924Board.org

MrKrik · Joined: 11 Jun 2006 Posts: 21

alrighty i got a 77 924 na .. and i got everything running perdfect n everything BUT the car will not rev whatsoever..
the airmixture plate moves freely and the fuekl distributer is working perfectly as far as i can tell seams jsut teh controll pressure is too hihg for teh car to even rev at al.. it WILL rev up to whatever i want if i manualy move the plate up while reving... is the WUR the only thing that controls that presure or ?? thsi is opre oxysensor rpe anything 924 jsut 100% basic.. any help would be great guys ... if necicarry ill jstu steal a WUR froma 80's jetta

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

The 77 924 does not have an O2 sensor.

The parts from a 80's VW Jetta are not compatible with your 924.

Your problem is either a defective or mis-timed ignition or camshaft, or a vacuum leak that is not allowing the airflow sensor to work correctly (check between the throttle valve and the airflow sensor for a loose clamp or a cracked rubber boot), or a defective fuel system (fuel distributor or fuel pump).

MrKrik · Joined: 11 Jun 2006 Posts: 21

actually i work at a parts stor and the bosh party number for the WUR and the Auxiliary air valve are both identicle froma 77 porsche and a 86 jetta GL..

but wouldnt the air not being able to lift teh plate be more from overly high control pressure this is what i understand about the system . and the only thing that makes the control pressure is the WUR . like it is physically hard to lift the plate against teh fuel pressure nwhen teh car is running btu EASY when teh car is off (very easy to move through range)

And sorry i am aware that there is no Oxy sensor i mistyped it .. it was ment to read this is a PRE oxygen sensor car...

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Airflow past the air sensor plate causes it to lift (Bernouli's Principal). If there isn't any airflow past the sensor plate, or the volume of air past the sensor plate is decreased (below design specifications) due to no seal between the throttle body and the airflow sensor assembly, how do you expect the airflow sensor plate to rise and allow fuel to flow?

I haven't had a problem with the WUR, and excessive control pressure in over 25 years of owning the servicing CIS fuel injected cars, but I will admit that it could happen.

Funny, I had a 77 924, and I have an 86 VW Jetta GL in the driveway right now. I don't remember those parts being indentical and interchangable. I am not saying that yoiur parts books are wrong, but Bosch Interchange, and Aftermarket Parts Store Books are notorious for giant/glaring part number mistakes.

Just look at the way that many people get the wrong starter motors for 924s and 931s.

MrKrik · Joined: 11 Jun 2006 Posts: 21

This is true. But what lead me to check it up was my buddy bought a 86 jetta 1.7 CIS and i looked at teh WUR and it was 100% identicle and i was liek WOW ur shittin me LOL

Ozzie · Posted: Sat Jun 24, 2006 9:37 am Post subject:

My car had a huge vacuum leak where the join at the throttle body boots had been overtightened, crushing the join and hose..

If your valve timing is off or valve clearances are wrong you'll get reduced vacuum as well.
Vacuum makes the whole thing work. The more vacuum the greater the plate lifts.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

MrKrik · Joined: 11 Jun 2006 Posts: 21

Well heres an update all cyl show even compresion numbers.. i reset the timming again and still same thing.. it pulls. 24in of vacume at idle

and when reving is ademted u can hear air rushing past teh air plated tryign to get into the engine but it cant lift the plate.. and liek i said when maunualy lifted teh car revs perfectly like it should smooth and crisply

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Where are you reading the vacuum?

A vacuum reading won't do you any good, if you're taking it at the throttle body, because all the air (both that comes through the airbox past the the airflow sensor, and whatever leaks between the air box and the throttle body is going to read between the throttle body and the intake manifold.

Have you checked the Aux Air Valve to make sure that it is opening when the engine is cold, and closing when the engine (or the heater) warms it up?

And 86 Jetta GL has a 1.8L 88hp engine, not a 1.7L.

Make sure that the throttle linkage is complete, and in working order. Maybe the throttle linkage has too much slack, and is not opening the throttle to increase the air flow and raise the airflow sensor. There is supposed to be a nylon or rubber grommet in the throttle body linkage where the throttle cable attaches. If and when, the grommet wears out, rots out, or falls out, the throttle cable becomes loose, and the throttle will not open when it's supposed to, or as far as it's supposed to.

MrKrik · Joined: 11 Jun 2006 Posts: 21

alrighty.. throttle cable is nice n snug opens fully open from within the car.. reading vacume from teh source that leads to the advance on teh distributer. and believe it or not in canada the jettas still came equiped witht eh 1.7L CIS engien until 89... and they are common liek that here in winnipeg as 2 autowrekers ahve mechanicle fuel injection aprts from teh 1.7

abnd yes i know 1.7 is close to 1.8 but they ARE completly diffrent engiens and the 86 DOES have tehn option

924RACR · Posted: Mon Jun 26, 2006 11:13 pm Post subject:

I have had many (most) WUR's fail and provide full system pressure to the fuel dizzy as control pressure. So yes, quite possible on old neglected cars.

If you move the mixture setting far enough, you can get a setting good enough to get around on, though you're way down on power, since your mixture will only ever be good at one spot.

If you can get the gauges on the system, it should ID a bad WUR real quick.
_________________
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Webmeister
'79 924 #77 SCCA H Prod racecar
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gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

As I stated before, and as you confirmed it, the vacuum readings you took are worthless because of where you took them.

Vacuum for the distributor is taken off of the throttle body. That means that you are reading the intake vacuum after the potential leaks that I suggested checking for. You could have a HUGE Leak in the plastic pipe or the boot on the throttle body or the boot on the airflow sensor, and it would not register a change in vacuum where you are looking.

Just how are you checking the airflow sensor plate and arm for movement? The parts are all but invisible, even if you remove the air cleaner cover and the air filter. You would have needed a mirror to look up around the corner into the bottom of the airflow sensor to check for movement.

If I were you, I would double check my thinking, before buying a replacement WUR, because you have some flaws in your investigative process.

MrKrik · Joined: 11 Jun 2006 Posts: 21

and how hard exactly is it to use a mirror.. im confused how else youn would think i could watch it for movement other tehna mirror

so ur saying take a PRE throttlebody vacume source check?
cause if i use the vascume source on the fuel dizzy side of teh throttle body (where teh air is comming in) then it sits at zero until i try to rev the car in which case it jumps to 23in . then drops to zero once the car does it s whole no reving thing a couple tenths of a second later

Ozzie · Posted: Tue Jun 27, 2006 10:51 am Post subject:

A leak in the boots betwwen the throttle body and the air plate will not affect readings at the the throttle body.
In fact you could remove the boots altogether and it wouldn't affect it.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Ozzie, that is my point exactly.

MrKrik is measuring the vacuum after the air that comes past the air flow sensor has a chance to mix with the air coming in from a leak between the airflow sensor and the throttle body.

To be of any comparison value you need vacuum measurements on a car that does not have problems outside of the aircleaner, between the airflow sensor and the throttle body, and at the intake manifold side of the throttle butterflies. Then you can compare them to measurements at the same places on the car that is not running correctly to determine is there is a vacuum leak and if it is located between the airflow sensor and the inlet side of the throttle body.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

MrKrik,

The only way to see if the airflow sensor is moving while the engine is working is to run the engine with the air cleaner cover, and air filter removed. The ENTIRE intake tract must be completely sealed for CIS to work correctly.

When you remove the air cleaner cover and the air filter, you will be able to see the airflow sensor arm and the bottom of the plate when you stick a mirror into the airflow sensor housing at an angle.

Now, you can move the throttle lever and watch the airflow sensor arm and plate to see if they move by looking at the mirror.

DO NOT BLOCK THE AIR PASSAGE WITH A HUGE MIRROR (a large blockage will affect the way the engine runs), OR LET GO OF A SMALL ONE (a small mirror could get sucked up).