454 Power Loss & Probable Vapor Lock

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454 Power Loss & Probable Vapor Lock

Home > Discussion Forum > Mechanic's Corner - Engines

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All Messages in Thread	Author	Date
454 Power Loss & Probable Vapor Lock	Goney	9-6-03
I have a troublesome 1984 Winn Brave P30 454 with Carb. Under prolonged driving or load and in high temps, such as the AZ desert heat, I lose power and at times have been brought to a dead stop. Most of the time, I can feather the throttle and keep it going, but at the cost of top speed. 52-58 mph on the highway, rather than the 70-75 mph in normal running. It acts like a bad coil. So I replaced it. Same proplem after. I replaced all fuel filters too, without any difference. Then I found the carb bowl dry after a dead stop, so I figured fuel pump. New mechanical pump. Still no cure. New distributor cap and wires. Same deal. The air intake hose was shot and was drawing air from behind the radiator and next to a hot engine so I put in a new 3'"x 8" snorkel drawing off the front grill unobstructed with new 4" hose directly to the airbox intake. Ran much better, but still no cure. I recently came to a dead stop again in the desert near Bylthe in mid-day, let the engine cool an hour the when I primed the empty carb bowl the gas boiled (large bubbles) and vaporized. Scary! (This was just before the intake fix BTW.) I have a 24' coach, main fuel tank at the rear and the reserve tank halfway back on the driver side. I experience the same problem with both tanks once it begins to occur. The tank switching unit is halfway down the coach on the passenger side. Now I'm thinking, in order of priority, in line auxilary electric fuel, then carb spacer (carb heat sink), then fuel line insulation. Maybe even an fuel line chiller. Have I overlooked something? Do I have the right priority? The pump has it own subset of problems. I first thought was the pump should be as close to the rear tank as possible, but then what happens if I have to switch to the reserve? A switch to cut power to that pump seems wise. Or if the pump goes after the tank switching unit it could just remain always on. Real fancy would be a pump at each tank and individual power switches for each. You see the problem. I'm going mad. Any input would be greatly appreciated.
Re: 454 Power Loss & Probable Vapor Lock	Chuck P32 454 Chevy 33K Mi	9-7-03
I have the SAME Chassis, I just went through Vegas, Mojave, I95 from Vegas to RENO on AUG 19th, 112 Degrees, and so prob... and I am betting you DID not used to have this PROB. So I am betting that your EGR valve is stuck open at least partly and THUS causing EXTREMLY hot intake manifold temps in turn super heating the CARB and fuel. Replace it is easy and cost about 77-100 dollars for the part... also Make sure your PCV is working well. You could test B4 replacing If you have or get a Infra red temp reader (Radio shack 29.99 or 49.99) and drive around town in your area and get on Freeway and then after say an hour, pull over open the dog house and point that IR temp reader at different points on your intake and if you see readings that are much higher then 200 degree's you have something SUPER HEATING the intake or your heads are getting too hot (cooling system prob.) as the intake should be around the same temp as the rest of the engine and that will be around 200 with a 180 thermo, or whatever the number, but remember the cooling system is mostly made for the top end of an engine an the oil system cools the lower parts (Very generally I am speaking Obviously the cooling system cools the whole engine, It is more responsible for the TOP END that is all.. I am now betting with 95% certainly that your EGR is feeding SUPER HOT Exhaust gases 100% of the time up into your intake.. Causing this prob..Let me know please if you find otherwise I like to expand my knowledge base.
Re: 454 Power Loss & Probable Vapor Lock	mike	10-16-08
So far all the answers and possable solutions sound reasonable. I have been a GM mechanic for 33 years and the on eproblem everyone overlooks is the ingition module inside the distributor cap. The most common issue is what apears to be vapor lock is after driving and the engine gets hot it shuts down and stalls,but then will start right up again after it cools down. This applies to any and all GM engines regardless of size.
Re: 454 Power Loss & Probable Vapor Lock	Russel	9-7-03
Make sure the heat crossover valve in the exhaust manifold is not stuck forcing the exhaust from that side to go up thru and across the intake manifold when it shouldn't. These can really heat the carb. second, if you go back thru the forum archives here for about 6 weeks I think there is a post similiar to yours that I told about rerouting the fuel line from the fuel pump to the carb to get it out of that heated area.
Re: 454 Power Loss & Probable Vapor Lock	Sam Watson	9-6-03
Have you considered gasoline circulation? That is, near the carb inlet fitting a tee is installed in the line. One leg of this tee has an orifice in it to restrict flow and so maintain volume to the carb. The gasoline going through this orifice is returned to the tank you are drawing from, ( a simple solenoid valve accomplishes this). By this installation, vapor lock doesn't occur as readily as vapors and fumes are bled off as they form, the gasoline in the line(s) stays cooler, etc. As you stated, gasoline does have low temperature boiling point factions in it for cold weather starts. Also, gasolines are regionally blended for the conditions found in different locals. Thus if one filled large capacity tanks in a colder enviroment and drove out near Quartzite in the summer, one would be beset by the dreaded vapor lock.
Re: 454 Power Loss & Probable Vapor Lock	Derek Dahl	10-5-05
We have a 1994 Flair Class A with the Chevy 454 engine. Throttle body fuel injection. We have a similar problem I hope to get some advice on. When I get started uphill, and it gets under a load, it starts cutting out and missing, and I have a SERIOUS
Re: 454 Power Loss & Probable Vapor Lock	Gary	9-12-05
I had the same problems, Changed fuel filters,coil,fuel pump cleaned carb. Still didn't solve the problems. Finally dropped the fuel tank and found a kin in the rubber hose from the regulator and the soak in the tank was doubled over and plugged with dirt. Now have lots of power was starving for fuel. This all took two seasons to solve. Was about to trade the motorhome in
Re: 454 Power Loss & Probable Vapor Lock	chuck P32 454 33K	9-9-03
Emm, they make a Thema a Jet Carb that has the exacta same body with themo barrier properties... Other the Buy a COOL Can and run some coils of fuel line (from Summit) and COOL the fuel, or FIND out what is heating it.. Mine never gets that hot and I just went through the DESERT ion the heat of the day for two days STRIAGHT 440 miles and NO heat related issues as yet (Over 110 degrees and in fact Dog house was some time 240 according to IR Temp from RADIO shack, (sale goes on and off on IR hand held, I talked the guy in to honoring sale price as I said he was out when I saw them and he gave me a RAIN check BUT I lost it (NOT) so I lied a little.. sorry Radio Shack, I only have spend untold thousands there,
Re: 454 Power Loss & Probable Vapor Lock	Goney	9-6-03
I did consider it. I believe there is one off the bottom of the fuel pump which is 1' to 2' below the carb. Is that not sufficient as a return? ( The fuel line does travel from the pump to the engine front, up, and back.) If I put in the bleed off near the carb, can I tap into the pump return line? Is the solenoid a one way valve? What specific parts am I asking for at the parts house? BTW, I filled up about 30 minutes from where I stopped so I had regional fuel. Thank you for your help Sam.
Re: 454 Power Loss & Probable Vapor Lock	Sam Watson	9-7-03
That's right, GM did use a bleed off line from the pump back to the tank. Follow that line back to see if you have a six port fuel tank switching valve, or two three port switching valves, ( the fuel return must go to the tank that the fuel is being drawn from, hence it must be switched also). If that is the case, then you can just remove the bleed line from the pump and plug the fitting on the pump--it is an inverted flare and they make plugs to do this---and connect the bleed off line to the tee at the carb inlet.Ford used just such a setup, and they were not known for vapor locking. You might also want to check if the hot air control on your air cleaner is shutting off the heated air from the "stove" on the exhaust manifold, that should happen at around 110-120 degrees air temp, feel the air cleaner lid after driving for awhile.
Re: 454 Power Loss & Probable Vapor Lock	Goney	9-7-03
No not new; this problem has nagged me for several years. It nearly dies EVERY lake trip near the top of a very long 30 mph uphill. A couple times it has died on the hill. I mostly pray and feather the pedal hoping to keep it going. I have had an empty carb bowl three times so I'm thinking fuel starvation. I had a friend with the same coach; he got so sick of it he sold it and got one without the same carb. He always blamed the Quadrajet. Said they were all like that.
Re: 454 Power Loss & Probable Vapor Lock	Sam Watson	9-7-03
Chuck, as you know, the EGR valve IS open when the engine is running. The only time it isn't is when the engine is at idle, or during warm-up, depending on design. A carburated engine doesn't compensate as well as a FI engine for a defective EGR that doesn't close when it should, therefore Goney would have complained of rough idle, and stalling at idle if this was the case. Can you still buy the infrared thermo sensors at RS for #29.99?
Changing a egr valve	Donald	11-13-03
I was told that I have a bad egr on the 2000 GMC 3500 rollback wrecker that I drive. It has a 454 engine. Is changing it something that I can do or should it be taken to a dealer or be done by a professional. I have done a lot of mechanic work but I'm from the old school and not up on all these new in fuel injected engines.
Re: 454 Power Loss & Probable Vapor Lock	Goney	9-14-03
The valve and exhaust manifold are less than a year old and the valve appears to be working correctly. It is real hot so it isn't easy to judge. I inspected and replaced all rubber fuel lines and I decided to install a 7 psi "Red" Holley Electric fuel pump. It is the same version pump which a friend had some success in using on his 32' RV. My friend says he has never had any fuel starvation issues. This install is in line after the tank switching unit and it is in addition to the stock mechanical pump. The psi is the compromise between the 2-4 psi and 10-12 psi ranges I was finding and the pump manufacturer touts it as one that doesn't need a fuel pressure regulator. I also noted that the switching unit for the tanks is close to an exhaust pipe. With two large pipes, that heat is hard to escape so I am also installing shielding, both commercial heat shielding from a hottrod shop and sheet metal screens as the primary shield in the area. I will let everyone know if this finally solves the problem after a test run. Someone asked that I do. I'll probably do a separate post usuing the same subject. Thank you everyone for your input.