Hola;

To make this easier, I will split the post into two parts, first what the car is doing, then what I think the problem may be.

I am working on an 89 Volvo 740 Turbo that will not start when hot. When its cold it is all good.The car is also running rich, although not nearly as bad since I replaced the Fuel Injectors. I have done two separate tests to confirmspark and also fuel pressureand also the spray of the injector. I'm thinking the car won't start because the engine is flooded. Once it starts it runs like garbage for10-20 seconds then is fine.

Ihave done several tests and I am having an issue with testing the Engine Coolant Temperature Sensor. According to several web sites you test the sensor by checking the voltage on the ECU by testing with Pin 5 (Ground) and Pin 13. You are supposed to get between 1 and 2 volts when the car is in the on position. Currently I get 12-14, basically whatever the battery is running. Then test for Resistence, first from Pin 5 and Pin 13 (which I get 450 ohms no matter what) and also each connector on the sensor (Which I get 2200 ohms, the correct reading for 70*). I wonder if I am doing this test correctly however as I get 450 ohms no matter if the sensor is plugged in or not. Also I am wondering if there is any spot that the ECT connects to on its way to the ECU? Any help would rock.

Thanks!

JH

 

Looks as though I found out my test failed, and if I learned to read

Instead of Pins 5 and 13, I should have been testing 5 and 2. However, when I test now my resistence at the ECU is 400 ohms higher then at the sensor but 3 volts higher at the ECU then what it should be. Its at 4.91 volts instead of 2.0 according to what the web sites say. Any advice would rock.

 

Is the check engine light on? Have you checked for engine fault codes?

 

replace temp sensor

 

Wow thanks for the quick responses

As far as the check engine light and a code scan I did not perform one as the check engine light does not come on at all.

As far as replacing the sensor, I have a known good one that is still getting these same faulty readings. I guessI'm curious as to how the wiring is set up. According to the wiring diagram there is a connector by the Right Front Wheel House that I haven't seen can anyone enlighten?

Here's what the car is doing, I may be off base with this check. In the cold, the car is great, runs great starts great. When it is hot, it will still run good but will not start unless I crank it for 20 seconds (Which isn't reasonable since the starter will die quickly). When it finally starts, it runs at a very low unsteady RPM,chuggingfor about 10 seconds and then idles normally. There is a puff of white smoke during this time, which would I assume be coolant. Once this phase ends then the car is running normally.

So far I replaced the intank Fuel Pump / Sending Unit, the Fuel Injectors, the Hall Sensor/Distributor, Fuel Injector Relay, Fuel Pressure Regulator, Radio Suppression Relay, Spark Plugs, Cap and Rotor.The car is not running nearly as rich as before, but the engine is still getting flooded at start, which is why I based my theory on the ECT. Any suggestions would be great.

Thanks

Volvo Noob

 

At this point I would check your grounds because if there is added resistance in the circuit the computer will think the car is colder than it really is and you will get a higher voltage reading too. There are a bunch of grounds up on the intake manifold, I think you should inspect clean with emery cloth and re attach. There are alot more grounds hidden about but you will need volvo wiring dia to get their location.

 

Wooohoo fixed it. It was really stupid too, the previous owner plugged in the Knock Sensor and the ECT Sensors were plugged in the wrong spots. However, now I have a new problem. Seems that since I did this the car idles horribly, any where from 700 to 1200 RPM. After a minute it would die. I haven't done too many tests yet for this problem since i figured I'd quit while I was ahead Any thoughts as to what may have caused this? I'm thinking possibly a bad lead to the in-tank fuel pump.

Thanks again all

 

i would start with cleaning and lubricating the idle air motor under the intake.