engine troubleshooting

[K10man1]

hi everyone. I have a 1986 chevy silverado that wont start. it will turn over but thats it. can someone help me?

 

[Driver4r]

Does it have spark? If it has spark at the wires, check the plugs. If it doesnt have spark at the wires, check the coil. There should be a Red/pink wire plugged into the HEI cap that feeds it 12v for the igniton, makes sure thats plugged in and feeding power.

 

[philjafo]

Lots of people here willing to help but we need details, what have you checked and what has been tried?

 

[K10man1]

Lots of people here willing to help but we need details, what have you checked and what has been tried?

I think its getting fuel because when it turns over fuel comes through the filter. I have checked the plugs and they are ok. thats about it.

 

[philjafo]

Ok, basics, you can see fuel in the filter so sounds like the pump is pumping. Pull the air filter off and see if the choke is closed, if it is pull the throttle just a little and open the choke by hand, no look into the carb and pull the throttle some more you should see a good spray of fuel. Then let go of the throttle, the choke should stay open when you let go. Now pull the throttle again and the choke should snap closed. If all that checks out you know for sure your getting fuel. Now we can check for spark, pull a plug and rest it against a clean ground, have a helper crank the engine. You should see a bright blue spark, small or yellow spark won't cut it. If you have a good solid spark then we need to know its timed correctly. If you don't have a timing light you might try borrowing one, but if you continue to work on old stuff your going to need it again they can be had for cheap if you don't need all the fancy features. If you've got fuel, and timed spark, the last thing is compression. Use a compression tester and check all cylinders, they are all supposed to be within like 10% of each other (not certain on that number though)

 

[chengny]

To diagnose a non-start condition (in car that I know nothing about) I remember the FACTS:

F = fuel
A = air
C = compression
T = timing
S = spark


The first checks are fuel and spark:

To check for lack of fuel: spray some ether (starting fluid) into the carb throat. If it temporarily fires up - you have a fuel supply issue.

To check for spark: Just as philjafo says - pull a plug, reconnect the wire, ground it and crank the engine. Lack of bright blue spark indicates an ignition issue.

Next would be timing. Since the engine won't start, the use of a timing light is not an option. Check rough static timing like this:

Use a Sharpie and make a mark on the distributor base directly under the #1 spark wire post. Pull the distributor cap off and click the engine over until the timing mark on the harmonic balancer is in line with 0 degree mark on the timing tab (just needs to be close - not exact). Look at the position of the rotor. It should be pointing to where the Sharpie mark is on the distributor base (If it is pointing 180 degrees off, click the engine over once more until the timing marks are once again lined up).

If the rotor points to the mark on the base that corresponds to the #1 plug wire post - the timing is okay - or close enough to at least start the engine.


Another check (again do as philjafo advises) is compression. Before checking compression, be advised that loss of compression does not generally happen suddenly. It is a slow process - unless you drop a valve for example - it doesn't happen overnight.

Exception - compression can be lost all at once if the timing chain breaks, but the check for ignition timing would not have passed if this were the case.

The check for air is usually not needed - it's only for when the intake filter is extremely plugged or if flow through the exhaust system restricted (usually happens when the vehicle has been sitting for a long time and the tail pipe is full of mice nests)

 

[Tim K]

hi everyone. I have a 1986 chevy silverado that wont start. it will turn over but thats it. can someone help me?

Did it run when it was parked? If so, how long ago? Was someone was messing with the distributor or it was parked because it quit running?