'85 Bronco Acceleration Mystery

courtesy of Bob, The Auto Answer Man

I have a 1985 For Bronco II, 2.8 liter, V6 with air con., 4X4 and manual 5-speed trans. The odometer says that the vehicle has 128,000 miles. Has carburetor (not fuel injection).
The engine does not run smoothly when accelerating. It really has to work to get up to speed. Jerky acceleration. The idle is smooth. Also, the engine runs hotter than normal (almost to top of normal range on the gauge).

I took the car to my local Ford dealer for a diagnosis. There computerized check turned up seven different codes. They said that the engine needed the following:

1. EGR solenoid.
2. EGR valve..
3. EVP sensor.
4. Processor.
5. Choke pulloff.
6. Carb. Kit.

The estimate for these repairs was $1368 including labor. They charged $65 for the diagnosis. Well, I didn't believe this diagnosis so I took the car to another Ford dealer in a neighboring city for a second computer diagnosis. Also, when I pulled in and parked the car, the radiator boiled over (overheated). Well, the computer diagnosis from this Ford dealer said that all engine needed was an EGR valve. But, the service representative told me that a bad EGR valve would not cause the symptoms nor would it fix the problem. Also, they told me that they couldn't find the cause for the overheating. They charged me $19.73 and sent me on my way.

I was determined to get this problem fixed so I took the car to a nearby independent service center. These people replaced the spark plugs, the plug wires and fuel filter (at the carb) and checked the timing. I drove the car away and the problem was still there. So, I took it back. They kept the car for a week and drove it around (it overheated while they had it.) The mechanic told me that it needed a new accelerator pump and a new thermostat. He installed these items and the problem was still not fixed. (However, by this time there was noticeable improvement in the performance.) I took the car back again. When I picked it up for a third time, the mechanic said that he had to blow out the gas line (with compressed air) back into the tank because the filter in the line at the tank was partially clogged. He said that this fixed the problem but, as you can guess, it didn't. However, it did run somewhat better. This mechanic charged me only for the initial tune-up (plugs, wires and filter). The cost was around $136.

I have noticed that when the fuel tank is full, the engine performance is much better. Also, before the engine heats up the performance is even better, but only when the tank is full. However, in the background, I can still feel the jerky engine performance. The uneven firing doesn't completely go away.

Several times, I have added carburetor cleaning fluid to the gasoline in hopes of cleaning the fuel components. I did replace the radiator cap and at least the radiator does not boil over now, but the engine still runs hot. Total cost so far is about $220.00 and going up. I am perplexed. What do you think the problem is?
V. S.

Well, you have two distinct problems that could cause the other to get worse. I think that you should first address the overheating problem. When the engine is cold, I want you to look in the radiator through the cap. Do you see any white scaly stuff attached to the walls? If so, then I would recommend replacing the radiator, or have it professionally re-cored. If not, then you might need to run an antifreeze flush. You might have a slightly plugged port in the engine block somewhere. Also, how is the water pump? When the engine is hot, do you have good flow? All of these things that cause overheating can reduce performance.

Now, after we get the overheating solved, let's address the performance issue. One mechanic said that he blew the fuel line out, that is good. Do we know that the fuel pump is good? Also, a bad EGR valve CAN effect performance. Especially if it is open when it should be closed. If it is stuck closed, then no, your emissions will just be up, but if it is open at the wrong time, this can hinder your performance. Since you had three diagnosis that said the EGR is no good, then I would have it changed... They cost around $80 from Pep Boys, and you can do it yourself.

You had also mentioned that one guy said the choke pulloff was not working.... Running with the choke on will foul out the plugs and quickly reduce performance. The way to easily check is when the engine is cool enough to work on, pull out the plugs one at a time and read them.... Look at the colors and residues left behind. There should be none other than a little orange from your cleaner solution. If they are sooty black, then the carb needs more work, if they are wet with gas, back to the carb... If they are wet with oil, then this is an entirely different problem. If they are spotted with white specs, then this indicates a lean run condition and will cause overheating.

If all this fails, then maybe your cat is plugged and causing excessive back pressure. This will cause both overheating and poor performance. BUT, they just don't plug for the fun of it, there must have been something else that failed to make this happen. You had mentioned that one guy said the computer was bad... this could do it. Try these things first then let me know.
Good Luck!
Drive Safely!
Bob, The Auto Answer Man

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