sam1904

Man, there really is a strong vacuum leak contingent on this forum!! I know it is most often the cause of these type of issues but when you have a checked for it 30 times you just have to take it off the list.
 

No, there was no misunderstanding. I stood and we chatted about it for about five minutes. While they were pulling the vacuum hose off with the car running the cylinder suddenly started firing. Prior to that you could put your hand on the exhaust manifold on number four and it would stay cold, when they left the nipple open it now fired, responded when you pull plug number four and the exhaust manifold heated up.

They specifically stated that although this would suggest an airflow issue there must be some airflow getting through as the plug would be wet after it running for a while. I believe it does fire to some extent beyond idle although this needs to be confirmed. (I have a hard time believing the car will do 90 mph running on three cylinders although it does seem a little flat getting there.)

The next step they suggested on Monday is to pull the carb (That poor thing has been on and off more times than my shorts in the last couple of months) and put a borescope down intake runner #4. 
 

sooooooo...... back to my question ? has anybody ever had any experience with any strange airflow issues causing number four to get starved?

They suggested that suggests an air starvation issue to number four. As I can’t imagine a mouse would’ve lasted that long in the runner! I am wondering if there is some strange aerodynamic affect going on as air flows through the carb. I also changed to a closed air filter about 500 miles ago so nothing could’ve got in there recently.  
I had already checked to make sure that the gasket was the correct way around on number four so that is not impeding airflow.

I had previously replaced everything in the brake booster line and insured no vacuum leak. My understanding from the shop is today when they run the motor with the line disconnected and the large nipple open it fired!

Update - it has been at the shop a couple of days and so far they have just duplicated findings (compression OK, leads good etc).

When I swung by today they stated that as opposed to a vacuum leak when they disconnected the booster hose it actually made #4 fire. Given this they are thinking air supply issue to #4. (all appear to be getting fuel as plugs wet, although how does fuel get there if enough air cannot...).

Aside from a blocked runner anyone got any ideas?

Any history of 32/36's with certain issues / air filters causing air starvation to #4?

Any other thoughts?

I do wonder if there is a common issue / cause that tips air flow under the limit to fire as when you search 'dead cylinder' it always seems to be #4 and very hard to track down (four strings on this subject on this site...)

Thanks All

Sam

OK, after being talked off the ledge by you good people there will be no wrapping of the waist of the car. You are right that the pictures of the blue / white car in race livery looked great (personally you could put a beige and pink car in decal strewn livery and I would love it - mid life boy racer) but the examples that were just two tone are not to my taste.

With that said I do have a 5' x 6' sheet of white and some knifeless tape so I am going to experiment with a white roof (curved with the roof, about 1/4" proud of seals etc) and see. Can always pull it off and it will keep me from roaming the streets or muscling in on my 4 year old daughters Lego box for a few hours!

Sam

22 minutes ago, tech71 said:

Wow, so frustrating! I admit to not reading the entire thread but from your summary above it sounds like you are getting spark right?

You have done so much troubleshooting and covered so much stuff...at this point nothing sounds too far fetched so just wondering,

Have you had the intake off?

Any chance you might have some kind of obstruction inside the intake manifold itself?  Paper Towel, baggie, leaves, gasket bit wedged in runner, mud dauber nest?

If this straw has already been clutched please disregard.

 Afraid not...

2 hours ago, '76mintgrün'02 said:

 

this is an interesting tangent.

 

they are fired when the little magnets inside the ring on the center post pass the sensor.

 

you could try removing the magnetic ring and reinstalling it in a different position on the shaft, putting the #4 magnet near a different lobe on the post and see if the problem follows the ring.  Maybe that one is missing a magnet, or something.

I did put an inline spark tester in line and it showed current. the question had been if it was 'strong' enough. As such it apparels the magnet is good?

2 hours ago, ray_ said:

Sam, tell me about your throttle shaft bushings....

There is no noticeable impact when I spray carb cleaner right at them, aside from that cant say much.

With that said - not sure what spraying will do. If there is a vacuum leak on #4 the spray cant make it deader than dead....

12 hours ago, Mark92131 said:

I'm sorry that you haven't been able to solve this issue.  It is strange that pulling #4 plug wire doesn't change your idle at all.  The idle did seem to dip/smooth out when you sprayed #3 intake runner at the head (bad gasket/surfaces? Any vacuum leak in this area will reek havoc with your idle).  I know you used an in-line spark tester and you moved spark plug wires, but did you pull #4 spark plug and ground it to the block to verify a nice healthy spark when cranking. Because you have no change with #4 wire pulled, stick a spark plug in it and ground it to the block to verify that healthy spark while idling.   The leads might be OK, but maybe bad cap/rotor connection at #4 causing a weak spark?

 

Keep us posted.

 

Mark92131

You were my irrational hope today as I dashed out of the bedroom! "it's that damn Bosch cap and I have a spare! - finally this will be over"

Run, run, rustle, rustle.

Damn it!!

Next!!!

Thanks. It states 'similar to Petronix' and the Dizzy is brand new.

https://www.iemotorsport.com/product/tii-mechanical-advance-distributor-with-electronic-ignitor/

Before I chase this could faulty igniter just impact one cylinder? (not sure how these are 'fired')

Thanks

Sam

All, thanks for all your help with this issue. After chasing it for weeks and checking and rechecking everything below over and over and over and over I am going to drop it into one of the local vintage BMW shops and see if they can diagnose. As I see many posts from others with similar issues, I thought I would document what I know to date (going to put in the two strings that people have helped me in) and if there is an answer share it later. There is also a video of the issue in the post above!

The car (the pertinent bits)

• 76’ 2002
• All emissions equipment removed
• Weber 32/36 with manual choke
• Still has fuel bypass valve
• IE Stepped long header
• IE Stainless exhaust
• Catch can
• Rear battery relocate (likely not related but…)

Summary of the problem

Car is hard to start and idles roughly. When idling I can pull lead #4 with no impact and #3 doesn’t seem to make the idle much worse. If I pull #1 or #2 it stumbles badly. The car mostly runs well at higher RPM although it does still sound like it is missing slightly when you rev it by hand under the hood. Sometimes it will pull strongly to 90 mph, others it seems a lot ‘flatter’. Video shows problem at idle.

Don’t know if related but it also smokes on throttle lift off when being pushed hard .

Pertinent work to date (Some to address issue, some along the way)

• Ignition
  • Installed IE Tii Mechanical advance distributor, Bosch cap and rotor (electric ignitor)
  • Installed new leads
  • After initially using an Iridium plug switched to BP6ES gapped per Haynes (does this need to increased with the ignitor?)
  • New blue coil, removed resistor wire
  • Set the timing per the IE instructions to around 32-34 advance at 3300RPM. Seems to be around 14 degrees at idle although hard to see with shaking motor!
  • Have experimented just retarding and advancing the timing at idle until it stumbles in both directions. Effects RPM but has no impact on misfire.
  • Used an inline spark tester and all plugs getting current
  • Have moved the plugs (and leads) from cylinder to cylinder with no impact.
• Rebuilt the carb (several times)
  • Set the brass floats to 41mm.
  • Re-jetted per CD prescription in picture below and plugged the hole’
  • Adjusted idle mix by ear, no mixture change solves the misfire, but it does seem to stabilize in RPM around 1.5 turns out. Have it set at 2 turns out
• Did a cold, dry compression test looking for a dead cylinder.
  • Results (1-4) were 120, 120, 110, 120 psi.
• Set the valves and then reset to check a week later.
  • All within 0.15mm – 0.20mm and don’t seem to be making too much of a racket
• Have chased vacuum leaks until I am absolutely blue in the face.
  • Have capped and recapped all nipples
  • Currently have the nipple on #4 connected to the fuel bypass, was initially connected to #1 with no change. #1 now capped.
  • Capped nipple on base of carb and beneath on manifold
  • Replaced all hose, check valve, elbow and rubber seal washer to brake booster
    • Also removed and plugged port on #4 to trouble shoot with no impact on misfire
  • Have liberally sprayed carb cleaner all around motor and any vacuum elements. Potentially a very minor stumble when squirting directly at #3 gasket but not definitive. No other noticeable issue. (All ports, throttle shaft, gaskets, block off plates etc etc)
  • Have checked the inlet manifold bolts on #4 and #3. All snug.

That’s all I have! Taking it to someone frustrates me enormously and may not sole the issue. Wit that said I have so much time in this car the chance that $500 to someone who works on many 02’s and may have a better relative feel is worth it.

I will keep you all updated and thanks again for all the help along the way!

Sam

All, thanks for all your help with this issue. After chasing it for weeks and checking and rechecking everything below over and over and over and over I am going to drop it into one of the local vintage BMW shops and see if they can diagnose. As I see many posts from others with similar issues, I thought I would document what I know to date (going to put in the two strings that people have helped me in) and if there is an answer share it later. There is also a video of the issue in the post above!

The car (the pertinent bits)

• 76’ 2002
• All emissions equipment removed
• Weber 32/36 with manual choke
• Still has fuel bypass valve
• IE Stepped long header
• IE Stainless exhaust
• Catch can
• Rear battery relocate (likely not related but…)

Summary of the problem

Car is hard to start and idles roughly. When idling I can pull lead #4 with no impact and #3 doesn’t seem to make the idle much worse. If I pull #1 or #2 it stumbles badly. The car mostly runs well at higher RPM although it does still sound like it is missing slightly when you rev it by hand under the hood. Sometimes it will pull strongly to 90 mph, others it seems a lot ‘flatter’. Video shows problem at idle.

Don’t know if related but it also smokes on throttle lift off when being pushed hard .

Pertinent work to date (Some to address issue, some along the way)

• Ignition
  • Installed IE Tii Mechanical advance distributor, Bosch cap and rotor (electric ignitor)
  • Installed new leads
  • After initially using an Iridium plug switched to BP6ES gapped per Haynes (does this need to increased with the ignitor?)
  • New blue coil, removed resistor wire
  • Set the timing per the IE instructions to around 32-34 advance at 3300RPM. Seems to be around 14 degrees at idle although hard to see with shaking motor!
  • Have experimented just retarding and advancing the timing at idle until it stumbles in both directions. Effects RPM but has no impact on misfire.
  • Used an inline spark tester and all plugs getting current
  • Have moved the plugs (and leads) from cylinder to cylinder with no impact.
• Rebuilt the carb (several times)
  • Set the brass floats to 41mm.
  • Re-jetted per CD prescription in picture below and plugged the hole’
  • Adjusted idle mix by ear, no mixture change solves the misfire, but it does seem to stabilize in RPM around 1.5 turns out. Have it set at 2 turns out
• Did a cold, dry compression test looking for a dead cylinder.
  • Results (1-4) were 120, 120, 110, 120 psi.
• Set the valves and then reset to check a week later.
  • All within 0.15mm – 0.20mm and don’t seem to be making too much of a racket
• Have chased vacuum leaks until I am absolutely blue in the face.
  • Have capped and recapped all nipples
  • Currently have the nipple on #4 connected to the fuel bypass, was initially connected to #1 with no change. #1 now capped.
  • Capped nipple on base of carb and below on manifold
  • Replaced all hose, check valve, elbow and rubber seal washer to brake booster
    • Also removed and plugged port on #4 to trouble shoot with no impact on misfire
  • Have liberally sprayed carb cleaner all around motor and any vacuum elements. Potentially a very minor stumble when squirting directly at #3 gasket but not definitive. No other noticeable issue. (All ports, throttle shaft, gaskets, block off plates etc etc)
  • Have checked the inlet manifold bolts on #4 and #3. All snug.

That’s all I have! Taking it to someone frustrates me enormously and may not sole the issue. Wit that said I have so much time in this car the chance that $500 to someone who works on many 02’s and may have a better relative feel is worth it.

I will keep you all updated and thanks again for all the help along the way!

Sam

This video relates to the post below!This video relates to the post below!

Me too, as there are no vacuum ports on number three I guess this would just mean the inlet manifold gasket? It also doesn’t explain why it is number for that is dead?

Thanks Buckeye, in no way was I suggesting I don’t need your help just didn’t want to drag everybody through a duplication of the questions I already asked elsewhere!

I have rerouted the vacuum cables in line with your recommendations.

I also took the video below spraying  carb cleaner around to see if I could find a vacuum leak. Is it just me or does it seem to dip slightly when I spray it at the intake manifold gasket around three or four?

This seems very minor, could this be the issue? I did check with an in-line spark tester and all plugs are getting spark.

Thanks all, I am deciding whether to drop the motor, look at rings inlet manifold gasket, valves etc or take it to one of the local 20020 shops... (Buckeye - I wont recreate here but there is a post as to my woes and actions taken - essentially de-smogged 76, new Dist, coil, plugs, leads, timing, valve set, carb rebuild, jetting per CD's prescription, vacuum hoses etc etc etc etc.)

While I consider next steps I was thinking about pulling the fuel return valve to clean things up and make myself feel a little better...

I believe I just plug the connection at the tank, remove the valve and cap the 'nipple'? I would also reroute the fuel line to the nearer side as shown in green to avoid a big loop?

Strong advice otherwise?

Thanks again,

Sam

On a good note got a great drive in with friends today!

Thanks a lot John, the nipple on number one is indeed connected to my fuel return valve.

Just went and pinched the vacuum hose closed to simulate that and no improvement!

 Damn it. 

Just to make sure I am correct. I already have one capped off port at the base of the carburetor that was going to the vacuum advance before I changed to the tii mechanical advance distributor. I also have another vacuum port on the carb that is connected by vacuum hose (red arrow) to the nipple behind the brake booster. Are you saying remove this hose and cap the nipple on the intake manifold and on the carb?

I keep reading about that nipple as I relentlessly search for a vacuum leak with the same issue. On my car that nipple is connected to the base of my weber 3236. Is this correct or should they both be capped off?

Thanks, after four stores I think this is as close as I can get!Thanks, after four stores I think this is as close as I can get!

I am struggling to find GL4 hypoid oil on a Saturday. Is the differential as sensitive to GL5 as the transmission or can I use a GL5 hypoid Oil that is in stock at my local big box auto store?

Last comment is we are going for a group drive tomorrow so it could be a hard hundred miles!

Sorry, car is a 1976 2002 with stock differential.

Hi all, I just made the mistake of putting MTL in my transmission and my differential.
 

Can I leave that in the differential for 100 miles or so until I can get a different differential fluid?

I also have some 80 W -90 gear oil that is GL4 and GL5 compatible. I know this is not good for the transmission but would it be better to put this in the differential? Many thanks, Sam

Going to try it myself!

Vinyl cost around $200, knifeless tape $30 and beer. Should not be that hard as no complex 2D curves like new cars