Ken Roberts
Supporter
Any update on this Glenn?
LS376-480 start problem
- Thread starter glennl
- Start date
I have tried all the suggestions that have been suggested including a different PCM, crankshaft position sensor, MAP sensor and none cleared the problem. But I have narrowed it down to a fuel problem. I accidentally started it while checking fuel pressure. The night before I was using a scan tool to check the PCM data and had run an injector leakdown test where fuel rail was pressurized and the injectors were activated. The next morning it started immediately and ran fine. It would not restart immediately after I turned the engine off. I did the injector test again later and the engine started. I also purged the fuel rail several times and had a start after that. Ran the engine for 15 minutes, turned it off and tried an immediate restart to no avail. So the problem seems to be a lack of fuel at start up. I am still open to suggestions.
Terry Oxandale
Skinny Man
If I understand this, your testing shows that it starts fine when you've had pressure to the injectors immediately or just prior to start-up, but if you don't do the testing, then perhaps you do not have the sufficient pressure for start-up; correct?
Do you have a mechanical fuel pressure gauge on a port somewhere where you could observe injector rail pressure in real-time (not electrical)? If the above is what is happening, this implies that the fuel pump is not on when you turn the key (or push the button). I'm not savvy on current injection fuel pressure schemes (mine is all manual - turn pump on, turn ignition on, push button), so I don't know when the pump is "turned on".
Do you have a mechanical fuel pressure gauge on a port somewhere where you could observe injector rail pressure in real-time (not electrical)? If the above is what is happening, this implies that the fuel pump is not on when you turn the key (or push the button). I'm not savvy on current injection fuel pressure schemes (mine is all manual - turn pump on, turn ignition on, push button), so I don't know when the pump is "turned on".
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Ken Roberts
Supporter
I'm with Pete. The first picture is correct. The second is wrong. The center pipe has a smaller diameter. The outer pipe is larger.
Ken Roberts
Supporter
Are you using a pre filter before the low pressure pump? If so it may be too fine. It should be about 75 microns. It is a mistake to use a 10 micron filter before the pump on the suction side.
Yep, according to Speedway, the 2nd pic is right.
LS1 Fuel Filter/Fuel Regulator Kit - Speedway Motors, America's Oldest Speed Shop
Ken Roberts
Supporter
I have two fuel pressure gauges, one on the regulator and one on the fuel rail. They both read 60 psi during the startup process. The fuel pumps are running all the time during start up. I went away from the Corvette regulator to an adjustible regulator. I have varied the fuel pressure from 58 to 65 psi and it has made no difference. As far as the plumbing of the regulator, the fuel goes throught a 40 micron filter, check valve, variable pressure regulator, to the fuel rail. The first filter in the system coming from the tank is 80 micron. Return line from the regulator to the surge tank. Running an injector test before starting the engine cold seems to work every time. It does not help the engine to start when the engine is hot. The problem seems to deal with the initial prime of fuel to the system. I am still looking for a solution.
If a check valve problem or something similar exists, would you not expect to see fuel rail pressure collapse as soon as the injectors fired?
Mike
Mike
Agreed. I would think that if you have a fuel flow problem to the fuel rail that your pressure at the fuel rail would collapse once you fired it up. Also, you wouldn't be able to run the engine for long periods of time, like you've done, without a lean condition.
What is beneficial about the fuel injector test sequence?
What is beneficial about the fuel injector test sequence?
Power for the fuel pumps is turned on by the PCM.
The injector test activates the fuel pumps and cycles each injector several times. This has been putting extra fuel into the intake manifold.
The injector test activates the fuel pumps and cycles each injector several times. This has been putting extra fuel into the intake manifold.
It certainly appears that you have a lack of fuel at start. That would seem to leave two possibilities:
1. Fuel injector issues - either not injecting enough fuel (air locks?) or not open long enough. Given that it runs fine once started, this one seems less likely;
2. Unmetered air. This would impact start more than running, so would be my focus now.
1. Fuel injector issues - either not injecting enough fuel (air locks?) or not open long enough. Given that it runs fine once started, this one seems less likely;
2. Unmetered air. This would impact start more than running, so would be my focus now.
Ran a scan on the PCM on my wife's G8 since the engine is about the same. The values were about the same except for the MAP sensor which had been replaced. After correcting that, the engine starts and runs fine. This has been a learning experience. Thanks to all who contributed ideas.
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