Texas993

I am having issues with my Turbo R blowing DME relays. I have blown 2 in the last year, and they "burn" on pin 7 when they go. They always blow when starting the car, never once the car is running.

Here is a brief summary: The first time I remember a DME blowing was after a very, very hard drive at high elevation. I heard the fuel pump humming, but it was working hard. 11k' elevation and I stopped for a hike. Shut the car down and when I came back an hour later, the DME blew and burned the DME and the fuse panel. Looked ugly, but installing a new DME worked and no more problems for at least a year.

Subsequent DME relays blew, but the car has always run flawlessly. So I have finally decided to see what is going on. I ordered and installed a new fuse panel then dissected the old panel. It really isn't pretty. I don't know if the damage was done at the first blow, or got progressively worse. But I cannot believe that it worked at all. See all the nasty pics.

So, here are my questions:

- Did my first DME blow, do some damage, and the subsequent blown DMEs were due to the corrosion in the fuse panel?
- Is there a short in the fuel pump? Or some wiring between the panel and the pump?
- I plan to replace my fuel pump, and I was not sure what pump RUF uses for the Turbo R. I purchased a Bosch 044 but realize that RUF uses a Bosch B261 205 413. Same pump with the same stats except that it is rated at 8 bar instead of 5 bar for the 044. What is the difference? I cannot find the 413 pump in the US and it is crazy expensive from RUF.
- How would I check for a short in the wiring?

The battery and alternator were checked. Battery is strong with 12V+ and full cranking capability. Alternator runs at 13.8V.

I suspect a random short in the fuel pump.

Help! Thanks.

ACEparts_com

The heat from the first relay failure probably weakened / slightly burnt the contacts causing higher resistance, more heat, more failures.

Crimping the contacts together would probably have avoided the problem. Of course you may have an usually demanding fuel pump but the the original problem was still high resistance.

Basal Skull

I don't have any useful comments. I will have to check/keep an eye on mine since afaik, I have 2 pumps (stock and 044) running off the same circuit. Interesting though that I haven't had any problems with the increased load (yet) so the system must be relatively robust.

Texas993

Thanks for the comments. Seems to be an extremely odd issue. Still can't decide if I should put the old pump back in or the 044 pump.

Basal Skull

The 044 is supposed to be the better pump, and probably better for the ruf that has the 5bar fpr(?). You just need the proper adapters.

Texas993

Ok. Putting the 044 on today. I'll see how it goes. Fortunately, the adapters are already in place for my current pump.

I'll keep y'all posted.

Texas993

After consulting with a few more folks, I cannot conclusively decide what is causing the issue. While it could be the fuel pump, it is more likely what ACE said - the first blown DME caused the damage that you see. That damage corroded the copper connections inside of the fuse panel and all of that caused problems for subsequent DME failures.

Yesterday I re-installed the old fuel pump (413) and got the car back on the road. I runs well, as usual. I didn't install the 044 pump due to the fact that RUF Germany installed the 413 at conversion and it has a higher 8 bar rating. (044 is 5 bar)

One opinion that I received thought that I might have a plugged vent in the fuel tank that, when at high altitude and a hot day, caused too much pressure in the tank and caused the fuel pump to spike. No telling what happened. I will check the fuel tank ventilation. But I have never experience much of a "hiss" when opening the gas cap.

I will continue to run it and see if the fuse panel is the fix. Additionally, I will seek the expert advice of more folks. Including Darin who will be in DFW this weekend.

Thanks for your help.

Droops83

First of all, you are using the phrases "blowing DME relays" and "blowing DMEs" interchangeably. I assume that you are only burning DME relay contacts, and not DME control units (the ECU that lives under the driver's seat), and if that is the case it is helpful to use the term "relay" each time so that your problem is clear to those who may be trying to help.

That said, it was a wise move to replace the relay panel. I'm surprised that subsequent DME relays lasted as long as you say they did with all of that pin damage. High electrical resistance can cause fires in extreme cases so consider yourself lucky!

I have never seen this pin burn up on a 993. It is possible that the fuel pump itself is on its last legs. When electric motors wear out they tend to draw increasing amounts of current. Yours is possibly doing the same thing, and while the slightly increased current draw isn't enough to blow the 25A fuse, it may be enough to burn up an already weak contact. The current draw on the fuel pump is greatest when the pump is first activated during startup, which concurs with your failures.

Once electrical resistance is increased, overall current flow in the circuit actually decreases. It is possible that your fuel pump is OK and there was simply a flaky crimp or weak pins to begin with that took out the first relay, but it is certainly worth checking the current waveform of your pump with a digital oscilloscope (any competent shop can do this).

I don't know what the nominal current draw specs are for the Ruf-installed 413 pump, but most factory Porsche and BMW pumps I've tested tend to draw 5-7 amps. Higher flowing replacement pumps like the 044 will naturally draw more current, and some recommend re-wiring such a fuel pump with heavier gauge wire if you are pushing its limits (which a Turbo R is likely not). A quick search found some current draw info for the 044 and similar aftermarket pumps (the stock 993TT pump is likely in the range of the 040 pump in this link) :

http://radiumauto.com/media/techarti...l-Pump-Test-87

Where are you getting your info on what PSI the 413 and 044 pumps are rated for? It is the fuel pressure regulator that determines fuel pressure, not the pump. A higher-rated regulator essentially pinches off the fuel return line more, thus increasing the pressure at the fuel rail. This slightly increases the strain on the fuel pump, and current draw is also greater.

Does Ruf install a higher-rated fuel pressure regulator on the Turbo R conversions? 8 bar seems awfully high to me; stock 993 fuel pressure is in the 3-4 bar range. Ruf likely installs a 5 bar regulator and runs a slightly higher flowing pump to meet the increased fuel volume demands of the Turbo R engine.

As for the plugged fuel tank vent line theory, it is possible but unlikely. If the vent line were clogged enough, the inside of tank would actually be under vacuum from the suction of the fuel, and in an extreme case, the fuel tank could implode (I've seen this once!). You would have likely starved for fuel if this were happening.

It is much more likely that pushing the engine to its limits at such an altitude for such an extent simply taxed the existing fuel pump circuit. At that altitude, air is much less dense, so the turbochargers overspin to produce the same amount of boost as at lower altitudes. This raises the intake air temp, which increases the chances of detonation. As long as pinging isn't detected, the engine management likely increases the injector pulsewidth in these conditions to cool the combustion chamber, and the fuel pump is working overtime just to keep up.

Hopefully you have solved this by replacing the relay panel, keep us posted!

dbf73

While Chris has forgotten more about this stuff than I'll ever know, my experience with these Bosch pumps is that if you can hear them without having to listen for it, they are on their way out and should be changed. Might try Gert at Carnewal for the 413 pump.

good luck

Texas993

Wow, Chris. Thanks for taking the time to post such an informative reply to my problem. I really appreciate your expertise on this issue as I have stumped many experts. Your explanation of the cause of the events makes a lot of sense. It even explains why most DME Relays fail at start up for all 993s - the fact that the current draw is the highest at that time.

I did intend to state "DME Relay" and not "DME". I have not had any issues with the DME module.

I found the information on the Bosch 44 vs 413 on this pdf. Note that they discuss 5 bar and 8 bar as well as current draw etc. The higher values refer to the 413.
http://www.bosch-motorsport.de/en-US...2776426379.pdf

I have even received conflicting information on fuel pumps and related parts installed during the conversion between RUF Germany, RUF US (Michigan), and RAC (former RUF Dallas). RUF Germany told me about the 413 fuel pump. And when I pulled it, it was, indeed a 413. I don't know about the fuel pressure regulators, but I suspect that it was upgraded at conversion.

So, for now, I will go with the theory that I really stressed the fuel pump during that mountain drive. At that time I messed up my fuse/relay panel and the subsequent issues were related to the fuse panel. If I blow another relay I will replace the fuel pump with a 413.

Again, many thanks for the thorough analysis and comments.

Droops83

You're welcome, thanks for the Bosch info on the fuel pumps. That is very helpful, as it shows that the normal current draw is indeed higher than that of the stock pump. I would be curious to see the current draw of the 413 pump at 5 bar; it could be that it is less than the stated 14-15A at 8 bar and that would be the reason that Ruf chose it over the standard 044 pump.

Get the current draw and pump waveform checked if you can, that would answer some questions. You likely have a bad contact in the relay to begin with, as worn fuel pumps will often burn the contacts/solder joints of the fuel pump/DME relay. This is why the relay gets replaced along the filter on any car when a fuel pump is replaced after failure at my shop.

Aus993

I have had the exact issue on my 993tt, found the hard way went for a long drive up the coast only had owned the car for about 1 month while driving just die, story short I am a auto tech by trade I was not hearing the pump come on I went straight to fuse box and pulled the relays and found the dme relay cooking hot as I remembered the previous owner saying he had a spare in the tool kit swapped it all sweet to get her back home, but I had to replace the whole fuse box and bought 2 oem relays as we'll, I did a lot of testing on the circuit to understand why so much load it's definitely not the pump, I ran external power to the pump and was still getting very high current draw I believe the O2 sensor heater circuit runs through this that may be why the large load other wise must just run hot......6months on I frequently check the dme relay and pins still looks like new. P.s I love this car

Texas993

Intesting that it occurred to you too. One for the archives....