I sent out a note a couple of days ago about my '87 S4 possibly having vacuum leaks. One gentleman said I might have an "MAF" going bad. I tried looking up MAF through the search engine and didn't get much help.

In aerospace the object that controls the gas turbine is the "main engine fuel control" and just possibly that is what MAF stands for.

I had the engine "brain" replaced less than a year ago when the car absolutely refused to start. Hopefully it is still OK.

To repeat my former question, I suspect that I have vacuum leaks as I have to depress the throttle to start the engine (it starts fine that way and runs fine). I also have a cruise control that is very inconsistent. One gentleman said it's "brain" might be defective.

This car is not a "garage queen". It has high mileage and has been used by me since I bought it new in 1987. I certainly can understand problems with a car so well used and am trying to slowly fix a lot of things that happened over years of semi-neglect.

I'm rather new to this forum and, at the age of 76 years, am far more used to servicing cars that didn't have all of these controls. My 1936 Oldsmobile and even my 1962 Corvette were far easier to figure out. Please excuse my ignorance.

 

After submitting this thread and re-reading it, it becomes obvious that I did not directly ask a question.

What is an MAF? Does replacing the "brain" constitute replacing the MAF?
In looking for vacuum leaks I would probably want to replace all hoses. Any other thoughts?
I have a vacuum gage. I'd appreciate knowing where to check and what values are appropriate.

 

To understand the vacuum system and leaks, you can start with the HVAC vacuum writeup by John Pirtle. While HVAC-centric, at the start it shows the vacuum source for the engine vacuum system and some on theory of operation:

http://members.rennlist.com/pirtle/svc_act.html

The engine vacuum system is covered comprehensively in Dwayne's thread on the intake refresh, conveniently performed on an '87 for your viewing pleasure.

https://rennlist.com/forums/928-foru...+vacuum+damper


Probably the easiest place to start to understand MAFs (Mass Air Flow meter) is probably John Speake's MAF FAQ:

http://jdsporsche.com/faq.html

And a little about your '87's 'Brain' (it's really 2 interconnected brains, one for controlling fuel delivery (The LH brain) and one for ignition timing (THe EZK brain)

http://jdsporsche.com/faq1.html


Lots to read, but these sources should give you a good baseline understanding of MAFs, brains, and sources of vacuum leak and how to test for them (Mityvac to the rescue!)

It's all a little more complicated than that Carter 3269 AFB and that dual point dizzy on your '62....

 

MAF = Mass Air Flow Sensor
http://en.wikipedia.org/wiki/Mass_flow_sensor

No

See above post by Rob E for vac leak detection.

 

When you psuh down the throttle on an S-4 while cranking it ADDS MORE AIR.....not more fuel. So a vacuum leak is not likely to be the problem as that be too much air already and more air would not help it start..

 

you should pull the vacuum lines off of the fuel dampers and the fuel pressure regulator smell them for gas if you smell gas then that part should be replaced,

The dampers are
1 in the front of the engine just in front of the water bridge then
2 at the rear of the left or driverside fuel rail ,
and the FPR is on the rear of the right hand side fuel rail.
NOTE the rear damper and FPR can only be inspected after removing the lower portion of the aircleaner housing.

this will also let you inspect your MAF though if the MAF is original it would be wise to consider sending it off to be rebuilt
otherwise putting your foot on the gas to start the engine could also be leaking fuel injectors.
try adding a bottle of Techron to the gas its found at most parts stores

 

If you have to keep the throttle open to start - do you also have to keep your foot on the gas to keep it idling?

Insufficient air to start could possibly indicate problems with the idle stabilization valve (ISV). Usually this would affect idling after start also. Could also be an ajustment issue with your throttle position switch (TPS) that is supposed to detect when the throttle is in the idle (not pressed position).

Alan

 

Thanks to all of you for your comments. Rob, my Vett had fuel injection, not a Carter. It was quite a nice car.

 

To Alan:

The car runs fine after the initial start. Smooth idle, good acceleration.

 

I looked at this thread to see whether someone had fitted an afterburning jet to their 928! (The fuel control unit usually is only called "main" when the engine also has an afterburner fuel control unit.)

 

To Glenn Evans

Your statement might be correct for fighter jets with afterburners but not with certain helicopter engines as well as a number of commercial engines that also have auxiliary fuel controls.

 

To Adam:

The engine runs smooth after start.

Thanks

Barney