I'm new to this fourm and have been previously using it to help me in trouble-shooting my son-in-laws "new" 944 hoping to help him in getting it on the road. I was not successful in finding the same problem posted. It was always "successful start then either running rough or stalling." This car runs perfectly once it is assisted with the "whiff of juice". The problem is the car will not start either hot/cold without just a "whiff" of starting fluid a this time. It was purchased as a "tired of it not starting and finally died car". The car was running and intermittently would not start. When it did it ran fine. It would always crank, but not fire up.The car was sitting for approx 3 months when he purchased it. I have all the records back from when it was purchased and all maintenance records. It was very well taken care of. I diagnosed at first that it was not getting spark. I have repaired/replaced the following over the last 2 months:
1. New coil,wires,plugs,rotor cap.
2. Rebuilt DME-(Attained spark)
3. New battery,hoses, belts,etc.
4. New injector seals and cap.
5. Re-soldered DME Relay circuit connections.
6. Engine compartment grounds all removed and cleaned.
I ran all the Haynes trouble shooting sheets from the manual; ie, TPS, injectors,AFM,resistance and voltage checks including fuel flow and pressure. ALL are within spec according to the book. I drained and replaced the gas and added fuel injector cleaner(Chevron Techron) to the tank. I feel it is a fuel delivery problem, but affordability of parts ,fuel pump,new injectors will kill his budget. If anyone has ran acroos the same problem or has any suggestions where to troubleshoot next, it would be most appreciated. The next step is to a shop. I'm backed into a corner on this problem, but would like to fix it for him and save some money. It really is a nice car waiting to be driven and enjoyed everyday! Thanks in advance for any help.
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1984 944 NA

 

Check/Clean/Replace the speed and reference sensors at the top of the bellhousing. Check out Clark's Garage for info on start troubleshooting.

 

Check the condition and resistance of the battery hot and ground cables. They can corrode internally leading to all sorts of strange behavior.

Dal.

 

Next time it won't start, try unplugging one injector (electrically) and then attempt to start. If this works, it's likely the fuel pressure regulator. Fuel injectors rarely need to be replaced - they can usually be cleaned and bench flow tested locally for ~$25/each. FPR failure is relatively common - and, is very common to cause intermittent start (hot or cold) problems.

 

I would check the sensors just yet. Checking the battery cable couldnt hurt, but I think this problem IS fuel related.

You say it needs some starting fluid... this usually means it is fuel related. I wouldnt start blindly changing stuff, but if you have haynes manual there is something in there about checking the fuel pressure and how much fuel is being delivered.

It could be a clogged fuel filter which is like all of 20 dollars. Or it could be a fuel pump which you could probally get for cheap from somebodys parts car on rennlist. Dont start blindly replacing parts hoping it gets fixed. It will usually end up just costing you a lot of money and not fixing the problem (ask me how I know). Anyway, you came to the right place for help and welcome to Rennlist.

 

check the position of the speed and ref sensors, they are supposed to be .5 to .8mm away from the starter ring gear, it sounds like yours may be too far away. The sensors output a voltage, a sine wave for the speed sensor and a spike once per rev for the ref. sensor. The amplitude of the signal is proportional to the speed of the engine and varies according to the distance from the flywheel. If the sensors are too far away, it is possible that at low engine speeds (cranking) the signal is too weak for the DME to detect. The starting fluid gets the engine started and then the engine speed is high enough that the output is large enough to be seen. Possibly.
If you have access to an oscilloscope connect it to the connector of the rearmost sensor, the outer two pins, and crank the engine, the output should be at least 2.5volts AC. If you do not, you could set the gap by loosening the bracket the sensors are mounted to, remove the rear sensor and glue a washer to the bottom of it, the washer should be about .5mm thick, insert the sensor and lock it down and move the bracket until the washer is resting on the starter ring gear, lock down the bracket. Remove the sensor and remove the washer and clean off the end of the sensor, then re-install it. Its much easyer to do than to describe, sorry too many words.
Good luck

 

WOW, noone mentioned the DME relay???? That's also a possibility too, it is also the relay for the fuel pump and anything electrically related to the motor, spark, fuel, etc...

 

944SM indicates that the car will start every time if he uses ether. That in itself verifies all electrical parts not associated with fuel delivery - IMO. The problem is fuel delivery, but he also mentions that he did flow tests that passed the standards in the Haynes manual (which are correct). There are some great answers here to why cars won't start, but many are off track dealing with the generality of it all. Maybe working on carbureted cars for so long has me boondoggled, but the only element missing from this guys fire triangle is fuel. Fuel comes from the tank, thru the pump, thru the filter, thru the lines, thru the dampener, thru the fuel rail and is finally dumped into the combustion chamber via the fuel injectors. It is a well known 944'ism (actually, Motronic'ism) that the FPR will fail causing fuel pressure to be too high and will result in shutting down the injector signal. In this case, most of the time, unplugging one injector will reduce the load enough to trick the injectors into firing - the engine will start but run rough (missing one cylinder). The FPR employs a vacuum controlled diaphragm to "regulate" fuel pressure. Without the regulated diaphragm, the FPR will remain closed (this is what keeps fuel pressure in the rail when the engine is off). If the vacuum is partially lost, in the case of diaphragm failure, the pressure will rise substantially. At least, this is the way I currently understand it.

This all said, there is a more scientific way to deduce your problem - but, it requires more test equipment and more time than simply unplugging an injector. Use an injector noid to test each injector pulse with the fuel pump off (pull fuel pump fuse). Assuming the injectors fire, with the fuel pump running attempt to start the car. If it fails to start, was the noid flashing? If it was, and you are still sure you have spark, the engine is either flooded or not receiving fuel to the rail (unlikely given that you've already tested this). If you suspect the engine is flooded, take the injectors out for a flow test and "rebuild". You may have just discovered that your no start problem was actually flooding of the chamber via a leaking injector or two (again, unlikely given your explanations). Ether overcomes flooding to a certain extent - that's why it's so popular among carbureted engines. FWIW, this injector leaking into the cylinder deal is more indicative of cold start problems - the cool down period allows the injector to drip-drip-drip for a while. In this case, it's imperative the car is not driven and the oil is changed and flushed immediately after the leaking injector is replaced. Blah, blah... blah, blah, blah, blah...

Good Luck!

 

944SM.................. Welcome....

I kinda lean towards the speed/reference sensors. Between the old connections and the tolerance at which they need to be set, they can cause ALL kinds of weird "no start" or "stalling" issues. Don't ask me how I know

Also, add your location to your user profile. Lots of people all over the country love to come by and break.....I mean, work on other peoples cars...

 

The fuel pressure is modulated by the vac. signal to the regulator, but the basic pressure is a function of spring pressure on the diaphram. At cranking speeds there is not enough vacuum generated to have much effect on fuel pressure. The usual failure with the FPR is that they will stick closed, raising pressure to well in excess of 100psi. 944sm also states in his oroginal post that he checked fuel flow and pressure.

 

Thank you all for your replies to my "challenging" problem. Great welcome and advice! You find sometimes that you second guess youself (and spend alot of money) when problems like these don't make sense. Sorry, I don't think I posted the year..its a 1984. This problem is throwing me beacause the engine runs strong and idles like a brick. I am not the type to throw money and replace parts without trying to narrow down the problem within reason. First step would be to test for too much fuel delivery by unplugging a fuel injector. This should eliminate the FPR. As I stated in my original post, fuel volume and pressure were within spec according to the manual., 850 cc's/30 secs flow, 29psi idle, 33-39 psi with vacuum hose disconnected and 58 psi fuel return hose clamped. All were within +/- 1% of spec. It still would not eliminate the intial proper flow on startup of the iinjectors themselves. DME relay?...could still be..I just don't know at this time; the car does run. Will keep that one on the short list after reading many posts.The battery cables and fuel filter will be on order today. Necessary preventative maintainance anyway. Next will be the reference sensors on the flywheel. Seems straight-forward to check adjustments AND connections. Will follow through with "sillyscope". Haven't used one since doing head alignments on computer disk-drives many years ago.

Question....does the DME sense/adjust to richen/lean the fuel when starting? As stated prior, the DME is "new". "Rebuilt" computers tend to make me a little uneasy. Skip.. can you educate me a little further on the "injector noid". Yes I am from the "carburated " days.

Again, can't thank you all enough for the help and direction. Will reply with results as I address them.

P.S. Anyone running ether injection????...only kidding!!!!!!

 

No one mentioned the check valve on the fuel pump yet. If you're having problems starting it then it could be that the check valve has failed and is not keeping enough pressure in the fuel lines. The fuel pump only turns on for a second or two when you first turn the key to start - to pressurize the fuel lines. The DME then senses whether the car has ticked over by the speed of rotation on the crankshaft sensors and turns on the fuel pump when that speed reaches some preset value (300 rpm???). If the check valve has failed (on the fuel pump) then the pressure will be insufficient to atomize the fuel into the intake when the injectors fire, leading to a no start or poor starting condition.

To test, put your fuel pressure gauge on the fuel rail and see how long it holds pressure, should be on the order of minutes, not seconds.

Just my thoughts.

Dal.

 

Do you have the spark plug wires hooked up in the right order on the cap?

The cyl numbers are 1 at the front of the car, 4 at the back. Looking at the cap as its on the car, #1 is bottom right, #2 is top right, #3 is bottom left, #4 is top left.

 

Buy a new DME relay. $18.00, I wouldn't rely on a re-soldered unit, espicially seeing the low cost of a new one.

 

Today I checked the fuel pressure on startup. I am getting 39 psi on continuous cold crank.
I left the gauge on for 1:15 minutes. It dropped to 29 pounds in the first 15 minutes and held there for over an hour. Again, this was on cold crank only...car never started. This test was for the fuel pump activating and the fuel pump check valve. I believe at this time that the fuel pump is working properly. I also disconnected one of the injectors in case of "pooling of fuel" in the cylinder causing a flooding condition on start. The car did not start.