Dyno'd Today - POOR HP Numbers - HELP!

[Treachery]

Thanks for responding guys. See this thread:

http://forums.stangnet.com/showthread.php?p=5552014#post5552014

I've attached my dynosheet to this thread which shows exactly where the engine drops off.

What's been done so far: I've replaced the distributior with an MSD; changed ignition to Crane Hi-6s; coil changed to PS1 (came with the ignition); changed spark plugs to Autolite 3923; changed wires to Motorsport 9mm; had the throttle body plumbing corrected; fuel pressure corrected (pressure WAY too high); cleaned the mass air sensor elements; replaced the FMU- calibrated for 30lbs. (190lph fuel pump); engine timing at 10 degrees.

I took the car out to test and appeared my Mustang still misses or cuts out at around 4500rpm @ WOT. When my Mustang is eased to 4500rpm, there is no problem. I managed to get my hands on another A9L computer and i installed it. Since then, i've tested only once and the engine held steady and did not cut out. I will test again this afternoon to see if the problem is really resolved or not.

Thinking back at the possiblity of the spark blowing out.. The plugs are gapped at .035". If the problem is the plug(s) blowing out, how much shorter must the gap be? When i first had the Vortech installed, i was advised that the plugs should be gapped to around 0.22" for starters.

 

[dderek]

dont even tell me youre running 19 or 24lb injectors. you should be in the 40s at least.
h/c/i and 8psi. upgrade your fuel system. check and replace all ground straps.
make sure you buy a mass air meter calibrated for your new injectors, make sure you get a blow through one. im not sure of the difference though

 

[boostang89lx]

Not much of an expert here either, but what jimc347 said makes sense to me. You noticed pinging under load. If you notice pinging under normal driving conditions, it must be much worse under boost. Computer may be shutting it down when noticing excessive knock. Just a thought.

 

[MatthewP]

These kind of problems can be very difficult to find, but here are some of my thoughts:

- If the mixture is too rich, it may not light off. Often when I see cutouts around 4500 it is because of a mixture that is too rich.
- Too much plug gap on a boosted application can cause this problem. Set them at about .035"
- A stock alternator, especially in a car equipped with electric fans, often contributes to misfires above 4500 because the system voltage is low and spark energy drops off. Use a volt meter to check your system voltage. If it's below 14V with the car revved up a little, and you haven't done a 3G alternator conversion, change the alternator.

I had an N/A car in my shop with this type of problem the other day, and he definitely had a system voltage problem. I did manage to get the car to run clean by advancing the timing a little higher than usual, but I gave him the same advice I am giving you about the alternator.

You're 5th gear pinging problem is there because running boost in 5th gear creates a very high load on the car. You will need to pull timing to resolve it if you really intend to run boost in 5th gear, otherwise I recommend you keep your boost use to 4th gear or lower.

Good luck.

-Matthew

 

[stang8urimport]

I had the same problem once. It turned out to be a weak coil. Ground the coil with the coil wire and an old spark plug... The spark should be nice and blue... if it's yellow or red it's not hot enough and you got a crappy coil.

 

[Treachery]

After doing some research, i'm going change the plugs again but gap them to .030" or so. They are presently gapped at .035" and the engine cutting out at high RPM is sounding more and more like the plugs are blowing out.

Then again every theory thrown at me sounded logical.

I'm going to drive off a cliff, if the spark plug gap is the problem. I've replaced working quality parts for *new* quality parts not to mention the price of the labor on the things i couldn't do. Thus far, i'm in the thousands $$$... But the the engine is running absolutely great!

Will post outcome later.

Oh yeah- I'm running a Powermaster alternator. The black 130 or 140 amp. It's one of the suspects in this mystery. I'll address that if shortening the plug gap does not work.