Over the past month, I’ve noticed that when the outside temperature is around 55-60F, the first start of the day (car sitting overnight, 12+ hours) results in longer cranking before the car starts up, has a bit of an uneven idle and then settles down.

This weekend, I drove the car for 35 mi, turned the engine off and restarted it after 25-30 mins and it started up just fine. When the outside temperature is cold, like today, it was 40F, the engine starts fine no problem.

The fact that it is not dependent on engine temperature has me confused. I think this rules out cold start injector and the ECT? As mentioned in my other thread, both fuel pumps run, the fuel filter isn’t terribly old and I replaced the fuel pressure regulator with a new Bosch unit.

Digging through the older threads, I am starting to wonder if this could be either due to ignition power stage becoming weak or due to the crankshaft position sensor failing/becoming weak? Assuming I’m on the right path here, is there a way to test either of them? Both of these parts from what I can tell are original to the vehicle.

 

I'd look at the Coolant Temp. Sensor, the one under the third intake manifold runner.

 

Appreciate the response. That’s what I thought initially as well.

I took ECT reading while chasing the surging RPM issue from my other thread.
When the car was nice and warm, I couldnt get a steady reading on my multimeter. The readings I got were constantly bouncing between 0.5 and 200/210 at pins 5 and 13 on the ECU connector. The car cooled down for an hour - I was able to get a steady reading of 57 in the 2k Ohms setting (so 570 Ohms? Sorry, my electrical skills need work). The engine was warm to touch but hot by any means.

Interestingly enough, I am unable to get any readings (DMM says 1 always) on pins 2 and 11 at the ICU connector.

Would you be able to shine some light here on how to better troubleshoot the ECT?

 

• 32F (0C)-- about 6000 ohms within a range of +/- 10%
• 68F(20C) -- about 2300 ohms
• 104F(40C) -- about 1300 ohms
• 140F(60C) -- about 600 ohms
• 176F(80C) -- about 300 ohms
• 212F -- about 190 ohms
• these are the values. I don't like to measure them as it is hit and miss, I don't have any great tips... I just swap it.

 

I ordered a new intake manifold gasket and sensor off FCP along with other parts. It was either pay $8.99 for shipping or $9 for the sensor to qualify for free shipping. So sensor it was.

Do I have to take the fuel rail off while removing the manifold or is there a way to do the intake gasket replacement and coolant sensor replacement without touching the fuel lines and the throttle linkage? Are there any other things in the way that should also be replaced like the throttle body gasket?

Edit: I went out and took a look at the car. I was initially thinking of trying to make a valiant effort at replacing the sensor without taking the intake off. But the intake gasket seems to be in a bit of a poor shape by cylinder 1



So I’m thinking of going about the following way:
1. Disconnect fuel pressure relay and crank the car for a few seconds to relive any fuel pressure.
2. Disconnect the intake accordion hose and the smaller hoses to the idle control valve and the flame trap.
3. Disconnect the injectors and label the wires
4. Remove the 8 bolts that hold the manifold in place.
5. Figure a way to zip tie the manifold to the strut tower or hood hinge.
6. Replace crusty manifold gasket and suspect coolant temperature sensor.

Does the above seem like a logical way of doing things? That way, I won’t have to fool around with any of the fuel or throttle stuff. Or is worthwhile to replace the throttle body gasket while I’m doing this. The throttle body gasket would most likely have been exposed to oil for a while due to the severely plugged up oil separator box that I cleaned recently.

 

I don't open the fuel rail.
I don't disconnect the injectors.
Once the bolts are off, there is a bracket on the front that has to come off too, then the manifold can be moved to the right 6-8 " and tied to the hinge which will give enough space to do the gasket and the sensor. The sensor can be done without taking the manifold off.

 

Makes sense. I’ll update this thread once the parts get here and I get started.

i debated doing the sensor without taking the manifold off. But, the intake manifold gasket looks very crusty. And with the cold start injector in the way, I couldnt really get my hands to the temp sensor without getting cuts and bruises. I guess smaller hands would’ve helped.

 

woohoo, I get to do this tomorrow, too. what year is your 2/7/940? on my 85 240, the temp sensor looks pretty easy to get to. little worried how much coolant may come out.

 

My 240 is a 91. Are you going to take the manifold off? If not, can you still get to the temp sensor without cutting and bruising your hands?

 

i dont plan to take intake mani off, but I do have PCV box out and distributor out currently. so I think I'll have a good bit of room to get around without those components. distributor out only helps to get a straight shot back along the block.

 

Sounds like a plan. What symptoms are you having that’s causing you to doubt the temp sensor on your vehicle?

 

Very little coolant seeps out, you'll hardly notice it.

 

The 740/940 is easier to get to the temp. sensor without taking the manifold off, straight shot with a long extension. On my 1993 240 was harder, less space, had to get the manifold out....

 

I also read that if you take the reservoir cap off and squeeze the upper hose for a minute and then tighten the cap back up while still squeezing the upper hose, it will create a vacuum and help with reducing the amount of coolant that spills out.

 

Makes some sense, but the amount that weeps out even without that procedure is so slight it's not worth worrying about...

 

Thats good to know. One more question, do I need to apply any sealant when installing the new intake manifold gasket?

 

you don't need sealant on the intake manifold.

i am swapping mine because, for whatever reason, the temp sensor plug that came with the new engine harness doesn't fit my current temp sensor. drag but it's a $15 part.

at 35 years, i'd probably see it go eventually anyway....

 

The temp. sensor is not a $15 part, but a $40+. Don't skimp on the few Volvo parts that are important or your car won't run right! Then we will hear how you replaced this and that and the car now has a problem! Sensors especially should be OEM, as well as ignition parts, fuel pumps, relays, etc.

 

wow, I am idiot. i neglected to distinguish we were talking about the coolant temp sensor i am talking about the LH temp sensor further back on the block by the PCV system.

https://www.ipdusa.com/products/1083...130026-1332396

https://www.fcpeuro.com/products/bmw...sor-0280130026

 

I thought this was the part to be used, at least for the 1990-93 vehicles

Hella Volvo 240 Temp Sensor - FCP

The blue sensor is for older BMWs and for pre-1990 Volvos.