Spark Plug gap? Flame out? 383 suggestions?
Thread Starter
Le Mans Master
Joined: Apr 2001
Posts: 7,411
Likes: 253
From: Little Elm TX
Spark Plug gap? Flame out? 383 suggestions?
Just did a dyno. The ignition fell flat on it's face at about 5200rpm. Everything has been replaced with less than 6000 miles on it. MSD blaster coil, MSD 8.5 mm wires, new opti, and NGK TR55's.
The 383 is running around 10.8-11.0 compression. Stock gap is .050. I think they are .050 now. (I didn't install them)
My question is, what would it run like if they were gapped too wide? What exactly is flame out and what causes it?
I know I don't want to go to small. It runs smoothly up to 6500rpms in 1st and 2nd but once it starts getting a load on it.........well........ :mad :mad :mad
Here are links to the runs: http://home.attbi.com/~r94lt1/dyno5.jpg http://home.attbi.com/~r94lt1/dyno6.jpg
Ideas or suggestions welcome. :yesnod:
For what it's worth, I'd rather not have to go to a MSD box "right now". I might do it later if I add a wet system but for now, I'd rather not mess with it, I'd like to get this working correctly first.
The 383 is running around 10.8-11.0 compression. Stock gap is .050. I think they are .050 now. (I didn't install them)
My question is, what would it run like if they were gapped too wide? What exactly is flame out and what causes it?
I know I don't want to go to small. It runs smoothly up to 6500rpms in 1st and 2nd but once it starts getting a load on it.........well........ :mad :mad :mad
Here are links to the runs: http://home.attbi.com/~r94lt1/dyno5.jpg http://home.attbi.com/~r94lt1/dyno6.jpg
Ideas or suggestions welcome. :yesnod:
For what it's worth, I'd rather not have to go to a MSD box "right now". I might do it later if I add a wet system but for now, I'd rather not mess with it, I'd like to get this working correctly first.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Spark Plug gap? Flame out? 383 suggestions? (R94 LT 1)
Are you sure it's ignition related? I only ask because of the A/F curve. If the plugs weren't firing then you would dump raw fuel out of the tubes and you'd see that A/F go way rich. Instead it goes lean. Perhaps your fuel system isn't keeping up properly? A friend of mine had a fuel pump that was failing him, he didn't really notice it until he couldn't hold enough fuel pressure to overcome the fuel pressure safety on a nitrous system.
It looks like you're running pretty lean across the board anyway, and then going leaner. Maybe something in the tuning, maybe your injectors can't keep up, or maybe it's a fuel pump going bad. I may be way off here, but ignition seems like it would really be more sporadic than what I'm seeing in your graph. It really looks like it just ran out of fuel to me. :cheers: I could be wrong, but it's something to think about.
It looks like you're running pretty lean across the board anyway, and then going leaner. Maybe something in the tuning, maybe your injectors can't keep up, or maybe it's a fuel pump going bad. I may be way off here, but ignition seems like it would really be more sporadic than what I'm seeing in your graph. It really looks like it just ran out of fuel to me. :cheers: I could be wrong, but it's something to think about.
Drifting
Joined: Jan 2001
Posts: 1,669
Likes: 1
Re: Spark Plug gap? Flame out? 383 suggestions? (Nathan Plemons)
I would say I have to agree. You might want to check the filter and which one you are running. The filter has to be able to allow the fuel to flow in volume. If you have not changed it make sure you use the GM one and not some cheapy one at the auto parts store. Try putting a fuel pressure gauge on the car next time and see what happens when it starts falling off.
Safety Car
Joined: Apr 1999
Posts: 4,623
Likes: 2
From: Ohio
Re: Spark Plug gap? Flame out? 383 suggestions? (R94 LT 1)
My immediate thought was fuel. Looking at your run pretty much confirms it. Running a 383 at WOT can use some fuel. If your injectors are sized correctly, and the pulse width is huge at WOT, gotta go with the fuel feed. At WOT the voltage to the fuel pump can drop, and can starve the injectors. Happened to a friend on a real hot 396 LT4 motor. He went to the Racetronix fuel pump set up and it cured the problem. So I didn't even think twice and put it in during the engine transplant. It's reasonable, and totally plug 'n play.
Thread Starter
Le Mans Master
Joined: Apr 2001
Posts: 7,411
Likes: 253
From: Little Elm TX
Re: Spark Plug gap? Flame out? 383 suggestions? (h rocks)
Thanks for the posts, keep the suggestions coming.
As far as the fuel filter, I'm running a wickes and it's got around 3000 miles on it so I doubt that's the problem. Fuel pump could be a possiblity, but then I have to ask, why would the fuel pump only come into play under load? I'm not having any trouble with it in first or second? I'll see if I can't get a fuel pressure gauge on it soon. :yesnod:
BTW, the injectors are FMS 30# and according to the log at WOT were only at around 60% duty cycle so they aren't being maxed out. I don't have a laptop so someone logged it for me. I'm still learning this stuff so I might not be "totally" correct on my statements. Once the files are sent to me, I can post them for anyone that's capable of reading them.
As far as the fuel filter, I'm running a wickes and it's got around 3000 miles on it so I doubt that's the problem. Fuel pump could be a possiblity, but then I have to ask, why would the fuel pump only come into play under load? I'm not having any trouble with it in first or second? I'll see if I can't get a fuel pressure gauge on it soon. :yesnod:
BTW, the injectors are FMS 30# and according to the log at WOT were only at around 60% duty cycle so they aren't being maxed out. I don't have a laptop so someone logged it for me. I'm still learning this stuff so I might not be "totally" correct on my statements. Once the files are sent to me, I can post them for anyone that's capable of reading them.
Pro
Joined: Sep 2002
Posts: 500
Likes: 0
From: Mississauga ONT
Re: Spark Plug gap? Flame out? 383 suggestions? (R94 LT 1)
what kind of a fuel pump have you got in there? sounds like a fuel pump to me. 1st gear accelerates very fast and the motor will go from 3500-6000 rpm alot faster than in second gear and so on. Because it requires more fuel at higher rpms for a longer period of time it cant keep up.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Spark Plug gap? Flame out? 383 suggestions? (388 SOLid RoLLeR)
Because it requires more fuel at higher rpms for a longer period of time it cant keep up.
Of course a cheap fuel pressure gauge taped to the windshield will give you the same information a lot easier if you can't data log while you're in the car.
Your fuel pressure should be around 39 at idle. If you remove the vacuum line going to the regulator it should go up to around 46. With the vacuum line in place at WOT it should go to 46 and stay there as long as the throttle blades are open.
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Thread Starter
Le Mans Master
Joined: Apr 2001
Posts: 7,411
Likes: 253
From: Little Elm TX
Re: Spark Plug gap? Flame out? 383 suggestions? (Nathan Plemons)
Thanks for all the response. I'm starting to think it's probably the fuel pump/regulator as well. Heck it's still the stock stuff, 151k miles, what should I expect? If they were working properly they should be okay, but the fuel pump is probably heading south. I've already got a quote for a Walbro pump and a new AFPR and if they go out I'll, HAVE to get them. For now, my budget is still trying to recover from the 383 being put in. So no more runs above 5k for now. I just hope it hangs on till after the holidays. I'll get a fuel pressure gauge on it and check just as soon as I get the chance. (don't have a gauge myself)
