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gengbret

911 DME yet again

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My car is an '84 911 and I've had it for 3 years. This year it began to stumble at RPMs higher than 3,500. One day it simply quit during accelleration onto a highway, but after coasting off the highway it started and I drove it home just fine. Last week i was leaving a friend's house, going up a steep hill, and the car simply stopped running. The RPMs were at about 3500 when it died. It refused to start. After towing home I ran through the standard tests. Good spark, fuel pump ran when the fuse was jumpered, etc. I bought a DME relay from Pelican and installed it this afternoon. The car started right up but stumbled and died at idle. Thought it might be the old gas that I added at my friend's place (just to prove to my wife that the fuel gauge was not bad) so after starting it I drove toward a local filling station. I was going uphill and at about 3500 - 4000 RPM the car simply died once again. The tach went to zero even with the clutch engaged and turning the engine over as I slowed.

So, another AAA call and the car is in my garage again. Any Ideas? I took apart the old DME relay and it looked just fine - no burned contacts or evidence of great heat. I'm at a loss but fear it might be the DME module. Is there a way to test the DME module or does one simply have to buy a new one or get one rebuilt? Is this something a Porsche dealer will do or is there an independent service that will test it for you? I live in Syracuse, NY.

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Does the car sit for long periods. Do you keep the tank full when in storage? Might be dirty/ rusty tank screen and/ fuel filter. I would suggest draining the tank through the bottom plug located smack in the center bottom of the tank. It has a tubular screen which should be clean. If it's dirty, determine whether it's rust from the tank. If the fuel filter ( located drivers side in engine bay) is not new, then pull it out and cut it open with a pair of shears and examine. Mahle makes a good well priced replacement fuel filter. For a good independent in NY, you may try contacting Joel Reiser through Panorama magazine.

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Have you checked fuel pressure and volume? sound like your starving for fuel.

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Thanks for the feedback. I'm fairly convinced I have an electrical problem at the root of my fuel starvation problem. First, the fuel pump doesn't run when the key is turned on. However, if I bypass the control system and jump 12V to the fuel pump (I did this at the fuse box) and the key is on, the fuel pump runs just fine and the car will start. It runs a bit ragged, but it starts. Next, the 3 times the car has quit, it just flat-assed quit. No chugging and acting like it was running out of gas (at least as in other cars I've really run out of fuel in). The tach dived to 0 RPM even though the engine was still turning over until I disengaged the clutch. Also, all 3 times I was up between 3,500 and 4.000 RPM. It just didn't sound like a blockage that was reducing fuel flow. Also, when I replaced the DME relay the car started and ran, at least until I got it up above 3,500 RPM. Does this line of thinking seem reasonable?

I was just going through the diagnostic values for resistance and voltage at the DME electrical harness (found online at www.ecudoctors.com) and things look pretty good there except that the high altitude switch input to the DME is wrong (infinite resistance) and the idle switch input values are reversed (continuity at throttle closed and no continuity when slightly open). I have not yet gotten to the oxygen sensor and volume flow sensor tests yet. It's happy hour and I'm definitely bummed.

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