Miss Firing

[Rolf]

I went on a 300 mile trip. The car ran fine for the first leg, 150 miles. On the way back, I got about 16, miles from home and hit some traffic. As I slowed down, I heard a sound almost like something was hitting the fan blade. I pulled over to the shoulder and the car started to run rough. I popped the hood and found nothing hitting anything. I had my son crank the car over, without the coil wire connected and heard and saw nothing hitting anywhere. I then started the car and it was hard starting and only started after giving about half throttle. After the car started it acted as though it was running on less than six cyclinders. As the revs increased, the car ran a lil better, no unusal noises could be heard. I got the car home and checked the plugs. They were all carbonized and 3 were very wet. I read some of the threads here and decided to change the plugs, points, rotor and condenser. All to no avail.I gapped the points and plugs according to the specs. I found on the threads along with timing The car starts but runs extremely rough. It does get up to speed on the highway, about 65/70 MPH. I have to keep my foot on the accerator when stopping or it will stall. The plugs, points, rotor, and condenser were changed about 1,000 miles ago. The car was running well when this occurred out of the blue. I have since looked over the car to make sure all the wires, tubing and hoses where still connected. I found nothing. I am still hoping it's an ignition promblem as opposed to a fuel one. The only thing different from the ride down was I got 7 gallons of gas before the return trip home and drove about 134 miles before the problem occurred, Sunoco 93. I syphoned some of the fuel from the bottom of the tank and let it sit to see if it would separate, it didn't. The car does not back fire. The plugs that were in the were Bosch WR9DC. I replaced them with Bosch W8DC.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

Check the plug wires with an ohm meter.  Next remove the plugs and get a compression reading.

Joe Alexander
Blacklick, Ohio

[Rolf]

Hello Joe,

  Would something like this happen all of a sudden? There was no indication of this situation. It ran like a top before.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[glennard]

Rolf, Correct oil level in FI pump?  Crud in fuel tank blocking make up around the electric pump return line?  'Loud Sound' only heard once?

[Rolf]

I siphoned out some gas from the bottom of the tank to see if there was any  water or caustic from getting gas the last time. There was no settling of the gas. it was crystal clear. I have run the tank almost dry several times with no problem. The sound was like something hitting the fan blades and only lasted a couple of seconds. It happened when I released presure on the gas pedal. Haven't heard it since that one time. The car runs better on the highway. It shudders horribly going slow and on idle. It even stalls if I don't put pressure on the gas pedal. Haven't checked the oil in the pump.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

Try starting the car and let it idle, pull the plug wires one at a time to see if you locate a dead cylinder.  Be sure to used good insulated spark plug pliers. Otherwise you can do a quick compression check  to rule out a lot of possibilities.  It sounds like you may be running on five cylinders.

It still could be a very minor fuel or ignition issue. Isolating the problem will lead us to the cause.



Joe Alexander
Blacklick, Ohio

[Rolf]

Joe,

  I pulled the wires from the plugs and the car seemed to run the same each time. As I said before, all of the plugs are carboned and 3 were extremely wet. The plugs had about 1,000 miles on them as did the points, condensor and rotor. I have not yet done a compression test as I have to locate a tester. I also checked the oil for water and water for oil. I experienced no loss of power until I slowed down to about 30 MPH. I plan on getting a tester and checking either today or tomorrow along with checking the plug wire resistance. I just don't understand that all the plugs are carboned and 3 were wet when the car was running good before. I feel as it may be something simple and overlooked.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[hands_aus]

Cold Start Valves (inlet manifold) are notorious for leaking so could you check the CSV for leaks?

There is a small 5mm screw on the side of it.

You remove that screw and turn the ignition on without starting the engine.
If there is more than 3 drops per minute you have a leaking CSV and hence a very rich fuel mixture.

How are your engine mounts?
Have you checked the radiator for marks near the fan (maybe below the fan)?
It is possible that something was caught between them for a short time.
It happened to me in a car park.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[Rolf]

Well, I got a compression tester and did a preliminary test. The engine was cold but, I got horrible readings.
1- 110 psi
2- 125 psi
3- 95 psi
4- 120 psi
5- 110 psi
6- 0 psi
 I rechecked 6 and still the same, zero psi. I am going to redo the test tomorrow and see if there are any changes. I don't like number 6 cylinder at all. I'm still hoping it's not something to serious.


Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

I would remove the valve cover and check for anything strange over #6 cylinder.

Joe Alexander
Blacklick, Ohio

[Rolf]

Hello Joe,


  How come it seems you are on whenever I am? Are you watching me?  I plan on doing that either tomorrow or Fri. I'm hoping it's something to do with the valves. I'm also going to squirt some oil into the cylinders and see if that makes a difference. Of course I shall test again with a warm engine. Aren't the readings lower then they should be?


Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[Rolf]

I took the valve cover off and found nothing unusual underneath. No bits of metal or anything out of place. The one thing I did find was I cannot get a feeler gauge between the rocker arm and the cam lobe. I used a .003" (0.0762 mm) feeler. Could it be possible that the intake valve is not seating all the way thus causing the zero reading on the compression test?

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

Adjust the valves on that cylinder and re-check the compression.  If the cylinder remains at no compression the problem should become obvious soon.

Joe Alexander
Blacklick, Ohio

[Rolf]

Joe,

  I tried to loosen the nut to adjust that valve today. No way would it loosen. I tried using a combination wrench, I don't have that adaptor for valve adjusting. I read thru the threads again and found one about removing the arm so one can get a socket on the nut. I'm going to try that tomorrow. I checked all the other valves and found them to be a lil loose. I still feel something isn't right for the readings to be so wide spread but then, I checked them cold.I also saw a thread about compressing the springs with a bar or screwdriver but, am not too sure where to pry.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[glennard]

Rolf, You need 'Glennard's Handy Dandy valve spring compressor #1'.  It compresses the spring while the cam shaft is still mounted.  'Compressor #2' compresses when the cam shaft is off.  1 and 2 make the job a whole lot easier and they press on both sides of the keeper.  Screw drivers tend to push on only one side - maybe bend the stems.  If the valve wasn't seating, you probably have burnt valves.  Check them all - 153624.

[glennard]

Rolf, While the valve cover is off, check the oil distribution pipe for free flow thru all the lube holes- one for each valve and the bearing pedestals and whatever.

[Rolf]

Glen,

  I did check all the oil ports and the oil flows good. i just have to get that nut loose and see if it makes a difference. There were no rub marks on any of the surfaces either. When the lobe of the cam is opposite the valve, the valve is really tight, can't shake it or get a feeler under it. I also looked and looked throught the threads for a pic of your handy dandy tool and came up empty handed. I know I think I saw it but, it escapes me now. Could you possibly direct me in the right direction?

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[seattle_Jerry]

Drawing from my vast lack of knowledge about the SL motor how about this:

Prior to reading the other posts I was already thinking valve problem. It goes with your symptoms of wet plugs, running rough, and low/no compression.

How is your timing chain play/slackness.

Here's a theory: you are running engine at high revs and back suddenly for traffic...causing some timing chain slap which causes a valve crash or jacked up cam timing from the chain skipping a tooth or two when it slapped.

Or just a messed up valve/ one that isn't seating properly

1967 230SL Havana Brown Auto with A/C

[al_lieffring]

Rolf

The easiest way i have found to take the rocker arms out is to insert the short end of a 5mm Allen wrinch into the oil hole above the ball stud then use the long end of the wrench and use as a handle to lift the rocker up and off to the side of the ball stud, then it will pull out from the side.

With a reading of 0 compression it is unlikely to come back with a valve adjustment, all you will need to do is to back off the ball stud to where there is some clearance then reinstall the rocker and recheck the compression.

A valve timing colision is not likely, to have been the cause, on these motors the valves are at 90deg to the piston top, so unlike most other cars, the valve wont bend, the camshaft towers and or the cam usualy end up breaking off. (personal experience)

My gut feelings on what is happening here, is that you have a burnt exaust valve or a blown head gasket. Most likely you will be removing the cylinder head in the near future.

Al



66 230sl
Tour de Cure 50km unicycle ride to benefit Diabetes research.
http://main.diabetes.org/site/TR?pg=personal&fr_id=4372&px=2737950
Click link to sponsor my ride on May 20th.

[Rolf]

Thank you ... The intake valve on number 6 is staying open, I thnk. There is no clearance at all, compression zero. Number 3 is low on compression, 95 psi. I am under the belief that the compression should be around 150 or so. I would like to free up the nut on number 6 intake and see if it makes a difference when I get clearance there. After that, I want to bring the car to operating temp and check the compression again. I did check it the first time cold. I am still baffled about the noise I heard for that couple of seconds. I did check all around the fan blade,radiator and any other place that type of noise could have com from, and found nothing amiss. if it is a blown gasket, that head is cominf off real soon, like tomorrow or Sunday.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[seattle_Jerry]

You'll have to take the head off regardless of it being a burnt valve or bad head gasket and more importantly to satisfy the curiousity of the peanut gallery. Mainly I would want to take the head off to check for any reason for that noise.

1967 230SL Havana Brown Auto with A/C

[al_lieffring]

Miss Firing, wasn't she the AC spark plug girl on the trophy podium at Pamona Dragway? I think she's married to John Force now.

Back on topic here, the "sounds like something hitting the fan blades" could be the sound of a failing (leaky) water pump.

Were you watching the engine temp when the car was acting up?
Was the coolant level low?
Does the oil have a milky grey color?
Is there more oil in the crankcase than there used to be?

Just a short run with low coolant and the temp up around the 250deg mark will make the head gasket let go. And hopefully the answer to question 2,3 &4 are no.

Al



66 230sl
Tour de Cure 50km unicycle ride to benefit Diabetes research.
http://main.diabetes.org/site/TR?pg=personal&fr_id=4372&px=2737950
Click link to sponsor my ride on May 20th.

[Rolf]

Update on, as Al says, Miss Firing. As soon as the car started acting up I kept an eye on the temp gauge. It stayed on 180 the rest of the trip home. I got the rocker off using an allen wrench as Al said to. Thank you Al, it took me about 3 mins to remove. I checked the compression on the #6 cylinder again and it now reads a whopping 25 psi. I squirted some motor oil down the cylinder and still got the magic number 25. I had checked the oil for water and water for oil. All of the liquids were where they were suppose to be. Jerry, I only heard the noise for approxiamately 3 seconds and have not heard it since. Bob, I did check the CVS and found no leakage. The engine mounts are doing their job perfectly and no leaks, dents or bumps in the radiator nor the cooling lines. Joe, I did all the things you suggested to no avail, hopig it would be a quick fix.  Since I really have nothing else to do, I am going to remove the head over this weekend or Monday. There is no scoring on the camshaft. The oil is flowly freely to it. The timing chain is nice and "tight" but not too tight. The car does not blow smoke at all. I am hoping it just needs a valve job. We shall see.I have been out of work since last September with a bad back so, this will fill up my idle time. I thank all tht have responded so far, for their help and guidance. I will keep you posted as to the problem and fix.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

It's always best to look at the simple and inexpensive solutions first. Now that the compression test has isolated the problem you will need to get into the more complex problems. If you can remove both rocker arms on number six cylinder and hook an air line up via the spark plug hole you will find out if the compression leak is in the head or bottom end. In either case the head, as you determined, will most likely need to be removed.

Possible problems you may find are, loose valve guide in the head, loose valve seat in the head, or possibly a broken piston ring. A broken or burnt valve could be an issue. Blown head gaskets, do not usually make noise. Remote possibilities may be something getting sucked into the engine and bending a valve. A jumped timing chain usually will cause the camshaft to break without bending a valve.

Removal of the cyl head is not that difficult unless you have factory AC.make sure you have a 10mm allen tool for the head bolts.  A few tips will save you hours of work so keep in touch!

Joe Alexander
Blacklick, Ohio

[Rolf]

Joe,

  I do not hear the noise any longer, only heard it for a second or two.It sounded as though something hit the fan. It seems that more than one cylinder is involved. All the plugs had lots of carbon and 3 were wet, real wet. It seems that the head will come off, whether it's the valves or gasket. I am going to double check the timing chain position before I remove the head. It seems to have not jumped a tooth but, one never knows.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS