[macdaddy5.7]

A couple months ago I bought a 2015 Challenger R/T plus STP with 4k miles on it. Got a hell of a deal too! Anyway, have not done many mods yet. Only did the hellcat airbox swap and AFE dry filter. Car came with a full flowmaster exhaust already from the dealer. After I did that, and repeatedly checking the seals on the box, connections and all that, my cold start each morning before work seams to be a bit lagged. A longer crank and almost a hiccup before starting? Sounds like an old school carb fart. Ive read a few forums that are a bit outdated now and was wondering if anybody has had that problem and fixed it or any ideas on what to check? No way its a fuel pump as the thing just eats when I need it too. I always fill up with 91-93. The car starts and runs just fine when its warm, its only after its been sitting around 8 hours. Its summer here in NJ so the temp isnt the issue. Not super concerned I just miss my clean ass cold start in the morning! Thanks in advance. Here is my car btw!

 

[Rockster]

A "carb fart" is a spit back through the intake. That is a sign of a lean mixture which can be due low fuel pressure or an intake air leak.

Low fuel pressure does not have to be a fuel pump issue. It could be the fuel system has an anti-drain back valve which if is the case could be letting fuel pressure and fuel drain out of the fuel lines.

If you turn on the key and let the fuel pump run a bit before you attempt to start the engine does the engine start better?

But before I went much further with the above possibility there is the good old last thing touched first thing suspected. You might have introduced an air leak.

 

[macdaddy5.7]

I have tried to cycle the the ignition to the run position for a few seconds to let the fuel pump run before starting, no change. Also I didnt let it run for that long before I started it so I will give it a shot. Ive gone over the airbox again and again and everything seams air tight. My thought is maybe a MAF sensor? Im just wondering if the hellcat intake may have reduced the amount of air pressure sucking in vs the stock air box upon start up?

 

[Rockster]

There is the possibility the air box has upset the laminar air flow past/through the MAF and the MAF is not able to correctly determine the amount of air thus it doesn't fuel the engine correctly at least at cold start.

(With another brand of car there was a plastic "mesh" screen not too far in the tube from the air filter box to the throttle body. Some owners felt this screen interfered with air flow restricted it and removed the screen. This caused the engine to run poorly. Not real lousy, just not quite as good as it had been running before that. Turns out the screen was there to smooth air flow right from the air box into the tube so by the time the air reached the MAF turbulence was greatly reduced.)

You can't be the first to put a Hellcat air box on a 5.7l engine, though. So if there as something inherently wrong with this mod I think it would be common knowledge.

 

[macdaddy5.7]

There is the possibility the air box has upset the laminar air flow past/through the MAF and the MAF is not able to correctly determine the amount of air thus it doesn't fuel the engine correctly at least at cold start.

(With another brand of car there was a plastic "mesh" screen not too far in the tube from the air filter box to the throttle body. Some owners felt this screen interfered with air flow restricted it and removed the screen. This caused the engine to run poorly. Not real lousy, just not quite as good as it had been running before that. Turns out the screen was there to smooth air flow right from the air box into the tube so by the time the air reached the MAF turbulence was greatly reduced.)

You can't be the first to put a Hellcat air box on a 5.7l engine, though. So if there as something inherently wrong with this mod I think it would be common knowledge.

Thanks for that. I will probably go through the airbox one more time, and maybe even return to stock just for a cold start test to see if that changes anything.

 

[Rockster]

Going back to stock is a good idea. If the air box accounts for the behavior you'll know. If not then the odds you disturbed something during the swap over go up.

 

[A Guy]

If you weren't so low mileage, I'd have suggested

5.7L intake bolts reminder: [email protected] miles

I know this is a known “thing” already, but just in case any of you haven’t heard already: the intake bolts on your 5.7L have a tendency to loosen up over time/miles and need to be re-torqued periodically. My neighbor bought a used Charger with 89K miles on its 5.7L, and we were going over it...

www.challengertalk.com

Make sure the IAT sensor is properly seated

A Guy

 

[macdaddy5.7]

I’m going to run back through everything in the morning, I’ll let you guys know what I come up with. Thanks man!

 

[macdaddy5.7]

Re-assembled my hellcat airbox and I think the seal was a tad off with the clips on the back of the airbox. Also the hose clamp on the intake in front of the throttle body was wayyy loose so I tightened that as well. Problem solved

 

[Chllngrswpr]

There is the possibility the air box has upset the laminar air flow past/through the MAF and the MAF is not able to correctly determine the amount of air thus it doesn't fuel the engine correctly at least at cold start.

(With another brand of car there was a plastic "mesh" screen not too far in the tube from the air filter box to the throttle body. Some owners felt this screen interfered with air flow restricted it and removed the screen. This caused the engine to run poorly. Not real lousy, just not quite as good as it had been running before that. Turns out the screen was there to smooth air flow right from the air box into the tube so by the time the air reached the MAF turbulence was greatly reduced.)

You can't be the first to put a Hellcat air box on a 5.7l engine, though. So if there as something inherently wrong with this mod I think it would be common knowledge.

Sorry but your misinformed. These cars do NOT have maf. They run a map sensor. Op probably has a bad injector thats leaking down at night or over extended periods of time. Hence the "carb fart" its a misfire. Quick check upon initial start up at the data in a scanner would verify a leaking injector from misfire code. Then as engine is running it cleans the plug off and runs correctly. Op stated that car runs fine warm or hot. Injector doesnt have time to leak. Ive seen it many times on the 5.7.

 

[Rockster]

Sorry but your misinformed. These cars do NOT have maf. They run a map sensor. Op probably has a bad injector thats leaking down at night or over extended periods of time. Hence the "carb fart" its a misfire. Quick check upon initial start up at the data in a scanner would verify a leaking injector from misfire code. Then as engine is running it cleans the plug off and runs correctly. Op stated that car runs fine warm or hot. Injector doesnt have time to leak. Ive seen it many times on the 5.7.

Ok. All my cars came with a MAF. A MAP is a bit foreign to me. Unlikely it would be affected by turbulent air flow.

 

[Chllngrswpr]

Only the hellcat runs MAF. Rest of the cars are MAP. Its more than likely leaky injector. Would have nothing to do with air flow