just cause a long crank and then just allow the engine to start?

 

Marty, usually a failing cam sensor will cause a "hard start" (longer than normal crank time) because the PCM is trying to figure out if the piston is on the intake or exhaust stroke...the car will start and run without the camshaft sensor...the crankshaft position sensor however IS needed for the car to start and operate !!...a scope is the best way to see if the CMP or CKP is sending its signal to the PCM...below is the cam and crank signal from my 01...each sensor goes from 12 volts to ground and if that doesn't happen that may cause issues as well as an intermittent signal...there are 24 "pulses" you can call them between each cam sensor "pulse". The 24X reluctor is crazy in that there are wider pulses and narrow pulses and not easy to spot the cam sensor out of place or as it's called its correlation between the 2.

 

We are not really concerned if the fuel pressure rises to 60 psi but how much it DROPS when the key is turned off...you mentioned it dropped 10 psi after the key was shut off so you have to go down that "funnel"...no more than a 5 psi drop after 1 minute...if the pressure stayed at 60 when the key was shut off its not a fuel rail pressure issue...as was mentioned turn the key on for 2 seconds (make sure the pump turns on each time) and then off and do this 2 or 3 times...if the car starts right up you'll have to diagnose that pressure drop...injector, check valve, fuel pump etc.

 

Thanks for the explanation of the cam and crank sensor timing and operation. I worked at a pulsed linear accelerator and had to deal with timing gates, length,delays and gates being coincident with each other, time scales were in the micro and nano second time scales.

 

Thanks for the input guys! I have a little more homework to do, and I will report back this afternoon.

 

I'm with C5Diag on a potential issue with the crank sensor.

I have an LS3 swap in my car, and I use the Lingenfelter conversion box to convert the 58T reluctor signal from the LS3 into the 24T signal that the LS1/6 PCM is looking for. It takes a good 1-3 seconds of cranking for my engine to start because it takes a bit longer for the signals to properly align and the box to work its magic.

You seem like you have eliminated fuel pressure as an issue, so I'm thinking it may be taking longer than usual for your PCM to resolve the information coming from your crank position sensor to then give the command to fire the coils. This is just a guess on my part though.

 

The OP said his fuel pressure drops on shutdown so that has to be addressed…starting or running fuel pressure of 60 psi doesn’t figure in to the equation…if fuel pressure drop is good then yes we should look to the CMP or CKP !!…we are looking at low fuel volume and not pressure at the injectors if that fuel drains back to the tank

 

Well I'm out of time to fix this for now, but I did go out and start the car again just now. It is 30 degrees outside. I tried a couple of different things. First, before I ever tried cranking it, I cycled the key 3 times to prime the fuel pump. The 4th time, I cranked it. It fired almost immediately but then died instantly as well - I never even had time to let off the starter. It cranked for another 5 seconds, popping a few times as it was cranking before it fired and ran. I noted that the tach needle did not move at all while I was cranking. After it fired I let it idle for several minutes, and then I revved it a few times and let it settle back down before shutting it off. To confirm the tach not registering during cranking, I cranked it again within about 5 seconds of shutting it down. Once again it took over 4 seconds to fire, and the tach did not register while cranking.

Last night I got on Rock Auto and ordered a new cam sensor and a new crank sensor. No, not GM parts, but still new. For $18 and $12 respectively I don't mind throwing a couple of parts at it to try to make it better. I am leaving on Monday to undergo a stem cell transplant process, so I won't be able to work on it for several months. But the parts will be waiting for me when I get back, and it will give me something to look forward to. If the $30 in sensors doesn't fix it then of course I will have to also look at the $250 fuel pump module. It may be a combination of both issues. FWIW, the car doesn't seem to have quite as much power as it ought to either, so something just doesn't seem quite right. Anyway, wish me luck! Thank you for your help so far!

 

Wish you well, take care, hope everything goes well