TheSamba.com :: View topic

Sat Nov 21, 2009 1:54 pm

First - I really appreciate all the suggestions and just because I may or may not comment on one doesn't mean I am not taking it seriously. Your suggestions that something as simple as changing fuel, putting on more miles or a timing tweak may be all that this bus needs. I am a good mechanic but not perfect and I find that at age 59 I am forgetting more in a day that can be imagined. Our minds just don't grasp things like they did when younger - my dad, 87 is losing much of his memory from normal aging and it scares me what life will be like for Cathy and I at that age as we have no children to help us, like my parents do. As to this bus AFM, my biggest concern is that FIC put much time into getting this one right, and the conversation with Tony was very good. His answers were thoughtful and when asked about changing spring tensions he said - "no. don't do that . This one is exactly the same as the NOS '76-77 one we use for calibration. If you change the spring you are treating symptoms." I asked him how they measure spring tension and compare - and he said they test several ways including a device that hooks up to the shaft and measures the tension at set points. So I believe that tweaking the spring or wiper on this AFM has got to be last resort. They run them on a simulator and both are identical as can be so again, I have to exhaust all other options first. That AFM is the heart of the FI bus engine. I think VW knew in their hearts that 14.7 to 1 was too lean on FI motors. Before smog, 12.5 to 1 was considered perfect for performance and 13.5 to 1 for mileage and power in general. This AFM is 13.7 to 1 under dyno loading so I have to believe that is close to where VW wanted it. The 1979 model went to 14.7 to 1 but that was to make the smog king happy.

The comment on the cam and vacuum. We lost control on the camshaft grind. Ours was reground but we got back a hydraulic from RIMCO instead of solid. When finally got a solid but no one could tell us the actual grind info. We also have that cam gear clatter like Colin had so to remedy these potential issues it I have purchased a new Webcam, lifters and have collected cam gears from 0 to -4 although I am missing a good -1. Next time we split the case we will put in this new cam and a tighter gear. But that won't happen tomorrow as we have too many other things to do first.

Tram - I 100% believe you on the Vanagons. My best friend since highschool spent three or four vacations in motels in the late 1980's waiting for VW dealers to replace his engine. In the end he said VWOA blamed a bad AFM for the problem. He sold the vanagon westy after the last engine - life is only so long. We considered a Vanagon new in 1981 when we had money and the old 1971 bay but decided that the bread box style bay was just more appealing to us. It still is and I should have kept that 1971 rather than sell it. Some folks love Vanagons, this household sees them as just another car but means no insult to Vanagon lovers. We do wish more of them were on the highways. We have a population of about 1.5 million here in this area plus people passing through from the SF/Oakland area on the way to the Sierra Nevada. We rarely see a Vanagon but bays are reasonably plentiful as we see two or three a week.

The question on dwell. I would have to try it to see. The coil pulse shown in the graph is the surge created in the primary winding when the field collapses. The pulse is a spike followed by ripples. The height of the spike is in part determined by the voltage the coil fires at, and I don't know what controls how many ripples there are afterwards - it may just be oscillations in the windings. Dwell could affect the final coil voltage especially at high rpms but this smog issue is at lower rpms. I will go over my distributor setup again to make sure everything is perfect there.

The book does mention that vacuum in these engines was designed for 20 inches of mercury and that is what FIC said too. I only have 18 inches of mercury at idle so maybe the cam is different or the timing off etc. We probably just need to take it to Reno or Tahoe soon and get some miles on it. Up and back would be 250 miles and a good solid hill climb so that would test it. I've got to adjust the spring plates in back and have a final wheel alignment done first as it is too nervous on the freeway. We set the front at home and it is close but it will need a 4 wheel alignment because of all the work we did. Nothing measures way out and the steering is still a tad sloppy. I am still looking for a nut and lock tab for the 1973 G gearbox as it is less worn. So far no one has come up with one and late gearbox nuts are too big.

I will keep everyone posted. And will write a short how to when done for the benefit of anyone else facing smog in California. As I indicated earlier - I believe it runs really well and only need a small tweak on it, not a major change. If we didn't smog here I wouldn't worry about it.

As for the CSV - I considered that or the fuel pressure regulator may be at fault. Both parts are new Bosch but they are on the list of items to check.

One thing that is interesting is Bosch later suggesting larger fuel rails as it reduces the fuel pressure swings which occur as the injectors fire. It might be worthwhile building some kind of larger tube between the two sides that meets this need. I will consider that too, however I would think that would cause it to be richer yet, and the fuel hose between manifold halves on the 1977 should absorb some of the pressure swings. I will also increase the size of the vacuum line to the FPR to be sure it is getting the full benefit of the manifold vacuum.

Sat Nov 21, 2009 2:09 pm

Very good. Keep us posted.

Side question....

Are you seeing any distributor timing scatter from the timing light?

Sat Nov 21, 2009 2:55 pm

sounds like the cam grind is the culprit if you don't know if its a "stock" grind. VW made em have lots of idle vacuum for a reason and if you are just getting the engine broke in that too can change the vacuum at idle. although I don't think 2hg less will change the FPR at all but ...maybe it does. Put a fuel psi gauge on and see if it changes when you add vacuum.. I know with my own testing that 1 psi does change the AFR. 4psi of change is worth about .5 of AFM.