Mast Motorsports L92

shrek tits · May 3, 2015

I am running the Mast Motorsports L92 H.O cam, computer,etc package on a 2010 L92 with about 28,000 on it. My problem is on cold start it will fire of then backfire through the intake then die. After that it will fire off and run perfect the rest of the day. If I cycle the ignition "fuel pump" 2 or 3 times it wont do it and will just fire up. Once it's warm it starts just fine. Anybody have any guesses or things to check? It's not that big of a deal but kind of anoying and I'm sure I have something just a little off somewhere. Thanks in advance.

b.boyd · May 3, 2015

I run a LS3 with the Mast package. Mine has done that twice. In both instances it was cold start up, and I did not hold the key in the start position long enough before I let go. I was starting it from outside the vehicle. It started up immediately after both instances. Feel free to call Damon at MAST if you have concerns..

shrek tits · May 3, 2015

Mine will do it bacically every time. I tried holding the key longer but doesn't help. A backfire through the intake is a lean condition correct? I will call if I can't figure it out just figured it was something stupid I overlooked. Any other guesses?

patooyee · May 3, 2015

shrek tits said:
A backfire through the intake is a lean condition correct?

This is a snippet from another site:

"Extremely Lean fuel mixtures burn slower because the fuel molecules are farther apart & if the the fuel hasnt all burned off by the time the intake valve opens again, the incoming charge will be ignited and blow back out the intake."

I'm combining that with my personal experience to hypothesize that you are loosing fuel pressure when the ignition is off. Possibly the Mast cam allows valves to open longer / wider / sooner to make the engine more prone to it.

On my buggy once I shut the pump off I can watch on my fuel gauge as my fuel pressure drops, it will go down to about 20-40 psi and hover there for a while. If it sits for a few hours it will eventually drop to zero. I have no clue where it is going because I have no leaks, I have checked all the injectors, and I have check valves after the fuel pumps. If I start my buggy at these lower pressures it will run rough for a second until pressure builds up again. It will be perfectly fine until it sits for a while again. My LS2 doesn't backfire though, possibly because I have a stock cam. Maybe GM was aware of this and designed their cams to prevent it? Or maybe Mast just pushed the envelope a little too far and doesn't want to recall a batch of cams?

In factory form the fuel pumps have built in check valves to minimize the loss of pressure. But even they aren't perfect which is why the ECM primes the pump for 3 seconds the instant you turn the key. If my rig has sat for a really long time that 3 seconds is rarely long enough to fully prime the system up to 60 psi. I have a manual pump button in my cab that I often use to finish priming.

So long story short, your have low fuel pressure during the initial start, lean condition occurs, takes longer to burn, and continues burning after the intake valve opens.

I've heard a backfire can destroy the plastic intakes. I would want this fixed, especially if you have a $1000 FAST intake.

shrek tits · May 3, 2015

patooyee said:
This is a snippet from another site:

"Extremely Lean fuel mixtures burn slower because the fuel molecules are farther apart & if the the fuel hasnt all burned off by the time the intake valve opens again, the incoming charge will be ignited and blow back out the intake."

I'm combining that with my personal experience to hypothesize that you are loosing fuel pressure when the ignition is off. Possibly the Mast cam allows valves to open longer / wider / sooner to make the engine more prone to it.

On my buggy once I shut the pump off I can watch on my fuel gauge as my fuel pressure drops, it will go down to about 20-40 psi and hover there for a while. If it sits for a few hours it will eventually drop to zero. I have no clue where it is going because I have no leaks, I have checked all the injectors, and I have check valves after the fuel pumps. If I start my buggy at these lower pressures it will run rough for a second until pressure builds up again. It will be perfectly fine until it sits for a while again. My LS2 doesn't backfire though, possibly because I have a stock cam. Maybe GM was aware of this and designed their cams to prevent it? Or maybe Mast just pushed the envelope a little too far and doesn't want to recall a batch of cams?

In factory form the fuel pumps have built in check valves to minimize the loss of pressure. But even they aren't perfect which is why the ECM primes the pump for 3 seconds the instant you turn the key. If my rig has sat for a really long time that 3 seconds is rarely long enough to fully prime the system up to 60 psi. I have a manual pump button in my cab that I often use to finish priming.

So long story short, your have low fuel pressure during the initial start, lean condition occurs, takes longer to burn, and continues burning after the intake valve opens.

I've heard a backfire can destroy the plastic intakes. I would want this fixed, especially if you have a $1000 FAST intake.

Good info thanks!! Kind of what I was thinking might be going on. I was going to replace my fuel pump and filter reg anyways just so I would have a spare. Possible my fuel pump check valve is bad. Was their any more info on that site? If you want you can send me a pm. My fuel tank is also in the very back of the rig so their is a fair amount of fuel line to prime. Also does anybody know if their is a check valve in the corvet filter reg or at the fuel rail?

patooyee · May 3, 2015

shrek tits said:
Good info thanks!! Kind of what I was thinking might be going on. I was going to replace my fuel pump and filter reg anyways just so I would have a spare. Possible my fuel pump check valve is bad. Was their any more info on that site? If you want you can send me a pm. My fuel tank is also in the very back of the rig so their is a fair amount of fuel line to prime. Also does anybody know if their is a check valve in the corvet filter reg or at the fuel rail?

Sorry, should have provided the link to begin with:

http://www.stangnet.com/mustang-forums/threads/back-fire-through-the-intake-question.841042/

My fuel tank is in the back, too. I think my supply line is almost 20' long the way it is routed. Most fuel pumps have a check valve built in. Both of mine do and I still did the redundant inline external ones and it still leaks down. NWFLYJ (My shop-mate.) seems to think the leak down is occurring at my pressure regulator which seems logical. Its made by Aeromotive and I called their tech department about it. They said their regulator may not always hold pressure so that kind of ticks me off since they are supposed to be the best.. If someone knew for a fact that another one didn't do it I would change it out in a heartbeat.

patooyee · May 3, 2015

Don't know what ECM you are using but I use the stock ECM and use HPTuners. The internets is telling me that the priming length setting can be adjusted. This would be a good band aid for me. I'll have to look at my tune when I have time. Don't know if that helps you though.

shrek tits · May 3, 2015

patooyee said:
Don't know what ECM you are using but I use the stock ECM and use HPTuners. The internets is telling me that the priming length setting can be adjusted. This would be a good band aid for me. I'll have to look at my tune when I have time. Don't know if that helps you though.

I am using the Mast ecm. I would imagine it would be adjustable as well seems like you can adjust about everything if you know what you are doing. I am also probably close to 20' on my fuel line. Are you using a Mast cam also? Thanks for the link!!!

patooyee · May 3, 2015

shrek tits said:
I am using the Mast ecm. I would imagine it would be adjustable as well seems like you can adjust about everything if you know what you are doing. I am also probably close to 20' on my fuel line. Are you using a Mast cam also? Thanks for the link!!!

No, stock LS2 with stock cam. I'm not backfiring, I am just having a measurable fuel pressure drop when the pump isn't on that results in a rough start after having sat for a while. The root cause it the pressure loss, the system should hold most of the pressure almost indefinitely just like it would in stock form. But a band aid fix would be to increase the fuel prime interval.

shrek tits · May 3, 2015

patooyee said:
No, stock LS2 with stock cam. I'm not backfiring, I am just having a measurable fuel pressure drop when the pump isn't on that results in a rough start after having sat for a while. The root cause it the pressure loss, the system should hold most of the pressure almost indefinitely just like it would in stock form. But a band aid fix would be to increase the fuel prime interval.

Thanks for the info!!! If the new fuel pump or fuel pump run time works I will report back. Otherwise I will just run it.

shrek tits · May 3, 2015

patooyee said:
This is a snippet from another site:

"Extremely Lean fuel mixtures burn slower because the fuel molecules are farther apart & if the the fuel hasnt all burned off by the time the intake valve opens again, the incoming charge will be ignited and blow back out the intake."

I'm combining that with my personal experience to hypothesize that you are loosing fuel pressure when the ignition is off. Possibly the Mast cam allows valves to open longer / wider / sooner to make the engine more prone to it.

On my buggy once I shut the pump off I can watch on my fuel gauge as my fuel pressure drops, it will go down to about 20-40 psi and hover there for a while. If it sits for a few hours it will eventually drop to zero. I have no clue where it is going because I have no leaks, I have checked all the injectors, and I have check valves after the fuel pumps. If I start my buggy at these lower pressures it will run rough for a second until pressure builds up again. It will be perfectly fine until it sits for a while again. My LS2 doesn't backfire though, possibly because I have a stock cam. Maybe GM was aware of this and designed their cams to prevent it? Or maybe Mast just pushed the envelope a little too far and doesn't want to recall a batch of cams?

In factory form the fuel pumps have built in check valves to minimize the loss of pressure. But even they aren't perfect which is why the ECM primes the pump for 3 seconds the instant you turn the key. If my rig has sat for a really long time that 3 seconds is rarely long enough to fully prime the system up to 60 psi. I have a manual pump button in my cab that I often use to finish priming.

So long story short, your have low fuel pressure during the initial start, lean condition occurs, takes longer to burn, and continues burning after the intake valve opens.

I've heard a backfire can destroy the plastic intakes. I would want this fixed, especially if you have a $1000 FAST intake.

Just put two and two together that you where talking about your buggy laughing1 I thought the whole post was from another site.