'78 Bus Runs Rough, Possible Vacuum Leak

dtrumbo · Post by **dtrumbo** » Sat Jan 09, 2010 7:34 am

So my bus runs rough and I can actually hear a vacuum "sucking sound" in my engine compartment. I've replaced all of the vacuum hoses except for the large ones on the breather box and decel valve because I can't find hose large enough. Scott at German Supply carries it, but is out of stock. I now think I need to replace the four short intake runner boots. They are almost certainly the original ones and they look a little ragged. In addition, I can rotate some of them by hand which implies they aren't really making a good seal. Before I dive in, I have a few questions:

1.) It seems one can replace these without removing the engine by simply removing the intake manifolds, putting on the new boots and re-assembling. Is this way too over-simplified or can I actually do this?

2.) I know I should also replace the intake gaskets while I have the manifolds off, but having never done it, I need help with the visual. Is the gasket just the thick phenolic piece or is there another cork gasket that goes on top of the phenolic piece? I want to make sure I order what I need and nothing I don't.

3.) Is there anything else I'm missing or any other traps of which I should be aware? Ideally, I'd like to get this done before my February 5th trip to Nehalem Bay and given I have about an hour and a half per day to work on my VW's, can anyone who's done this give me an estimate of how difficult/time consuming this job is?

Thanks everyone!

Ritter · Post by **Ritter** » Sat Jan 09, 2010 8:42 am

1) you should be able to replace with the engine in. Pull the injectors and fuel rails, EGR tube (if you've got it) and probably the stuff on the air filter box side of the throttle to give yourself some space. Even then, you'll have a bit of a swear-fest with lining things up. A bit-o-lube inside the runner boots helps. I used slobber because it was close at hand. Others suggest carb cleaner.

2) the gaskets are those thick ones and that's it.

3) replace the injector seals and fuel rail lines just for the hell of it since you've gone through the trouble of removing them.

Others will certainly chime in and tell you a better way!

dtrumbo · Post by **dtrumbo** » Sat Jan 09, 2010 10:10 am

Ritter wrote:3) replace the injector seals and fuel rail lines just for the hell of it since you've gone through the trouble of removing them.

Already done about three thousand miles ago. I shoulda done ALL of this at the same time. This is how we learn!

More clues to my original "rough running" problem. The bus runs really bad when cold. So much so that I had to turn up the idle speed to make it more drivable. Once it's warm, it idles high. No surprise there and hopefully when I get it all nice and air-tight, it will run better. So anyway, I drove the bus to work this morning and when I parked in the garage, it was idling a little high. Just for fun, I removed the oil filler cap and the RPM's dropped by as much as a couple hundred (I'm guessing by ear since I didn't have a tach with me). I remember reading about the oil cap/RPM phenomenon, but can't recall what I read. Is this anything and is it anything important and/or critical? Sorry to mush all of this in one topic, but I'm pretty sure it's related and I'm also pretty sure a rebuild is in my near future (hopefully after Maupin!).

Post by **Amskeptic** » Sat Jan 09, 2010 2:55 pm

dtrumbo wrote:
More clues to my original "rough running" problem.
The bus runs really bad when cold. So much so that I had to turn up the idle speed to make it more drivable. Once it's warm, it idles high.
I removed the oil filler cap and the RPM's dropped by as much as a couple hundred (I'm guessing by ear since I didn't have a tach with me).

How does it run when fully warmed up? That is the only time that you are allowed to adjust timing, mixture, and idle speed.

Your cold-running issue will only be solved with a look at cold-running systems. Auxiliary air regulator and the intake air and cylinder temperature sensors are next. Recall that the cold start valve and temperature time switch are not involved here.

The intake runner boot leaks will show up when warm IF the idle is lean by the idle speed going up when you spray the boots with WD40 or GumOut. If the mixture is already too rich, the above test will either result in no discernable change or a drop in idle speed.

Try getting back to the AFM after a cold start and play with the wiper. The BobD tells me right away that it assuredly does not want any more fuel after a cold start. Let us know if it is rich or lean when cold.
Colin

dtrumbo · Post by **dtrumbo** » Sat Jan 09, 2010 3:26 pm

Amskeptic wrote:How does it run when fully warmed up? That is the only time that you are allowed to adjust timing, mixture, and idle speed.

It still runs rough which is why I temporarily increased idle speed. I would never manipulate the timing or AFM settings until the engine was warm and I'm POSITIVE I have an otherwise air-tight engine.

Amskeptic wrote:The intake runner boot leaks will show up when warm IF the idle is lean by the idle speed going up when you spray the boots with WD40 or GumOut. If the mixture is already too rich, the above test will either result in no discernable change or a drop in idle speed.

I have done this with GumOut and, at the time, there was no discernable change possibly because the engine was running so rough and the idle was "hunting", I may not have been able to perceive any change. This is why I temporarily increased idle speed so that the engine would smooth out a little so I could maybe see what's what.

Amskeptic wrote:Try getting back to the AFM after a cold start and play with the wiper. The BobD tells me right away that it assuredly does not want any more fuel after a cold start. Let us know if it is rich or lean when cold.
Colin

Will-do, once I'm reasonably certain I have no vacuum leaks.

Post by **Amskeptic** » Sat Jan 09, 2010 5:25 pm

dtrumbo wrote:
Amskeptic wrote:Try getting back to the AFM after a cold start and play with the wiper. The BobD tells me right away that it assuredly does not want any more fuel after a cold start. Let us know if it is rich or lean when cold.
Colin
Will-do, once I'm reasonably certain I have no vacuum leaks.

You can play with the AFM right now cold warm whatever to help you determine what the engine is suffering from and this will give you a basis for knowing if your efforts are helping or hindering. If you can clean it right up by moving the wiper, you will get ignition/leaky valves/destroyed cam lobes, etc. out of the picture.
Colin

dtrumbo · Post by **dtrumbo** » Sat Jan 09, 2010 5:31 pm

Amskeptic wrote:You can play with the AFM right now cold warm whatever to help you determine what the engine is suffering from and this will give you a basis for knowing if your efforts are helping or hindering. If you can clean it right up by moving the wiper, you will get ignition/leaky valves/destroyed cam lobes, etc. out of the picture.
Colin

Ignition I can deal with, those other heinous things you mentioned I don't want anywhere NEAR the picture!

Post by **Amskeptic** » Sat Jan 09, 2010 5:36 pm

dtrumbo wrote:
Amskeptic wrote:You can play with the AFM right now cold warm whatever to help you determine what the engine is suffering from and this will give you a basis for knowing if your efforts are helping or hindering. If you can clean it right up by moving the wiper, you will get ignition/leaky valves/destroyed cam lobes, etc. out of the picture.
Colin
Ignition I can deal with, those other heinous things you mentioned I don't want anywhere NEAR the picture!

Whenever I have an engine that has changed on me, I start with all tune-up parameters, valve adjustment, compression test, points/timing, then fuel system. How did this lousy running happen upon you?
Colin

dtrumbo · Post by **dtrumbo** » Sat Jan 09, 2010 5:48 pm

Amskeptic wrote:How did this lousy running happen upon you?
Colin

I drove to Bellingham to look at a blue and white '73 Sunroof bus. During that trip, I noticed that when I would be at a stop light, it would idle a little rough. That has gotten gradually worse since then and then my issue with the hole-in-the-AFM-flap and Beetle attention put all other diagnosis on hold. I'm just now starting up on it again. Number 1 cylinder isn't contributing as much as his brothers and compression is low (upper 70's) on that cylinder. I'm notorious for doing compression tests when the engine is stone cold because I'm paranoid about removing the plugs on a hot engine which may contribute to the low reading. Tell me to get over it. When I pulled the plugs out to do the compression test, they all looked to my un-refined eye to be a nice shade of brown with #1 a tad leaner than the others. I tuned it up (points, cap, condenser, rotor, plugs, wires) about five thousand miles ago. I'll revisit all of those things after I change my intake boots.

In other news, the engine seems to run cool as a cucumber which I find encouraging.

Post by **Amskeptic** » Sat Jan 09, 2010 5:56 pm

dtrumbo wrote:
Amskeptic wrote:How did this lousy running happen upon you?
Colin
I drove to Bellingham to look at a blue and white '73 Sunroof bus. During that trip, I noticed that when I would be at a stop light, it would idle a little rough. That has gotten gradually worse since then and then my issue with the hole-in-the-AFM-flap and Beetle attention put all other diagnosis on hold. I'm just now starting up on it again. Number 1 cylinder isn't contributing as much as his brothers and compression is low (upper 70's) on that cylinder. I'm notorious for doing compression tests when the engine is stone cold because I'm paranoid about removing the plugs on a hot engine which may contribute to the low reading. Tell me to get over it. When I pulled the plugs out to do the compression test, they all looked to my un-refined eye to be a nice shade of brown with #1 a tad leaner than the others. I tuned it up (points, cap, condenser, rotor, plugs, wires) about five thousand miles ago. I'll revisit all of those things after I change my intake boots.

In other news, the engine seems to run cool as a cucumber which I find encouraging.

That is a classic Itinerant Air-Cooled Warning Sign. If your idle ever changes on you whilst out on the road, investigate! Tight valves, caught in the first 50 miles, will often reseat. By all means do a compression test after your valve adjustment. After you do the valves, loosen the spark plugs and reseat barely more than hand tight. Run the engine for four or five minutes. Then you can do a warm compression test and the plugs will come out easily.
Colin
(p.s. after your compression test results are posted, we can move this to "Troubleshooting" forum)

Bleyseng · Post by **Bleyseng** » Sun Jan 10, 2010 9:48 pm

here they are:
http://www.pelicanparts.com/cgi-bin/sma ... 1973-76%29

dtrumbo · Post by **dtrumbo** » Tue Jan 12, 2010 10:55 am

Alrighty then. The numbers are in.

First, the results of the valve adjustment. Remember, this is a '78 with hydraulic lifters so the numbers indicate how many turns loose or tight the valve is from when the 'reference' valve adjustment was done during Colin's visit a year and a half ago. Once 'zero' was reached, the adjusters were turned in one and one-half turns.

#1E - 1/8 turn tight
#1I - 3/4 turn tight

#2I - 1/8 turn tight
#2E - 1 to 2 turns tight *

#3E - 1/8 turn tight
#3I - 1/8 turn tight

#4I - o.k. **
#4E - o.k.

* This is the valve with the lifter that I replaced early last year. I adjusted the valve when the new lifter was installed and have not touched it since. This large discrepancy could be due to lifter break-in or by the fact that I might have lost count when doing the check or sumpin'.

** These valves might have actually been adjusted by Colin rather than me the student due to the difficulty accessing them caused by the EGR filter. When I did the adjustment yesterday I removed the left rear wheel, the heater-box-air-valve-dump-hose and the EGR filter to give myself ample accessibility. The repeating 1/8 turn discrepancy in the other valves might be due to the newbie adjustment technique versus the technique I used yesterday. An 1/8 turn isn't much so I'm not worrying about it.

Now for the compression check. I loosened the plugs and hand-tightened them as prescribed and then did a ten minute warm-up. Boy howdy, that sure makes a difference! I now know that this is the only way to do it unless you enjoy giving yourself a coronary with artificially low test results. Here we go.

#1 - 95

#2 - 130

#3 - 130

#4 - 140

I know, #1 is low as evidenced by it's diminished effort observed when plug wires are individually removed. That said, that cylinder has always been lower than the others since I've owned the bus. Even though previous tests have been on a cold engine, the #1 cylinder has been low relative to the others. Long story short, this is nothing new. It may be getting slightly worse over time, but it isn't an acute symptom.

During the warm-up period for the compression test I played with the AFM wiper. At both idle and high RPM settings, I could move the wiper CCW and get as much as a 300 RPM increase. This is at least a 1/4" movement of the wiper to the left or CCW.

Dick's Bus wrote: Oh waiter, can I please have a large glass of fuel to go with the extremely large vacuum leak I'm currently experiencing?

What this tells me is I have a large amount of un-metered air entering the engine causing a fair to extreme lean condition. Here's more evidence.

I have the intake boots already (good quality Continental brand from AutohausAZ) and I have intake gaskets on the way which should be here by the weekend. As mentioned, I have replaced every other vacuum hose except for the decel valve 18mm hose and the oil breather box 21mm hose. The S-boot is in very good shape with no cracks and even the original rubber elbow coming off the AAR is in great shape. Unless I have a breach in the intake plenum itself, the only other source of this leak must be the intake boots. Please enlighten me if I've forgotten and/or overlooked something.

Post by **Amskeptic** » Tue Jan 12, 2010 5:28 pm

dtrumbo wrote: the numbers indicate how many turns loose or tight the valve is from when the 'reference' valve adjustment was done during Colin's visit a year and a half ago.

Unless I have a breach in the intake plenum itself, the only other source of this leak must be the intake boots. Please enlighten me if I've forgotten and/or overlooked something.

The above valve information confuses me. Loose? Tight? Those are solid lifter valve clearance terms.

Do I assume correctly that "tight" means it took more than 1 1/2 turns to find "0" and "loose" means it took fewer than 1 1/2 turns to find "0" ??

Please sand your intake flanges on a known good flat surface like a thick old mirror until they are friggen perfect. Then wash them until you can't stand it, and wash them again. No nicks at all on the phenolic spacer paper gaskets, no nicks or crap on the head manifold surfaces. Clean clean clean. Good good good luck.
Colin

dtrumbo · Post by **dtrumbo** » Tue Jan 12, 2010 5:42 pm

Amskeptic wrote:Do I assume correctly that "tight" means it took more than 1 1/2 turns to find "0" and "loose" means it took fewer than 1 1/2 turns to find "0" ??

Correct.

Amskeptic wrote:Please sand your intake flanges on a known good flat surface like a thick old mirror until they are friggen perfect. Then wash them until you can't stand it, and wash them again. No nicks at all on the phenolic spacer paper gaskets, no nicks or crap on the head manifold surfaces. Clean clean clean. Good good good luck.
Colin

O.k. Having never done any wet sanding (or any type of precision dry sanding for that matter), what grit paper should I use? Wet, dry?

vwlover77 · Post by **vwlover77** » Tue Jan 12, 2010 7:39 pm

I'd like an expert read on those spark plugs (Colin?). They actually look perfect to me, except for the one on the far left which appears a bit rich.

Don't forget about the injector seals!

And back to your original comments, I think ALL the FI engines sound like they have a vacuum leak at idle. I think it's just the air whistling through the idle circuit.