Classic failed ECT?

2manyturbos said:

I wouldn't be at all surprised if the CPS is the problem. I have had several 2-7-9s that had spark, fuel and good compression and wouldn't start and it turned out to be the CPS. I have learned to recognize the behavior. The first one I spent 10-30 minutes each session over a period of a week working on it and finally came to the conclusion it had everything it needed to run, yet wouldn't and threw another CPS in it. The 240 fired right up and ran perfect. The previous owner had spent $1,200 at various Volvo shops trying to solve the exact issue you are dealing with. They finally gave up and put it up for sale on craigslist. When I went to look at it, they went in for dinner and said "Let us know what you decide". It fired right up and I loaded it on the trailer. They came back out when I just finished chaining it down. They were surprised it started for me. Then, they elaborated on how it does that, runs perfect, then, strands them. I brought it home, unloaded it and didn't get back to it for a few days. It would not start, period. I could try until the battery was dead from cranking and nothing.

Click to expand...

Recognize the behavior? Recognize it as "works now and then" with no correlation to anything, I say.

Here's how I came to the conclusion that our CPS is a difficult-to-make item of an early design. I say early, because I believe modern use of crank sensor systems do not sit on top with a wire exiting straight up in what is always a wet environment. Difficult to make because the reluctor core is wound with some seriously fine wire and then potted. I can't believe the manufacturing yield on these parts is anything over 85%, and that's just go/no-go test without any temperature stress.

This was a Bougicord sensor that drove me to these lengths. One I had replaced proactively after finding the original working sensor with the typical broken cable sheath inviting water to find its way into the iron core. Had all those recognizable "won't always start" symptoms. My better half's daily driver too.

Scope or meter, you have to catch it when it isn't working. Temperature is probably the biggest influence on a connection poor enough to become a part-time semiconductor. I wired in a tap to watch it without disturbing any of the external connections which could have been the issue.





The meter isn't connected to measure AC volts -- that measurement has always struck me as inconclusive while cranking, with a digital meter. The meter is just measuring resistance, so it is disconnected until needed. The CPS, with all that fine wire, measures about 200 ohms and varies significantly with temperature. This is just an easy way to get a resistance reading without disturbing anything.



Aha. No start. Resistance nearly 1K.



The Bougicords were being sold for almost $80 at the time. Not only does the quality vary but the marketplace does as well. I found some aftermarket sensors for a price that begged me to experiment.



Used one and still have the second one as a spare. Still working well.

Bottom line for me? If in doubt just replace the sensor, but keep in mind, a new one is not necessarily a good one.

cleanflametrap said:

Recognize the behavior? Recognize it as "works now and then" with no correlation to anything, I say.

Here's how I came to the conclusion that our CPS is a difficult-to-make item of an early design. I say early, because I believe modern use of crank sensor systems do not sit on top with a wire exiting straight up in what is always a wet environment. Difficult to make because the reluctor core is wound with some seriously fine wire and then potted. I can't believe the manufacturing yield on these parts is anything over 85%, and that's just go/no-go test without any temperature stress.

This was a Bougicord sensor that drove me to these lengths. One I had replaced proactively after finding the original working sensor with the typical broken cable sheath inviting water to find its way into the iron core. Had all those recognizable "won't always start" symptoms. My better half's daily driver too.

Scope or meter, you have to catch it when it isn't working. Temperature is probably the biggest influence on a connection poor enough to become a part-time semiconductor. I wired in a tap to watch it without disturbing any of the external connections which could have been the issue.

The meter isn't connected to measure AC volts -- that measurement has always struck me as inconclusive while cranking, with a digital meter. The meter is just measuring resistance, so it is disconnected until needed. The CPS, with all that fine wire, measures about 200 ohms and varies significantly with temperature. This is just an easy way to get a resistance reading without disturbing anything.

Aha. No start. Resistance nearly 1K.

The Bougicords were being sold for almost $80 at the time. Not only does the quality vary but the marketplace does as well. I found some aftermarket sensors for a price that begged me to experiment.

Used one and still have the second one as a spare. Still working well.

Bottom line for me? If in doubt just replace the sensor, but keep in mind, a new one is not necessarily a good one.

Click to expand...

Recognize the behavior as in, the engine is sometimes harder to crank over. The spark is occurring every time so it will fool you on the simple spark inspection and injector test. It is occurring, yet, it is not occurring at the right time. One that I bought from a T-Bricker on here would actually kick the crank backwards (wrong direction of rotation) occasionally when attempting to start it. That car was a low miles 940 Turbo that was given to him by his parents. Several members on here tried to help him diagnose the car. This went on for several months with zero success. It had everything it needed, they thought. I had it transported to Oregon and when the driver showed up, I tried to start it to unload it. I knew immediately what it was due to the 240 I went through this with. We rolled it straight from his 7 car transport on to my car trailer and I took it home. 20 minutes after getting it home I had it running, PERFECTLY. The PO had just done the head gasket and put in all new tune up parts, hoses etc on the car. The assumption he made was something must have gone wrong in that process. Sound familiar so far? I took a chance on that car sight unseen. I figured worst case, I have to replace the engine on a 100K miles pristine 940 Turbo sedan in 406 blue metallic with grey leather interior that was adult owned and garaged its whole life. It ended up costing me a crank position sensor and about 20 minutes of my time.

Trying to fire at the wrong time sounds exactly what was happening. Weird popping sounds from the engine bay at random times while cranking, also the occasional fart out the back.

So today, with the car not even attemping to fire, I bought 2 gauge wire for battery to block, (mine has seen better days and i's too loose on the battery terminal for my liking) 4 gauge for the battery to frame and alternator ground, a fresh set of NGK BPR6ES, and oil and filter.

Came home and replaced all the ground's for the battery, cleaned the bolt threads of where they bolt onto the block/frame. Cleaned and retightened the injector grounds on the fuel rail sprayed electrical connection cleaner on the AMM and harness and CPS and harness. Also pulled CPS and cleaned with a paper towel. (Kinda real dirty)

Tried to start, sputtered but same result.

Went to JY and acquired 2 more crank sensors. Swapped in the best looking one and no change. Attempts to fire but will not run.

Pulled the plugs. Black as can be. Swapped with fresh ones and car fires up instantly.

Now, I'm not exactly sure the issue is gone. Or what caused the plugs to foul out in the first place. My fuel pressure not holding is kind of worry some in regards to a leaking injector. My brothers 940 holds fuel pressure at 39psi after turned off. I guess we will see tomorrow morning as it's supposed to be in the 20''s.

What you described there is what I've seen of 4-5 different cars over the years. They all had spark when a simple visual spark test was performed. They would pop, hit on a few cylinders, sometimes stop cranking because the timing was so far advanced. While doing all of this they would not start. Not even for a second. That's what the garage queen 940 Turbo did. I understand why it fooled everyone. It wasn't that the crank sensor worked and didn't work altogether, as in on/off, it was that it worked all the time, improperly. There never was a lack of spark when conducting a spark test.

We had a 2012? Honda at the shop once that had spark, fuel pulse, fuel pressure but no start. It would even run on ether. It ended up being a physically damaged crank sensor from contact with a rotating component.

On modern cars I would be using a scan tool and look at RPM data.


On an old car, I would probably use a scope. Or parts darts, whichever is faster/more convenient at the time.


Yes. ^^^^ when a crank sensor fails it can cause erratic rpm signal= erratic/incorrect fuel/sprak.

My hopes are very high at this point. It is frustrating having a problem in which you dont understand, yet, how to diagnose without the part cannon. Fuel pressure testing is easy, so is looking at the plugs, but after that I'm not experienced...

Fingers crossed it is the CPS.

^^ I hope so too. I'm sure plenty of these cars have ended up in the crusher for this issue.

It's a not an easy part to swap using the 100 piece Craftsman tool set from last Christmas. Be careful. If you snap that bolt, strip the bolt, or break the bracket you will be dropping the trans next.

I recommend diag over parts-darts in this case.

I use a 1/4" long extension setup and a universal joint. Or maybe buy a cheap 10mm universal/ "wobble" socket.

Really? It took me all of 5 minutes with a quarter inch ratchet and long 10mm. I do have skinny arms, which helps. I'd honestly say that is one of the easier parts to swap.

In the jy, I pulled one of of a 240 and it was TIGHT up against the firewall.

2manyturbos said:

Recognize the behavior as in, the engine is sometimes harder to crank over. The spark is occurring every time so it will fool you on the simple spark inspection and injector test. It is occurring, yet, it is not occurring at the right time. One that I bought from a T-Bricker on here would actually kick the crank backwards (wrong direction of rotation) occasionally when attempting to start it. That car was a low miles 940 Turbo that was given to him by his parents. Several members on here tried to help him diagnose the car. This went on for several months with zero success. It had everything it needed, they thought. I had it transported to Oregon and when the driver showed up, I tried to start it to unload it. I knew immediately what it was due to the 240 I went through this with. We rolled it straight from his 7 car transport on to my car trailer and I took it home. 20 minutes after getting it home I had it running, PERFECTLY. The PO had just done the head gasket and put in all new tune up parts, hoses etc on the car. The assumption he made was something must have gone wrong in that process. Sound familiar so far? I took a chance on that car sight unseen. I figured worst case, I have to replace the engine on a 100K miles pristine 940 Turbo sedan in 406 blue metallic with grey leather interior that was adult owned and garaged its whole life. It ended up costing me a crank position sensor and about 20 minutes of my time.

Click to expand...

I forgot about the thing destroying the starter.

https://www.brickboard.com/RWD/volvo/1408914/220/240/260/280/cranking_issue_timing_starter.html

I have never had a problem with one, but I live in a desert.

My 1991 740 died all of a sudden this year on the street in front of the shop. I took an educated guess and installed a crank sensor and it fired right up.

Black magic or Voodoo if you don't have a scope or know how to use one. In my case, it was pure observation of the symptoms that led to the root cause. Logic tree sequence of events. IOW, old school diagnostics.

A resistance check is legit. We had a case on a Saab where a meter was left on the crank sensor and after lunch it went open circuit.

I would prefer to have proof of failure and a confirmed repair on a customer car before putting mom and the kids back on the road in a car that MAY stall.

Unless I've got another bad cps, doesn't seem like the problem. Went outside after 5ish hours and car won't start.

Looks like imma pull the rail tomorrow. Check valve also came in today, but I'll check/swap injectors first.

Get a test lamp.

Got a test lamp.

Grounded the pin hanging off to the block and 12v to the injectors starts when key is turned on. It does not flash on the test light when cranking. It stays solid the whole time and after done cranking, it will take a few seconds for the light to go out. I hear a click (rsr maybe?) When it does turn off.

Is the pulses to fast for a test lamp?

https://youtu.be/TGygYAWC_Qs

I also grabbed a multimeter, time to learn...and an in line spark tester from harbor freight. I wanted to get a noid light, but they only sell a kit for 40 bucks. I'm sure I'll never use the other ones in the kit besides the bosch one, so I went test lamp thinking itll be the same?

Started checking around. So far I have learned how to check grounds via positive battery terminal and whatever ground I need to check. Ive read about a voltage drop test that you compare not running to running numbers, I haven't checked running, but so far fuel rail bolts show same voltage as battery, same with the ignition module ground and the ground strap from the valve cover to firewall.

Coil pack gets 12v (11.something while cranking) and I put the grouND of the test lamp on the pins that fire the plugs and the test lamp part on the positive battery. They both pulse like I would expect the the injectors to pulse...

https://youtu.be/8Eol2AXpJuo

I decided to put the positive pin on the ground of the injector clips, grounded the meter on the block and it showed .50 volts and dropping by .01volts every second...again no idea what that means. I figure a good ground should have no voltage when connected to the block

And cleanflametrap...in your pic of resistance checking the cps, did you just cut open the sheathing and connect the leads to the wires inside? Or are those wires coming from the ecu?

Looking again it seems it's on the ezk side?

Realizing the ecu grounds the injectors when firing....I put the ground on the ground pin and test lamp on positive battery terminal.

I ended up with this. I'm not sure what to take of it. I tried to get a good grip on the injector ground pin, but it looks weak from the start and then kinda dies off towards the end of cranking.

https://youtu.be/pdATs2z6RgQ

Injector pulse test:

-Test lamp clip to batetery positive
-test lamp probe to injector ground wire
-crank
-blink?