Starting Problem

Pritchard · 05-24-1999, 04:37 AM

I need some help! I have a '74 2.0 with FI that is incredibly hard to start. The problem started a while back. I have to try to start the car 10 - 12 times before it actually will fire enough to keep itself running. After the third or fourth cranking attempt, the car will start to fire but not enough to keep running. Finally after about the 10 th try it will finally keep running. I have replaced the spark plugs, wires, points and condensor, cap and rotor, coil, adjusted the valves, set the timing, checked the aux air valve as perscribed by Auto. Atlanta, and tinkered with the fuel pressure (I don't have tool to measure the actual pressure). I have pulled all injectors and tested to make sure that they will at least squirt fuel when signaled. The car runs great when engine has warmed up. Fuel usage is very high (approx. 15 MPG, used to get about 30 MPG). I have ordered an electronic ignition module, haven't installed yet.

If anyone can help me with this starting problem, I would be very greatful.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Check Kjell Nelin's FI article on the 914 Fan page, http://www.914fan.net . It has a lot of specific component tests as well as general D-jet info.

My first guess would be your head temp sensor. I'd suggest checking its resistance when cold and when warm.

--DD

Pritchard · 05-24-1999, 05:59 AM

Also, I have replaced the head temp. sensor. Forgot to mention that.

michael · 05-24-1999, 07:17 AM

I would also check fuel pressure.

John Rogers · 05-24-1999, 08:50 AM

Did you also check the starting injector? Does it start with a shot of ether? Our starting injector had a broken wire in the connector and wouldn't open the injector at all. Does it happen only when cold or when hot too? I agree with Dave, check each component as per the check list.

Pritchard · 05-24-1999, 10:34 AM

This starting problem only occurs when the engine is cold. Starts fine when engine is warm. Starting injector? Is it on the side of the trottle body? Haven't checked that yet.

jmcleod · 05-24-1999, 10:43 AM

i agree with the previous post about checking the cold start valve. it is sometimes called a "5th injector" as it only injects upon a cold start. the thermo-time switch tells it whether or not to inject (thermo: cold; time:after about 5 min approx). the cold start valve may leak or fail. i also agree with the previous post about trying to start with a shot of starting fluid or "a shot of gas down the throat". if (when cold) it kicks over on the start attempt, you can suspect, more, the cold start valve. the cold start valve is a little valve on the intake air distributor with wiring from the harness going to it and a fuel line going to it. it's very easy to replace. i'd say 1/2 hr easy.

Pritchard · 05-25-1999, 04:32 AM

I checked the resistance of the head temp sensor. When cold, it only read 1080 ohms and when hot it read about 15 ohms. The cold reading should be in the 1500-2500 ohm range. Is the cold reading too low? Could this be leaning the mix to the point that it would make the car difficult to start?

The head temp sensor is basically brand new. Could I place a resistor in-line with the sensor to increase "perceived" resistance?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Yes, it could be doing that. You can rig up a temporary fix by putting a high-quality (wire wound) potentiometer, 1W, 0-1000 ohms in between the wiring harness and the sensor.

If you simply put a fixed resistor in, there will be too much resistance when the engine is warm and the mixture will be too rich. You'll have to crank the resistance up to start and let it warm up, then turn the resistance down for when the engine is warmed up.

This can at least tell you if having more resistance will fix the problem.

As you can see, that's a bit of a pain. In the long run, it will probably be easier to just replace it.

I have found that the standard 914 sensors I checked at my dealer ranged from 1500-1700 ohms resistance when cold. VW Type III sensors ranged from 2000-2300 ohms when cold.

--DD

Pritchard · 05-25-1999, 09:00 AM

Thanks for the advice. I'm going to have the injectors flow tested and fuel pressure checked and adjusted. Also, temporarily use a POT to adjust the head temp sensor resistance to verify if this is a problem.

Wayne 962 · Wayne 962's Garage

Gas + Spark = Fire. Everyone knows that, but you need to have the spark at the right time. Make sure that you check the timing, as that could be causing all your problems too...

-Wayne

Pritchard · 05-26-1999, 05:15 AM

Thanks for all the tips and advice! I placed the POT in series with the head temp sensor, dialed it in to about 3400 ohms, turned the key and she fired right up! I am concerned that that high resistance number might not be reproducible with any head temp sensor, even the type 3 sensors. I am sure that there are some small vacuum leaks in the system. Could the extra air cause enough problems that would cause the ECU to require that high of a resistance number to get the car started?