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vdubr928 · Joined: 26 Jun 2011 Posts: 39 Location: Colorado Springs

I got my fuel pressure issues solved. Now my mixture is fine in the low end. Nice to see good idle mixture without screwing up the whole map. Now that this problem is eliminated I have moved on to other troubleshooting.

Problem is that the car will not run up under boost. I now know that it is because my distributor is advancing and not retarding. Something is not right with the spark control. I am going to test the vacuum line that feeds it and I'm wondering where it comes off the manifold? Also, what other things should I look for? I will pull the center console and such this week but how do I go about testing the control box? If the vacuum line is good then what? Just assume the unit is bad and source another? I have searched and searched but I can't find alot about testing and verifying timing on a turbo much less any troubleshooting. Thanks for all the help. I'm almost there.
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81 931
87 944
86.5 928 (in 81 chassis)

Grenadiers · Posted: Fri Jul 29, 2011 3:55 am Post subject:

There's ways to pull the box apart and resolder bad joints, or buy another one. The former has been documented by Vaughan and others. The vaccum line attaches to the intake manifold on the firewall side. I have three DITC boxes if you need one. The vacuum line is part of the flywheel sensor setup and difficult to replace by itself.
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'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
2004 Winnebago Vectra monster RV
2012 Jeep Wrangler
2014 Kia Soul
2001 Ford F350 powerstroke

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Time for an FSM.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

The control line for the DITC box is separate from the crank sensor and should be fairly easy to check. It attaches at both ends using a banjo bolt, one at the DITC box itself, and the other on the back side of the intake manifold, right next to the cold start valve. It's possible that the line may be zip-tied to the crank sensor lead, but it should be no big deal to snip that if necessary. However, I doubt that is your problem. I would check the DITC box first, and also specifically the large multi-pin connector. I would strongly recommend taking the black cover of the connector off and one by one, gently squeezing each of the female connectors on the inside of it. The connector is only held to the DITC box by the interference fit of these connections and are notorious for getting corrosion on them, being susceptible to moisture, and generally coming loose, contributing to poor running conditions.
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erstwhile owner of just about every 924 variant ever made

vdubr928 · Joined: 26 Jun 2011 Posts: 39 Location: Colorado Springs

vdubr928 · Joined: 26 Jun 2011 Posts: 39 Location: Colorado Springs

Ok, thank you guys so much. I am positive that my spark controller is toast. The line holds vacuum pretty well and leaks down slowly. I pulled and dissembled the unit and tested the electrical side of the air input and found an open circuit (no continuity) pushing the button has no effect. The input from the motor is not working. It is a sealed switch of some kind and cannot be repaired. I am going to need a controller for an 81 so for sure I will take you up on one of those, PM sent.

It was a little late for me to check timing. I did have a bad wur so I needed to go down that road anyway but, in the end this has been the majority of my problem. The end result of the air input being bad is the computer was advancing based on the RPM sensor but compensating for a cruise equivalent MAP. Not a good thing. Would have killed it if I drove it.
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81 931
87 944
86.5 928 (in 81 chassis)