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240 Old Volvos hate hot Southern Summers...or the Nordic gods are laughing at you.

Got the PCV system cleaned up, and the intake and rest of the stuff back on the car. Took it for a drive and it was fine, but eventually after about 40 minutes started to lose power (but didn't stall). I could floor the car and it wouldn't go past 50mph or so...felt like I hit a brick wall (LOL).

Picked up a coil at the j/y, and will get a cap and rotor as well. Seems like everything I am doing helps a bit more with each step, so at least getting somewhere.

check those relays and check back pressure at your cat hot
all you are doing now is shot gunning
 
check those relays and check back pressure at your cat hot
all you are doing now is shot gunning

I don't know what relays you are referring to in the engine bay, there are none on an LH 2.4 91 240 that control anything under the hood that I'm aware of. Can you explain describe more?

Something gets overheated under hood for sure that is causing the problem. On a warm or cooler engine it runs fine, once engine is hot it starts to break up and bog with full throttle, especially when engine is under load going up a hill.
 
Okay so after posting a question how to probe ECU connector to measure voltage and continuity, I tested the ECT (coolant temp sensor) circuit on terminals 5 and 13 at the ECU connector plug. Note I did this with the plug disconnected from the ECU, and I was not keen on trying to connect it without the cover to guide it in place - not sure if this is the correct way or not (i.e. plug connected or disconnected from ECU).

Measured continuity with ignition off across the terminals with my multimeter set at 20K ohms setting and got 2.23 +/- consistently. When I tried to test at 2K ohms setting, the meter jumped around and would not give an accurate reading. Since the cold engine spec is 2300 ohms, I think this tested okay for continuity - I think I'm reading this accurately.

For voltage I turned ignition on (dash lights illuminated) and probed 5 and 13 with voltage set to 12V setting on multimeter. I got nothing at all, no reading. I checked voltage at the battery and it was 12.6V, so I think the meter is okay. To me this indicates a bad sensor. With a zero voltage reading I would think the ECU considers the engine to be quite hot (since voltage drops on the sensor as the engine warms).

Car still starts okay and will run okay until under hood temps get quite high (20+ minutes of driving) and then it starts struggling for power, bogs with wide open throttle, will putz along under light throttle load, struggles up any type of incline.

What do you guys think...is this ECT sensor bad? Or am I not measuring the voltage correctly at the ECU connector?
 
The ECU supplies voltage, thru a resistor, for the ECT. If ECU isn't plugged in, no voltage on ECT. Your 2.23 resistance reading seems fine.

There's a different ECT pin used by the EZK box. You can pull the plug, find the correct ground/ect pins and measure the resistance. (The LH2.4 ECT sensor uses 2 pins and is actually a dual-sensor, with the block used for ground -- one pin goes to ECU, the other to EZK.)

Edit: Have you thought about vapor lock? Maybe the fuel in the engine compartment lines is heating up enough to start to boil/vaporize, causing a very lean when hot condition. Normally, the fuel is recirculated and cooled off going through the tank.
 
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Okay so I managed to carefully plug the connector into the ECU without the cover on and I'm still not getting any voltage between terminals 5 and 13. Mind you it is a bit of a contortionist act to do so, and it seemed a bit difficult to get the probes seated into the holes because the plastic bracket on the ECU was somewhat in the way (especially terminal 5). One question, does the ECU need to be bolted in place - i.e. cover is grounded to body? It would certainly be easier to try to measure things if the ECU wasn't bolted to the passenger side footwell (which is how I attempted to measure voltage).

I'd consider vapor lock, but the car has new fuel pressure regulator, relay and both pumps, so I imagine fuel is flowing back to the tank. It certainly behaves that way. Maybe I should drive it to the point where it is acting up, and then spray some freeze spray on the fuel rail...see if that makes a difference.
 
Okay so I managed to carefully plug the connector into the ECU without the cover on and I'm still not getting any voltage between terminals 5 and 13. Mind you it is a bit of a contortionist act to do so, and it seemed a bit difficult to get the probes seated into the holes because the plastic bracket on the ECU was somewhat in the way (especially terminal 5). One question, does the ECU need to be bolted in place - i.e. cover is grounded to body? It would certainly be easier to try to measure things if the ECU wasn't bolted to the passenger side footwell (which is how I attempted to measure voltage).

The ECU case does not ground through the mounting screws to the chassis -- you can test it floating in air. Measuring no voltage with key on is most likely from not getting good probe contact.

I'd consider vapor lock, but the car has new fuel pressure regulator, relay and both pumps, so I imagine fuel is flowing back to the tank. It certainly behaves that way. Maybe I should drive it to the point where it is acting up, and then spray some freeze spray on the fuel rail...see if that makes a difference.
A cold/wet towel also works, or if you're stumped for too long, try removing the return line and the gas cap, then see if you can hear bubbles if you blow through the return line.
 
Just to throw this in the mix. You must test the resistance of the coolant temp sensor at all three temperature levels. Cold which yours is good. Warmup, and then fully hot. I have experienced bad sensors that go open circuit on the hot engine. This immediately overrides closed loop o2 sensor reference on the engine and the ecu thinks the engine is cold and dumps a ton of fuel in there. Stalls because it is too rich. Also a good idea to do the three tests on both the fuel ecu side of the sensor and the ezk side as bob pointed out.

Use the freeze spray on stuff that gets hot in operation. Like the powerstage, or computers.
 
I think that I will bite the bullet and pull the intake and test the coolant sensor resistance out of the car (even though I just had it off to clean up the PCV stuff LOL...at least it's clean now). I don't know which pins to probe on the EZK (I really need to get a Bentley manual).

I did retest the voltage with the ECU unbolted from footwell and was able to get .34V reading...low for a car that is between cold and warm. I'm leaning towards the sensor going wacky once good and hot and then ECU dumping fuel.

I was going to continue my deferred maintenance by replacing the passenger side motor mount and trans mount, but will probably wait til hurricane passes through (don't want to get stuck and then have car we can't move). I did the driver mount when I cleaned up PCV.
 
Okay so I pulled the coolant sensor to test it. I think my multi-meter is on the fritz as I couldn't get a consistent resistance reading (probing both of the tabs in the plug with the multi-meter).

Room temp I got 1100-1700 ohms (should be 2300)
At about 100 degrees I got 800-1300 ohms (should be 1300)
In boiling water 200+ degrees I got 300-700 ohms (should be 190)

However...the readings while off were going the right way. I had already bit the bullet and purchased a new sensor and put it in before I ohm'd the old sensor. Guess what...it is still acting up.

Here is where we are. Car runs fine for about 30 mins, but then randomly bogs when you add throttle. If you try to speed up by increasing throttle car will almost stall it bogs so bad. If you add light throttle it will chug along albeit very slowly. It is very noticeable on hills (even slight) as you naturally tend to add throttle in these circumstances to climb the hill.

Here is the weird thing. If you pull over, turn car off and then turn it back on immediately it goes away! Eventually problem will return, more quickly than your first 30 minute run from a cold start, maybe 10 minutes or so.

I tried pulling the AMM plug when it started running poorly (without turning off car) and it immediately threw a CEL, and ran perhaps even a bit worse. Pulling the AMM should put the car in some type of limp mode, right?

Any advice?

I also threw a new Bosch cap and rotor on the car, and finished up the motor and trans mounts. It is so close...ugh.
 
As it acts up, what do you think is happening to make it bog down? While misbehaving, it feels down on power with partial/light throttle, but literally falls on its face if you open the throttle. Would those symptoms indicate a lack of fuel or too much fuel? If lack of fuel I'd agree the fuel pump/delivery is wonky. If too much fuel I'd think it is related to some type of wiring/voltage issue with the computer messing up rate of delivery.

As my other 240 runs well, it is worth a shot to swap ECUs and eliminate that as a problem? Not sure how temperature would impact the ECU as it wouldn't get hot when car is running hot.

The other option is to replace the wires on the main fuel pump. The plastic on the connector wires is a bit crunchy (old)...I did cut out a better pair of wires from a JY car. Thoughts?
 
Your symptoms remind me of a failing in-tank pump and finally failed power stage (?)


* Car would bog out going up hills, replaced in-tank pump solved that issue.
* Car would stall after 30 min or an hour then start after cooling off, power stage issue
 
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It is not a pink label, but it is a 561 serial ECU. I'm going to replace the fuel filter again as it was changed prior to PO selling the car (old one was plugged) and he drove car to my house about 30 miles with a tank of old, smelly fuel which may have plugged up new filter. Main pump is a new Bosch unit.
 
So to bring this thread to an end...I think it was the ECU. I say think, as our weather has turned cooler, so the blazing heat is gone. However I did replace the 561 ECU as I noticed it was pretty warm to the touch when the car would go into loss of power mode. I had a junkyard ECU from a N/A car (think it was a 940 as the build date was 1994). Since replacing the ECU the car has been running normally. Fingers crossed!
 
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