1985.5 944 no start issue UPDATE :(

Llamalord478 · 10-28-2021, 02:19 PM

I made a pervious post about how my 944 was having issues starting, and what I've done to it. As of right now it's still not starting and here's what we've done in order. Cranks, but no start at work, I called my dad who's more mechanical inclined than I am and he found a disconnect vacume line and re connected it and we limped home. First thing we did was a new DME relay, dropped it in, no dice. At this point we had tach bounce still and we figured it was spark and we replaced the cap rotars, and wires. Still no dice. We then went through the fuel system, and replaced the pump and filter. (The old filter was clogged pretty well). No dice. We then assumed there was a lost of vacume, and did new vacuum line across the fuel system. No change. New speed reference sensor, (the one furthest from the car). We then assumed it was fuses, and fuse 34 had a weird bypass and we found that it was barely held in with shody electrical work. We redid a few wires, and reconnected some that were bad and then we thought we had it. No dice. We then realized that when had lost spark and tach bounce after disconnecting and reconnecting the battery, and we assumed the ecu had gone out. Welp, we've replaced it and now we're still trying to figure out what's wrong. The reference sensors have been tested, and almost every thing I can think of has either been replaced or tested as working. Our current state is no spark, and no power to the fuel pump. The fuse box is getting Power from the ignition as well. Any help would be awesome. As of right I think it's an ignition relay that somehow went bad while we were testing.

originalowner · 10-28-2021, 04:53 PM

No fuel pump & no spark with a good, powered up DME and good DME relay would indicate that it is not getting signal from one or the other engine position sensor. Wiring to sensors, wiring to DME, wiring to DME Relay, and sensor position adjustment are all possible.

kdjones2000 · kdjones2000's Garage

Get the DME Test Plan document and follow the troubleshooting in there. You would need an oscilloscope to read the waveforms from the speed/reference sensors, but this way you are not throwing $$$ at perfectly good parts.

b2524 · 10-30-2021, 11:45 AM

This sounds like what happened with my son's 944.
Get out the pin assignments for the ECU connector. Make sure that the correct connectors are going to the position sensors. Use a VOM to check them. It’s easy to get the two connectors at the sensors switched. No tach bounce was the give away for us. His ECU was bad and during the search the sensors were hooked up wrong.

FWIW: I would strongly recommend you send your ECU in to be rebuilt. The capacitors they used are starting to fail and it is only a matter of time and they will go bad if they are original. This is happening in all types of electronic devices. High end stereo units can run $1500 and up to get fixed.
$400 for a rebuild is cheap peace of mind.

walfreyydo · walfreyydo's Garage

No offense man, but guessing and throwing parts at it isnt the way to solve the problem efficiently. Recommend you read through Clarks Garage as your first step to any problem you have going forward. It seems to me you are working reactively instead of systematically following a process of elimination and diagnosis. Clarks has laid that groundwork and process to follow.

Step by step guide here: https://clarks-garage.com/shop-manual/ts-01.htm

At the beginning of the article it tells you to test for spark and test for fuel, and if either of those are missing, it will have links to other pages to go down additional diagnosis steps for either fuel system troubleshooting (https://clarks-garage.com/shop-manual/fuel-16.htm) and ignition system troubleshooting (https://clarks-garage.com/shop-manual/ign-04.htm). Recommend following this guide first and come back if you have more specific questions.

Sometimes taking other people's advice without doing a proper diagnosis will only lead to more confusion and money wasted. Sometimes there is no way to diagnose a problem (like exhaust gases in the cabin) and you have to take guesses, but for something like this, there is definitely a formula and procedure to follow.