wierd starting almost fixed

[john 928]

ok guys i replaced all the vacuum lines and still the same issue. all regulaters are good and vacuum is good. i took off the airflow meter apart from the throttle body and it looks like there should be a rubber gasket or something putting the two together and all i see is a oring in the throttle body joining the two together. is that the way it goes together or am i missing a gasket. the two just sit into each other loose ???
if i stick a screw driver in the airflow meter the car starts everytime and i have no issues
does anyone know what controls the flap on the airflow meter
thanks john
its a 82 928 5speed

[neil30076]

Just answered some part of your question in your other post:
No gasket, just the big O ring. The air box holds it down in place.
The flap on the MAF is controlled by suction from the engine, and if it isn't moving then you probably have a big vacuum leak below it, quite likely the O ring is bad, or the bearings that the flap sits in are so frozen that suction can't pull it open. See the attached for a better idea.

[JK McDonald]

Hey John - Since you've looked at all the vacuum hoses Neil is probably right on target in suspecting a vacuum leak around the large "O" ring on the under side of the Air Flow Sensor (AFS). For the fuel injection system to operate properly it is critical that all the intake air to the cylinders be metered down through the AFS.

Once the AFS unit is removed you should also consider the checks and mods illustrated in this video. It may help in preventing any potential intermittent electrical issues in the future as the miles add up. I've worked over 6 units with good results.
https://www.youtube.com/watch?v=-11J8XawQtc

Neil - Great photos of the Air Flow Sensor internals. I always add illustrations I don't have to my DNK (Did Not Know) file.....

Good Luck, Michael

[john 928]

that is a awesome video and i think it might solve one of my issues but what im trying to figure out is once the car is hot it starts only with a screw driver in the throttle plate if i pull the screw driver out it just cranks away and never starts.
i was leaning towards the time switch but not sure if the time switch operates or does anything when the car is warm.
i sealed the throttle body and the car will idle but wont restart on its own.im trying to figure out what opens that flap on initial start up

[neil30076]

Look at the first attached diagram, pin 5 of the air flow sensor sends a signal to the ECU, telling it how far open the flap is. The 'signal' comes from a collection of resistors ( #4 in the previous pictures i sent) . I am going to guess that the AFS is either bad and there is no signal coming off pin 5, or the wire in the harness from the AFS to the ECU is broken ( less likely).

Note pin 5 is numbered differently in the porsche wiring diagram ( see also below)
5 corresponds to 7 in the wiring diagram, and 3 to 27.

2 ways to check:
1) borrow another AFS from a know good car
2) get a digital volt/ohm meter set on the 2k ohm range
Remove the AFS. Check you see a resistance between pins 6 and 8, and 6 and 27, record the readings.
Now put the meter between 6 and 7, record the reading, then move the flap, does the reading change, record it.
Repeat for pins 8 and 9, note the reading.

One other check, due you feel suction if you put your hand almost completely over the intake side of the AFS when you use a screwdriver to hold it partly open?

Post back what you find.

[john 928]

I only need to put the screw driver to start it. Once it runs I can take the screw driver out and runs fine. It's only when I try to restart it thT it won't start on its own. When it's cold it fires up and dies after a few seconds. So I ohm out temp 2 and it ohms out ok but there's also the cold start valve which I also ohm out and when hot should read 120 to 160 on both leads. One side is good the other reads 70. I'm going to clean the afs tonight and see if that works then ohm it out. I put about 40 hours into it and it the car was non running when I got it.
IM ALMOST THERE !!!!!!

[neil30076]

You are moving it off the lowest position on the resistor chain, so that may be a bad contact.
You can remove the cover over the contact side ( carefully) and check it out, clean it. When you put the cover back on, use a good silicon sealer to prevent anything getting back in.

[john 928]

Ok guys
6-8 525 275 Wide open
6-27 560 560 wide open no movement
6-7 0. 0. Nothing
8-9 324 75 Wide open

[neil30076]

6 - 7 nothing indicates the wiper that moves across the resistor bank is not making contact, and that would be a big problem! Time to open up ( carefully) the plastic cover on teh side and look for the cause, post a picture if you can of the inside.

[john 928]

Originally Posted by neil30076

6 - 7 nothing indicates the wiper that moves across the resistor bank is not making contact, and that would be a big problem! Time to open up ( carefully) the plastic cover on teh side and look for the cause, post a picture if you can of the inside.

[neil30076]

Thanks John, with the flap at the rest position, make sure the 7 pin is connected all the way through to the wiper, and from the wiper to where it runs on the strip of contacts. No connection at flap closed, but starting when you move the flap suggests the contact it is touching at closed is probably corroded , burnt or just shot!
If so the ECU gets no signal, so no start.
The resistance ( ohms) at pin 7 should change as you move the wiper across the contacts.
Make sure you are reading the pin numbers correctly. The wires to pins 7 and 8 are both green, 7 has a tracer color, possibly red.
6 - 27 is good.
8 -9 should not be changing.
6 -7 should change, and so should 7 -8.

Also if you can, send a good close up picture looking down onto the unit just like the drawing in figure 12 in 1 of my earlier posts.

You are getting close, keep at it !

Best,
Neil

[john 928]

i have a guy that has a parts car 81 928 and he has a afs im getting for 50.00
ill check that one before i buy it and go from there.
the one i have has some good scratches on it

[neil30076]

Originally Posted by john 928

i have a guy that has a parts car 81 928 and he has a afs im getting for 50.00
ill check that one before i buy it and go from there.
the one i have has some good scratches on it

Good move, i'm sure you will be driving it soon, without that screwdriver in hand

[john 928]

[john 928]

Nothing in this sensor has any color coded wires
Now is 6/27 on the right or left of the unit?
I'm seeing it as 6/27 on the right and 7/8 on the left.
If that's the case 7/8 is 560 no movement
And 6/7 goes up and down with sweeps
And 6/27 no reading
8/9 is 200 no movement
I think this unit is shot
I'm taking this thing to the range
Lol

[neil30076]

from the top in your photo, top is 6, second down is 7, then 8,9,27
8 -9 is correct, no reading on 6 to 27 is not, but I don't think this would not prevent starting, it measures the intake air temp.
7 -8 is correct, and 6 -7 changing with movement of the flap is also correct.
SO.......
Your AFS looks to be good, but swapping in another known good unit will confirm one way or the other.
Two Long shots as it sounds like it will run after you trick it to start, but
1) You have replaced relay XVI ( 16) with the correct known good one, haven't you?
2) Also, did you remove the wiring on the no throttle and full throttle microswitches on the side of the throttle body? Did you put them back right, not crossed over or on wrong pins?

Good hunting.....

[john 928]

Ok new update the previous owner said he cleaned the tank out before I bought it but he didn't.
I found crap all on the bottom of the tank and the strainer is wiped.
I'm deathly afraid of trying to unscrew that strainer. The last time I tried that I needed a new tank.
I will be pulling the tank tomorrow and cleaning it out and see if that's my issue.

[john 928]

I got the strainer out and was shot. I'm flushing the tank out with water and getting all the crap out
I have some pics

[john 928]

[john 928]