Hello collective board members,

My name is Greg and I am constantly lurking here but not always posting.
My other car is a 1998 S70 turbo saloon which I love but always needs love.

I have just acquired another beautiful late model Volvo which I am falling in love with.

It is a 1990 740 turbo wagon in good shape at least on the exterior and interior. The engine is another story. It has a hard time starting, idles low and then dies. This can happen 3-4 times before it gets going. After that it runs good. However the check engine light is on so I'd rather not go to far in it right now. Maybe it can sit until a few things are fixed and it's road ready.

Supposably the last person to own this car put in a new engine and turbo in. I'm not sure if I believe that because there is no documentation. The car has an oil leak in the front by the bumper on the passenger side. Seems to leak only after the engine is on? I'm thinking maybe an oil cooler line but will have to investigate further. Of course these cars only hold three codes per port but this is what I pulled from the Haynes manuel.

I am a DIY repair guy but always have difficulty with accurate diagnoses. So I thought I might ask you fine people for your help.

The codes read these errors:

#6 port, 224 Coolant temp sensor faulty.

# 2 port, 123 Coolant temp sensor.

312 No knock enrichment signal from ignition system.

232 Adaptive Lambda control, lean or rich, idle.



So I'm thinking both coolant sensors but What else?


Also can anyone tell me the "must replace items" on this model so I can be ahead of the curve.

Thanks to all for this great board,

Greg

 

There are indeed two temp senders but only one is a sensor for the computer. The other is simply for the dash gauge. A bad temp sender will definitely affect starting. They are located side by side on the driver side of the head under the intake. The one you need to check is located by cylinder #3. Would not hurt to check and most likely install a new O2 sensor. They are quite important and often ignored. You might check to see if they ever reinstalled the knock sensor.

 

The coolant sensor is responsible for ALL those codes. Cold starts are difficult on LH2.4 with a bad CTS and will cause mixtures to go out far enough to trigger lean/rich condition in ECU. These conditions and the lack of a coolant signal will also prevent the ignition ECU from adding much advance and the fuel ECU from adding much enrichment, without a CTS signal that is within preset parameters, the ECU's assume the sensor is faulty and default to very conservative maps for fuelling and ignition.
When the ECU's don't receive a CTS signal, or one that is outside parameters (ie, disconnected or broken) they will substitute data for 20 degrees c coolant temp for ALL conditions. As you can imagine, this really hurts cold starts and running.
I would check the plug to the CTS for corrosion and poor seating initially as they can have a tendency to corrode. The CTS for the ECU's is the SECOND one long on the head, with the rectangular Bosch spring clip plug.
I'd also clean the idle control valve and flame trap components whilst you are in that area of the engine, they'll both need doing.
As Swiftjustice said, a new 02 sensor always makes a difference as well, particularly on LH 2.4, although I don't think it has anything to do with your current problems, it's a good thing to replace on higher mileage engines.

 

Before you start buying new sensors, check and see if the temp sensor and the knock sensor were swapped. They use the same plug connector and will easily reach. I found out the hard way when we swapped motors on our 85 turbo. Made a world of difference starting when warm.


Russ

 

I think I'll try to replace the sensor first it's only 35 bucks.

After that reset the codes, see how it starts and what pops up on the OBD.

Already bought a few parts and will report back after putting them in.


We also have oil being pushed out of the oil filler cap.

Now I'm thinking of doing a few other jobs like the flame trap.

Still can't trace down that oil leak but one thing at a a time.


Thanks for responding.

 

OK so tried to flip the plugs for the coolent and knock sensors.
Cleared the system and went for a spin.
Pulled codes.......

#6 224, 143

#2 123

The 143 says the knock sensor is faulty.

So maybe they were plugged in correct and the coolent senser is bad?

So what do you think replace both?

Also the oil cap sprays oil and dances a jig if you do the PCV test.
Smoke from the dip stick as well.

How could someone replace an engine all those seals but not the flame trap and PCV system? Dumb.

 

I would replace the coolant sensor.

 

Thank you to all who contributed possible solutions.

It was the coolant sensor after all. It was involved but I removed the intake manifold just to get to it. Also thought I might as well do the PCV at the same time. Good thing too because the flame trap container was broken in half and spilling oil all over the block. Cleaned the intake manifold and the throttle body too which was filthy. Found some wires that needed better connections and grounding along the way. The vac lines were a bit of a nightmare but with some searching I found out how to rout them correctly.

Started right up with no hesitation, idles at 750-800. No check engine lights or codes to be found. Now on to the oil and exhaust leak but maybe another thread for that. I’ll post some pics when there’s time.

Thank you for this invaluable forum,
Greg