Fine Tuning Minor Issues - 392 w/ Cam

[mxatunerjg]

My issue tho is if I shut the car down hot, and immediately (or within 5min or so) go to refire it fires right up. If I wait 20min or so from hot shut down, no fire at all. I checked my coolant temp and it was still sitting right around 180* or so. My 158 and 266* columns are sitting right about 50% of stock.

What injectors are you using?

I've been reading through this whole thing. Honestly there are so many different people having issues here I had trouble keeping up with who was having what issue.

I do agree with you about injector timing capabilities would be helpful. That said I would be a little surprised if the difference in the Edelbrock heads and factory heads is drastic enough to cause the issue you are having. Not saying it's not possible, just would be a bit surprised.

I have 2 thoughts about the issue otherwise...

1. I know it is simple and maybe seems stupid, but have you checked fuel pressure at the rail on those starts that you are having issues with? The fact that it is good on a quick restart hot, as well as a cold start, but a delayed restart hot causes a problem is one of those basic things that causes me to immediately look at fuel flow/pressure issues. On early efi systems with inline fuel filters an old dirty fuel filter would cause this kind of problem. If you would cycle the key prior to cranking and allow the system to build fuel pressure it would fire up on the first starter cycle. The stupid part about it is the vehicles generally would start fine on a cold or quick hot restart. It's probably not likely, but if it were me I'd check it because it would make a lot of sense for your issue. I always believed it to be caused by the fuel on the intake runners would evaporate off over the 20 mins of a hot engine sitting, then your prime pulse and injector pulsewidth during cranking on a hot engine was so low if the fuel flow/pressure wasn't there it caused the engine to be too lean to start. By cranking it some fuel flowed, and then when you went to crank again it would have some amount of fuel on the runners, and you have some fuel pulse from the injectors causing it to be much more like a 5 minute sit time on a hot engine. On the cold engine, the injector prime and pulsewidth were not programmed to rely on wet runners, so the engine started like normal. Obviously if the fuel flow was too low it would not work in any situation, but over the years I've replaced a lot of fuel filters or leaking in tank fuel lines that fixed this exact issue.

2 You said about checking coolant temp, but I would look at intake air temp. I don't know where you have the intake air temp sensor installed, and what type of material it is sitting it (alum, plastic, rubber, carbon fiber ect.). I've had a lot of issues with heat soaked IAT sensors give issues like this over the years as well, basically it would be a situation of a sensor reading hot but an actual air charge temp that would be much lower. Based on the injector pulsewidth you said you are seeing I'd doubt this is the issue, but it is worth checking. If you have an intake temp sensor showing 200 degrees at startup it could be causing some issues with cranking ignition timing and fuel flow.

Just some quick thoughts I had when reading through this.

[06300CSRT8]

I've been reading through this whole thing. Honestly there are so many different people having issues here I had trouble keeping up with who was having what issue.

I do agree with you about injector timing capabilities would be helpful. That said I would be a little surprised if the difference in the Edelbrock heads and factory heads is drastic enough to cause the issue you are having. Not saying it's not possible, just would be a bit surprised.

I have 2 thoughts about the issue otherwise...

1. I know it is simple and maybe seems stupid, but have you checked fuel pressure at the rail on those starts that you are having issues with? The fact that it is good on a quick restart hot, as well as a cold start, but a delayed restart hot causes a problem is one of those basic things that causes me to immediately look at fuel flow/pressure issues. On early efi systems with inline fuel filters an old dirty fuel filter would cause this kind of problem. If you would cycle the key prior to cranking and allow the system to build fuel pressure it would fire up on the first starter cycle. The stupid part about it is the vehicles generally would start fine on a cold or quick hot restart. It's probably not likely, but if it were me I'd check it because it would make a lot of sense for your issue. I always believed it to be caused by the fuel on the intake runners would evaporate off over the 20 mins of a hot engine sitting, then your prime pulse and injector pulsewidth during cranking on a hot engine was so low if the fuel flow/pressure wasn't there it caused the engine to be too lean to start. By cranking it some fuel flowed, and then when you went to crank again it would have some amount of fuel on the runners, and you have some fuel pulse from the injectors causing it to be much more like a 5 minute sit time on a hot engine. On the cold engine, the injector prime and pulsewidth were not programmed to rely on wet runners, so the engine started like normal. Obviously if the fuel flow was too low it would not work in any situation, but over the years I've replaced a lot of fuel filters or leaking in tank fuel lines that fixed this exact issue.

2 You said about checking coolant temp, but I would look at intake air temp. I don't know where you have the intake air temp sensor installed, and what type of material it is sitting it (alum, plastic, rubber, carbon fiber ect.). I've had a lot of issues with heat soaked IAT sensors give issues like this over the years as well, basically it would be a situation of a sensor reading hot but an actual air charge temp that would be much lower. Based on the injector pulsewidth you said you are seeing I'd doubt this is the issue, but it is worth checking. If you have an intake temp sensor showing 200 degrees at startup it could be causing some issues with cranking ignition timing and fuel flow.

Just some quick thoughts I had when reading through this.

#1 has been verified, it builds full 58psi of pressure after the pump runs for about 1-2 seconds, so after it cranks for 10 seconds of the 20 seconds you would think it has all the fuel it would need. I have an analog fuel pressure sensor in the passenger rail that I log the 0-5v output.

#2 I will have to verify, but I know for sure its not 200*F, my sensor is about 12" from the throttle body, in a rubber grommet, in the aluminum uppipe going from the cold side of the intercooler up to the throttle body. It def does heat soak a little while sitting, but only maybe 15-20* if I recall correctly, so is usually 100-110*F.

[mxatunerjg]

#1 has been verified, it builds full 58psi of pressure after the pump runs for about 1-2 seconds, so after it cranks for 10 seconds of the 20 seconds you would think it has all the fuel it would need. I have an analog fuel pressure sensor in the passenger rail that I log the 0-5v output.

#2 I will have to verify, but I know for sure its not 200*F, my sensor is about 12" from the throttle body, in a rubber grommet, in the aluminum uppipe going from the cold side of the intercooler up to the throttle body. It def does heat soak a little while sitting, but only maybe 15-20* if I recall correctly, so is usually 100-110*F.

Keep in mind on the cranking, the initial injector pulse tapers off as the car cranks longer, so if the fuel pressure is taking time to come up that could be causing the issue. I'd check to see what it is prior to the pump running. If you are using an analog sensor I'm assuming it gets power when the ignition is on, so maybe pull the fuel pump relay so the pump doesn't run when you turn the key on. Check the pressure at maybe 5 minute intervals for say 20 or 30 minutes after you shut off the engine. If it isn't holding some pressure, probably at least 20 psi after 20 minutes it is probably worth looking into that.

If the IAT is at 100 degrees or so it should not be causing any issues, at least not enough to keep it from starting.

[06300CSRT8]

Its a Fore triple pump fuel setup, fuel pressure is near zero seconds after priming stops, which is the normal. I have run many Fore setups in customer and my own cars, I always prime for one cycle (hit start button to run position, pressure comes up to 58psi for 3-4 seconds), then press run button without foot on the brake (same thing pressure comes up to 58psi) then I hit the run one more time while its in the middle of that 3-4 second priming, so its trying to fire with full pressure in the rails.

[mxatunerjg]

Its a Fore triple pump fuel setup, fuel pressure is near zero seconds after priming stops, which is the normal. I have run many Fore setups in customer and my own cars, I always prime for one cycle (hit start button to run position, pressure comes up to 58psi for 3-4 seconds), then press run button without foot on the brake (same thing pressure comes up to 58psi) then I hit the run one more time while its in the middle of that 3-4 second priming, so its trying to fire with full pressure in the rails.

Ok...the fact that you are priming the system prior to starting eliminates all of this. I'll think a bit more about it.

[mxatunerjg]

Its a Fore triple pump fuel setup, fuel pressure is near zero seconds after priming stops, which is the normal. I have run many Fore setups in customer and my own cars, I always prime for one cycle (hit start button to run position, pressure comes up to 58psi for 3-4 seconds), then press run button without foot on the brake (same thing pressure comes up to 58psi) then I hit the run one more time while its in the middle of that 3-4 second priming, so its trying to fire with full pressure in the rails.

Not sure if you stated earlier in this discussion, but what fuel are you using on this setup?

[06300CSRT8]

Straight 93 octane at the moment.

[PurpleRam]

I know this is old, but I’m bored , one thing to keep in mind when dealing with start up issues AFTER swapping to a larger cam, the vacuum signal changes and that will affect the draw on the injectors.