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DIY027 My Engine is running rough..What do I do?

Posted: Fri 12. Aug 2016, 16:43
by 59lincolnrag
OK .. so lets begin.
...How old is the fuel in the tank?
What is the condition of the fuel lines?
Check the firing order. Inspect the cap and rotor. Are there carbon tracks or discolored / burnt terminals? replace.
What about the plugs? Are they blackened with soot? Is the gap correct? clean with a brass brush or replace with the correct part.
When the car is running and you slowly close the choke plate does the engine speed up? Himmmm sounds like a vacuum leak.
....spray some carb cleaner around the base of the carb ...does it speed up? If yes that indicates a leak at the gasket or spacer plate. Examine the carburetor base gasket. Has the spacer been removed and cleaned?
Replace the gasket between the spacer plate and the intake manifold. ...DO NOT OVER TIGHTEN THOSE BOLTS!.
Look for broken or disconnected vacuum lines.
If the car has been sitting close to a year or more remove the gas. Add fresh gas 5 gal is good. Do you have fuel pressure ? Install a gauge if you have one how much pressure ? Does it meet spec?
When running you can adjust the carb (2 screws) mixture and set the idle to 800 RPM. After warm up re-set the mixture and idle. Set timing 4 degrees more than factory setting with the vacuum advanced disconnected and plugged. Reconnect the vacuum advance and re-set the idle to 800 RPM.
If the car has sat for a long time you will have multiple issues ...starting with the fuel...
If your sure its a miss fire ...Then ..disconnect the coil (12 volts). Remove the plugs.....charge the battery ....Remove the vale covers. Using a starter button crank the motor and watch the valves / rockers opening and closing. Is everything working ?? Look for a stuck valve ...bent push rod....broken rocker arm... You can also do a compression test at this point...

Just some ideas .....Hope it helps.

Re: DIY027 My Engine is running rough..What do I do?

Posted: Tue 26. Sep 2017, 16:22
by 59lincolnrag
A Common Problem Rough Running Engine more on the subject in order.

A properly-operating engine should run smoothly and without excess noise. If your engine starts operating in a manner that gives you the perception of “running rough”, it is likely due to a handful of common causes. A mechanic would investigate these common causes first in order to rule out a simple explanation for the engine’s unsatisfactory operation.

The common causes for rough running in an engine are:

Engine miss
Vacuum leak
Carburetor problems
Ignition coil
Spark plug wires
Mechanical reasons for a rough idle or engine miss...

High mileage vehicles with over 100,000 miles are the most likely to start having engine miss problems (it can be less in some vehicles), and it is advisable to have a compression test performed to rule this out. If you have low compression on one or more cylinders, this could be indicative of a more serious condition that would need to be fixed immediately.

The normal procedure for a compression test is to remove all the spark plugs, insert a compression gauge into the spark plug hole, and then turning the engine over about three times. Record the reading and do this for all the cylinders. If there is more than a 20% difference in any of the readings, a further test would be required to determine if the variance problem is due to an issue with the piston rings or the valves.

How can a mechanic (or you) tell which is the cause? The next step would be to squirt a small amount of oil around in the cylinder that had the low compression reading, and repeat the compression test on that cylinder. If the compression rises from the previous test reading, the problem is due to the piston rings. The oil helps to improve the seal, thus compensating for the compression that was lost from worn piston rings in the first reading. That’s why the compression would be higher in the second test.

If no increase is seen in the compression the second time around, the problem is most likely a burned valve. So now you have a better idea of which kind of mechanical fault is contributing to the problem.

If either problem is found, disassembly of the engine would be required to repair the problem. Special attention should be paid when removing the valve covers to make sure the valves are all moving the same amount of downward travel. Some engines have issues where the camshaft lobes will wear down and prevent the valve from opening which can also be the cause of the misfire. At this point, a good mechanic will be able to take the problem on and fix it. It may not be a cheap fix, however.

Rough idle caused by a vacuum leak

Most engine compartments have a maze of vacuum hoses which can wear out from use at any time. What we mean is they get brittle and hard over time. It’s just one of those things that happens during the life of the engine. If any of these hoses spring a leak, a lean air/fuel condition will result, causing a rough idle from the resulting engine misfire. The misfire could be in one cylinder or in multiple cylinders, depending on the size or location of the leak.

Vacuum leaks can also be caused by leaking intake manifold gaskets, vacuum brake boosters or vacuum supply tanks. How can you tell if the problem is caused by a vacuum leak? When driving a vehicle with a small vacuum leak, you will notice that everything feels normal at higher speed or RPM, but runs rough when the engine is at an idle. The engine could seem to rev up and down on its own at idle, but it’s more likely that it will simply rev up abnormally and stay there at idle. Either way, that’s a big indicator of a vacuum leak.

A mechanic will seek to get confirmation of a vacuum leak by looking for a lean running engine. This makes sense because a leak in a vacuum hose means more oxygen is entering the system than is needed. That results in a lean reading – not enough fuel, too much air. The engine can’t run properly if the air/fuel mixture isn’t right.

Once a mechanic has narrowed down the problem cause to a vacuum leak, they will want to determine where the leak is located at. It would be helpful if you can pinpoint it yourself. Who knows, you may be able to fix it at that point. When attempting to diagnose the source of the leak, the first thing you do is to listen for a hissing sound in the engine compartment. Many times it can be a simple thing like a vacuum hose that has become dislodged – in this case, all you need to do is reinstall it. If you suspect the leak is caused by a component like a vacuum brake booster or vacuum supply tank, you can pinch off the hose to the suspected component with a pair of needle nose plyers. If the component tested is the problem, the idle will smooth out.

Lastly, if you suspect the intake manifold gaskets are leaking, you can take a product like WD40 and spray it along the edge of the intake manifold while the engine is idling. If the gaskets are leaking, the idle will smooth out or change when spraying the WD40.

Rough idle caused by carburetor problems

When we start talking about carburetors, you know we’re thinking of both older vehicles with higher mileage. One of the indicators of a carburetor problem is a considerable amount of black exhaust smoke when the engine is up to temperature. A properly-working carbureted system shouldn’t produce volumes of black smoke – this would be a sign that something is amiss.

The first thing to check is the choke to make sure it is fully open when the engine is warmed up. If the choke is open, the likely problem shifts to an internal issue requiring a carburetor rebuild. A damaged float might be an example of this. In many cases, the floats in the carburetors have been damaged from the ethanol in today’s fuel.

Another area of concern is the throttle shaft in the base of the carburetor. Over time the throttle shaft will wear the carburetor base housing at each end of the shaft, causing a vacuum leak. You can check this in the same way I explained earlier in this article by using WD40. Just spray it at both ends of the throttle shaft and see if the idle straightens out or changes. Should this be the problem, the repair for this condition is a carburetor replacement.

A word of warning when purchasing rebuilt carburetors. Before you buy, check for wear or play in the throttle shaft. Some of these rebuilt carburetors have just as many miles on them as yours does. Excessive play in this area means you want to avoid that particular piece.

Rough idle caused by spark plugs, spark plug wires or ignition coil problems

If you have a rough idle that is caused by either the spark plugs, spark plug wires or ignition coil, you will also feel it when accelerating. If these parts are bad enough to cause a miss at idle, it will continue to miss while driving. If either one of these items is starting to go bad but not missing at idle, a jerking sensation will usually be felt when accelerating the vehicle under a load. So paying attention to how the vehicle feels at different point of driving is what will help diagnose this.