Misfire and backfiring

[blindrooster]

Ran into a problem I'm having a real hard time diagnosing on my 83 320i. Last week I started getting rough cold starts and very low idle when hot. Pulled the wire to the 4th cylinder and the engine made no change, great. The Misfire does not follow the plug or wire, the spark on the distro looks strong. The distro was also replaced about 1.5k miles ago. The 4th cylinder spark plug was pretty oily and the car is shooting out white/blue smoke out the tail pipe, no other plugs looked oily. Could bad valve stem seals cause a misfire? The car also reeks of fuel, so maybe the plug is covered in fuel? The entire kjet fuel system was replaced last november and has done about 3500 miles since, and I have not had any fueling problems whatsoever. It kind of feels like the car doesn't misfire while driving, like above 2k rpm, but I'm not sure. Coil, plugs, and wires were also all replaced 3500 miles ago with the fuel system. I'm at a loss as to what to check now and any and all suggestions are welcome, even if you suggest I re-test something.

[Mike2002]

#4 plug could be fuel fouled and will not spark. Change that plug and see if the issue goes away. If it does then just keep an eye on it. You may have oil getting past the valve stem seals and causing oiling on the plug and eventually it will foul that plug again.

[blindrooster]

#4 plug could be fuel fouled and will not spark. Change that plug and see if the issue goes away. If it does then just keep an eye on it. You may have oil getting past the valve stem seals and causing oiling on the plug and eventually it will foul that plug again.

I swapped the plugs around and it didn't make a difference, just fouled the new one up a bit. Hoping I don't have to replace valve stem seals just to get the 4th cylinder firing.

[Somjuan]

What's the distributor cap look like? Check that out. If it's bad it's worth replacing the condenser(?) and rotor as well, then oiling the shaft underneath the felt cover

[epmedia]

Maybe the valves need adjusted. The M10 valve clearances tend to tighten rather than loosen. I've noticed that a valve clearance of less than .002" can cause a terrible misfire.

[blindrooster]

Interesting new development. I got the car warmed up and drove it around the block and a friend came by to look at it. It was running a bit rough but sounded like it was running all four. Pulled the wire to 4 and no change, pulled 3 and no change, wtf. Pulled 1 and it very clearly started to misfire, same for 2.

[GDAus]

Interesting new development. I got the car warmed up and drove it around the block and a friend came by to look at it. It was running a bit rough but sounded like it was running all four. Pulled the wire to 4 and no change, pulled 3 and no change, wtf. Pulled 1 and it very clearly started to misfire, same for 2.

Hi ....

Has it been running a bit hotter under load? Have you checked your water level in your radiator? Any sign of oil in the water? You could have a blown head gasket between cylinders 3 & 4.

Whitish smoke from the exhaust is often a sign of water mixing with oil in the combustion chamber. A compression test is the definitive test of course, but if you don't have a compression tester, then try warming up the engine from cold with the radiator cap off ... and check for gas bubbles as the engine heats up to operating temperature.
The water level needs to be high enough for this to work, but be careful, as the water heats it can spit out of the radiator filler neck. Continuous bubbles are bad news.

Cheers

[gsumzzz]

timing and valves spot on? make sure of these first.

[blindrooster]

Hi ....

Has it been running a bit hotter under load? Have you checked your water level in your radiator? Any sign of oil in the water? You could have a blown head gasket between cylinders 3 & 4.

Whitish smoke from the exhaust is often a sign of water mixing with oil in the combustion chamber. A compression test is the definitive test of course, but if you don't have a compression tester, then try warming up the engine from cold with the radiator cap off ... and check for gas bubbles as the engine heats up to operating temperature.
The water level needs to be high enough for this to work, but be careful, as the water heats it can spit out of the radiator filler neck. Continuous bubbles are bad news.

Cheers

Coolant level is good, have had no issues with temp or heating, no gas bubbles. Phew, you had me worried. Struggling to start on this cold morning with only 2 cylinders...

Timing was set ~1500 miles ago when the distro was replaced, could it have changed? Cap and rotor look good, and are about a year old, ~3500 miles. Car still reeks of fuel when it runs. Losing hope I don't have confidence in removing the valve cover and checking the valves, but they were adjusted 3500 miles ago.

[GDAus]

Coolant level is good, have had no issues with temp or heating, no gas bubbles. Phew, you had me worried. Struggling to start on this cold morning with only 2 cylinders...

Timing was set ~1500 miles ago when the distro was replaced, could it have changed? Cap and rotor look good, and are about a year old, ~3500 miles. Car still reeks of fuel when it runs. Losing hope I don't have confidence in removing the valve cover and checking the valves, but they were adjusted 3500 miles ago.

Hi again ....

Umm ... unfortunately head gaskets can also "blow" between the cylinders without leaking into the cooling system. Again, a compression test is the only way to positively confirm or deny that .. and a compression test will also show if the valves are leaking.

Reeking of fuel? In the engine bay? Have you checked all the fuel lines? A leak in a fuel line to the injector could be dropping the pressure enough so that it is not atomising the fuel at low RPM's ... Or if the fuel smell is at the exhaust pipe, then an injector may have a partial blockage and again not atomising the fuel at low RPM's. K-Jet systems need their fuel filters changed at the required service intervals!
You could try using fuel injector cleaner in your tank, but to be honest, if you aren't confident taking off the valve cover, then pulling injectors to check spray patterns etc, maybe is something best left to a mechanic.

cheers

[blindrooster]

Hi again ....

Umm ... unfortunately head gaskets can also "blow" between the cylinders without leaking into the cooling system. Again, a compression test is the only way to positively confirm or deny that .. and a compression test will also show if the valves are leaking.

Reeking of fuel? In the engine bay? Have you checked all the fuel lines? A leak in a fuel line to the injector could be dropping the pressure enough so that it is not atomising the fuel at low RPM's ... Or if the fuel smell is at the exhaust pipe, then an injector may have a partial blockage and again not atomising the fuel at low RPM's. K-Jet systems need their fuel filters changed at the required service intervals!
You could try using fuel injector cleaner in your tank, but to be honest, if you aren't confident taking off the valve cover, then pulling injectors to check spray patterns etc, maybe is something best left to a mechanic.

cheers

Good tips. Fuel filter was replaced ~3500 miles ago . I'll probably pull the injectors, check lines, etc. Only original part in the fuel system is the lines and the fuel distributor. I appreciate the insight.

[blindrooster]

The car does not hold idle when cold and spews white/blue smoke, I let it warm up to the point where it would hold idle while running on 2 cylinders and when warm it no longer smokes out the tail pipe. I noticed a whurring/wooshing noise coming from under the manifold that got louder when i adjusted the idle speed screw to raise the idle. There also seems to be a 'buzzing' noise coming from the fuel distributor I think. No idea what to make of this. Car will most definitely be going to my mechanic as soon as possible. Any further insights would be greatly appreciated. I made a little video where you can kind of hear what I'm talking about, https://www.dropbox.com/s/w7dwl54i05...oises.MOV?dl=0 . I've never heard these noises before on this car.

[blindrooster]

Also just noticed that it seems to now be running on only 1 cylinder. Pulled the plug to cylinder 1 and it didn't change, so this problem has been getting progressively worse. Could my fuel distributor be going bad?

[epmedia]

Check to see if the engine oil is diluted with gasoline.
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Regarding valve rocker adjustment; you'll want to learn about doing it if you plan to own the car for awhile. A note on valve adjustments: The nuts #17 here on realoem.com may be getting worn out (because screwed so many times in their life). It's good to have spare eccentric nuts (all eight) when adjusting the valve rockers. Also, it's possible that some of these eccentric nuts should have been replaced during the past valve adjustment! *Have a couple spare #15's too, just in case.

[blindrooster]

Hmm. Ive done a valve adjustment on an MGB, was incredibly easy. Good call on the eccentrics.

The car has a somewhat bad oil leak from the front cam seal so it gets a fresh quart like every 300 miles. I supoose I shoild drain and change and what it looks like.

[epmedia]

Hmm. Ive done a valve adjustment on an MGB, was incredibly easy. Good call on the eccentrics.

The car has a somewhat bad oil leak from the front cam seal so it gets a fresh quart like every 300 miles. I supoose I shoild drain and change and what it looks like.

My front crank seal was doing the same awhile back.. makes a huge mess under there! Leaky crank seal causes a slight vacuum leak too (crank case side).
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You can pull the oil dipstick and give it a 'sniff' and a 'cling' test between your fingers. if the oil has no 'cling' or smells like it's been diluted with gasoline, it needs to be changed - if it's been diluted with gasoline, fix the cause (if possible) before changing the oil.

[Mike2002]

From reading the continuing explanation of what is going on I am thinking you have a blown head gasket between 3 & 4. Do a compression check. That will tell you a lot with very little effort.

I chased a rough idle/miss for a long time (several months) and never did figure it out until the head came off. It was a crack between the valves on #2. I did have low compression on #2. The engine ran great once warmed up, no coolant loss, no smoke.

[blindrooster]

Oil does smell like fuel, fingers cling a bit to the dip stick. It's going to sit for a few days, my other bmw is in the shop for something else, so when that's out I'll have a compression test done and we'll see. Thanks for all the suggestions guys, new to the classic bmw world.

[epmedia]

Oil does smell like fuel, fingers cling a bit to the dip stick. It's going to sit for a few days, my other bmw is in the shop for something else, so when that's out I'll have a compression test done and we'll see. Thanks for all the suggestions guys, new to the classic bmw world.

That fuel smell in the engine oil is hopefully what's causing the 'blue' smoke out the tail pipe. Fixing the engine running issue and changing the oil will hopefully cure all.. I'm being optimistic the problem is Not the head gasket, even though some symptoms point to it, fingers crossed for you! Tight valve(s) have some same symptoms too and would be an easy fix!

My head gasket blew between cylinders twice, because I did not resurface the head during the first head gasket replacement. The first time, it was between 3 and 4, then between 1 and 2. There was terrible detonation (pinging) when the head gasket was blown between cylinders. And of course, engine ran like crap, was difficult to hold idle speed and obvious 'symptom' of misfiring. None of the spark plugs were fouling like you describe, just some unusual carbon deposits on the affected cylinders.

This blown head gasket progressively worsened with 'pinging' over a couple weeks of daily driving. There was no apparent symptom of mis-firing at engine idle speeds until the last two days of driving.

Here's a pic of the (second) blown head gasket. Click to enlarge.
blown-hg-1-2.jpg

[blindrooster]

Had a mechanic buddy come look at it and he's convinced that the car is simply running way too rich for whatever reason, as all four cylinders will run at higher rpm, 3k +. The car also idles better at cold when the cold start injector is unplugged. So.... further confused. He's not familiar with kjet, and neither am I so I'm confused as to what to check now.

[epmedia]

Had a mechanic buddy come look at it and he's convinced that the car is simply running way too rich for whatever reason, as all four cylinders will run at higher rpm, 3k +. The car also idles better at cold when the cold start injector is unplugged. So.... further confused. He's not familiar with kjet, and neither am I so I'm confused as to what to check now.

Way too rich on all the cylinders or mostly just on #4?
If just on #4, this is a sign of maybe a bad injector, or the fuel distributor needs some work.

[Somjuan]

Progressively worse and richer could be the fuel distributor going out, yeah. Did you do a leakdown test while he was there?