jrmdir

Thanks again to several of you who've helped me in recent threads as I've been chasing an issue with my '96 Vram operation. I wanted to post this progress report in case anyone else has this strange issue in the future. (And to ask for a little more help

I've now concluded there's a short to ground in the engine wiring harness that causes the left and right bank Vram actuators to always be engaged. This was missed in the PPI earlier this year, but they did find a - previously mysterious - error code 209 that did not show up in any on-line searches. But recently I found documentation that 209 translates to one of these three P codes: P1593, P1594, P1595. P1594 is for: "Intake Manifold Length Tuning - Short Circuit to Ground" Sure enough that's what I'm seeing. I've isolated it to the section between the x60 connector and the Vram actuator solenoid.

The weird thing about this problem is that it mimics the proper sound/visual check that every write up suggests - turn the key on and look for the actuator bellows to engage. What's usually not suggested is to look again after the engine starts to make sure they release. Mine don't. (FYI, the resonance flap action is normal)

So I've been driving around thinking my car runs pretty well, but have not yet experienced actual Vram operation. And not knowing the difference as this is my first 993.

Now I'm debating whether to slice open a perfect looking and complex section of engine harness sheathing to repair the issue, or to simply cut and bypass with a new wire. But before I start modifying anything, what I could really use most at this point is a legible Vram wiring diagram showing everything between the DME and Vram actuators.

Thanks in advance if anyone can point me in the right direction.

Also, if anyone knows what, if any, impact there may have been for this car running in Vram mode for (who knows how long) I'd appreciate input. FYI, this is a "new" harness replaced per the recall in 2012.

Thanks once more....
Ron

SwayBar

Yes, first get the diagram and measure via a mutimeter the wire in question before any repair attempts are made.

jrmdir

Thanks SB - I agree. I've got good test equipment and have isolated it to a two foot length of green/white wire that, with nothing connected to either end, shows zero ohms to earth at both ends. Thus permanently overriding the DME's job of grounding that wire when VR action is called for. But of course the challenge is that between the ends of this section, it passes through several large trunks and branches of the sheathed loom.

Bypassing would be easy, but I'm thinking I may need to eventually do some surgery. If two wires have kinked to the point of metal contact I may want to see what else is happening in that area.

But first I need the diagram to be sure - as you wisely advise.

Regards,

Ron

SwayBar

I've recently had a similar problem with my 928 racecar where a bad relay caused a wire to burn. I ended up splicing in a new wire, soldered both ends, and shrink wrapped both, good as new.

I also exhaustively checked the rest of the circuit connected to that wire using the workshop wiring diagrams.

If I were home I'd look that up for you.

AOW162435

I've had the same issue since 2005.







Andreas

nine9six

When I get home, I will check for the wiring diagram for you, but I will need you to PM an email address that is capable of transferring at least a 10 Mb file, as the resolution of the file will be quite high..

pp000830

Check for a short to ground or simply too great a resistance load inside one of the actuator solenoids. They should all have the approximately same ohm value across their coils. If a coil is bad or internally shorting to ground in a specific solenoid valve it could still function but with the greater load it takes the computer may be diagnosing it as a grounding issue.

jrmdir

^^^ - Thanks - great advice – that could indeed look like a short to the DME. And the first step in the diagnostic was to ohm the solenoid. All readings are nominal.

The short exists within the length of the green/white signal wire that runs between the engine bay connector (X60) and the primary Vram solenoid. It persists when nothing is connected to either end. There is no short present in the other section – between DME and x60 - when that section is isolated.

I’ve done a lot of electrical/electronic troubleshooting in my time and, as rare as it seems, there appears to be no explanation other than defective or damaged engine harness.

Ron

jrmdir

But on further thought, maybe not so rare? Been thinking how curious it is that of all the "what if" error conditions to program into the DME, not one, but three, separate routines are watching for wiring damage in this one specific circuit:

P1593 - Open Circuit
P1594 - Short to Ground
P1596 - Short to B+

Overly cautious/paranoid/bored firmware programmers? Or a result of issues found during long-term testing?

pp000830

Sounds like it is time to run a bit of primary wire running along the harness to replace the damaged conductor.

jrmdir

Well, I decided to give up tracing the short and got a new 993.

Seriously, this morning I stopped looking and bypassed with a new wire (as suggested above)- and it's very much like having a new car!

Unbelievable (and a bit embarrassing) that I've been driving this car for 7 months thinking all was fine when in fact it was running in VR mode at all RPM's - actually not even in correct VR mode since the resonance flap was not in VR mode all the time. But it's not just me - how long was it this way before I bought it?

Regardless, the improvement in driveability and performance is amazing. What's more, it's significantly quieter from the cabin. I’ve been “enjoying” the Varioram sound all the time! It really is like having a new car.

So, in all, a very satisfying couple of days’ work. Thanks again to all for the help and advice!

Ron

pp000830

I drove my car for years with faulty vacuum actuators on the Varioram. Stumbled over the issue quite by accident as no OBDC codes were tripped. Wow, replacing them was like getting 15% more car in the mid RPMs!
Andy

https://rennlist.com/forums/993-foru...naware-of.html

SwayBar

OP, excellent job, glad to hear it!

jrmdir

Thanks SwayBar - much appreciated! I just came back from a morning drive and still can't believe the improvement!

I thought I'd post the diagnostics for posterity in case anyone else comes up with DTC 209 - unlikely as that may seem. Actually, the first shot below correlates some other interesting and perhaps rare error codes as well.

(Big shout out to Jeff Brubaker of Kraftwerks Performance for getting this info to me!)

Ron

DTC 167, DTC 168, DTC 169, DTC 175, DTC 39, DTC 107, DTC 108, DTC 105, DTC 164, DTC 165, DTC 135.