Backfiring out the intake:

Sir Sam · **Posted:** Fri Aug 12, 2011 1:42 am

So on my recent CRD purchase I have started digging into it, it made a weird misfire when at idle, I thought maybe the timing belt jumped a tooth which was causing it to misfire, today I checked the timing on the belt. Cams and flywheel timing hole all line up correctly.

Next I pulled the injector connector off of each injector in order, when I get to the #3 injector I notice a change in how the engine runs. Then with the engine running I feel the intake by the FCV, well there is a helluva blow back.

So with the injectors all connected there is a helluva misfire, and a helluva burst of air coming back out of the intake at the FCV, with the #3 connector off there is a fairly regular pff of air out of the intake.

So right now my best thinking is that someone it fubared with the #3 intake valves, and its blowing back out the intake during a compression stroke.

tomorrow I will pull the intake off and then the head, but my best thinking is that a glow plug or something broke off and is causing a stuck #3 valve.

warp2diesel · **Posted:** Fri Aug 12, 2011 6:45 pm

Before you yank the intake and then the head, pop the valve cover and take a look.
You may get real lucky and you may have a stuck hydraulic lash adjuster that is causing the intake valve to fire back into the intake. It is a long shot, but worth the time. I have not had it happen on my CRD, but it has happened a few times on customer cars when I ran the repair shop. Since there is virtually no heat when the cylinder does not fire, the intake valve may still be OK.

Sir Sam · **Posted:** Fri Aug 12, 2011 6:58 pm

warp2diesel wrote:

Before you yank the intake and then the head, pop the valve cover and take a look.
You may get real lucky and you may have a stuck hydraulic lash adjuster that is causing the intake valve to fire back into the intake. It is a long shot, but worth the time. I have not had it happen on my CRD, but it has happened a few times on customer cars when I ran the repair shop. Since there is virtually no heat when the cylinder does not fire, the intake valve may still be OK.

Warp I don't think you can pull the head without pulling the valve cover. (ie the valve cover will be off before the head is off)

But yes I am going to check out the topside of the head before pulling it.

Sir Sam · **Posted:** Fri Aug 12, 2011 9:35 pm

man this valve cover/intake just does not want to come off. guess i need to read the FSM and see if I have missed anything holding it on.

Sir Sam · **Posted:** Fri Aug 12, 2011 11:53 pm

Well I got the intake off, nothing obvious in the valvetrain is wrong, can't see the valves/valve seats from here, so since I can't see anything wrong tomorrow I guess I get to pull the head off and see what the bottom of the head looks like.

That is unless you guys have any thoughts for me before I pull it, I'm really wishing I had a fiber optic camera right now, I saw one for sale at costco for like $180 or so last week, pricey little bugger, but it could come in handy at times like this.

Turbo Tim · **Posted:** Sat Aug 13, 2011 9:44 am

You might want to try and spin the valve against the seat before you pull the head.
This has been done before using a drill.
Just make sure you have the piston all the way up BEFORE you take the valve spring off.
We also fed nylon rope down the spark plug hole and then ran the piston up so the valve wouldn't fall down inside the cylinder.
Ya I know "We" don't have spark plugs, but "We" do have glow plugs.
Just a thought. Good luck.

flman · **Posted:** Sat Aug 13, 2011 10:19 am

Turbo Tim wrote:

You might want to try and spin the valve against the seat before you pull the head.
This has been done before using a drill.
Just make sure you have the piston all the way up BEFORE you take the valve spring off.
We also fed nylon rope down the spark plug hole and then ran the piston up so the valve wouldn't fall down inside the cylinder.
Ya I know "We" don't have spark plugs, but "We" do have glow plugs.
Just a thought. Good luck.

I have used compressed air to change valve seals as a way to keep the valve from falling down. I am pretty sure this would make an easy test for Sir Sam to check for valve leakage?

Sir Sam · **Posted:** Sat Aug 13, 2011 11:59 am

yup I am aware of the rope trick as well as the compressed air trick.(and the fact that we don't have spark plug holes)

What didn't occur to me was to use the VM tool meant to go in place of the injector that allows you to hookup testing equipment, I ought to be able to jury rig something to put it under a little pressure, and now with the cam out all of the valves ought to be sealed.

I still haven't gotten my head wrapped around how this overhead cam and rocker setup works exactly, gotta say this is one of the most "unique" engines I have ever torn down, you can see why jeep dealers don't want to touch them, too much of a learning curve.

(I gotta post some pics off all the tools in the VM toolkit, its 4 big boxes of all sorts on nifty stuff you need for tearing down these engines)

dkenny · **Posted:** Sat Aug 13, 2011 12:23 pm

not sure if this a valid idea, but I thought I send it anyway.
can you measure the height of the valve spring and compare it to another one?

use compressed air in the glow plug and push the #3 intake in. don't remove the keepers, just manually push the valve in..
this might blow out with causing the problem

for what is worth

-dkenny

Backfiring out the intake:

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