TheSamba.com :: View topic

Mon Nov 02, 2009 9:36 pm

Vamstad wrote: You may also check the "door/flap" inside the AFM to see if there is a sticky place in its movement (if there is, hit it with throttle body/carb cleaner). I seem to remember having one that seemed to stick a little when fully closed and that it had an effect on idle or diveability. Thats what I was going to suggest.

Mon Nov 02, 2009 11:24 pm

post reply - I watched the afm wiper today and it moves just a tiny bit as the rpm ups and downs. Next time I look at it I will hold it steady and see if the rpm holds steady, It might just be an oscillation of sorts caused by the dynamics of the FI system.

Tue Nov 03, 2009 5:12 am

SGKent wrote: post reply - I watched the afm wiper today and it moves just a tiny bit as the rpm ups and downs. Next time I look at it I will hold it steady and see if the rpm holds steady, It might just be an oscillation of sorts caused by the dynamics of the FI system.

If this is the actual cause then you might install a capacitor as added to the Vanagon FI system to prevent Vanagon syndrome. One of the side affects of adding the resister is that it evens out the idle. IIRC the Vanagon capacitor is a 22 micorfarad non-electrolytic capacitor. On the Vanagon the capacitor is sized to have the largest value possible without causing objectionable delays during changes in air flow.

Sun Apr 03, 2011 9:52 pm

I thought I would update this as the answer probably revealed itself to me this week. 914-4 longer duration GA engine camshaft.

We found a NOS T4 1/2 band camshaft recently and had trouble figuring out what it was. Steve at WebCam was kind enough Thursday to test it on his special camshaft indicator to see what it was. It turned out to be exactly as marked, a half-band 021.109.101K. It was by the numbers he came up with identical to every other 1/2 band camshaft they have ever seen used in a North American 73-74 914-4. My research had pointed at that as being what it was, however I could not get the duration to work out on a set of v-blocks and that is why I let him check it. It still doesn't match the published numbers I could find for the GA engine except that since it matches every other 1/2 band that they have seen, it is safe to say it is not unique. VW measures duration at the valve instead of the cam and it is hard to compare the two types of measurement. VW made many cam grinds and they are not well documented however the most aggresive 914-4 NORTH AMERICAN engine was the GA 2.0L which was fuel injected, ran 7.6 compression and produced 95HP @ 4900 RPM VS the bus's 67 HP @ 4200 RPM GD bus engine at 7.3 compression. Compression, heat exchangers and camshaft timing were part of that GA Porsche package.

So when I compared it to the WebCam #140 / #142 stock 2,0 solid cam we have in the bus now guess what - the duration and lift are the same. I can't get timing or lobe centers without mounting it in a case. What it appears is that when WebCam chose which "stock" camshaft of the many to pattern after for their stock 914-4 grind, they chose the GA /K variant cam which makes the 95 HP at 4900 RPM. That "stock" #142 cam is in our bus which explains the hunting at idle (actually a mild loping is all it turns out to be) and why the bus pulls so strong on the top end. I noticed that the day I let it pull close to redline and kinda wondered why it had so much power still at 5200 RPM. VW later went to milder cams in order to cut down on the hunting at idle and neuter the bus engines. The hydraulic lifter cams are about 15 degrees less with no overlap so they draw more vacuum at idle. This means an AFM mounted on a manual trans with a WebCam 142 will run slightly richer at a lower RPM on a bus with a hydraulic cam - and the HP coming from the solid WebCam #142 would be about 10 - 20 HP more than the same Hydraulic cam as a guess. Another reason to chose a solid lifter cam although the hydraullic camshaft engine is probably a little more efficient at lower RPMs.

So now my hunting issue is resolved - it is nothing more than a mild cam causing it, most people would not even notice it. Also know now why it runs so strong up those hills. Only regret is had I known this going in I probably would have raised the compression from 7.3 to 7.6 because of the overlap. Live and learn.