924Board.org

[techfx]

Hello,

This is my first Porsche (former VW Scirocco owner for 14 yrs).

I purchased a 1981 924 Turbo over a week ago and I knew it had some tinkering done by previous owners and mechanics. It is low mileage, but currently has an issue where the engine cuts out right at 3k RPMs while driving (not while revving in neutral, however).

Things I know that may be factors at this point (but not sure where to start):

*Mechanic replaced the ignition distributor w/ an older (pre 80?) one that does not use the crank sensor

*Has what appears to be Bosh number 0438100058 (Saab?) Fuel Distributor

*Sensor missing wire going in intake that passes over valve cover

* Vacuum line T by the head light motor appears to have a line capped off.

*Fuel may have been in the tank for over a year (I did put on about 5 gal of 93 octane last week).




I'll have time to look at things more when the weather improves here, but would like to get as much info as possible when the chance comes. The rest of the car seems close to passing PA inspection.

thanks!

[ideola]

The non-DITC ignition distributor is not a good sign. The car might be running, but will never run correctly unless you get the correct distributor, or retrograde from the DITC setup to the earlier capacitve discharge arrangement.

In the meantime, here is A Systematic Approach to 931 Diagnostics.

Do you have a Haynes manual yet? Do you have a (digital) copy of the Factory Service Manual (FSM)?
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erstwhile owner of just about every 924 variant ever made

[techfx]

[Rasta Monsta]

Assess condition of timing belt.

READ THIS.

Smoke test intake, check system and control fuel pressures, fuel pump volume.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[techfx]

Thanks for all of the helpful hints and sites to follow up on! Lots to take a look at, it looks like. I'm also assuming that having the Saab fuel distributor wouldn't be an obvious issue since no one mentioned it?

[ideola]

The Saab fuel dizzy is not a good sign either. The WUR, AFM, Fuel Distributor, and AAV are all a matched set in order to deliver the proper fuel curve.

The first thing we need to isolate is what is cutting out at 3000 RPM: fuel or spark. Since you state that it will rev past 3000 in neutral, I am inclined to believe it's not a spark/ignition issue. If I were in your shoes, I would start with CIS testing. Here is a tutorial:
http://www.924board.org/viewtopic.php?t=35734

First, you should verify proper injector flow. Remove all four injectors. Put them in individual glass jars. Jumper the fuel pump relay. Press on the AFM plate. Make sure you're getting a good conical spray pattern across all four injectors, and make sure they all deliver roughly the same volume of fuel (no dribblers, and no gushers). This will help you diagnose whether the fuel dizzy is at least in the ballpark of proper functioning. It will also tell you something about your fuel pumps (which may not be delivering enough fuel under load).

Once you've eliminated the injectors, fuel dizzy, and fuel pump as the possible culprits, proceed with the full battery of CIS tests. You will need the Haynes manual to provide the correct pressures for the S2 car (chapter 13 supplement). You will need a proper CIS testing unit in order to measure the pressures as described in the above tutorial. Following the diagnostics in the tutorial thread, this will tell you which if any of the CIS components might be a problem (WUR being the most likely).
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erstwhile owner of just about every 924 variant ever made

[techfx]

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I have a supposed tested/used correct 924T fuel dizzy to install, but cannot find a 93111013701 Paper gasket for the fuel/air box and 93111090800 o-ring for the bottom of the dizzy. I could possibly make/repair the paper gasket, but am wondering if the O-ring would be a generic size that could be ordered elsewhere.

[techfx]

I now have the proper Dizzy in place, have an approximate mixture adjustment as best possible without a CO2 meter (it didn't idle at all after switching from the Saab part, before this adjustment ). It seemed like it had a little more power, but still continues cutting out at 3-4k rpms now.

I also just found that one of the stated "new" vacuum lines going to the conical end of the distributor had a crack. I ran out of time at this point for the week, but will replace the vacuum lines. I also found that this line also had a T fitting where one other part of the line (that seemingly was run under the WUR) didn't appear to be connected to anything and was very short. I'm not sure where this goes and I think the other end of the T fitting goes to the throttle body

Since this was a DITC to S1 ignition "downgrade", I'm not quite sure what vacuum diagram to go by and if there may be possible missing needed vacuum parts (ie Vacuum amplifier)?

[techfx]

[ideola]

It wouldn't hurt to run a bottle of Techron fuel system cleaner in each of your next two fillups. That stuff does wonders for the fuel system.
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erstwhile owner of just about every 924 variant ever made

[Wiese]

Check the ignition coil with an Ohm meter. My 931 had similar issues as yours and my primary resistance on the coil was way too low. It revved freely, but hesitated under load and would sputter. A $45 coil was the fix, but my 931 was otherwise in excellent tune already.

[techfx]

Here's where I am after a few weeks since the last update. I managed to get the car past PA state inspection, but still has a misfire. It looks like plug #2 always has some fuel/oil residue. I pulled the injector to test and, while cranking the engine (ignition disabled) I saw one quick spray and then nothing after. we tried w/ the injector off of the line and no fuel even dripped out until I pushed down on the air/fuel metering plate, pulled the line off and it can be blown through. It was decided to finally do the CIS fuel system checks.

This weekend, i found a CIS pressure tester and was going to attempt to jump the fuel pump relay to run the pump, but my fuse box does not look like any diagrams. The top row has one relay on the far left, then a gap, then the others. The gap is seemingly where the fuel pump relay would have been. I found the relay on the far left had a part number of 944-613-113-00 which looks like the stock fuel pump relay number, other than starting with 944 instead of 931. I tried to jumper 87 and 30 on that relay, but no pump would run. We decided to try to measure system pressure while cranking, and got 4.1 bar, the control pressure was 3.8 bar. These do not seem to be within the proper range, but I'm not sure running the fuel pump while cranking is an acceptable way to measure fuel pressure

One other thing; I'm waiting for a new fuel filter and I noticed when researching part numbers that the current Mann WK 726 part on the car seems to match for a 928 on some sites, but not 924 Turbo. I will try to switch out with the correct fuel filter next weekend, but not sure if that is what could be the cause of the possible pressure issue.
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81' 924 Turbo, 02 Golf TDi, 88 Scirocco 16v (RIP)... and the Subaru.

[techfx]

Actually had a break in the weather and got to go back an find the proper fuel pump relay (2 over to the right from where I tested), found the correct part number and jumpered that 87 to 30. This time got sys pressure of 5.5 bar and control of 4.5 (this is also cold, but it is 74 deg ). Still seems low system and high for control?

also, after approx 14 min, I was at 1.6 bar.
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81' 924 Turbo, 02 Golf TDi, 88 Scirocco 16v (RIP)... and the Subaru.

[techfx]

This weekend was a little bit more of a nightmare.

I replaced fuel filter , did another fuel pressure reading, sys pressure reading of 5.5 bar, cold control 4.7 bar (still seems high?) My Dad suggested checking timing, looked like Cam was off by one tooth and distributor by 180 degrees. I tore everything down and got everything lined up as Hayes described and it still runs the same . Could there still be an issue like blockage in he distrubutor/WUR?
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81' 924 Turbo, 02 Golf TDi, 88 Scirocco 16v (RIP)... and the Subaru.