Power Loss on 1987 E-150

[CapriRacer]

I've posted this on another web site, but thought I might get some good responses here as well. If you've already responded on that other web site - Thanks!!

I'm experiencing power loss on a 1987 Ford E-150 351 4 bbl with 150,000 miles. The air pump and all the associated plumbing has been removed and all the air lines plugged (There are a bunch of those!!) Did this about 2 years ago.

Since then the van has always run rich, especially at idle. This makes the van hard to start in hot weather when the engine is hot - in fact I have to hold the throttle open while I crank it.

The van works fine until the throttle opens more than 10%. Past 10%, I'm getting some kick back through the carb.

It came on quite suddenly. I was towing, then the van started to slow down like I was going up a grade - except I wasn't.

I'm leaning towards a vaccum leak - the engine starts much easier now, even when hot - except that the leak would be most active under high vaccum situations, and that's just the opposite of what is happening.

I'm also thinking the vacuum advance diaphram might be leaking and not working when the engine vacuum changes. I'm also leaning towards coil since the plugs, wires, rotor and cap have all been replaced.

I am sure it's just a simple, single thing - I've experienced this type of thing before, but it was so long ago, I can't remember what the fix was.

Sure would appreciate some help.

 

[NYEngineer]

I think you hit the nail on the head with the vacuum leak since you said you had to open the throttle to start it and now you don't. It will also run hot if it's lean.

 

[punisher]

Assuming Motorcraft/Holley- Check your power valve for a rich idle condition. Blown diaphragm= fuel sucked directly into the intake manifold. Sparkplugs get nice and carboned up when that happens usually.

Vac advance is easy to check- disconnect vac from carb, and apply vac to the hose while idling. If idle RPM increases when vac is applied to dist advance, it is good to go. Verify dist vac is hooked to venturi vac and not manifold vac port on carb.

 

[c502cid]

Sure it is a 4bbl? I've never seen anything but a 2bbl from the factory on these.

Another direction to look at. I think your timing chain is getting ready to give up the ghost. I owned two of these vans and the stock timing chains will stretch a ton, so much you are surprised they stay running, and eventually the nylon gears will go. Same symptoms you are describing. Throw a timing light on it and see if you can see any jumping around.

 

[CapriRacer]

Quote:

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Sure it is a 4bbl?

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Absolutely. I've changed the carb twice trying to chase down other peculiarities.

But I don't think the timing chain is it either, because the problem seems to only occur when the throttle is opened more than about 10%. Otherwise it is fine.

 

[ms21043]

You can check for things like burned valves, weak/broken valve springs, cam/ lifter/rocker arm problems, late valve timing (timing chain) late ignition timing, clogged exhaust (suspect cat since you say it's been running rich) and vacuum leaks using a simple vacuum gauge. All these things could cause problems you describe.

 

[mechtech2]

Sounds like cam timing - at least look into it.

 

[CapriRacer]

For those who are interested:

After much frustration and lots of changing of parts, it turned out to be:

Ignition control module.

 

[TedT]

It could be that the cat. is blocked. This can cause a pulse of air to come back through the carb. and pick up more fuel. Sometimes you can see fuel shoot out of the top of the of the carb. Try disconnecting the exhaust ahead of the cat. just to test. Also when the engine is running, is the exaust too quiet, just a woosh sound? That is the sound of a plugged cat.

Ted

 

[punisher]

Glad you got it fixed. Ignition modules are usually a go-no go concern, but a fix is a fix. I learned to always carry an extra Duraspark module when I had my old F-150. None of my later TFI equipped Fords stranded me (knock on wood). Being stranded is not one of my favorite pastimes