my 82 Z28 has an interesting dilemma...which is completely heat-related. If things are cool/cold outside and the car isn't too hot, nailing the throttle yields a nice rush of power all the way through to the 7000 rpm redline.

If its hot outside and I've done a pass or two, the car will completely fall on its face in the upper rpms. Sometimes the shift from 2nd to 3rd will cause a bog, sometimes the bog comes on before it even shifts into 3rd.

It isn't a miss or ping, but an all-out "shut down" of power (as if the ign key were turned off). Funny, tho, since backing off the throttle to let it "wake up" and then nailing again will yeild clean acceleration right to redline.

Ideas?????? The cat isn't plugged (there isn't one), the Roch Qjet was just rebuilt/tweaked by a local pro, the fuel pump is a brand new Holley hi-po piece. I've been told that my ign might be to blame (overheating coil). Is this possible?

Any ideas as to where to look? I haven't double verified the obvious (could very well be a bum f.pump), but I want to hear some ideas...

thanks!
b

 

Fuel. It's boiling in the line before it gets to the carb, possibly before it gets to the pump. Key piece of info is that letting off the accelerator brings it back. Been there, done that.

I'm assuming you aren't using the fuel return line, since the typical hi-po pump doesn't have one. Hooking one up via a 3-port regulator may help, since unused fuel from the pump goes back to the tank, keeping a cool supply coming up to the engine.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

Nope, not using the fuel return line. Interesting, tho, since my feed line from about 3 feet under the firewall to the pump is 3000 psi hydraulic line (3/8 inside). Its some thick, stiff stuff that I used thinking that my regular rubber line was colapsing at high-rpm. Its got a thick metal braid inside.

The fuel lines aren't anywhere near the headers/exhaust. The feed line is at least 6-8" away from the collector (at its nearest point). I've purposely run the fuel line up and out of the way of the headers to avoid this!!! The pressure side of the pump is also run back around and out of the way....

I guess testing with a cool-can will tell the tale....what about a fuel cooler??

b

 

Can't tell the players from the fans without a score card.

Rig up a fuel pressure guage and duck tape it to the outside of the windshield where you can see it while driving. Go driving. Watch fuel pressure take noseidive at top of every gear. Figure out why. Fix it. Never have problem again. Fuel pressure readings at idle/in neutral are meaningless. Only under the exact conditions that cause the problem are the readings meaningful for diagnosing a problem like this.

Who says high performance isn't easy?

If you DO have good fuel pressue at the inlet then ditch the stock fuel filter in the nose of the carb, if you haven't already- it's restrictive. Use a nice big external filter with a see-through plastic shell- Fram makes a nice one.

Last but not least: Your fuel pump. I know, I know. It just CAN'T be that!! But I swear it can. And it's not the pump's fault. Somtimes the draw from the tank is just too much for a block-mounted mechanical pump under hard acceleration. That was the case with my Malibu. Plenty of pump, big lines, big filter, still couldn't hold pressure at the top of second. Answer- a "booster" pump. Carter makes a low pressure electric that is easily mounted near the tank. Tap into the fuel line and it'll give the fuel just a little boost up to the mechanical pump which will finish pumping it up to the carb as well as do the final fuel pressure regulation. Works like a charm right into the 11s. Without it I was having fuel starvation only running high 13s! MAJOR improvement.

 

This is the whole reason why I asked the question here...some real answers!

Very interesting thought....that even though its a hi-po mechanical pump, it still cannot feed the beast. Another person told me that running electric AND mechanical was the way to go...and I thought he was nuts.

So there is an electric pump designed just for this purpose? Interesting....but how do we explain the heat-relatedness?? The hotter it gets (outside and engine-wise), the worse the problem becomes....

What about ditching the mechanical for an all-out electric? I've already ditched the carbs fuel filter, and do run a large glass unit just outside the carb.

What about proximity....I've got the fuel filter on the pressure side of the pump....would it work better on the inlet side?? (perhaps help my prob)??

Thanks for the advice.

b