I have been having startup issues with my GMPP LS7 crate engine. In the attached table what is the unit of the time used from 0 to 43,200? It seems to me that it would be milliseconds. Correct?
Also when does the clock start? Key on, cranking starts or what? It seems to restart every time the key is cycled..
Thanks in advance.
LS7 Startup AFR Table.png
It looks like seconds ( s ) , what problem your are facing ?
It seems unlikely to me that the table would extend to 43,200 seconds. I don't know of a starter motor or battery that would crank a V8 engine continuously for 12 hours. I think the commas probably should be decimal points, which would make the end of the table 43.2 seconds.
My problem is that the engine became progressively harder to start as i leaned low rev and low TPS AFR's from GMPP's overly rich/safe stock calibration that came in the crate engine's VCM.
I have increased the numbers in this table in the 0 to 60 columns and helped my problem but it still often takes 3 or 4 cranking attempts to get the engine started. Does the "60" column represent 0.060 seconds, 0.6 seconds, 6 seconds, 60 seconds or what?
The engine will now normally start by the 3rd or 4th cranking attempt if I make an attempt for a second or two, turn off the key and try again. If i continuously crank it will not start. HPT's help explanation for that table does not seem to apply correctly.
I feel that I am flying blind and am trying to better understand what this table does.
Thanks for your thoughts and suggestions.
The axis value is in seconds - but it is the number of seconds since the engine's last run time. If you drove to the mall, went shopping, and then restarted the vehicle an hour later, it would reference the 3600 column.
Thank you Jon. In your example after being in the mall for an hour and I attempt to start the engine, the VCM uses the 3600 column and the engine does not start. I then cycle the key off and on. Does it go back to 0 or continue from 3603 or however long i cranked it? I.E. does it reset when the key goes to off or the engine actually stops running? It seems that it uses the last time the key went to off.
Your thoughts please.
This may be a fuel system issue. Sometimes the fuel pressure regulator will not hold pressure in the fuel rail, after the engine has been sitting (not running) - even briefly.Originally Posted by midgetracr
When you cycle the key, you should hear the fuel pump run for about 2 seconds. In some custom applications, this is not long enough to fill the fuel rails, and to also get the fuel rail pressure up to 58 PSI.
As a test of this possibility, try cycling the key (without attempting to start the engine), until you get 2 or 3 of the 2 second fuel pump “primes” occurring - then try starting the engine.
The table is linked to run time, not key cycles - but the best way to test this for certain with the GMPP OS, would be to monitor the commanded fuel from a cold start situation, but to have cycled the key several times prior to attempting to start the engine.
Most often in these situations (if the tune is reasonable close overall), hard starting is either a lack of fuel pressure in the fuel rail, or insufficient cranking air (i.e. opening the throttle a little improves starting).
Good theory.
I do have a small fuel pressure gauge on the fuel rail and did the following test.
Engine had been off for about 20 hours. Coolant and intake air temps around 85*F. Fuel pressure 0 psi. Switched key on. Fuel pump ran for a couple of seconds and fuel pressure went to about 52 psi. Key off for several seconds. Key on again and pump ran again and raised fuel pressure to about 58 psi as i cranked engine for several seconds. Did not start. Repeated the key off, wait, key on and crank routine. Still no start. On the third key on, crank etc. The engine started. All above with no foot on the throttle pedal.
I am baffled and welcome your thoughts.
Thanks
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