850 GLT 1993 failing to star

v8_und_sw kirjoitti:

My favourite suspect is the cam shaft sensor (especially if it's of the "black plastic cover" design), but that would be indicated by the appropriate trouble code. What trouble codes are you getting, by the way? Any code will point you in the right direction. If there are no codes, the fuel pump relay or the pump itself is the most likely culprit.

Other possibilities that come to mind right now are the ignition switch and dirty/sticking idle speed controller.

Jari

When this happens, then engine turns with starter, but doesn´t start. After 5 to 10 minutes of attemps, geting in and out of the car, this starts pretty fast and easy! I changed two days ago the main realy (located above the radiator), but the problem remains the same.

Some idea or tip?

The relay you just changed is the fan relay. Nothing to do with the ECU.

Tim. .

Tim.. kirjoitti:

Not necessarily, since the main relay for the ignition system is also located above the radiator.

I think the device you're referring to is the idle speed controller. At least in my 850 there is a buzzing noise when the ignition is on, and a few seconds after it is switched off, so I figure it's normal. I'm not sure if it comes from the controller though.

The camshaft position sensor is located right below the upper engine mount that can be seen above the shiny thick S-shaped hose right of the "20 VALVE" text in the picture. (You probably don't have that hose in your car, but the engine mount is there.) The sensor is a disc about 5 centimetres across, fastened by two screws. If it has a shiny design instead of a black plastic cover, it has probably already been replaced at some point.

The control system uses the camshaft sensor to determine whether a given cylinder is at the compression or exhaust stroke. A missing signal will stop the engine and prevent restarting. I had a failed sensor some time back and it caused exactly the symptoms you've described.

The crankshaft sensor, in turn, is used by the control system to determine the speed of the engine. I've had this one fail as well - it would first cause very short losses of power, then make the engine stall but NOT prevent an immediate restart.

As I said before, the sensors should give a trouble code when faulty. If there is a recurring TPS code, I'd check that sensor first.

Jari