Help with diagnosing engine/ Update with Pic

[jlembke]

Sooo,,,My bronco was running fine but occasionally would flood while driving. The last time I drove it, it flooded out and I had to let it sit for an hour before I could get it to start up. I was able to drive it home about a half mile and towards to the end of that drive it was running rough and I had to give it a lot of pedal keep it going. Made it home but it died in the driveway. The next day tried to start it and it was difficult to start. When it finally fired up, the engine immediately revved extremely high then died. Did this a few times. I thought it must be a carb issue so rebuilt the carb, same problem. I bought a new carb online, set it up, and it did the same thing. So, I'm guessing its not entirely a carb issue. I used the same fuel filter on the new carb so I could switch that out but I don't believe that would cause this. What else would cause the engine to rev high then die immediately upon starting?? Its a pretty original set up with the original engine and carb. Engine has about 50K on it. Any suggestions is appreciated.

 

[DirtDonk]

From my point of view, it has to be a carburetor or mechanical linkage issue.
The flooding sounds like a typical needle and seat/float issue. But the high revving has to come from the carburetor because there’s nothing else on a carburetor engine that can cause that.

Unless perhaps a huge vacuum leak could?
Check all your lines, especially to the PCV valve and any vacuum brake booster if you have one.
What year vehicle?
If you can get it running for a minute or two, check for vacuum leaks with a spray bottle full of water, or even a spray can with WD-40 or carb cleaner or whatever.

 

[73azbronco]

Throttle linkage sticking?

Vacuum leak?

How often is it driven? Is the gas good? I'm going in and saying ignition is probably good if it runs. This is a fuel/throttle control thing. Which could mean really bad intake leak. Do what Dirt D says ^^

 

[jlembke]

From my point of view, it has to be a carburetor or mechanical linkage issue.
The flooding sounds like a typical needle and seat/float issue. But the high revving has to come from the carburetor because there’s nothing else on a carburetor engine that can cause that.

Unless perhaps a huge vacuum leak could?
Check all your lines, especially to the PCV valve and any vacuum brake booster if you have one.
What year vehicle?
If you can get it running for a minute or two, check for vacuum leaks with a spray bottle full of water, or even a spray can with WD-40 or carb cleaner or whatever.

Thank you. Its a 74 no vacuum booster but I will check the PCV valve. I was thinking when it ran rough home that it could have created pressure and created a large leak possibly at the intake manifold, if thats possible. I will check. Appreciate it.

 

[jlembke]

Throttle linkage sticking?

Vacuum leak?

How often is it driven? Is the gas good? I'm going in and saying ignition is probably good if it runs. This is a fuel/throttle control thing. Which could mean really bad intake leak. Do what Dirt D says ^^

I don't think the linkage is sticking but will double check that. Gas was good when I was driving it. It has sat now for a while so its likely bad. Intake leak could be it because it has to be getting air from somewhere else to rev that high. Thanks for the replies.

 

[joebronco73]

The carb cleaner trick is super helpful in finding vacuum leaks (that's how I found my intake manifold leak). My leak didn't keep the engine from running, though, just kept it from running well and I couldn't get the carb mixture right. Have you checked your fuel pump?

 

[jlembke]

The carb cleaner trick is super helpful in finding vacuum leaks (that's how I found my intake manifold leak). My leak didn't keep the engine from running, though, just kept it from running well and I couldn't get the carb mixture right. Have you checked your fuel pump?

Not yet. Its on my list to check. Its also hard to start as I have to turn it over a long time and give it plenty of gas before it will fire up. Spark plugs look good though.

 

[73azbronco]

Manual choke, auto choke?

Is your EB jetted for altitude?

 

[.94 OR]

Not yet. Its on my list to check. Its also hard to start as I have to turn it over a long time and give it plenty of gas before it will fire up. Spark plugs look good though.

Give it plenty of gas, or holding the throttle open to allow enough air through the carb to lean out the flooded mixture?

 

[Johnnyb]

So is there observable black smoke when it's flooding, or gas smell?
This doesn't explain the high Rev on startup but I'm thinking about other things entirely, especially with all of the discussion of vapor lock recently.

-JB

 

[jlembke]

There is no issue with the jetting. It’s run perfectly in the past. It’s an auto choke and there is a strong smell of gas when it finally starts. It also has, and I should have mentioned this first, kind a shrieking sound when it starts. I think I may have a large leak somewhere and I’m leaning towards intake manifold. It’s hard to test it because it won’t stay running long enough but it’s all I can guess at. Is it possible that there was a manifold leak which was causing it to have to run rich and caused it to stall at stops or low RPMs. Those were the symptoms prior to the last drive. Then when I was driving home after the stall it was running really rough and I needed to give it a lot of gas to keep it running then died when I got home. I’m thinking that during the rough running there was pressure built up that possibly opened up the small leak that I had in the manifold. I’m hoping this is it anyway because that could be a pretty easy fix. Been looking at videos of replacing intake and it seems straight forward enough. Let me know if this doesn’t seem logical!! Thanks for the replies!

 

[Oldtimer]

EGR valve stuck?

 

[Johnnyb]

I don't know, in my experience intake gaskets don't fail that way. They're not too hard to change but it can be a p i t a to get the front and rear parts of the seal to sit in place while you're setting the manifold down, and if they don't it will leak oil.
I think I would look at the PCV valve or hose, it could have just split and cause a huge vacuum leak. The brake clean test will also work if it's the intake manifold.
And since you mention automatic choke, it could have flopped closed. That would cause the flooding.

JB

 

[jlembke]

EGR valve stuck?

I really don’t understand how the EGR operates. I have the one that’s attached to a plate that sits on the carb mounting bolts. But I assumed this thing hasn’t been working forever. It has two hoses off of it. One is currently plugged but has not been plugged in the past and didn’t seem to make a difference one way or another. The other goes to a metal tube possibly to the canister? Not sure. Is there a way to test the EGR valve? I’m pretty pot committed now in replacing the intake gasket since it’s all stripped down and ready to take off. All of hoses looked good. Couldn’t find any holes or apparent leaks. Is it normal to be able to pull the PCV valve out from the valve cover? I seem to recall it has always been that way.

 

[gr8scott]

The other goes to a metal tube possibly to the canister?

C4 transmission?

 

[DirtDonk]

I don't think the linkage is sticking but will double check that.

I forgot to mention, that along the lines of the linkage sticking, your choke fast-idle linkage can stick as well. They almost always do eventually.
Even if the area around the choke looks clean, I would still spray the whole linkage under the choke housing with cleaner, then a light lubricant.
WD-40 actually works very well, but is not really a lube per sé and does not last as long as some others that are dedicated to this task.
In a perfect world, this linkage does not need (nor does it want) to be lubed. But once 50 years of wear and tear have taken their toll, the aluminum and pot-metal bits develop "stiction" and don't always cooperate with reality.

Paul

 

[jlembke]

C4 transmission?

Yes

 

[jlembke]

So the intake is off. Man that is heavy. When I turn it over there a bottom pan thing that has half inch slot/hole in it. The hole doesn’t seem clean like it’s meant to be there but it doesn’t look entirely out of place. Just can’t think of why there would be a hole there

 

[jlembke]

Here’s a pic

 

[jlembke]

Also took the last gasket off and underneath there was this oil deposit. Where could that have come from? Seems like that’s just an empty cavity that would’ve sealed off by the gasket.