fuel delivery issue

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fishy68

Tyr Fryr's Inc.
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Got a gremlin in the fuel system on my Cuda that's got me stumped. The engine is a 408 that produces approx. 450 hp. When it's cool out (75* or less) it runs just fine all the way through the 1/4 and the AFR shows about 12.8 at WOT. As soon as the outside temp hits about 80* the darn thing falls on it's face at about 85-90 mph and I see the AFR meter go full lean.

Here's a list of everything I've replaced

Fuel tank

3/8" pickup (stock location, not a rear sump)

3/8" pre-bent fuel line that has no kinks or sharp bends

Very large high volume 100 micron fuel filter before the fuel pump

Edelbrock #1720 6 valve mechanical fuel pump that says it's good to 600 hp.

#6 braided fuel line to a high volume 25 micron filter screwed into the fuel feed line

#6 Dual feed line to the carb

In addition to replacing all those items I have added a heat sleeve to the lower radiator hose because it's pretty close to the fuel pump and I shot it with a temp gun and the fuel pump was nearly as hot as the radiator hose. Now with the heat sleeve in place I can grab the lower radiator hose with my bare hand when the engine is 190 degrees and it doesn't burn me.

I have also added insulation to the fuel line that's in the engine compartment to keep it cooler.

When it's 80* or less outside the engine runs right on 180 and even when it's 90* degrees out the engine doesn't go above 200 degrees.

Been thinking about adding a rear sump to the tank but I'm not sure it'd solve the problem because this happens even when I have a full tank of fuel.

I have a fuel pressure gauge on the feed line and it shows 6 psi cold at idle and when the engine is warmed up drops to 4 psi at idle. I know that's a little on the low side but since it's a mechanical pump the engine has to be running and when it's running it's using fuel so unless the pump output was deadheaded I don't think it'd show more psi, maybe I'm wrong with that thinking???

I've checked and triple checked the fuel filters for trash/restrictions and never find anything

The only other thing I can think of is the tank is not vented. Could the fuel requirements be such as to require a vent? If so what's the best way to do it?

Any ideas sure would be appreciated. In my 35 yrs. of slinging wrenches I've never ran into a fuel system I couldn't work out, but this one's got me.

Sorry to be so long winded.
 
Not clear--can you determine if pump pressure is dropping when the problem shows up? The pump should have enough reserve that it can maintain pretty much regulator set point pressure. If not, something's restricted, vapor lock problem, or the pump is falling off. Could be something like a worn or loose cam or a pump arm tryin' to fail. It happened to me on a 440 (pump arm)

Now you say "the tank is not vented" and I'm not intimately familiar with 'Cudas but I thought ALL pre 70 A bodies were vented via a vent welded into the fuel filler tube. (70, I believe, was a split year for the addition of the carbon can system and "pressure vacuum" caps) Since your body went "E" in 70, I don't see how that could be an issue, unless the vent was removed, or otherwise somehow plugged (bugs, gum, rust, etc)
 
Unfortunately I don't have a fuel pressure gauge to watch when it happens. I may have to install one to verify it. I have checked for restrictions from the tank all the way to the carb and can't find anything that's glaringly obvious. No tight bends on the line and all the hose is relatively new. When I built the engine year before last I put a new pump eccentric in it, a moly coated one. I'd think it's ok but no way to say positively without pulling the pump off and looking inside at it. I just picked up an inspection camera and if I don't find any problem soon will do that.

I bet your right about the tank being vented via the filler tube. Forgot about that but I think I remember seeing a small tube running along side the filler tube.

Thanks for the input Del
 
What carburator are you running?
I fought heat issues with my 750 vac secondary holley all summer.
It would only start starving for fuel when it idled more than 5 minuates in temps over 85 degrees. Tried everything 1" phenolic spacer, raised the heater hose support on the front of the engine up 4".
The motor was not running hot, about 1/2 way up on the gauge.

I put a 625 street demon on it with a plastic body, and braded lines, it helped alot but it still started acting up in 90 degree temps stuck in traffic for 5 miles.
Once I drive it for a mile or so it would clear up.

I am thiniking that I also have a vent issue, because I have never had this problem before on any Mopar and I have a bunch from 1956 to present day.

I have never seen heat issues like I have on this old truck in 30 years with playing with these small blocks.
 
................my pink duster acted the same way as urs does..........replaced fuel pump=problem solved........kim.......
 
What carburator are you running?
I fought heat issues with my 750 vac secondary holley all summer.
It would only start starving for fuel when it idled more than 5 minuates in temps over 85 degrees. Tried everything 1" phenolic spacer, raised the heater hose support on the front of the engine up 4".
The motor was not running hot, about 1/2 way up on the gauge.

I put a 625 street demon on it with a plastic body, and braded lines, it helped alot but it still started acting up in 90 degree temps stuck in traffic for 5 miles.
Once I drive it for a mile or so it would clear up.

I am thiniking that I also have a vent issue, because I have never had this problem before on any Mopar and I have a bunch from 1956 to present day.

I have never seen heat issues like I have on this old truck in 30 years with playing with these small blocks.

Carbs a Holley 750HP. My engine is pretty efficient so I didn't have to jet it very fat at all, 71's in the front and 78's in the back. You'd think with jets that small it wouldn't require much fuel.

I have a 1" Moroso plastic spacer under the carb and I shot the carb with the temp gun and it's actually a little cooler than the fuel pump runs. Read 150* off the fuel pump and 140* off the carb.

Know what ya mean about the fuel issues nowadays. I wonder if some of it isn't due to the Ethanol they put in the fuel?? Seems like I read something about it having a much lower boiling point than gasoline.
 
I think most ALL the problem is alcoholized gas.
 
................my pink duster acted the same way as urs does..........replaced fuel pump=problem solved........kim.......

Every time in the past that's what I've found but this is the 4th fuel pump I've had on it and it acts exactly the same way. Of the 4 pumps 2 were new (1 Carter HV and this Edelbrock HV) and 2 were used (1 Carter HV and 1 Holley HV). The used Holley pump came off a buddies low 10 second race car. Worked fine on it when he took it off so I'm sure it was a good pump.

Been looking around for a cheap HV electric pump to put back by the tank and bypass the mechanical pump and see if that solves the problem. I'm also going to rig up a temp fuel pressure gauge that I can watch when I'm running it to verify that's the issue. Find it hard to believe it's anything else since the AFR meter goes full lean, but I think it'd be good to positively verify it.
 
Fishy,x2 on the fuel. If you use ,one brand of pump gas,try another. Or throw a couple gallons of race gas in,see if it acts differently.
 
Fishy,x2 on the fuel. If you use ,one brand of pump gas,try another. Or throw a couple gallons of race gas in,see if it acts differently.

Would you (or anybody else) know if they have to post on the pump if it has ethanol in it? I thought they did and have seen it on some pumps but never on Shell pumps so I assumed it's ethanol free and that's where I got gas the last time and it still does it. Next time I need gas I will try a different station just to see how it acts. Wish I had a place to get race fuel close by but the closest place is 40 miles away. Next time I'm going that way I will pick some up and try it also.

Thanks everyone for the tips.
 
Have you gotten any further with this?
 
Have you gotten any further with this?

I believe the biggest problem is the ethanol content in the fuel. That explains why it only acts up mostly on hot days. I bought a little fuel tester to test the fuel from some of the stations around me. The station that I used the most is the local Shell station. It doesn't advertise having ethanol added and the 93 octane checks ethanol free but the mid grade which is what I usually run tested at 10% ethanol. 87 checks ok. Strange that the mid grade has ethanol and the others don't? So far I've only found 1 station with mid grade that checks out ok.

I thought about buying a cheap electric pump and putting it back at the tank just for a test but the more I thought of it I decided if I was going to do all that work I might as well just buy a real good pump and do it once and be done with it so I bought a Holley Gerotor pump. Also upgrading all fittings to Russell high flow fittings. From what I've read the electric pump mounted right at the tank should should help with any vapor lock issues, which I believe this is. I just got the new Holley Gerotor fuel pump bolted in and wiring ran today. Fittings should be here tomorrow to plumb it. Took me a while to save up the money for the pump cause it's pretty expensive.
 
Will do. Had something come up today so I didn't get it finished but I will tomorrow. May not get to drive it till Tues. though cause their calling for rain the next few days.
 
Fishy - have you ever tried to jet up when it's doing this? The fuel mix could be going lean and causing detonation - which loses combustion control and releases oxygen in the exhaust and shows it as lean. Just curious...
 
Fishy - have you ever tried to jet up when it's doing this? The fuel mix could be going lean and causing detonation - which loses combustion control and releases oxygen in the exhaust and shows it as lean. Just curious...

I haven't tried jetting it up when it acts up because on cool days it never lays down. Have held it to 120 and it was still pulling hard. When I put the carb on I started out with 75's and 82's and it was real rich. Down in the high 10's if I remember right. That's why I have it jetted way down where it's at now. I've heard it spark knock when I had inferior gas in it but I never hear it ping even when it lays down unless it's a really hot day. Although at the speed I'm moving when it lays down things are pretty loud so it's possible I'm just not hearing it. That's an interesting thought you have though. Never considered that possibility. Right now I'm in the middle of installing the new Holley HP150 electric pump so when I have it back on the road (was hoping to have it done today but it didn't work out) hopefully it'll be solved. If not I'll try going back up with the jets and see what happens. Thanks
 
Well it took me long enough but I finally got the new Holley HP150 pump installed. The weather has turned off much cooler so it's hard to say if the problem is solved but I think it should be cause it holds a constant 6.5 psi under full throttle all the way through the 1/4 but I guess I won't know positively until next year when it warms up again. I'd be surprised if it acts up now even if I get fuel with ethanol in it as I have the pump mounted right at the tank which will keep the fuel line charged at all times. Thanks everyone for their input
 
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