I Have A 460 That Runs Great When Its Cold, After It Heats Up Something Brakes Down And Loses Power Bad. Any Suggestions!

 

EFI or Carb?

 

carb and heats up really quick

 

Make sure choke is fully open after warm-up. Thermostat stuck in closed position could cause rapid heat up. Make sure distributor vacuum advance is operating properly. Make sure timing is set properly (at idle with vacuum line to dist. disconnected and plugged the timing should be 8 to 10 deg. BTDC). If the thermostat has been changed recently make sure it is installed properly, i.e., sensing element toward engine.

 

I have the same problem, runs real spunky when cold, then after complete warm-up, sluggish feeling begins.
Cat converter is currently off, had it diagnosed with no codes.
1996 E-350 460 EFI

 

Sound like a bad ignition coil, breaks down when Hot. Just how hot is the engine getting anyway? And how long is the time from cold to Hot?

 

The time frame is approx 10 minutes. Coil sounds like a culprit and inexpensive. And something that the diagnostic may not pick up. The van passed smog no problem, also light throttle seems to feel fine when hot, but mid to full is sluggish (when the coil needs to put out more voltage).
I also (think) I hear slight pinging. Is there a way to adjust the fuel mixture on this thing?
And Oops, the van is a 1995, not 1996.

 

Pinging requires a timing retard, mixture adjustment probably won't change the pinging unless you are super lean (the tips of your spark plugs are white).

 

Could also be a bad vacuum valves. Don't remember the years, but some trucks were equipped with a temp controlled vac valve in the dist advance line. Not a common problem, but easy enough to check (just bypass the valve).

Brad

 

A bad carburetor power valve can cause a lean mixture that probably wouldn't be noticed when engine is cold (i.e., choke on). Power valves for Holley 4180's are two stage units that are tailored to a particular engine/vehicle. If the carburetor has ever been rebuilt with an aftermarket "kit" the power valve was probably replaced with a "one-size-fits-all" unit resulting in less than desirable performance. If you decide to replace the power valve, get all the numbers stamped on the carburetor and send them to the Holley Technical Service website ( http://www.holley.com/TechService/ ) and ask them for the proper original equipment P/N. You can then get a Holley or (cross to) a Walker exact replacement. You can change the power valve without removing the carburetor from the engine--be sure to use new float bowl and main metering block gaskets. It wouldn't hurt to ask the Tech folks for the main metering jet sizes too, just in case somebody has changed them in the past.

 

The two stage power valve was for trying to help fuel economy without leaning the motor out to badly under heavy payloads, not taylored to a paticular engine and vehicle otherwise there would be different power valve in different weight rated trucks and there aren't. His problem appears to happen when engine is warm and carb problems rarely cause that. In this case a single stage power valve should work fine. The main jets actually only control fuel flow at or near WOT and his problem is when warm only, main jets can't be the problem and I doubt a power valve is causing this problem. Still sounds like electrical and in this case the ignition coil.

 

Walker lists 44 different two stage power valves for the Holley 4180 carburetors each with different combinations of operating vacuum levels. Walker part numbers are 70-25 through 70-68. Dont believe me--look it up!

 

I know there are a bunch of different daul stage power valves, but all those numbers listed will fit any Holley carb 4150/4160/4180. Years ago I installed them in my 1968 F250 390 that I upgraded to a 4 barrel (4150, List 1850) , dual exhaust and a 390 GT "S" code intake for carrying the camper and towing my race boat. I tried 4 different valves before I found what I wanted, improved preformance with improved milage. But the factory only chooses the valve for the best all around performance for the base engine and it doesn't matter which truck/drive train/ load capacity it goes into. The purpose of the dual stage power valve is to enrichen the fuel system a little under low vacuum drop situations under heavy loads then full enrichment as vacuum drops farther, instead of full enrichment as with a single stage valve. It helps gas mileage while still protecting the engine from being too lean under heavy load. An empty truck shouldn't need that protection. You will have to get up pretty early to teach me about Holley carbs and the toys that there are to improve them. I have been playing with these carbs since 1960 in street cars and trucks, race cars, boats, both pleasure and race. I've had 2 barrel setups, dual 2V setups, tri-powers, single 4V and dual 4V on just about every kinda of manifold there is from the old dual plane to a lonf runner cross ram and and I even attended a Holley tune-up class put on by Holley techs in the 70s. I started installing power valve protectors 10 years before Holley got around to it because the dual stage valve were really expensive back then.

 

Bear 45/70,
I defer to your superior knowledge and experience. I based my statements on what I was told by a retired Ford dealership mechanic who suggested I contact Holley Tech. to get the proper Holley power valve p/n for my particular carburetor list number, which I did. I replaced the existing unknown brand power valve, that the previous owner had had installed, with a Walker equivalent (p/n 70-29) of the Holley #125-216. This cured my problem of poor throttle response under light acceleration at highway speeds. I assume the problem was due to improper calibration of the previous power valve since it was not "blown out" and I had already corrected other problems including replacing the main jets someone had drilled out and improper choke operation.
With regard to your statement about the 4180's having one base size for all vehicles here is a direct quote:
"POWER VALVES and ENGINE VACUUM There is a lot of misunderstanding concerning power valves in Holley carbs. Many 4-barrels come with a particular power valve depending on the carb list# and application." From: http://www.lovefords.org/tech/holley.htm
There is a similar statement at http://www.mortec.com/carbtip1.htm .
Maybe it only applies to 4180's but getting the right power valve for my carburetor list # certainly made a noticable improvement.