Could it be valve float???

[kilby94]

I've searched and searched for the answer to this question but all i can find is other people asking the same thing. I have a 91 GT with an e-cam, upper and lower typhoon intake, 351 Windsor heads (D0OE casting), 1.6 RR's, 70 mm TB, Msd wires, blaster coil, K&N, and a few other odds and ends. My problem is that it will not rev past 5000 RPM, at idle or first gear. It pulls really hard up until about 4000 RPM then gets weaker and weaker until 5000 when it starts to pop. Not a loud devastating pop just a low pitch missing noise. Fuel pressure is good, i've replaced the ignition module, timing is 10 degrees, and the check engine light is not on, but does work. I have foung other posts where people have the exact same problem but they never say what they did to fix it or if they have fixed it. I was told that it could be valve float and i've been told that if it were floating valves it would have blown up by now. Any help woul be greatly appreciated.
Thanks, Richard.

 

[lang williams]

what kind of springs are on those heads? with the roller cam you might need to upgrade them if they are not already.

 

[88mouse]

If the valves are floating it would sound like a rev limiter. Like lang says what springs you running on those heads?

 

[kilby94]

Not sure what springs are on the heads. It has new 1.6 rockers and the springs don't look like they are from 1969? I bought the car and the heads were already on the car and assembled. Just wanted to make sure someone else thought it sounded like valve float before i went out and bought new springs. The car ran like crap when i first got it i'm now just getting all the twirks worked out of it. The timing was at like 24 degrees when i first got the car, so who knows?

 

[gnx547]

How does valve float happen?

 

[kilby94]

From what i have gathered when the valve springs lose their strength they cannot close the valve quick enough to seal the combustion chamber before it should open back up again. So the valve isn't opening and closing like it should it kinda just floats around. Does that make sense? It does to me!!!!

 

[jtfairlane]

the springs don't look like they are from 1969?

Which really means that you have no idea what springs are on the heads. So what if they don't look like they are 40 years old. Is it within the realm of possibility that those heads were rebuilt once with stock replacement springs? Stock replacement 351w springs would not be suitable for a performance cam, even one as mild as the E303.

Valve float occurs when the valve spring binds due to mismatched spring pressures for the installed cam, leaving the valve stuck open, which in the worst scenario could result in the piston smacking the valve.

 

[kilby94]

Which really means that you have no idea what springs are on the heads. So what if they don't look like they are 40 years old. Is it within the realm of possibility that those heads were rebuilt once with stock replacement springs? Stock replacement 351w springs would not be suitable for a performance cam, even one as mild as the E303.

Valve float occurs when the valve spring binds due to mismatched spring pressures for the installed cam, leaving the valve stuck open, which in the worst scenario could result in the piston smacking the valve.

Well the words preceding what you quoted from my last post said that "i don't know what springs are on the car". And i guess it is within the realm of possibility that they are factory replacement springs, which is why i was asking if my problem sounded like valve float. Thanks for your help!!

 

[gnx547]

From what i have gathered when the valve springs lose their strength they cannot close the valve quick enough to seal the combustion chamber before it should open back up again. So the valve isn't opening and closing like it should it kinda just floats around. Does that make sense? It does to me!!!!

So when this happens, what happens then? Does the engine stumble? Can valve float damage the engine?

 

[kilby94]

The problem that i'm having is that it loses power in the higher rpm's and just won't rev like its supposed to. It could do some serious damage if the valve stays open and the piston is at the top of its travel. They will collide causing catostrophic failure. When my car gets to 5000 RPM its starts sputtering and almost sounds like a rev limiter, but from 4500 RPM and up it just has no power.

 

[88mouse]

Yeah i would say it have some valve float there.