motor falls off at 5k....

sndrummer · May 19, 2007

ok here it is.....
ive got a 94 gt vert with a 331 stroker. it has scat forged crank, rods, pistons, tfs heads, track heat intake, bbk 75mm tb with edelbrock elbow, c&l intake with afm 75mm maf calibrated for 30# injectors, msd 6al w/ shift light set at 6200.....etc....
my problem is that when under load, the rpm's hit 5k and the engine cuts, it's not a rev limiter cut, but almost feels like a fuel cut to me.....i am at a loss as to what it could be, it doesn't do it when you rev the car just sitting in the driveway at an idle, only when under load. so any help you guys could give me would be great...and feel free to ask more questions about the set up if you need to....

-Mike

True 5.0 · May 19, 2007

You say you have the shift light set to 6200. Do you mean the rev limit? Did you some how bypass the computer rev limiter? The factory rev limiter works by shutting down the fuel supply around 5800 RPM IIRC. The 6AL works by cutting spark to random cylinders and is set using a variety of plug-in modules.

sndrummer · May 19, 2007

im not 100% about the stock computer rev limit, because i bought the car 2 days ago. it came with a sct tuned chip, so im not completely sure what the tunes are. but you said the stock one cuts fuel at 5800, and my engine is falling off right at 5k.

final5-0 · May 19, 2007

Mike

If you are using an aode they got a pretty low rv in place with the
pcm's used with them.

Has it always done this

Maybe

valve springs
fuel filter

I see you got MSD stuff ... have you by passed it for testing

Grady

blksn955.o · May 19, 2007

What cam? I may just be blind but I didnt see what cam was used?

I would look at valve train...the springs and PR length/rocker setup for float if your not running the stock cam.

Like Grady said the auto may play a role as well with its diff. tune and extra drag.

True 5.0 · May 19, 2007

True 5.0 said:
You say you have the shift light set to 6200. Do you mean the rev limit? Did you some how bypass the computer rev limiter? The factory rev limiter works by shutting down the fuel supply around 5800 RPM IIRC. The 6AL works by cutting spark to random cylinders and is set using a variety of plug-in modules.

Whoops! I need to correct myself. The stock rev limit is set to 6250 not 5800.

What rev limit module are you running in the 6AL? It'll be printed on the back of it.

FWIW - The 6AL rev limit module should ALWAYS be set lower than the limit in the EEC. The fuel shut-off of the EEC is a great way to run lean and burn up parts. The 6AL's random spark kill is a much better way to go.

go-stang5.0 · May 19, 2007

factory fuel shut-off wont hurt anything...if there is no fuel in the cylinder...how can there be a lean condition?

The only time you run lean with a factory fuel cutoff is if your adding fuel from elswhere (not via the injectors) such as a wet nitrous kit. Fuel cutoff very very bad in that situation .

But otherwise your dandy .

Now for your problem, I'm assuming you have a stick (since I saw a shift light in there)...You say you have only had the car for 2 days...do you know what kinda cam is in the car now...maybe you run out of powerband there (not likely tho since youo say its very abrupt.)

Have you checked fuel pressure? As rpms increase, the fuel press. should increase also...if it drops off at high rpms than you have a fuel flow issue....chances are you need to change the fuel filter...but it could possibly be the pump going bad.

I'd start with checking the fuel filterand go from there.

sndrummer · May 19, 2007

thanks for all the help guys. i am running an aode that has been rebuilt with a lentech shift kit and all the other goodies. we are in the middle of adjusting the valves right now, and from what ive seen from the previous valve settings, the adjustment should help a bunch. the cam i am running is a comp cams xe274hr. and im gonna look at the back of the msd, but it will take a little work as the previous owner had it mounted inside the drivers side fenderwell. again thank you all for the help and keep it coming if there is more ideas out there. we are looking into the fuel system right now because there is still the stock pressure reg. on the car, and we will change the filter. it has a 255lph pump which was put in last october so it should still be good.

-Mike

hollywoodstang · May 20, 2007

FUEL need more fuel

Redsnk95 · May 21, 2007

Spark blow out or the fuel filter is dirty. I would start with a basic tune-up...new plugs, cap, rotor, fuel filter, and clean the mass air element.

95opal · May 21, 2007

go-stang5.0 said:
factory fuel shut-off wont hurt anything...if there is no fuel in the cylinder...how can there be a lean condition?

go-stang.... the eec shuts down fuel but not spark, thus a lean condition.

After you verify everything is ok with the valvetrain, try and see what type of fuel pressure you are getting when she shuts down. Possible the stock regulator is on its way out.

Click to expand...

Redsnk95 · May 21, 2007

95 opal. GoStang has it correct. If there is no fuel at all in the cylinder how can you have a lean condition. The fuel cutoff in the stock EEC does not hurt anything, it is a common misconception. I run the PMS in my car which it uses Fuel Cutoff as it's rev limiter. I run the 2step used in the PMS which cuts fuel, which I use the 2step with the transbrake. Been that way for a long time and no problems. If you really think about it you cannot have a lean condition if there is no fuel in the cylinder. Cutting back spark, like using an MSD ignition, is worse on the motor due to fuel wash on the rings.

sorry for the thread hi-jack

sndrummer · May 23, 2007

so i replaced the regulator with the aeromotive unit, set it to 48 psi. i haven't changed the filter yet, i will do that today and give you all the heads up. thanks for the help.

WhiteDevil · May 23, 2007

sndrummer said:
so i replaced the regulator with the aeromotive unit, set it to 48 psi. i haven't changed the filter yet, i will do that today and give you all the heads up. thanks for the help.

You want 39psi vacuum off.

Also, if there is no fuel then there is no comubstion so there cannot be lean condition. Everytime you downshift your car cuts fuel (0 pulsewidth verified by my TwEECer and wideband) so if that was bad we would all be in a world of Hurt.

motor falls off at 5k....

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