Engine: 70 T5: Cutting out when hot

[stevepcar]

Originally Posted by Cookeh

Hi Steve, yes it is as simple as measuring the resistance between the two pins with your multimeter. I would recommend doing this outside of the car, with the sensor in a ho****er bath (boil a kettle!) and a thermometer. You can then test resistance at the correct, or close to, temperatures as suggested by Volvo in the testing procedure.

Coolant temp sensors can cause hot-starting issues, so it is definintely worth checking. Whilst you have your multimeter out, it is also worth checking the crankshaft position sensor and camshaft position sensor - they are two other culprits for hot starting issues. For the crankshaft you test in the same manner as the coolant temp sensor; place your probes on the pins once they're been disconnected from the wiring harness. For the camshaft sensor, you'll have to backprobe them (i.e. the plug in the harness needs to be connected so battery power gets to the sensor). To do this simply, just push some pins up through the back of the plug until you're through the insulation. Then just attach your probes to the pins.

The last usual suspect for hot-start issues is the fuel pump relay. Jump the relay and try starting that way.

As an aside, my car stuffed a fuel pump relay AND a camshaft position sensor at the exact same time, so I'd definintely check all the above!

Well just had a go at ECT with multimeter. Not sure if I am reading correctly with range set at 20k I get the following: at 10C I get 4.5 ohms at 20C I get 0.5 ohms at 45C I get 0.25 ohms. I've seen a chart somewhere that says it should be 7300 at 0C, 2800 at 20C & 300 at 80C. My thermometer only goes up to 50C so I was a bit scuppered at the higher temps. My readings seem to be way out. But I tried my T5 ECT at 10C at it gave me the same 4.5 reading. This was all with the ECT still installed. So I am not sure if the ECT is at fault or not. When I restarted the car after running it up to 45C it ran for a bout 5-seconds very lumpy & cut out. I can only get it to rev smoothly past about 3000revs if its hot. It starts & runs ok from cold. Before I start checking the Crank pos sensor & the cam pos sensor I need to eliminate the ECT as a fault. Any ideas please?

[Cookeh]

Personally I'd test it outside of the car, for ease of temperature control and to see what condition it is in (i.e. corrosion wise). If it is not so good, you'll be getting decreased mpg over normal and the car will run richer. So if that's a trend you've noticed prior to the issue developing into lumpy running and poor starting then it would indicate ECT at issue.

If the thought of removing it is a bit daunting currently and you're confident the T5 is running spot on, then move on for now and try and other culprits. If they all test A-OK then you know the ECT is the issue. Fuel pump relay, crank position sensor, and camshaft position sensors are all a pass/fail test. If they don't meet the ohm or voltage readings they are shot. If your hot start issue goes away on jumping the relay then you know the relay is shot.

[stevepcar]

Originally Posted by Cookeh

Personally I'd test it outside of the car, for ease of temperature control and to see what condition it is in (i.e. corrosion wise). If it is not so good, you'll be getting decreased mpg over normal and the car will run richer. So if that's a trend you've noticed prior to the issue developing into lumpy running and poor starting then it would indicate ECT at issue.

If the thought of removing it is a bit daunting currently and you're confident the T5 is running spot on, then move on for now and try and other culprits. If they all test A-OK then you know the ECT is the issue. Fuel pump relay, crank position sensor, and camshaft position sensors are all a pass/fail test. If they don't meet the ohm or voltage readings they are shot. If your hot start issue goes away on jumping the relay then you know the relay is shot.

Thanks for your help, I think testing the other items first is a good idea. I will post the results.

[stevepcar]

850 10v NA 1995 2.4l engine.
I have just run a test on my ECT as the car is very hard to start when hot & will only run smoothly above about 3000 rpm. Its fine when cold. The readings I got were as follows: Multi-meter set to 20k Centigrade scale. 16deg 3.2. 20deg 2.49. 40deg 1.18. 60deg 0.54 80deg 0.27 100deg 0.17. I have looked at a chart I found on Mathews Volvo site & the readings are not too different. I have checked the Crankshaft sensor when the engine is warm its 320ohms & cold it is 288ohms, so that is within the 200-500ohms specified.. The cam shaft sensor reads ok too. I have swapped the fuel pump relay with the one from my T5 and that has made no difference. Any6body have any other ideasplease.

[Cookeh]

Is camshaft reading correctly on both voltage and resistance? If yes, then consider testing the coil and your HT leads. Both can have excess resistance or deliver insufficient amperage if worn and in hot-start scenarios. Beyond that, I'm fresh out of ideas.

[stevepcar]

Thanks Cookeh I must confess I have not tested voltage on the cam sensor. I will do that if I can find out what it should read. I replaced leads, distributor cap & rotor about 2000 miles ago & regapped plugs. I will try the other tests you suggest.

[Baffler]

Just something else for you to check, Steve, seeing as it's starting and running. A difficult hot start or continuous cranking can also point towards a lazy Fuel Pressure Regulator.

Locate the FPR to the left and rear of the fuel rail. Remove the cover for the throttle housing and from under the rail follow FPR's vacuum line back to the vacuum tree on the inlet manifold. With the engine at idle disconnect its rubber elbow and check for evidence of fuel. If you're seeing any trace of fuel the diaphragm is ruptured/damaged.

P/n 9146761 for your engine...best be seated if you need to price one up

Also check the condition of all those rubber vacuum elbows, given their age and location, as they're subject to perishing and creating leaks.

[stevepcar]

I now have a list of things to check. Some of which have tested ok. I can swap sensors & coil from my T5 as a last resort. I have recently done the PCV, so most of the vacuum hoses have been replaced, but you never know.