Trouble Starting
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Trouble Starting
Having trouble starting a 78 Bronco 351M.
Starter turns but engine does not fire. Replaced battery and checked coil. Had coil replaced. Replaced fuel filter. Distributor cap is fairly new and in excellent condition. Getting current to coil.
What is the best way to check for spark at plugs. What else should be checked. How to test ignition module?
Thanks
Starter turns but engine does not fire. Replaced battery and checked coil. Had coil replaced. Replaced fuel filter. Distributor cap is fairly new and in excellent condition. Getting current to coil.
What is the best way to check for spark at plugs. What else should be checked. How to test ignition module?
Thanks
Post Fiend
Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Trouble Starting
The Haynes manual should have a good ignition diagnostic procedure. To check for spark, just pull the coil wire, put a screwdriver (or other metal rod) into it, lay it NEAR BUT NOT ON a metal part of the block, and crank on it for a second. You should have about a 1/8" gap.
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Trouble Starting
This is Biscuit working on my buddies Bronco, thanks for your help woth "Bob" in the past, glad you responded I am sure you will help us through this. We are using the Haynes Manual. Been through it and just not sure what we are missing. We took the new coil back and had it tested and they tell us it is woking and the correct rplacement for the truck but we are not getting the arc you mentioned. Beleive me we have tried it, although I did get two freaky shocks out of it when I am not sure of what I was touching so I figure we are getting current into the distributor. We'll try the test again. Same works for spark plugs right?
Any thought that this might be a fuel issue. It has set for awhile and started initially with a little gas in the carb, so he changed the fuel filter and was giving carb cleaner a go, but it hasn't started since the carb cleaner. We just changed the plugs as well they were pretty oily and grimy.
Thanks
Any thought that this might be a fuel issue. It has set for awhile and started initially with a little gas in the carb, so he changed the fuel filter and was giving carb cleaner a go, but it hasn't started since the carb cleaner. We just changed the plugs as well they were pretty oily and grimy.
Thanks
Post Fiend
Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Trouble Starting
If it'll EVER fire, it's probably getting spark. Even if it take starting fluid. If not, see if the distributor is rotating while you crank - the chain may be broken. I don't know much about the old ignition systems or the pre-'80 Haynes.
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Trouble Starting
It hasn't fired since at all. After cranking as you turn the key off it then acts if it would like to fire a sort of cough. Guess we will check the distributor a place we really didn't want to go. If you happen across Milion would you mention this problem to him, he has helped me in the past as well. Thanks
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Trouble Starting
Okay newest findings. The distributor turns, yeah!!!
There is a spark but is is very weak and yellow. It is difficult to get the spark at all about 1/16th inch or less.
Thoughts on the module? Thinking of just trying it, can always return it I guess.
Thanks.
There is a spark but is is very weak and yellow. It is difficult to get the spark at all about 1/16th inch or less.
Thoughts on the module? Thinking of just trying it, can always return it I guess.
Thanks.
Moderator
Joined: Jan 2001
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From: Virginia
Trouble Starting
A quick way to eliminate the fuel thing is take the air cleaner off, and while looking down the carb throat(you may have to push the choke plate out of the way), push back on the throttle with your hand. You should see two strong streams of gas shoot in the carb throat.
I think you said you have voltage at the coil + right? If you are not sure, verify this again.
If you have voltage to the coil +, then do the screwdriver in the sparkplug wire test again.
If you don't have any spark from the screwdriver with voltage at the coil +, I would try swapping out the ignition box mounted on the inner fender. As a last resort, after all the above, you could try the pick-up coil inside the distributor.
There is also the chance that you have fuel, and spark, but it still won't start. In this case the engine could be flooded, and the plugs could be fouled. If you find this to be true, get a new set of sparkplugs. Once the are fouled, it takes a long time for them to start firing again.
I think you said you have voltage at the coil + right? If you are not sure, verify this again.
If you have voltage to the coil +, then do the screwdriver in the sparkplug wire test again.
If you don't have any spark from the screwdriver with voltage at the coil +, I would try swapping out the ignition box mounted on the inner fender. As a last resort, after all the above, you could try the pick-up coil inside the distributor.
There is also the chance that you have fuel, and spark, but it still won't start. In this case the engine could be flooded, and the plugs could be fouled. If you find this to be true, get a new set of sparkplugs. Once the are fouled, it takes a long time for them to start firing again.
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Trouble Starting
Plugs and spark have been changed and checked. Fuel is making it through the filter, and we have good pressure from the fuel pump. We poured a substantial amount of gas directly into the carbs (and used starter fluid as well), without so much as a sputter.
Additionally, the fuel did not back back up into the carbs.
We have been contemplating the ignition box, due to weak spark. How should we best test the ignition box? Also - any idea what replacement costs would be? Or wondering if the jets may be clooged from the carb cleaner.
Thanks again for all the help.
Additionally, the fuel did not back back up into the carbs.
We have been contemplating the ignition box, due to weak spark. How should we best test the ignition box? Also - any idea what replacement costs would be? Or wondering if the jets may be clooged from the carb cleaner.
Thanks again for all the help.
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Trouble Starting
Hi Guys, After readig this I have the sneaking suspicion that the timing gears are stripped.
Try this.
With the distributor cap off>
Take a breaker bar and socket and put it on the crankshaft bolt.
Turn the crankshaft one direction > When you see the rotor of the dizzy start to turn then.... STOP.
Now reversing the direction of the breaker bar watch for the rotor start to turn again (keeping track of how many degrees the breaker bar has travelled in a circle to make the rotor turn)
Does the bar travel 45* > 90*
Get back with this measurement.
I think the timing set is worn out
Also, Take your ignition modulator to a parts store and have them test it for free.
Try this.
With the distributor cap off>
Take a breaker bar and socket and put it on the crankshaft bolt.
Turn the crankshaft one direction > When you see the rotor of the dizzy start to turn then.... STOP.
Now reversing the direction of the breaker bar watch for the rotor start to turn again (keeping track of how many degrees the breaker bar has travelled in a circle to make the rotor turn)
Does the bar travel 45* > 90*
Get back with this measurement.
I think the timing set is worn out
Also, Take your ignition modulator to a parts store and have them test it for free.
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Trouble Starting
Still no results. The angle is 10 degrees or less between distributor movements in both diresctions. Took the module in and it checked out okay.
Pulled the new plugs back out and they are still clean so we are thinking that that means there isn't a mess in the combustion chambers clogging the gas from entering.
The strangest symptom is that when you relase the ignition switch from the start position to the run position the truck attempts to start or coughs like ignition is about to take place. The only other thing sitting on my mind is the weak spark from the coil. We tried another new one and had the same result.
When the coil was checked it was the low end resistance that was bad. Is there some cause that we should look at for that.
Thanks
Pulled the new plugs back out and they are still clean so we are thinking that that means there isn't a mess in the combustion chambers clogging the gas from entering.
The strangest symptom is that when you relase the ignition switch from the start position to the run position the truck attempts to start or coughs like ignition is about to take place. The only other thing sitting on my mind is the weak spark from the coil. We tried another new one and had the same result.
When the coil was checked it was the low end resistance that was bad. Is there some cause that we should look at for that.
Thanks
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Trouble Starting
Do you havea test light ?
If so, attach it to the + side of the coil.
Watch the light for when it comes on and goes off when you go from Off <> to run <> to Start <> to Run.
Do you have a tach you can attach to the - side of coil ?
With the tach attached you will see of you have spark 8 times a rev.
If so, attach it to the + side of the coil.
Watch the light for when it comes on and goes off when you go from Off <> to run <> to Start <> to Run.
Do you have a tach you can attach to the - side of coil ?
With the tach attached you will see of you have spark 8 times a rev.
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Trouble Starting
Well we don't have either of those, and will go to the store to see if they fit into our budget. Prior to that I/we are hoping that there is something/someplace to check to strengthen the spark from the coil. Look forward to your advice and will keep you posted
Posting Guru
Joined: Aug 2002
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From: Minneapolis, MN
Trouble Starting
Originally posted by Mil1ion
With the tach attached you will see of you have spark 8 times a rev.
With the tach attached you will see of you have spark 8 times a rev.