c6z06ron

Having another issue with my newly purchased C6 Z06. Intermittently getting a hard start, (long crank) issue with the car. A couple times it was hard to start and would stall. I did a key on engine off fuel pressure test several times and almost every time there was 0 fuel pressure. Needle didnt budge. Only 1 time, I turned the key on and actually got it to read about 50 psi on the gauge. When the engine starts, the fuel pressure is between 50-60 psi. I read somewhere that it could possibly be a bad fuel pump relay. I read that the ecm energizes the f/p relay for 2 seconds to prime the pump when the key is initially turned on, and that after that the ecm wants to see oil pressure to energize the fuel pump, thus explaining why I have good pressure when the engine is cranking or running? Sounds like my problem. Can anybody verify that is how this system operates? The info I found was for older vettes so I wasn't sure if it was the same or not. Thanks.

schpenxel

I'm almost sure that isn't how it works, as far as requiring oil pressure to keep the fuel pump running

I'd bypass the fuel pump relay first and see if the pump will come on consistently (and that the car will start..) when the relay is taken out of the picture before doing much else. Very possible it's a bad relay that is working intermittently

HOXXOH

I have a somewhat similar problem or maybe the early stages of the OP's problem that's been happening recently. When the car has not been driven for more than 4 or more hours, the engine fires on the second or third crank. (several years ago it was first crank) But now after a short or longer drive and a period as short as 5 minutes after shutting it off, it'll crank once, then stop for about 2 seconds and crank again. Most of the time it'll fire up on the second try, but a few times it's taken multiple stops and attempts to fire. This is with me only pushing the button one time. The repeated attempts to fire happen without my input. It's not a battery problem, since I swapped batteries just to eliminate that issue. The start voltage cold, warm, or hot is consistently in the 12.5-13.2 range and the run voltage hovers around 14-14.4. I have no fuel starvation during WOT from idle through 3rd gear (125 mph). I swapped the fuel pump relay with a different one, which made no difference. It makes no difference if I hold the button down or just one quick touch nor whether the fuel tank if full, empty or anywhere in between. I find nothing in the service manual that addresses the problem.

Any thoughts? And do they apply to both the OP's issue and mine?

C5 Diag

Hi !!...I'm usually on the C5 side but I did a YouTube video on the fuel pump relay circuit testing...it might help...I don't have a wiring diagram for your car but basically you have a LOAD side and a CONTROL side of the fuel pump relay...the load side on the C5 is pins 87 and 30 on the relay and 86 and 85 are the CONTROL...maybe this will help...you can take a jumper wire between 87 and 30 or whatever numbers your relay shows and the pump will run continuously...hope this may help !!...oh, and BTW oil pressure NOT involved !!...you MAY have a bad crank sensor...with bad crank sensor there is no injector pulse or ignition during start...if during cranking you see NO Tach movement that is a pretty good sign you are getting no ignition ref. pulse !!...if you watch fuel pressure during cranking it will drop steadily if it's a bad crank sensor !!

Dano523

As stated, the fuel pump should pre-prime the system to bring it up to pressure before the car attempts to starts.

Could be relay going out, or could be bad,corroded, split open spade connector for the relay in the upper fuse box.

So start off by using the relay jumper method to see if that solves the problem to begin with. The spades connectors often will push the slightly widen fuse connector open at touch more/better contact to the connect that the relay spade itself, and if this solves the problem, the swap out same type relay from another part of the fuse box into the fuel pump relay to just weed if the relay is the problem of fuse box.

If the jumper does not solve the problem, then suspect fuel pump, or bad ground to the fuel pump the problem at hand.



If fuse box connector corrode or split open.
And note that the copper trail wire clips into the side of the connector that it too could be corrode as well.



Also, when you do go to check the upper fuse block,pull it out and check the lower spade blocks to make sure one of the connectors did not get pushed down into the lower block, or one of the connectors is burnt/melted.



If you need to pull the upper fuse box apart to correct the problem (so you don't have to buy a new upper fuse box).
Just remember to drill the head off the rivet on the bottom side, since you want the top of rivet in place when you put the upper fuse block back on for the bolts.


https://www.corvetteforum.com/forums...dlights-5.html

One more thing and if you are using the factory oem wiring from the fuse box to the fuel pump with a BAP to drive the fuel pump, bank that the wiring did a melt down between the fuse box and the tank. The OEM small gauge wiring can not take the extra amperage/voltage from the BAP to drive the fuel pump, and this is the reason that the BAP is wired all the wall back to the fuel pump connector at the tank.

Mike's LS3

Yes, when you press the ignition there is a 2 sec fuel prime in the tune.

I had a bad check valve in the fuel pump which made the car hard to start, but once started it ran fine. Put a fuel pressure gage on the fuel rail Schrader valve and try to get the car started. Once started, the pressure should read about 58 pounds of pressure. Then turn off the engine and watch the fuel pressure gage. If it drops quickly, their is a good chance the check valve in the fuel pump is bad. This happened to me, I could actually hear fuel retuning to the gas tank. It seriously sounded like the my car was tanking a leak!

As a side note, fuel pressure dropping after the engine was shut down can also be leaking fuel injectors.

As far as the BAP, if a BAP wiring is damaged or not properly working the car will not start. It's all or none. Easy to check with a volt meter.