Well it's time to bring out the big guns (that's you guys). Last year I swapped in an LQ4 into Fat Konnie (Yukon XL). Specs are in my sig. I have a very strange, but not unheard of, starting issue. When I did the swap I put in all new AC Delco sensors on the motor) with the exception of the MAF, which I cleaned with MAF cleaner. One odd thing was that when BlackBear did the tune with the data logging, I was told I needed to clean my throttle body, which I had done prior to putting it back on. I cleaned it again and still have the same problem.
When starting the vehicle from sitting overnight it starts right up about 65-70% of the time. The remaining 30-35% it will just crank and crank if I continue to hold the key down. Yes, I've tried the flood clear procedure to no avail. If I turn the key, let it crank, let off the key, then try again it fires up like it's supposed to. If I try to start after the engine has run AT ALL, then I have the same non-start issue on the first key turn 97% of the time. For example: yesterday, after sitting overnight, I started Fat Konnie on the first key turn and moved her over to the other side of the driveway. The engine ran about 30 seconds. I looked under the frame rail to find the fuel composition sensor and filter, went inside to grab my wallet, then hopped inside to head out for a filter. It took maybe 2 min, but when I went to leave I had the same no start on the first key turn.
Fuel pressure does leak down to about 20psi after a couple hours. Cycling the key 1-50 times before starting has no effect on the starting problem. I have also pulled the fuel rail off and pressurized the system and there are no dripping injectors. FPR seems to work fine (no gas smell, no gas dripping) and I have tried to run it with vac line to FPR uplugged with same results.
I don't want to spend the money that mpope2 did here with his rig: https://www.tahoeyukonforum.com/threads/delayed-crank.125739/#post-1557535
We've been messaging and the one thing we can identify as being the same is that our vehicles sat for an extended period before the problem started. Varnish?
So let's throw out some ideas please! But let's also try and give a helpful explanation as to why. Simply saying "Fuel Pump" doesn't help. It would be nice to have a logical explanation as to why it starts the majority of the time correctly after sitting, but poorly after being started.
Thank you in advance for your insight!!!
When starting the vehicle from sitting overnight it starts right up about 65-70% of the time. The remaining 30-35% it will just crank and crank if I continue to hold the key down. Yes, I've tried the flood clear procedure to no avail. If I turn the key, let it crank, let off the key, then try again it fires up like it's supposed to. If I try to start after the engine has run AT ALL, then I have the same non-start issue on the first key turn 97% of the time. For example: yesterday, after sitting overnight, I started Fat Konnie on the first key turn and moved her over to the other side of the driveway. The engine ran about 30 seconds. I looked under the frame rail to find the fuel composition sensor and filter, went inside to grab my wallet, then hopped inside to head out for a filter. It took maybe 2 min, but when I went to leave I had the same no start on the first key turn.
Fuel pressure does leak down to about 20psi after a couple hours. Cycling the key 1-50 times before starting has no effect on the starting problem. I have also pulled the fuel rail off and pressurized the system and there are no dripping injectors. FPR seems to work fine (no gas smell, no gas dripping) and I have tried to run it with vac line to FPR uplugged with same results.
I don't want to spend the money that mpope2 did here with his rig: https://www.tahoeyukonforum.com/threads/delayed-crank.125739/#post-1557535
We've been messaging and the one thing we can identify as being the same is that our vehicles sat for an extended period before the problem started. Varnish?
So let's throw out some ideas please! But let's also try and give a helpful explanation as to why. Simply saying "Fuel Pump" doesn't help. It would be nice to have a logical explanation as to why it starts the majority of the time correctly after sitting, but poorly after being started.
Thank you in advance for your insight!!!
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