This post showed up on the 924 Owners page in Facebook this morning from Markus Baumann in Linz, Austria. Engine doesn’t start?! 924 S out of 1986 stood for a year now. Battery is new. 5 liters of gasoline filled because tank was almost empty. What can that be? Anyone have any tips? Thank you very much! This is a typical situation, different from finding a badly neglected car in someone’s back yard, but rather a car that has been put away for a period of time (winter?) and now won’t start. The first thing that people do is put in a fresh battery and some fresh fuel. If that doesn’t do the trick, then what’s next?
If the cranks over, then listen to it – does it “sound right?” If not, there may be a problem with the timing belt – jumped time, skipped a tooth or two, etc. If it doesn’t sound right, don’t keep cranking it! Find out what happened, starting with that timing belt. Look it over and look for anything that is out of place. Have furry friends been making nests out of your under-hood wiring?
Typically, no-start after a period of time is centered around the reference sensors or fuel. There is no fuel pickup in the tank, but instead there is a screen filter in the bottom that keeps the big nasty solids living in the tank out of the pump. Over a period of time where the car has not been run, sediments have had a chance to drop to the bottom of the tank. If the tank has not been full, rust can form (in steel tanks) and flecks of rust can fall to the bottom and possibly clog the screen filter. Smaller particles can foul the pump (even though it’s running) and/or foul the fuel filter. We have also seen the screen filter in the tank break and allow all kinds of big chunks into the pump and the filter.
As for the reference sensors, there is an easy three-prong check for that. First, if the sensors are sending a signal to the DME, the tach will show a little bounce in the needle while cranking. You can also pull one of the plug wires and stick a plug in it, lay it on the intake, and check for spark. While having someone crank it over, feel to determine if the fuel pump is actually working. If so, investigate further.
If there is no tach bump, no spark and the fuel pump is not working, it is a reference sensor/DME issue. The DME will not operate the ignition and fuel until it hears from the sensors, so the issue may be in the DME relay or in the actual sensors and/or connectors themselves. Check the connectors to the sensors visually to see if there are any cracks or frayed wiring. The connectors have a tendency to get brittle over time and crack, causing a failure in the connector itself. Also check the DME relay – Clarks-Garage.com has a great article on testing the DME relay.
We recently had a car in the shop that would not start. It had a tach bump, spark and the fuel pump was running with new filters and a new pump, but no start. It turned out that one of the connectors to one of the reference sensors had a fault, and while everything else was working, there was no signal going to the injectors telling them to fire. The fault was on the harness side, so we replaced the harness section from the DME to the reference sensors, fixing the issue. See more here.
If you find a problem with the reference sensor connectors, no amount of tape, glue, silicone or magic will fix them. Replace them. Normally the problem is on the sensor side of the connector, so replacing the sensors will fix the problem. If the problem is on the harness side, Ian and 944Online.com has a replacement kit. It is a little “fiddly” to install, but it can be done at home.
“No Start” can be time consuming, money consuming and frustrating. It prevents other work from proceeding, and of course makes the car undriveable. But if you work through the problems methodically, carefully and completely, you will fix it in the most efficient and effective use of your time and money.
Kevin Duffy is an Associate Professor of Criminal Justice at Daytona State College in Florida and a dedicated car guy. He divides his time between teaching criminal justice topics in the online environment and working on/driving cars, particularly Porsches. Kevin is one of the principals in InspiringLifeOver50.com.