Fuel injectors

I had a diesel mechanic on board yesterday and he showed me how to check my injectors to see if they are working properly.

**All that was required was a wrench and a rag or blue paper towels.

To check them you crack open the injector with the wrench and listen to the sound of the motor.

The towels is to collect the diesel fuel that will spurt out when you loosen the injector nut

there is a*noticeably difference in the sound of the engine.

If the injector is bad there will be no change.

This was for a Cat 3208. *Is it the same for most diesels.

SD

That works well for most older diesel engines. Not so much on the newer common rail electronic injectors. When you loosen the fuel line to the injector your are shutting off the fuel to that cylinder. Like pulling the spark plug wire off of a gas engine. That cylinder stops firing while the fuel is shut off.
But this doesn't always let you know if your injectors are good or bad. If you have poor compression on that cylinder for any reason you might not notice and change in the sound or smoothness of the engine.

skipperdude wrote:
I had a diesel mechanic on board yesterday and he showed me how to check my injectors to see if they are working properly.

**All that was required was a wrench and a rag or blue paper towels.

To check them you crack open the injector with the wrench and listen to the sound of the motor.

The towels is to collect the diesel fuel that will spurt out when you loosen the injector nut

there is a*noticeably difference in the sound of the engine.

If the injector is bad there will be no change.

This was for a Cat 3208. *Is it the same for most diesels.

SD

Click to expand...

Skip,

That is how*one checks to see*if they are working true enough.* But that is not how they are checked to see if they are working correctly.* They need to be pulled and the pop off pressure is checked as is the spray pattern.* Working is one thing working correctly is another matter.* The cook at Waffle House will feed you but the Chef at a fine restaurant will amaze you.* Unfortunately engines need to be amazed to operate correctly.

I'm not being critical just explaining the difference.

Yeah, I didnt mean to say it will give you a full report on the condition of the injectors.

Some Mechanics are less than truthfull when it comes to a job.

But if someone tells you you need new injectors this is a way to check for yourself.*

*It is what a mechanic will do to check them.

SD

*

Happily with the 3208 removing the injectors to have them checked is fast and really EZ..

In FL the local shop wanted $5 each just to bench test them and $65 to $80 each if they needed a rebuild , depending on what was shot.

More happiness is it is probably the easiest of all to time the injection.

Back off a bolt or two, insert a pin , or drill bit through a hole into the block, lock it up, remove pin.

Wish it were that EZ on DD's.

"But if someone tells you you need new injectors this is a way to check for yourself.*

*It is what a mechanic will do to check them."

Sorry I can't agree with this either.

This is how a mechanic will diagnose to find a faulty injector. An injector that is so faulty it will not function properly at idle.

Many (or possibly most) times when an injector starts to degrade, it will spray a poor pattern or*fire at the improper time due to*pop pressure degredation**or leak after shutdown (and contaminate the oil).

Your mechanic prbably didn't mean it to be taken literally. True enough this procedure is similar to pulling a spark plug wire on a gasser, but it not the way to find if an injector is performing properly.

jleonard wrote:Your mechanic prbably didn't mean it to be taken literally. True enough this procedure is similar to pulling a spark plug wire on a gasser, but it not the way to find if an injector is performing properly.

Click to expand...

*What it is best at is discovering which cylinder is not firing right when you have a rough running engine to begin with.* When you find one that makes no difference with the line cracked open or not, you have found at least the cylinder that's misfiring.* Could be the injector, or something all together different.* I used that method a couple years ago to discover that I had a valve adjusting screw that had lost it's hardface, and was wearing rapidly resulting in a loose valve.* I knew it was running poorly, but not which cylinder.* Cracking the lines told me................Arctic Traveller

jleonard wrote:
"But if someone tells you you need new injectors this is a way to check for yourself.*

*It is what a mechanic will do to check them."

Sorry I can't agree with this either.

This is how a mechanic will diagnose to find a faulty injector. An injector that is so faulty it will not function properly at idle.

Many (or possibly most) times when an injector starts to degrade, it will spray a poor pattern or*fire at the improper time due to*pop pressure degradation**or leak after shutdown (and contaminate the oil).

Your mechanic probably didn't mean it to be taken literally. True enough this procedure is similar to pulling a spark plug wire on a Gasser, but it not the way to find if an injector is performing properly.

Click to expand...

*Well*I had one mechanic that was hard up looking for work.

*He told me I needed new injectors I got a second opinion and watched and learned as he checked the injectors. No fault was found.

I agree it is not a definitive test but it will tell you if there is a problem that needs more attention

SD


-- Edited by skipperdude on Friday 17th of June 2011 03:41:20 PM

Arctic Traveller wrote:jleonard wrote:Your mechanic prbably didn't mean it to be taken literally. True enough this procedure is similar to pulling a spark plug wire on a gasser, but it not the way to find if an injector is performing properly.

Click to expand...

*What it is best at is discovering which cylinder is not firing right when you have a rough running engine to begin with.* When you find one that makes no difference with the line cracked open or not, you have found at least the cylinder that's misfiring.* Could be the injector, or something all together different.* I used that method a couple years ago to discover that I had a valve adjusting screw that had lost it's hardface, and was wearing rapidly resulting in a loose valve.* I knew it was running poorly, but not which cylinder.* Cracking the lines told me................Arctic Traveller

*Exactly you may have found the problem cylinder but not the problem per say.* Move the injector to a good cylinder and the good injector to the bad cylinder.* If the problem follows the injector you know it is the injector, if the problem stays put the cylinder has other problems and a compression check is in order.

skipperdude wrote:
*Well*I had one mechanic that was hard up looking for work.

*He told me I needed new injectors I got a second opinion and watched and learned as he checked the injectors. No fault was found.

Click to expand...

Now you know why he was hard up looking for work.* Thief comes to mind.*

Roger that.

That is the jest of the thread. If someone tells you you need this or that. Nothing wrong with a second opinion and learning what to look for as a tell tale sign of injector problems can give you an edge.

There is enough things I need my boat bucks for.

SD

skipperdude wrote:


Roger that.

That is the jest of the thread. If someone tells you you need this or that. Nothing wrong with a second opinion and learning what to look for as a tell tale sign of injector problems can give you an edge.

There is enough things I need my boat bucks for.

SD

Click to expand...

Good point. And I like the way the mechanic "proved" the injectors were fine. A good mechanic should always be able to prove his case if you ask him to.

Skipper Dude -

As the others have already said, there is a LOT more to the story than what that "mechanic" told you. He neglected to tell you about pop pressure, spray pattern, carbon build up, etc.

I pulled all my injectors last winter on my 1982 Lehman 120....had 6500 hours on it.

What I found was the bleed off line was INCORRECTLY attached to the injectors by some "mechanic" before me. See here to know what I am talking about

[url]http://tinyurl.com/2868qbo[/url]

The bleed off tube was crooked when mated up to several injectors. THe pictures show it. You can see how the bolt head is cocked and not flat to the bleed off tube ring. The screws that hold the bleed off tube into the injectors were CROSS THREADED !!!! What a NUCKLEHEAD that "mechanic" was ! So the bleed off tube was NOT holding the bleed off fuel as it was supposed to.

Took them all to a shop to be tested and rebuilt if needed. Shop calls me and says "Yeah they needed to be rebuilt because the threads were crossed and the nozzles were all crapped up. BUT they are all popping at the correct pressure."

So I ask them how they know what the correct pressure is, because they didnt know what engine they come from. Turns out the rebuilder looked them up in book to get the pop pressure. BUT, his looked up pop pressure was only 2/3 of what the Lehman book said it should be ! So I tell him NO! Set the pop pressure at what my Lehman manual says it should be (and I told him the correct pressure).

*

So be careful when dealing with "mechanics" and I especially shutter when boaters use the term "had it done by a professional".

R.