Solved - Name that misfire? Help! Video-1977 US 930 Missing?
 

Sorry for upside-down video. Tried flipping it then upload again to google drive but still upside-down?

Click for video----->https://drive.google.com/open?id=1C2U79piZaYAI9N9y2JqGVKqAI0aQ2NLX

1977 US Turbo 930. Has run great since engine rebuild. This started out of nowhere after a few thousand miles. Putt, putt, putt, putt at idle and AFR goes slightly lean. Not lean enough to stall but it will stumble before clearing up when getting on throttle. Seems to rev and boost fine. Not driving it, don’t want to get stuck. When it started doing this was on my way home and I did get into boost. I did notice afr seemed to fluctuate/react faster to throttle modulation and may be going richer on boost? Wideband has data logger but haven’t used that feature yet. The video doesn’t show the sometimes quite lean condition 15-16.5 but mis sound can clearly be heard. At idle it does go away sometimes but only for a few seconds?

System Pressure: 95 psi
Volume Delivery Test: Passed
Cold Control: 20psi

Is this right? Hot Control: 35psi with wur vent vac hose plugged in(This is the reading with the engine running) (Car has run great this way the hole time?)(Only discovered this now after testing for misfire)

Is this right? Hot Control: 51psi with wur vent hose unplugged(Plugged Vac hose)(This is the reading with engine off and fuel pumps running)

New parts: Wires, Plugs, Cap/Rotor, WUR, Front Fuel Pump, Fuel Injectors, Fuel Filter, Porsche bov(Not vented to air)
Old parts: Coil, Fuel Head, Rear Fuel pump, Fuel accumulator, all other devices that come on 930

Checked for vac leaks but nothing found. Used water spray mist. Continuing to check…

Now I’m jonesing to drive! It’s like taking away drugs from an addict! Thank you all in advance.

pull the plugs and look for one that is drastically different
look for fuel leak at the fuel lines, injectors and head
plug wire came off/bad
is the IC securely attached/ got blown off on boost. check O rings
check intake bolts

run a quick compression check while plugs are out

Thank you for reply and will report back with compression test or any other finding.

Swapped coils and no change. It did idle great with no missing while cold. Once warm the misfire returned. Next up, compression test. Went to pull first plug and the wire boot end broke clean off. These are brand new beru wires. The end is still on the plug. Couldn’t get it out. Will try again tonight. For the record the ignition system is 100% oem stock.

if it runs better cold then you could be looking at a mixture issue, probably too lean.
could be due to air leak.
check your fuel pressures.
fix ignition issues.

T77911S, Please give your thoughts on my pressure data. Have adjusted it both ways(rich/lean) with no change in misfire. Hoping it turns out to be the wires. Thank you!

System Pressure: 95 psi
Volume Delivery Test: Passed
Cold Control: 20psi

Hot Control: 35psi with wur vent vac hose plugged in. This is the reading with the engine running. Car has run great this way the hole time?. Only discovered this now after testing for misfire. At this pressure with the old injectors engine would run on/stumble quite a bit when turned off. With new injectors it shuts down clean, no run on. Did adjusted afr to 13.6 for this pressure setting.

Hot Control: 51psi with wur vent hose unplugged or reading with engine off and fuel pumps running. Note: did plug the unplugged vac hose so no leak. With the new injectors engine runs on alot and backfires after shut off. It runs on so much I felt like it would never shut off! Did adjusted afr to 13.6 for this pressure setting also.

Happy to report the mis-fire has been solved. It was the new beru wires. Replaced new set with the old set. It appears the new set quality is very poor. Noted a few differences.

New Beru Wire Set:
Boot that snaps on cap is not marked in any way and tears easily when trying to install or remove. It doesn’t snap into cap and is next to impossible to remove once pushed on. Most times the wire pulls out. Because it doesn’t snap into cap its difficult to know if it’s fully seated. The stem part of the plug boot seems to be my failure. Either the heat cycles or poor factory quality caused it to crack. #1 split clean in half when trying to pull it off plug. Didn’t measure them but they appear shorter in length than the old ones. Old set had more slack when installed.

Old Beru Wire Set:
Boot that snaps on cap is molded with the beru logo. Boot material is heavy/stronger rubber than new set. When pushing into cap they have a series of two snaps which I assume indicates fully seated. They can be removed easily without boot tearing or wire pulling out.

Side note on new fuel injestors: I always planned on getting new injectors but put it off because it ran pretty good. Replaced them while trying to solve the mis-fire but they made no change. Once mis was fixed the best way to decsibe new injectors is wow! They have totally transformed the car. Rock solid AFR’s and smooth as silk. No run-on at shut down either. If your thinking about new injestors just do it!

yes, injectors are a wear item and are very often over looked.

new someone that had issues with new (I think beru) wires years ago. thought it was just a one time thing but maybe there is a quality issue with them.

Sounds the same as mine on startup.
Usually clears up by the time I get to the end of the block. - if not, I just push on the plug wire tops to re-seat the connection.
Bill K