Thank you for the thorough reply kittysgreyvolvo. I think answers to most of your points are buried in my detailed message about the problem but I'll go through them one-by-one to be sure - and for others who may look at this later. My comments begin " - [" and are placed below yours.


The ECT connector for your 1992 Volvo 240 can be broken at times of prior repairs that may or may not be related.
- [ The ECT was installed after the motor was bolted up in the car with the intake manifold still off. I assume it broke when (or after) the wiring was clipped onto it. It could have been weakened when the engine overheated.


The ECT is two separate sensors, as you know with one wire two the fuel control ECU and the other to the ignition ECU.
- [ Yes, the is the black ECT w/ 2.


Replaced the 1992 engine with one from a 1986? Did this person swap all components?
- [ Yes, all of the 1992 components and ancillaries were removed from the 1992 block and installed on the 1986 unit - or were replaced with new eg. the CPS. .

The timing in a 1986 uses an impulse Hall-Effect sensor in the distributor under the rotor. The 1992 engine would have the (as you mention) crank position sensor (CPS) on a plate mounted at the rear of the engine block at the top of the bell housing.

The knock sensor is different.
- [Yes, we used the newer-style unit. New connector won't hook to the old single-spade.

I'll guess you have the 1992 air intake manifold and injector fuel rail and the like?
- [ Yes, all new or 1992 components.


Indeed, a faulty ECT can cause hard starts: https://www.brickboard.com/FAQ/700-900/EngineSensors.htm#DiagnosingECTFailures
- [ What I see there is flooding "Thus, if you have a broken wire, defective sensor, or bad connection (I've seen it happen) the resistance measured by the ecu will be very high or infinite. The ECU interprets this as minus a zillion degrees and pours in the gas"

- [ Flooding symptoms IME are fuel in oil, much cranking, smoke when finally running, rough running even when warmed up ... This car acted more like fuel starvation eg. start immediately, stop, start, stop .... once started it ran OK after a bit; and restarted easily. Yet it had the black spark plugs and black exhaust pipe of a car getting too much fuel.


Have you checked codes and given an inspection before parts replacement?
- [ Yes, it had 1-2-3 (ECT signal failure) but when cleared the code did not return.


Socket 2 for fuel, emissions and socket 6 for ignition, emissions. You do not have EGR.
- [ Correct, it is a non-EGR car w/ABS - I should have mentioned that..


Though replacement of an ECT with a broken connector is pretty hard to miss under intake manifold runner #3. I'll guess you had to remove and replace the air intake manifold to gain access to the ECT (under the #3 intake runner) sensor after moving the air intake manifold out of the way. (Some may try to get at the ECT without removing the air intake manifold which results in destroying the ECT.

- [ I have broken ECTs by removing through the intake manifold but not in a while ie it's not a difficult task. I light it with a bright flashlight positioned to the right & below the manifold. I go in from the top using a 1/2" drive with an impact swivel. The risk is that the swivel will flex and twist the ECT top off - I've done that with 3/8" swivels. With the 1/2" swivel, I position it manually a) to break the ECT loose; and b) again for the final tighten.

The hard part is unclipping the connector but that's accomplished with a long-thin screwdriver if the release is positioned (on a clock) ~1500-1800.


May want to test the AMM (or MAF). If you disconnect the AMM (while the battery is disconnected), reconnect the battery, and it starts and runs, if poorly and rather richly, the AMM is at fault.
- [ Yes, we tested the AMM/MAF and also replaced with 2 known-good units. No difference. Ditto the IAC once.

(Disconnect the silver preheat hose between the exhaust manifold and the bottom of the air filter box, if connected.)
- [ Yes, I remove this and the flap from all cars I work on; and then block the pre-heat air intake with a plastic cap from a grease tube.


Though this you tube video shows ECT replacement without air intake removal. Huh. https://youtu.be/n_x5g2XhKug I never quite had the tools to do it this way. And now known. Huh.

Uses deionized water to mix with Volvo coolant. So, we can get deionized water from Sweden for both your Volvo 240 coolant mix or your nuclear reactor where we store all the misnomered depleted nuclear fuel rods.
- [ Some friends use deionized water in their exotic/classic cars. My air isn't so rarefied. I have an electric deionizer to make water for batteries but have never used that water in a coolant system.


Yes, you can replace a -561 ECU with a -951. http://www.nuceng.ca/bill/volvo/database/ecu.htm If fitted with the cold start injector on your 1992 240, the -951 does not make use of the cold start injector (or valve).
- [ Yes, I knew you could go that way but wasn't sure about going 951 -> 561. I think a 1992 should have a 951. This car has a 561.


The proper ECT for your 1992 Volvo 240 is: https://www.ipdusa.com/products/6210/112946-fuel-injection-engine-coolant-temperature-ect-sensor And: https://www.fcpeuro.com/products/porsche-volvo-engine-temperature-sensor-0280130032
- [ Yes, I plan to get one from eEuro next time I place an order at the free-shipping level.


Indeed ECT sensor may fit to the cylinder head and to the wire harness ECT connector. If the ECT you installed, using a multimeter, does not indicate proper resistance for a temperature, you may have merely removed a fault ECT for another faulty, or incorrect, ECT.
- [ We ended up with 2 spare black ECTs. One tested within specs, the other didn't. The car starts and runs the same with either one.

What's puzzling is the hard-start with the broken (swiveling, not snapped off) ECT connected. I need to test resistance on that one. I'm guessing that the short sent a signal to the ECU causing a hard start - not the typical ECT-fail that causes severe flooding.


There may be other hard starting causes. You are in Ohio, and suffer this same Mexico Gulf and Atlantic generated dog-awful humidity and the single snowflake with mounds of ice snow melt salt on the wintertime.

So, you may have other issues with corrosion at ground, engine control wire harness connectors, power. You may have other faults causing these symptoms. You may want to test the sensors and ensure proper wire harness connection between the sensor, through the wire harness, and back probe using your multimeter at both ECU connectors. See http://www.volvowiringdiagrams.com/?dir=
- [ The car ran well before the motor swap; and now starts and runs well with the ECT replaced. Aware that we could have damaged wires/connectors/pins during the motor swap, we did test several of those.


Can you ask the person that performed the engine swap what they did in case they took a shortcut to get it to run.
- [ No shortcuts. The car will be driven by a student so any potentially low-MTTF items were replaced.


When you do get it running and it warms up, how does it run? Any exhaust leaks?
- [ It runs well. Perhaps some small post- O2-sensor exhaust leaks, as on most 240s I see.

Certain the timing belt is aligned properly? A new timing belt will stretch, so it is a good thing to set the timing belt tension a few times in the first 1000 miles of a new timing belt.
- [ Yes, set and double-checked. Seems right on.


Inspect the air intake system from the air filter box, to the AMM, and after the AMM, for vacuum leaks. The air filter is clean (enough?)
- [ Yes, checked thoroughly and spare accordion hoses tried. Air filter is new.
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240 drivers / parts cars - JH, Ohio