98 300D Turbodiesel misfire on cold startup

[spmarfatia]

Hi,

I don't have any Glow plugs lights on, but on cold starts, I think I am getting misfires from one of the cylinders. Engine shakes, smoke comes. Goes away after I guess the compression starts to take over.

Engine runs normal after that first couple of minutes. This goes on shorter on warmer days and little longer on colder days. So, all symptoms point to bad glow plug(s).

Anyone seen glow plug being bad without light coming up?

May be my light is bad...but when starting, glow plug light comes on and usually goes away after 5-7 seconds as expected.

Looking for suggestions from fellow diesel owners of this engine.

Sam

[Kajtek1]

How your fuel lines look like? Any air bubbles in them?

[sokoloff]

Depending on how many and which glow plug(s) are bad, you may not get a check engine light. I have had one bad plug a couple of times and did not have a check engine light at least once. maybe twice. You can feel one bad glow plug upon start up. It's nothing like a misfire IMO and only lasts a few seconds in warm weather. I would bet that most folks would not even feel it or be bothered by it. Take an ohm meter to the plugs and see what you get. Good plugs will read about 0.7 ohms.

[spmarfatia]

No bubbles. I have had this for over couple of years now.

Only gets bad in cold weather....is dripping injector a possibility? Just throwing it out there.

few seconds after start up, shacking and smoke is gone and everything is normal. Engine sound too. when shaking and smoke, I also hear a kind of knocking from the engine too. just few seconds after start up. like may be lifters hitting hard with cam shaft when no oil or something....

Len, do you know if all glow plugs are reachable to read OHM? I know some are under intake manifold....wondering if possible to read it at the other end?

[Kajtek1]

All glow plugs have separate wires going to the relay conveniently located on inner fender.
Takes a minute to check all of them.
At least that was the last I heard as I have not replaced GP for like 20 years.
Leaky injector will not create symptoms going into long seconds as this is mechanical injection not a common rail.

[sokoloff]

Yep, drivers side fender well is the glow plug relay. Unplug that - might be tight, but it will come apart. Then you can test each glow plug right there. If you have good eyes, you can also see the number of the glow plugs on the relay and tell which one is bad.

[spmarfatia]

Thanks guys. Found the relay side of the connector and measured the resistance.

To the shame of my college physics teacher, I was blanking out and didn't know which two points to measure. so I put one to my shocks mounts (black/negative) and one(red/positive) to each six connectors going to the glow plugs. I am getting around 15K ohm for 5 of them and 0 for one of them. Sounds like one of them is bad. When I reversed the black to red, I got about 2.8M ohm, again on five of them and one 0.

Either way, it looks like one is bad.

I tried to look hard to see the numbers on the connector or relay box for cylinder# for each, but couldn't find it anywhere. When plugged in, connector had 3 connections on the top and 3 at the bottom. middle in the bottom is the one reading 0 all the time.

Anyone has a clue which cylinder would that be? My guess is 5th, most likely or 2nd.

also, what are the correct values when I measure? 15K ohm too much/little? May be time to change all? Car still starts in 20F around NYC. just a little shaky and smoke at start up, so don't want to take on a big job of taking intake manifold off to change all if I don't have to. Also to take the risk of one of them breaking that was not bad to bigin with... If I can find which one is bad and if it turns out to be the easier one to change, I would prefer to just change one.

Thanks

[Kajtek1]

I hope you did not use shock rod mount as this is bad ground. Maybe it doesn't matter in resistance measuring, but don't make habit of hooking up electric wire to nuts mounted on the top of the rubber.
Since you measure out one plug bad, you can try to put the meter on the plug connector directly. Some of them are pretty accessible. Probably pulling the plug from the relay will be necessary to avoid back-feed.

[sokoloff]

There are a lot of good ground locations within easy reach of the relay. Not too far away on that fender well is an actual ground bolt with a number of wires going to it. You really need to look closely at the relay to see the glow plug numbers, but they are there. I can't remember for sure, but they may go 1,3,5 across the top and 2, 4, 6 on the bottom. Don't hold me to that. If you are going to change the bad plug, the manifold has to come off anyway and you can recheck each plug right at the plug to confirm.

[spmarfatia]

Yup. Took a look again in good day light today and could see the numbers behind the wires. Bottom middle would be 4th.

I guess I need to start getting ready to take Intake Manifold off. I see that everybody talks about take it apart under the EGR module. Although I can see there are 4 bolts and a gasket between the manifold and the EGR module.

Wondering what are the Pros and Cons of focusing on those 4 bolts instead of under the EGR module?

Also looking out to see if anyone have any tricks to do 4th cylinder glow plug without taking the manifold off?

Also, there recent thread in W210 forum here that is confusing me, says some mishandled manifold gasket is causing vacuum loss. Can't image how this could be related...did not know of vacuum inside the intake manifold....could be a gas engine thing...

Although I have had this problem since I bought the car 2.5 years ago, the check engine light finally come up with glow plug fault, p1369 or something, after I manually checked it. I think something I did finally ticked it...


Thanks,
Sam