Glow plug replacement

Ron Hill · May 06, 2022, 02:44:14 PM

Alex : When was the last time you ran a compression check??

A thought

waughoo · May 06, 2022, 07:15:04 PM

I haven't but I dont have any reason to think it is low at this point. The condition only presents itself on a cold start. After the engine has been started once, it stats right up with all 4 cylinders, which points to glo-plugs.

Ron Hill · May 07, 2022, 01:17:29 PM

Alex : If the engine starts on 3 cylinders and it takes some time for the 4th cylinder to kick in - it well might be that the glow plug is NOT the problem!!

A thought

waughoo · May 07, 2022, 05:47:49 PM

Sounds good Ron. I'll make sure to call my mechanic first thing Monday morning and have him get started right away. ;-)

That said, it isn't near as dramatic as you are projecting. It takes about one or two ignition strokes and it lights off just fine. This is why I suspect glo plugs.

KWKloeber · May 08, 2022, 09:48:20 AM

Ron

I'm interested why you don't buy into the glow plug theory?
That would be my guess not ever having experience running into that issue.

I'd think that the cyl could mis fire until it gets up to temp and the fuel properly ignites. I suppose but don't know if low compression would rectify itself after she warms up?? But if every cylinder doesn't fire what would be the first suspect - compression or preheat?

It's simple to verify if one has a bad glow plug!!

Ron Hill · May 08, 2022, 01:06:02 PM

Ken & Guys : When the cylinder piston of a diesel is at TopDeadCenter the distance between the top of the piston and the bottom of the head is the thickness of a piece of paper! Boyles Law states that when a gas is compressed it raises in temperature!! So when the air diesel mixture reaches TDC (and a hi temp) there is an explosion driving the piston down (so no need for a spark plug!!). If the piston reaches TDC and that mixture is NOT ignited it could be that mixture is NOT compressed (like it is in the 3 other cylinders?). Hence, I'd check the compression on that cylinder.

If the other glow plugs are heating how likely is it that one plug is not?? My opinion is that it's slim.

My thoughts

KWKloeber · May 08, 2022, 05:16:56 PM

Ok, I agree about how diesel ignites. But how/why does that cylinder ignite ok once the engine runs a bit?
And if the engine is still warm why would that cylinder not misfire if it's low compression?
I'm missing how those two situations relate to low compression.

If the glow plug is ok, I'd also suspect an injector that's "acting up" at startup.

Check the temp and the resistance of that plug compared to the others.

Ron Hill · May 09, 2022, 01:23:56 PM

Guess we'll all just have to wait for Alex to tell us how he/his mechanic fixed the lazy 3rd cylinder problem!!

A thought

waughoo · May 09, 2022, 08:58:06 PM

Prob not going to be for a while as it really isn't a problem. I am the mechanic that will do it and it will mostly be a process of replacing the glo-plugs for "known good component" as the boat is new to me. It is a process I go through with most mechanical things I acquire. I often replace service parts JUST to know their age vs getting stuck with a problem due to a part of an unknown use life.

KWKloeber · May 09, 2022, 10:32:53 PM

Alex

VERY simple.... Preheat 30 secs (unless you have a preheat solenoid then 10 secs); feel each plug - if you can constantly hold onto a plug it's not heating enough. See if you feel a noticeable difference to the suspect plug.

Measure the resistance from tip to engine ground of each plug (at least the suspect one) or as many as you can get the wire off. See if the suspect is noticeably lower than the others (or zero -shorted, or very high -bad winding.

Being new to it, even if you systematically replace parts J.I.C. it's always better to know the condition of what you're replacing if there's an issue. Otherwise you might NEVER locate the root cause of a problem and never make more than one related change/replacement at a time.