Electronics > Projects, Designs, and Technical Stuff
Improvised oscilloscope probe for Automotive ignition analysis.
<< < (8/16) > >>
tpowell1830:
Sight unseen is not a good position to do troubleshooting for an engine, however, there are a multitude of causes of an intermittent miss on a cylinder. Theses problems could be of either electrical or mechanical issues. Here are only a few that could be checked fairly easily.

1. Check the plug or plugs in question for arc tracks, especially if they have a boot type spark plug wire.
2. If this is a carburated engine, is that cylinder starved at higher RPMs due to a vortex in the air flow, i.e. in the intake?
3. As mentioned earlier, valve float at high RPMs due to weak springs.
4. Is the cam new or is the cam lobe worn on that cylinder more than on others? Is that lobe higher than others, was this checked out before installing?
5. The distributor parts turn and this can cause runout at higher RPMs if the rotor bearing is worn, which can cause misfires.
6. The rotor itself can move up or down if rotor is worn, causing collisions on distributor cap.
7. The distributor cap can have cracks or problems seating on the rotor, yes, even if they are new, which can cause problems with firing.
8. The plug wires could be the wrong type for the distro/plugs causing unmatched firing characteristics.
9. If a condensor is used on the distro, it could be causing this behavior.
10. The spark plug itself could be the problem, try a different brand or type.

As far as checking the firing for this cylinder, a current probe around the primary of the coil would work at low voltages and when a misfire occurs, the shape of the pulse can tell you a lot about what the problem might be. The voltage on that pulse will rise if there was no spark due to an open and will fall if there was a short. You can use a portable scope or one of the modern automotive computers with a scope on it to do this, such as the Autel or OTC, or a portable o'scope such as the µScope, using a current probe.

There are many more reasons that this could happen, hope this helps...

joeqsmith:

--- Quote from: tautech on January 05, 2019, 12:46:27 am ---Ah, the two step.  :clap: Boom, bang, boom.  :wtf:  8)

All hell breaks loose.  ;D

Buddies 20B on Meth with 40lb of boost is something that is heard for miles !  >:D

Oh yes Joe, I left EGT off the list.  :palm:

--- End quote ---

Mine are pretty tame.   My street bike is injected and the low speed limiter on it is so smooth you hardly notice it. 
Jim-0000:

--- Quote from: tpowell1830 on January 06, 2019, 06:04:47 pm ---............................ Autel or OTC, or a portable o'scope such as the µScope, using a current probe.


--- End quote ---

Thanks for the reply.
I would like some more details of these scopes. Can you provide full names and any links please?
We are considering purchasing one specially for working on the two cars owned by the brothers. I will order one of the auto probes from Aliexpress linked to somewhere in a post above.

Jim.
tpowell1830:

--- Quote from: Jim-0000 on January 06, 2019, 09:14:39 pm ---
--- Quote from: tpowell1830 on January 06, 2019, 06:04:47 pm ---............................ Autel or OTC, or a portable o'scope such as the µScope, using a current probe.


--- End quote ---

Thanks for the reply.
I would like some more details of these scopes. Can you provide full names and any links please?
We are considering purchasing one specially for working on the two cars owned by the brothers. I will order one of the auto probes from Aliexpress linked to somewhere in a post above.

Jim.

--- End quote ---

I will do you one better and give you a link to an awesome mechanic who uses these tools and the µScope for troubleshooting, link in comments for scope.



Hope this helps...
Jim-0000:
After another long day working on the problematic Holden grey motor (circa 1950,s), the two brothers, one of whom owns the vehicle have reluctantly agreed to change the plug leads over to solid cored ones. I first mentioned this many weeks ago. Their first response was: "we don't like copper cored leads"!
New spiral wound, stainless cored leads have been ordered on ebay and we will await delivery. (It appears that copper cored leads are no longer available)  Local suppliers could not get them, which seems astonishing to me! The also ordered some Platinum spark plugs.
Meanwhile, I found out that a fellow member of the local Mens Shed does have an oscilloscope along with two suitable probes for ignition analysis.
If the new plugs and leads does not fix the miss fire, we will be borrowing that and using it on the engine. I will ask the owner of the scope to come out and assist, as he is an electronics engineer.

So, we will have to find the problem some day soon, I figure.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod