TheSamba.com :: View topic - Please Help with Fuel Injected 79' Beetle

Tue Aug 12, 2008 4:22 pm

Hey Eveyone,

We have owned a 79' Beetle Convertible for 26 years with the same mechanic the whole time. He really has been working on them since before many of us were born. He has kept this car in "perfect" running order since I was 15 years old and I am now 42. But he is completely stumped on a recently developed problem.......

I brought the car to him to for a medium mechanical refurbishing since we are really going to start using it more often including interstate travel. I felt since my Mom and Dad were done with the car that I would get it back to perfect shape. It has always had its' oil changed every two thousand miles and valves adjusted every four thousand. It now has 107,000 miles on it.

He did the normal tune up, points, plugs, new belt, valve adjustment, replaced the cv boots, fuel lines, a injector or two, "tried" to fix the faulty gas gauge with a new floater/sender, gauge itself in speedo, vibrator....still only partially working..he is stumped on that too, replaced the alternator(more on why he replaced the alternator in a little bit) etc......We did, for the first time, in the cars' 29 year history, switch to a summer oil viscosity of SD-40 from the normal SD-30 (this viscosity is listed in the owners manual and we have never had a problem with leaks or anything from following the book). It has run its whole life on Havoline SD-30 and since I wanted to make sure it would be ok for the interstate in 90 plus degree temps we have here in NC, I felt we should do this small switch for the summer.

As soon as I got the car back, I noticed it has this more than normal "airy-whooshing" noise when you rev it up and the rpms are very slow to come down to below the 1000 rpm mark. You can sit there in the carport and rev it up to 2500 rpm and it will slowly come down and then it just hangs around 1200-1300 rpm's for a few seconds and then eventually (He added a tach for me while he had the car)comes down to the 850-900 mark where it is suppose to be.

He and I both have checked all the connections for the vacuum lines and fuel lines, he dialed down the idle adjuster that is on the spring above the big screw adjustment as far down as possible ???...and then played with the big screw adjustment.....No luck. He even sprayed ether around the hoses and lines and fuel injectors to see if the idle would raise (an old german mechanic trick to find a air/vacuum leak....the idle did not raise.

He did (on the first try to fix this problem) take off the alternator belt for a few seconds of running and the whooshing noise disappeared with the old alternator and the idle seemed to come down faster since it was not turning the fan shroud or the alternator....... He thought it may be the alternator....So he replaced it with a brand new Bosch unit and the same problem still exists.

He said if there were any problem with the Mass Air Flow Unit the car would not run at all. So he has ruled that out as well.

I Know This Is Wordy...but I am trying to give you all the information possible...

Does any goodbuddy out there know what could all of a sudden cause this excellent running machine to suddenly develop this problem.......It used to have a steady idle when you first started it in the morning and now that is even struggling until you give it a tiny little bit of throttle and warm it up for about 10 seconds...then it holds the 850 rpm range until you get going and go on down the road as normal.

Is the new oil the culprit?...the computer is adjusting for it? or something else?
Is there greasing to be done to the fan shroud?
Are the two idle adjustments just way off?
Has he simply hooked something up wrong?
Is it just a strange coincidence that something went caput from the tune-up?
What could it be??????

The car still runs great in the city and on the highway.....It is doing 2450 rpms at 55 mph like it is suppose to and sometimes the idle does come down relatively quick but not like it used to do "all" the time.

It is just that it is "whooshy" sounding and the idle is like speed shifting when you are going through the gears and it is taking way to long to come down when you come to a stop......

Please help......I would really appreciate any advice from many people to take back to him because he feels really bad that he himself is stumped on this one..

Thank you so much to anyone who can figure this out.

Tue Aug 12, 2008 4:44 pm

First thing to do is to check the timing again.

Wed Aug 13, 2008 4:52 am

I appreciate the quick reply!

But......the timing is perfect.

Anything else I can do??

Wed Aug 13, 2008 6:19 am

I don't know about the wooshy sound, but I did notice that my '78 had a problem with the accelerator cable sticking in the tube that houses it. I squirted some motor oil into the end of the housing where it comes through the fan shroud - and it helped. Maybe the cable is getting hung up and that's why the idle is messed up?? Just a thought... good luck!

Wed Aug 13, 2008 6:47 am

Does this thing have a EEC valve in it (that runs ported vacuum rom the throttle body and usually shares that ported vacuum with the distributor) located insiide the air cleaner that draws fuel vapors into the air cleaner?

Take out your hand vacuum pump and see if that valve will hold a vacuum?

Do the same to the distributor can and let us know.

Wed Aug 13, 2008 10:41 am

Thank you again good people for the advice. I will take this to him either this weekend or next when he can meet up with me.

If you all come up with some other possibilities or if anyone else has an idea as well, please go ahead and post your replies now.....I want to take as many possibilities to my mechanic as possible.

Wed Aug 13, 2008 11:39 am

You may want send a PM to Tram.

He seems to know his stuff when talking about Fuel Injection.
http://www.thesamba.com/vw/forum/viewtopic.php?t=21015

Wed Aug 13, 2008 2:07 pm

Definitely talk to Tram, but my bet is still on a vacuum leak. I have a DeLorean with Bosch fuel injection (K-jetronic) and the car will do that (and other odd behavior) if the engine is sucking air anywhere other than the mass air-flow sensor. Un metered air is bad, can make the car run lean, causes the computer module to incorrectly compensate.

I'd ask if you noticed a degradation in your MPG's but it doesn't sound like you drive it enough to notice. That would also be another sign of a vacuum leak.

Randy in Maine also makes a good suggestion on where to check for the leak.

I don't think Bug FI has this, but the DMC has an idle speed regulator- an electro-mechanical cylinder attached to the intake, controlled by a computer module. The module opens and closes the ball valve to regulate SOME of the air going to the engine and this air does NOT flow through the mass air-flow sensor. The idle reg unit is shut, and off-line after you depress the accelerator pedal so that all air is now measured by the mass air flow sensor. After years of age, the electrically controlled ball-valve gets gummed up and doesn't track quickly enough with the control module so the idle is all wonky. See if you have this device.

I realize that this may not seem like a good comparison, but bear in mind that the DMC was designed in the mid-to-late '70's right along with the Bug FI and uses a similar system by the same manufacturer. I think the bugs are L-jetronic...the biggest difference being that my engine is 6 cylinder.

Wed Aug 13, 2008 9:31 pm

Sticky vacuum advance plates in the distributor. The dist needs to be stripped down and rebuilt every 20 years or so.

Thu Aug 14, 2008 7:58 pm

Thanks again everyone for the advice. I will take this list back to him and see what happens....

I'll keep you posted.

If anything else comes to mind, let me know.

Cheers,

t.