Fronkenstein

Ok my 1978 (1984.5 powered M28.22) running CIS, not LH is having a left bank rich problem all of a sudden. And to make matters more perplexing and concerning, upon cold start one of the cylinders is loaded up and runs very rough. If I wait 10 seconds and raise the idle she clears up. Additionally I also feel there is too much moisture burn for the first 10 minutes. Once the WUR has reached warm up all is good. BUT the AFR runs at least 1 full point different from one side to the other. I have had the boroscope down the four cylinders more times than I can count and compression test all show good. I have yet to do a leak down. There is no water in the oil and no bubbling in the reservoir. Plugs are darker on 7 & 8 than all others. I am running 1.1mm gap on all plugs W7's copper.

This problem did not exist 45 days ago. I have brought the RPM's to 5000 under load with no issue.

Oh and I changed out 2 injectors and removed cleaned out the fuel distributor which I have done in the past for a misfire issue which solved that problem.

There is no sign of misfire after she warms up on the timing light.

I have a Porken, but have not checked cam timing yet. Anyone think this could be the issue?

Any ideas from the crew here would be very helpful. The only similar post for this topic is LH related.

Thanks,

Fronkenstein

Fronkenstein

So I found the culprit is cylinder #7. Swapped out the plug and plug wire and plug - no change. Checked the T-belt and its fine. Put the scope down the bore and I don't see anything wrong. There are no vacuum leaks.

Leak down test tomorrow. Does anyone have any other clues? I feel like I am missing something blatantly obvious.

Thanks

Fronkenstein

SMTCapeCod

Time to swap out the injector I would think?


OOPs/DOH, was cyl #7 one of the swapped injectors already cited above?

Also, IIRC cold start valve is offset to pass side, but it seems that is the wrong/Normal bank given cylinder designations.

Hope it isn't a spastic FD.

You don't happen to have the hot-start valve on the Pass side of your CIS do you?

BTW, is the sampling of banks via pyrometer/EGT, wideband O2s or what?
Where are the sensors located? Presumably, you don't have euro heads that use air induction.

Fronkenstein

See my comments in ()s


Thanks,

Fronkenstein

SMTCapeCod

Air induction- (edit) I screwed up the terms, should've been "air injection".....in some euro applications the air pump forced air into ports in the heads, so the free O2 completed combustion right outside the chamber, rather than downstream in the cats. Hope I'm explaining it right, my Euro work was many years ago.
(edit) see: https://rennlist.com/forums/928-foru...tio-meter.html


Hot start valve was a wag....but I guess that bears on the entire system regardless of its positioning on the pass side. That was a bad call.

Just to continue the trend- is there still an air pump feed on the pass side such that it might read leaner? I expect that would be at the cat, if not deleted.

Sounds like maybe the FD...particularly if the niggling little in-port filters are still installed in it under the fittings for the lines.
Thanks for entertaining my WAGs, look forward to reading the final diagnosis.

Fronkenstein

No CAT
No EGR
No Air Pump
No emissions junk

Those horrible little filters were tossed after the last FD clean out.

Keep in mind things were good until a month ago or so.

A new event on Monday worth noting. After a long day of driving from the Pcar event at NHMS in Loudon my fuel pump started to get loud. I was hoping it was going to be ok. As soon as I said that to myself the car quit.

After ramping the car home, and as I suspected, the car started because the pump had cooled down. Either it was plugged in the suction or between the pump and the filter.

The more I read through my own writings i am pretty well convinced it's the FD.

If anyone feels I am off base please chime in.

Thanks,

Fronkenstein

SMTCapeCod

Already then, enjoy.

Fronkenstein

Was it something I said?

Dave928S

To get the unequal feed you're getting I'd be suspecting the FD, and the fact that you've recently had issues with it makes it more likely. Any other issue should be affecting all cylinders.

SMTCapeCod

Might've been the all caps and I didn't see the underlying comments...
...but also I was acknowledging that I was tapped out for tech insights and not likely to be adding value beyond prior posts.

Frustrating for you if it is the F/D, always nice when they are squared away and work well for years. But sometimes they don't.
I got to the point where I had one running well on the care and TWO rebuilt backups in reserve! F/Ds and Wurs....evil. A good kindof evil sometimes, and sometimes notsomuch.

Fronkenstein

The all caps were for emphasis not shouting. This mobile app isn't too good for inserting _emphasis_ marks. I'll fix it.

The engine is emissions free.

Fronkenstein

Fronkenstein

I have a couple of aluminum Mercedes FDs from euro 4.5L CIS cars. Has anyone had any experience using these units on a 928? I could use one of those as a spare.

Fronkenstein

SwedeInSiam

My car have one of those, a 068 (and a WUR from a Ferrari ).
Have been running with it since long before I bought the car.

Fronkenstein

Well I may have found it. The vacuum advance unit was not working throughout its range. In fact it was hardly working at all. That doesn't really explain it totally for me but there is definitely a difference in the AFR reading while driving. I will drive it a bit before I see how it stabilizes at idle. 02 sensor may be carboned up. For that matter the sensor may be toast. I may remove and put the torch to it.

I will keep you posted.

Fronkenstein

Fronkenstein

It turned out to be a damaged diaphragm in the fuel distributor.

Fronkenstein