Fuel Issue? need help. :-/

pelaeon · 01-05-2007, 07:06 PM

OK. Here's the issue:

Car has had trouble starting (cold or hot) since i bought it. It's normally not too much trouble, just a long crank time. After driving home from across the state on new years eve i parked at my house and proceeded to party. I wake up the next morning and my 1987 924S will not start.

I pull my hair out trying to troubleshoot it.

I have read this forum before, so i know about the DME relay and other issues. I notice i'm not getting spark off my front-most (cylinder 1?) spark plug when i lay it on the intake. There is voltage going to my coil, so i assume the coil is to fault. Well, an 80 dollar ignition coil later and still no start. My previous owner had taken the plastic cover off the DME relay, so when looking at the relay housing and fuse area (this had to be a good sight for the neighbors... Me lying inverted on my drivers seat with my feet on my headrest and my head up against the gas pedal) i could actually see one of the contacts snapping and making contact. I assumed the relay was good due to me witnessing a connection.

Anyways, I just completed the "Five-Minute Test" and found that i have voltage to the coil (around 9-10v) injectors (11v), and at the in-tank fuel pump(9ish volts) with the ignition set to ON. I bought a can of starting fluid and got the car to studder when i turned it over. So now i know that i have a fuel issue. I can hear my fuel pump clearly when i jump aux. fuses 2 and 3. I don't remember hearing this for the half second after cranking. I have yet to attempt starting the car by jumping the fuel pump. Is this possible, or will i risk damaging/blowing something up? Any comments or ideas of what might be the actual problem would be greatly appreciated.

Also, still no spark when i pull a plug and lay it on the intake... perhaps i'm just doing it wrong but i've done it before on previous cars.

pelaeon · 01-05-2007, 07:37 PM

I just read something about the reference sensor causing some issues also. They mentioned checking for the RPM gauge movement during cranking. I noticed mine barely jumped when i was cranking. What rpm does the starter turn the engine to? I doubt very fast... I've also noticed no (obvious) inaccuracy with the rpm gauge.

Yet another variable to throw in the mix.

onZedge · 01-05-2007, 07:40 PM

I had a similar problem with my '87 924S as a newbie. Same symptoms with difficult hot restarts as well. Turned out to be a bad fuel pressure regulator. If you're not getting spark however, the first thing to suspect after the "five minute check" thingy is one of the crank position sensors. Similar symptoms can occur with these when they are on the verge of failing.

pelaeon · 01-05-2007, 08:32 PM

The reference sensor is the crankshaft sensor, correct? Since that is the sensor controlling the tach...

Razorback1980 · Razorback1980's Garage

It's actually run off the flywheel but it does the same job. Take the connections going to the speed and reference sensors apart. THey are two square plugs in a single bracket at the back of the engine next to the hot water valve. Clean the connectors and coat with dielectric grease and reassemble them. AFter you have ruled out everything else, it has to be the DME. They have a solder joint that seems to cause problems in them sometimes. I don't know where it is or how to fix it, I have just read about it here. The first thing to do though is make sure you have fuel pressure on your fuel rail. Put a gauge on it and eliminate that as a possibility. Then move back to the spark.

pelaeon · 01-06-2007, 02:56 AM

Anyone know if i can run the car (safely) by jumping the aux. fuses?

pelaeon · 01-07-2007, 03:15 PM

Eh. Anyone?

Razorback1980 · Razorback1980's Garage

yes you can. You shouldn't do it only because there is no shut off system. It won't hurt anything and if you are diagnosing a problem, that is the thing to do.

SoCal Driver · SoCal Driver's Garage

You can jump the fuel pump from aux fuse 2 to aux fuse 3. This is the fuse block with out the cover. Count from the drivers door. Try to start it with the jumper in place. If it runs be sure to take the jumper off when you park the car.

If the cover is off of the DME relay I would get a new one or two.