Vacuum troubleshooting WITHOUT MityVac???

[TrevorC]

Car is my 1980 450slc. Here in South Africa I can't find a MityVac nor anything like it for sale anywhere. I need to start testing for vacuum leaks because, after reading a lot of posts here, I definitely think my car has got vacuum issues - bad idling, central locking not working...

According to my logic (which may not be very logical ), I presume that (without the luxury of a MityVac), I should disconnect ALL vacuum devices from the main vacuum source (which I presume is the main vacuum line at the firewall-end of the intake manifold??) and then start connecting them one by one to try and isolate the vacuum leak(s). My only reference point will be the running of the engine, so I'd like to isolate it from all potential vacuum leaks and firstly make sure that it then idles and runs smoothly and then start re-connecting the vacuum lines one by one.

Is this practical? Can I disconnect and plug this main vacuum line? Will the engine then be running totally independent from the vacuum system or are there other sources of vacuum I need to plug? Will the engine run properly without this vacuum source?

Can anyone please help me with some pointers...

[Lee Wireless]

Order it from Amazon and they will ship it to you. http://www.amazon.com/Mityvac-7000-Automotive-Tune-Up-Bleeding/dp/B000BPFB3A/ref=sr_1_6?ie=UTF8&s=automotive&qid=1234973703&sr=1-6

[Gurunutkins]

your car has the cis injection so doesn't rely on the vacuum to run the MAP for the engine for the fuel injection but you still need to keep the vacuum lines connected to the distributor for ignition advance and also to the evaporative loss system if that was installed in SA cars. You will also have a vacuum line off the rear of the manifold going to the transmission (if its automatic) to the vacuum modulator (If you have that line it does tend to crack so check it). Other than that you can pull the main vacuum line and isolate systems although its easier to keep the main vacuum connected to the vacuum tank (from memory under the front right wing) and isolate lines as they come out of the vacuum tank. Also dont forget the brake booster they can leak vacuum something awfull
sterkte broer
cheers
barri

[Richard Wooldridge]

Another thing to keep in mind while following the previously posted good advice is that the vacuum check valves tend to get old and begin failing by not "checking", or in other words they allow air in both directions. I had this problem on my '79 450SL, several check valves just didn't work.

[TrevorC]

Thanks guys,

I've still got to get used to on-line shopping! I've ordered a MityVac from ebay. Will probably take a while to get here, but in the meantime I'll check out Barri and Richard's advice.

Just a few questions:
1. What's the "evaporative loss system"?
2. I suspect that the rubber grommet on the vacuum tank is perished, so it may be safer to exclude that from my testing as well. (Yes, it is under the front right wing!) After 29 years, most of the rubber which has been exposed to heat or the elements is not very "rubbery" anymore!
3. Barri, I think you could have a good point there about the brake booster, because if I pump the brake while idling, the revs rise. That can't be right?

I'll check the check valves this weekend - hadn't thought of that.

(Barri, wat maak jy daar in Seattle?)

[Gurunutkins]

Hi Trevor
the evaporative loss system pulls fumes from the fuel tank and the crankcase breather and into a tank at the front of the engine near the radiator and then pulls them into the engine when its running. the system is controlled by vacuum solenoids running off engine vacuum. you can disconnect it (if you have it) but be careful of a buildup of highly combustible gasses in the tank, always vent it

yes you shouldn't get a change in revs when you press the brake although it may very well be the check valve to the brake booster as Richard suggested, I had forgotten that. I dont remember either if your year had moved away from the vacuum door locks (I have a 73 and a 74) but they are a real PITA. I converted mine to electric and bypassed all of the vacuum stuff.

ek sal 'n pm stuur oor seattle
cheers
barri

[meltedpanda]

if you PM me your email I can send some vacuum PDF files to you if you need them

[TrevorC]

This weekend I checked a few things on the car. I don't see any indication of an evaporative loss system, so maybe my car never had one or else it was removed by a PO.

I removed and checked the thick vacuum hose to the brake booster and it seems to be OK and the check valve seems to be working.

The vacuum tube to the auto transmission seems to be metal, but not in a very good shape - lots of rust or maybe just dirt, but it's difficult to get to. I'll wait for my Mityvac to arrive before testing further there. The rubber hose at the tranny end seems nice and flexible.

I have plugged the main vacuum hose at the firewall side of the manifold. As per Barri's advice and per some diagrams from Ron, I started checking the remaining vacuum hoses to/from the distributor. I found one short red tube from the distributor to the manifold and it just broke in my hands. Its rubber end was also very brittle. I replaced it (VERY difficult to get to the manifold side). While I was there, i noticed two plugged-off rubber hoses which were plugging vacuum sources on the front end (top) of the manifold. The one was cracked, so I replaced both.

All in all, the car is now idling much better, but still hunts a bit. Tranny vacuum is still connected, so maybe there's a leak there. Otherwise, all I can think of is perhaps the 8 rubber o-ring seals between the two castings of the intake.

There's what looks like a vacuum "switch" under the washer bottle. Has a vacuum tube coming from the distributor and another going back to the distributor. What's the function of this switch?

[Gurunutkins]

Hi Trevor
remember with the vacuum booster that it could also (expensively) be the rubber diaphragm in the brake booster itself. if you get a major surge in idle when you push the brake its more likely to be an engine vacuum problem as the engine struggles to replace vacuum in the booster once its used. if it has low vacuum all the time then it could be the diaphragm leaking constantly.
Have you put a vacuum gauge on the engine to check the vacuum. I have checked lots and they have wide variation and still run, just not well. They should be above 16 inches of mercury and generally run well between 16 and 18. the amount of timing on the engine can change the vacuum as well. I will set the timing at idle by the vacuum gauge to the maximum vacuum I can get then check it at 3000 rpm and it normally never needs to be touched.
The little valve with the 2 wires and the vacuum in and out is a vacuum switch that works on engine temp to switch on you distributor vacuum advance. most cars you vintage in the US have a vacuum control switch in the manifold that does the same (vacuum from manifold to vacuum switch in a waterway then on to the distributor). Mostly only the djet car here have a vacuum switch between the manifold and distributor (I'm assuming in SA the date switch was the same as the US and you have a CIS car?)
The little donuts between the 2 halves are easy to replace but getting the manifold in and out to do it is a PITA. but once you have it out its also easy to check the banjo fitting at the back of the manifold that goes to the transmission and the little but of rubber tubing between the metal pipes
cheers
barri

[meltedpanda]

that is your control valve , i dont think both lines should go to the distributor, but I could be wrong, on my Kjet one goes to the dist. and one off the intake on the intake body.

I will send you a PDF of the CIS system and how it works , perhaps it will help

[danwashuk]

If you are lacking vacuum at the transmission modulator valve the transmission will shift very hard going into second gear. This can also be caused by the modulator not working. If your transmission is shifting into second gear ok then I think you can assume that the line to the transmission is ok. When I had a slow vacuum leak on my "74 450SL it would shift hard for the first minute or two until the vacuum pressure built up and then it shifted ok...........Dan

[TrevorC]

Dan, your description is spot on! When I took the car for a test drive after the weekend's work, I initially noticed a firm but quick 1st to 2nd shift, but later on while driving, I noticed that the shift had softened up and wondered about that. Looks like I have a leak in the tranny vacuum tube and I'm not surprised because it doesn't look too good as previously mentioned.

The car is a CIS (K-Jet). meltedpanda send me some very useful docs on the CIS. I need to check the vacuum switch and the routing of the vacuum lines to and from this switch as I think it's not as it should be.

Thanks so far for everyone's contribution.

[TrevorC]

Guys, please take a look at the two pics attached.

In the Vacuum1 pic, I've marked the two vacuum lines to and from the vacuum switch/control valve (vacuum2 pic) with blue arrows. meltedpanda, you were right, the one goes to the distributor and the other to the large diam. black rubber tube between the aux air valve and the cold start injector (i think). The vacuum2 pic is of beneath the windshield washer bottle. Barri, your'e correct - apart from the two vacuum lines, the switch also has an electrical connector. You say that this advances vacuum dependant on water temperature? Are the two wires then from a thermostat somewhere? This needs to work properly for correct idle then (advance timing while cold)?

BTW, the red vacuum tube (circled in red in Vacuum1 pic) is the one which crumbled in my hands. The two red arrows point to the two plugged-off vacuum sources on the manifold. Anyone know what is normally connected here? Maybe for the evaporative loss system previously mentioned?

[danwashuk]

Hi Trever.........Sounds like you are getting to the root of your problems. Your vacume leak affecting the transmission could be anywhere in the vacume system. When you start your engine it starts sucking vacume in all the lines, and storing that vacume in a box. The check valves hold that vacume in the box when you shut off the engine. Otherwise the vacume would leak back through the engine when you shut it off. You can easily tell how well your vacume system is storing vacume by turning off your engine and then waiting a few minutes before locking your driver side door. If you have stored vacume the pasenger side door will lock automatically when you lock the drivers side with the key. On my '74 450 SL that box is located under the right front wheel well. So my transmission would shift hard until there was sufficient vacume stored in that box to overcome the slow leak. My leak was not in the vacume line to the transmission but it sure affected the transmission shifting......good luck......and remember, " It's always the last thing you do that fixes the problem...!!! "..............Dan

[meltedpanda]

someone really messed those lines up, or tried a bad bypass. Keep after it ,looks like you are on the right track