Bought a 1985 944 about 2 months ago, and when I got it, I was going to see if I could get it started, and it would not start. So I started doing research (first 944), and was told to look for tach bounce, and it had none, so found out that the speed and reference sensors, being bad would cause this. So I replaced them with 2 new FACET brand sensors, made sure I had 0.8 gap on the sensors to the flywheel, and it fired up, and ran pretty good. I let it set and run, till it came up to temperature, so I thought to my self, that I got lucky on this one. so this is where it starts to go downhill. every time after that, it seemed to get harder and harder to start, to the point now, that it wont start. I have cleaned the tank, new fuel pump, new filter, and completely flushed fuel system. It also has new water pump and belts and rollers, and a new battery and alternator, and I bought a 2nd computer, which the car ran off of both of them, when it was running. I think the alt. is bad. when I did have it running the light never went off, while it was running, so I had 2 different people test it, and both say its bad. I have no tach bounce, but is will run on starting fluid, and you can hear the fuel pump running, and even when its running, tach dosen't work, but it did in the beginning. sometimes it would start, and run about 10 seconds and die, like you shut the switch off, and wouldn't start again, and then I could go out the next day and start right up, but runs about 10 seconds and die, but now it wont start at all, but still will run on starting fluid. If I swap the s/r sensor wires around, it will not start on starting fluid. I have noticed that when you turn the ignition on, the battery light will not illuminate, but when you start cranking it over the battery light will pulse on and off. Is it possible, the the 2 new FACET sensors I bough have went bad? Is that possible? I did test them with an ohm meter, at the sensor, and at the DME plug. According to the specs, they ohmed out at about 950 or so, and I think I read they were supposed to be between 600 and 1500. I cleaned my grounds, and made sure I had good connections. I think it is super close to being resolved, but I am out of ideas. Any help, appreciated. Thanks.

 

I suspect your injectors are fouled after cleaning the fuel tank and system. The fuel filter collects the marbles, let's pass the micron particles that foul the injector.
Pull the fuel injector rail with the fuel injectors attached. Place each injector in a jar of equal volume. Crank the engine for 10 sec. Evaluate the fuel volume in each jar. All should be the same, if not, switch injectors that are not.
Rerun test. If the same result occurs, then the injectors need to be cleaned.

Contact SouthBay Fuel Injector Service, located Long Island, NY, do not remember the name of the town, for cleaning and testing. Might want to consider adding a 10 micron fuel filter upstream of fuel injector rail because if fouled now, they will continue to foul multiple times until all if the varnish particles are eliminated.

 

Yeah i thought that might be a problem, so i took them all out, and they were super clean, and I have a little tool I made to test injectors, and the all work fine. I think since I have no tach bounce, that is preventing the fuel injectors to fire on the car. I ordered 2 new Bosch reference and speed sensors, so I am going to see if that solves my problem, hopefully. thanks for your reply.

 

[QUOTE=944BRAN;17612239]Yeah i thought that might be a problem, so i took them all out, and they were super clean, and I have a little tool I made to test injectors, and the all work fine. I think since I have no tach bounce, that is preventing the fuel injectors to fire on the car. I ordered 2 new Bosch reference and speed sensors, so I am going to see if that solves my problem, hopefully. thanks for your reply.[/QUOTED
Did you dismantle the fuel injector for inspection or visible external inspection?

 

The engine runs on starter fluid indicates the 2 sensors are working properly, no tach bounce could be an issue with wiring/connector to the tach.

 

yes, but dosent the fuel injectors fire , from those sensors? my tach bounce was intermittent, and it slowly went away all together. if the tach was bouncing it would start everytime. in the beginning it would run and idle, till i shut it off, and toward the end it would only run for about 10 seconds and shut down. even if the tach was bad, shouldnt it still start, if the sensors are good? the fuel pump works, and the ignition works, and will run from starting fluid. i dont think the injectors are firing. if i could find out why, i think the car would run. i think this is the only thing it lacks to run.

 

The speed sensor provides the feedback for engine rpm yo tach and DME. If the engine does not increase above 500rpm crank speed in X seconds, then the fuel pump is shutdown via the DME Fuel Relay. So the injectors do pulse for X sec. even if a bad speed sensor.
I was not correct in saying if the engine runs on starter fluid that that indicates both sensors are good, only the reference sensor for sure.

 

I have 2 new bosch sensors coming. Is it possible that the 2 new off brand sensors I installed, when I got the car have already gone bad? FACET brand.

 

My race engine experienced a 2+ years random start, no start, stall. I documented the trials and tribulations and for 2 years, no engine issues.

 

what caused it, and what did you do to fix it? if you do a 200amp start on these cars with a jump box, will it kill the dme?

 

The 12v supply lead (red/blue wire) from DME to Fuel Injector harness had excessive resistance causing voltage drop so fuel injectors could not pulse properly. I believe the issue was corrosion in the 9 pin disconnect connector located above the brake vacuum unit on the firewall, driver side. I did not clean the pins but installed a bypass lead from the positive side of the battery to the fuel injector 12v supply near where the 4 individual fuel injector wires are connected to the "fat" red/blue wire. Because it is a race car, I eliminated the keyed ignition switch operation and installed a DPST kill switch to shutdown power to ignition, etc and to Fuel injectors

Others have disconnected the male/female plug and cleaned the pins, removing the corrosion.

I do not believe the use of the jump box kills the DME.

On the fuel injectors, there is a very fine mesh internal screen. Did you say it was very clean?

 

Update. after many hours trying to diagnose problem, it turned out that the new FACET brand reference and speed sensors, that tested in spec, with my ohm meter, was the problem. I bought 2 new BOSCH sensors, installed them, crossed my fingers, and procceded to start my 944, and as soon as I turned it over, the tach started to bounce, and I kept cranking, until fuel made it to the engine, and it fired up. I cant tell you how excited I was, jumping up and down in the yard. I am sure my neighbors, thought I was having a fit, but I didnt care. This is a lesson learned for me. I will never skimp on parts for the 944 again. It caused me a lot of heartache. When I replace a part, I will put back what it came with from the factory. If I had done that at the start, it would have saved me a lot of trouble. Thanks to everybody that helped me with this.