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ChrisJMcA · 06-26-2017, 06:16 PM

I have a 1987, E-350, carbureted 460 (vacuum secondaries), mated to a 3-speed auto trans, ending in dual axles under a 26 foot motor home. I bought it at 50,500 miles and it now shows 53,000 miles. It idles fine, and been told by a professional that he doesn't think anything is wrong inside the block. I have a couple of problems that may or may not be related:

The vacuum secondaries do not open under load. The carbs been rebuilt twice, once professionally (after I took a swing at it). They open on the bench when blowing air through the primaries, but not on the manifold. There are no obstructions on the manifold preventing the valves from opening, and vacuum was measured at the manifold (via port) at 20-25. No exhaust obstructions because the pipe was cut through prior to the muffler and there was no change in performance.

Also, this thing loses power and runs a temperature going up hills. It is not hesitating or misfiring. I have to manually downshift into second as there is no kickdown (the linkage is connected, it just doesn't do anything). I thought it was because the secondaries were not opening. The fuel filter near the tank was loaded with Mars-like dirt (it was cleaned and has since stayed clean), & I've Mickey-Moused the secondaries into opening at least partially by putting a nut and bolt in the linkage, but I still get the same problem, albeit a tad more power. Nothing dramatic. I can get it to stay at 45 mph, but my normal operating temp of 200 goes up to 235 on hills and looks like it would still go up if the road didn't level out. The temp also likes to climb when going 55-60 up a slight incline. It's a stock radiator that was checked for flow (good), the water pump was replaced 2 years ago when I bought it, and the radiator hoses were replaced with rigid ones that do not collapse. I'm looking into getting a fuel pressure gauge installed so I can see if fuel pressure drops under load. Since the fuel filter was full of crud, perhaps the fuel pump, after pushing all that crud, is crapping out under load. But I'd like to know instead of guess.

I've already put my soul and a ton of cash into this beast (somewhat affectionately known as The Pig), so I'd rather not give up on it, but I'm getting close.

She's a heavy girl and I'm asking her to tow my Honda CR-V too (the problem occurs with or without the Honda attached, and I'm lead to believe the motor should be able to handle it all).

Any ideas?

subford · 06-26-2017, 07:08 PM

As far as the C6 transmission goes you might want to watch this video:

https://www.youtube.com/watch?v=Zv5Pw8QMOfs

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tderonne · 06-26-2017, 07:22 PM

Had a 1977 Holiday Rambler (it's in my registry) with a similar setup, including the tag axle, for almost 200,000 miles. I think you're on the right path checking basic stuff like fuel pressure. As for the secondaries, have you verified that the throttle pedal is fully opening the primaries? What's the state of other maintenance? You mention it having a new water pump, safe to assume stuff like plugs, wires, cap, rotor etc. are in good shape? Has it ever run better? Did it run any better when you found the dirty fuel filter? When you did the water pump you didn't dig into the timing chain did you? We did that to a buddy's 1977. Between the really sloppy chain and ditching the emissions era retarded cam timing gears, it picked up about 20° of cam timing. Went from barely running to awesome.

ChrisJMcA · 06-26-2017, 07:40 PM

I'll look at my linkage to make sure it's set up correctly.

I've read your post on the secondaries elsewhere. While aware of all of that, I tend to not think they would apply in this case since the secondaries opened up while on the bench (and the ball check/gaskets/adjustment screw were all as they would be while on the engine).

I bought it running pretty much the way it does. There was a slight improvement in the power loss/heat buildup after cleaning the filter, and again with forcing the secondaries to open.

The plugs, wires, rotor and cap were checked out by my mechanic and given the green light. And, though it doesn't have a lot of throw before it hits the boards, the pedal opens the primaries all the way.

I do not believe the timing chain was investigated when the water pump was put in, else I would've been charged for that. I've read about advancing the timing at the cam in other forums, but tearing the motor down to that point is a last resort. I plan on exhausting less invasive avenues first.

wildcat2015 · 06-27-2017, 09:48 PM

Hi having been a big block chevy man all my life I suggest you replace the carb. It appears you dont have a manifold leak given your vacumn readings and if your ignition timing is correct its the most likely cause. The fact that its getting hot suggests a lean out so you may have blocked passages or jets within the carb. You may want to install a fuel pressure gauge to make sure your fuel pressure isn't dropping as that could also cause a lean out. Cheers Graham

ChrisJMcA · 06-28-2017, 05:46 AM

Quote:

Originally Posted by wildcat2015

Hi having been a big block chevy man all my life I suggest you replace the carb. It appears you dont have a manifold leak given your vacumn readings and if your ignition timing is correct its the most likely cause. The fact that its getting hot suggests a lean out so you may have blocked passages or jets within the carb. You may want to install a fuel pressure gauge to make sure your fuel pressure isn't dropping as that could also cause a lean out. Cheers Graham

Thanks Graham.
Something is definitely up with the carb, but those secondaries open up under vacuum on the bench. It's also been rebuilt/cleaned twice. I'm looking into a possible fuel delivery problem (which, in my mind would not explain the secondaries failing to open - they open with vacuum, not fuel, correct?). However, an electric fuel pressure gauge I can monitor from in the cab runs about $200. A new, in-tank electric fuel pump is less than that. Given the sludge that was found in the fuel filter, I may just go ahead and replace the in-tank fuel pump and give it a whirl.

wildcat2015 · 06-28-2017, 01:57 PM

the secondaries open when the vacuum drops to a low level at med to full throttle (ie: high vacuum holds them closed). If you are sure there are no blocked passages in the carb it is likely to be a fuel delivery issue, have you tried blowing through the fuel line with compressed air from the tank forward? If that appears Ok then I agree that changing the pump should be the next step. High running temp is definitely caused by lean out which is lack of fuel. Cheers

subford · 06-28-2017, 02:10 PM

By the way the vacuum is generated by the primary venturi and not the engine to open the secondaries.

fcbbob15 · 06-28-2017, 02:39 PM

Is the carb a Holley? If so do you know the model #? Does it have a secondary metering plate or a block with jets and power valve? Was a Holley rebuild kit used. Exhaust manifolds can glow cherry red under load if lean! Does it have a catalytic converter? I know a lot of questions but they are important and may help solve your problems.

subford · 06-28-2017, 05:23 PM

Quote:

Originally Posted by fcbbob15

Is the carb a Holley? If so do you know the model #?

He should have the Holley 4180-C Carburetor.

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wildcat2015 · 06-28-2017, 06:11 PM

if the secondaries arent opening you will have a loss of power but NOT excessive engine heat as described. It must be either lack of fuel or badly blocked exhaust in my opinion (assuming timing etc is all ok). Cheers from little old NZ (Home of the Americas cup !!)

CampDaven · 06-28-2017, 06:23 PM

Colder plugs. New wires, cap, rotor.
Replace fuel filters. There were 2 on my 84 P30.
It worked! Not a lot of $.
But I did fight it for a month.

Bob_C · 06-28-2017, 07:38 PM

Easy way to check timing chain.......remove dist cap, rotate crank by hand till timing mark on crank is on 0 and rotor is on #1.......rotate engine backward till the rotor just starts to move....make a mark on crank pulley, measure about how many degrees of rotation......more then 10 degrees of crank rotation and i'd be in there.....Could have the 'run silent' type cam gear, aluminum and plastic, which wears.....

ChrisJMcA · 06-29-2017, 02:56 PM

Quote:

Originally Posted by wildcat2015

the secondaries open when the vacuum drops to a low level at med to full throttle (ie: high vacuum holds them closed). If you are sure there are no blocked passages in the carb it is likely to be a fuel delivery issue, have you tried blowing through the fuel line with compressed air from the tank forward? If that appears Ok then I agree that changing the pump should be the next step. High running temp is definitely caused by lean out which is lack of fuel. Cheers

This is deep, and I'm going to ask you to explain it to me because I want to understand it. When I think of vacuum I think of air movement. The stronger the air movement (atmosphere evacuating an area) the stronger the vacuum, and hence, the secondaries want to open. You're saying when vacuum drops (that sounds to me like when the engine is struggling, not a lot of pull), the secondaries open? Why then wouldn't the secondaries want to stay open all the time, if everything was operating smoothly, with my foot on the accelerator a touch (to free-up the linkage)? Looking at Subford's post of the secondary throttle explanation above, I don't see where additional fuel would remedy the failure of the secondaries to open.
Given the time constraints (camping the weekend after this one) and my mechanics availability in the next couple weeks, I'm asking him to drop the gas tank, clean it & replace the in tank sending unit. If this is how vacuum is supposed to work, I'm now hopeful the secondaries will engage on their own.