hows it going all?
« on: Yesterday at 04:43:43 PM »




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my name is Shawn. i have a 86 mustang with a built 306 and a 76mm turbo.

having troubles with the car. it wont rev past 4500 under boost/load. feels like it hits a rev limiter. car runs like crap and wants to stall. once i shut it off and restart it, i runs great again unless i try to hit the 4800 mark. will rev to 6300 if a half throttle run is made with no boost. had it on the dyno getting tuned when we found this problem as its a new build. i will eliminate some problems for you guys, but any suggestions are welcome. plugs are brand new gapped at .26 and cold enoug for my set-up. has a brand new msd 6al2 box, brand new msd coil, tfi module and next to new wires and cap and rotor button. has 2 brand new 255 pumps in it. one in the tank and one in the line. has an adjustible fuel pressure regulater with gauge that is reading i am 43 psi even when it falls off at 4800. air/fuel is right where it should be. we even tried taking timing out and putting more in. also tried fattening it up and leaning it out but nothing worked. my tuner tried everything he could think of, but he has never had this happen to him before. also the maf is not pegging out either.

so what do you guys think?

 

.026 sorry.

 

Carb? EFI? Tuner?

 

efi with 42 lb injectors. 70mm tb and aeromotive adj. fuel pressure regulator. stock a9l comp. with an sct chip. i am from Alberta, Canada and my tuner is up here.

 

So as long as you mainting no boost, then it revs fine? How about feathering it at low boost?

 

maintaining no boost or pedaling it with low boost (3-5lbs) it will go to the revlimiter at 6300

 

You said your fuel pressure is reading 43psi @ 4800? How much boost is it making @4800. 43 should be ballpark before boost. Is the pressure rising with boost. What is the AFR when it won't rev? What cpu are you using? Auto or Manual? My buddy was having issues when he swapped to manual and left the auto cp in it. What do the plugs look like?

 

You symptoms point directly to spark blow out. I would try adding a ground to the engine and ignition components, or just closing the gap up further on the plugs.

Try to stick with NGK plugs, good MSD or Taylor wires, and keep teh gap tight. See if that does the trick.

 

It is a c4 and using the stock a9l with an act chip. The car is doing everything fuel wise it is suppose to be doing on the dyno. The afr is reading around the 12.5 mark With around 11 lbs of boost when it cuts out.

 

Is this pump gas? If so I would add some fuel to that thing and get the afr to 11.5-11.8. 12.5 is leaner than I like to see it.

Anthony

 

Ya it is pump gas. 94 octane. I can't add fuel to it myself unless I am at my tuners which is 2 hours away

 

Well, I should retract my statement a bit. If you are in fact having spark blowout issues then your wideband readings are useless at wot and boost. The unburnt fuel can give a false lean condition. I would do like others have said and diagnose spark blowout issues first, especially if your tuner is that far away. As chiaj mentioned, reading your first post would lead some of us to assume your fuel pressure is 43psi at 11psi. If your base FP is 43 psi, and the reg is a 1:1 then your FP should be 54psi at 11psi boost.

Anthony

 

i have no idea what the fuel pressure is at when the boost is that high. it is a base pressure of 43psi though. the gauge is on the pressure regulater which is under the hood. never thought to look at it while it was on the dyno

 

Im with disney on the spark blowout. What kind of ignition system are you using? Under wot cylinder pressures are higher, which means its harder for the spark to jump the gap. Without boost and free revving the pressures are much less so the spark wont have a problem. Most guys put some sort of ignition box in conjunction with gapping the plugs tighter on boosted cars.

 

Did some more research on my motor and found out it's is 9.8:1 not 8.8:1. So we are thinking I don't have enough valve spring for the boost. I have the edelbrock 5.0 heads and am still using the springs they come with. So in turn we are thinking it's floating the valves which is causing my issue. I replaced everything to do with spark with brand new stuff. So that's not the problem. What would you guys recommend I use for a spring now. I will be going about the 13-15 lbs of boost range. Also there will be a brand new water/meth kit going on it next weekend just for safety reasons now that I know the static compression is a full point higher