Fresh Rebuild with Mild Cam Hard Starting

[bman22]

I'm definitely what you'd call an amateur tuner, but I've done a handful of Gen 3 vehicles at this point, everything from small cam 5.3s to big cam turbo 408s, and I've come across one that I just cannot figure out. I'm leaning towards something outside of the tune given the symptoms, but I've combed across every single thing I can think and wanted some input.

I've always been able to more-or-less use the stock tune with some additional base running airflow and some higher RPM as a starting point for idle tuning on something this size. This one is absolutely refusing to fire. It cranks like there is no spark or fuel, except the occasional light popping. We've figured out some light tricks to get it to start very occasionally, and once it's running it idles well despite the fact that this was the initial base tune I guessed at.

Can somebody look through the idle/startup tune and the logs of trying to start it and confirm that something outside of the tune is going on? Every sensor on the vehicle is brand new, we've tried injectors, throttle body and IAC, checked fuel pressure, tried another computer, and it just will not fire reliably, so I'm running out of ideas.

[blindsquirrel]

What part of the world are you in? As in, altitude. Is 84 kPa a normal baro reading for your location?

[blindsquirrel]

Every sensor on the vehicle is brand new

So, presumed defective until proven otherwise?

[horsepowerguru427]

What part of the world are you in? As in, altitude. Is 84 kPa a normal baro reading for your location?

I wondered about this as well...

[bman22]

I bounce between 7500 and 3000ft a lot, so I have to admit I'm not sure exactly what's normal for where this was, but it was at 4500ft so not too unusual. Joys of elevation. I have a bunch of spare parts, will try swapping the MAP to see if it makes any difference.

[SiriusC1024]

84kPa is about 6000ft.

[SiriusC1024]

Try the Cranking Fuel and Spark settings from a Corvette. Cranking VE is already there.

[edcmat-l1]

Uh, any idea what the complete specs are? This a stock engine? Injectors? What vehicle is it in? Is there a fuel pressure gauge on the vehicle? If not, why? That's the very first thing you should do. Put a fuel pressure gauge on it and leave it for the duration of tuning.

[Alvin]

I'm definitely what you'd call an amateur tuner, but I've done a handful of Gen 3 vehicles at this point, everything from small cam 5.3s to big cam turbo 408s, and I've come across one that I just cannot figure out. I'm leaning towards something outside of the tune given the symptoms, but I've combed across every single thing I can think and wanted some input.

I've always been able to more-or-less use the stock tune with some additional base running airflow and some higher RPM as a starting point for idle tuning on something this size. This one is absolutely refusing to fire. It cranks like there is no spark or fuel, except the occasional light popping. We've figured out some light tricks to get it to start very occasionally, and once it's running it idles well despite the fact that this was the initial base tune I guessed at.

Can somebody look through the idle/startup tune and the logs of trying to start it and confirm that something outside of the tune is going on? Every sensor on the vehicle is brand new, we've tried injectors, throttle body and IAC, checked fuel pressure, tried another computer, and it just will not fire reliably, so I'm running out of ideas.

The occasional pop you describe leans me torwards a bad cam sensor. They often will not throw codes. When they act up at least every other start will have popping like the engine is out of time

[bman22]

Try the Cranking Fuel and Spark settings from a Corvette. Cranking VE is already there.

I'll give that a try.

Uh, any idea what the complete specs are? This a stock engine? Injectors? What vehicle is it in? Is there a fuel pressure gauge on the vehicle? If not, why? That's the very first thing you should do. Put a fuel pressure gauge on it and leave it for the duration of tuning.

Engine is pretty much bone stock with the exception of the cam. It's got the 216/220 Elgin (1838p) cam. Vehicle is a '99 2500. Only thing not stock on it right now is the cam and the heads are 317s instead of the original cast iron pieces. It still has an EGR valve as well as all other emissions controls.

Injectors are stock right now, especially while trying to deal with the starting issues. I've tried a few different sets to see if it was an issue. Fuel pressure is a rock solid 58psi, was one of the first things I checked.

The occasional pop you describe leans me torwards a bad cam sensor. They often will not throw codes. When they act up at least every other start will have popping like the engine is out of time

I've also had cam sensor issues, including one that just didn't get plugged in, and this hasn't been exactly the same. I hooked up a tech2 and verified I seem to be getting good cam sensor counts. Additionally, with the ones I've seen in the past, they'll pop and backfire pretty aggressively on one crank, and then fire without issue on the next. This one will virtually never fire without a problem, and the pops are much smaller and tend to only happen when you start playing with the throttle trying to get it to catch. I do have more cam sensors though and can swap one out to see.

I appreciate the pointers everybody, just trying to make sure I'm not missing something. I don't have access to the vehicle again until Friday, but I'll run through the suggestions and see what happens.