TLDR: Car started to not crank at all, waited 15 minutes and starts. After that, car cranks but wont start, and when it did would idle 300-500 RPM for a few seconds and turn off. Waited 15 minutes and drove home without a problem..

My 1989 Volvo 740 GLE has been having a really weird problem when starting after driving a certain amount.. So I'm going to try and explain it my best..

I drove back from a 400KM trip, no hiccup or anything, and continued to turn it off. Roughly 15 minutes later I tried to start it again, but no crank. All the lights turned on the dash, the interior light was on, just no crank. I do some research and couldn't find anything so I go back to start it, and it starts without a hiccup roughly another 15 minutes later.

I go drive somewhere and back again about 3-4 days later, (while driving to places with no issue in between those days), and again the same thing, no crank and I waited a bit and it started perfectly.

Fast forward another few days, I'm driving on the way home and take a turn, and all of a sudden I lose power (engine power) for half a second. The RPM had dropped significantly but quickly got back up. As I'm driving home, this happens again, and another few times. I turn onto the highway, and all of a sudden I'm losing a lot of power, and the RPM's were around 300-400 and I'm trying to lightly pump the gas and nothing is happening. The car stalls and I had to pull over to the side.

But this time, when I turn the key, there was actually a crank, and it keeps cranking but it just won't turn on. I keep trying to crank it but no luck. After cranking a certain amount of times, I got the same issues where there was no crank at all. I was stumped at this point so I waited roughly 20 minutes. After 20 minutes, it cranks and starts up fine, but I did lose a little power on the 5 minute drive home.

I was thinking it was my alternator at this point so I tested the battery, getting 13.9 on it with the lights on, so I thought it was fine.

The next day, stupid as it sounds, I drove ~30 minutes away.. I turn off the car, come back 5 minutes later, and when I try to start my car, it cranks but is not starting again. After roughly 5-6 tries, I manage to get the car to start, quickly put the accelerator down so it goes up to 4-5k RPM, but it went down right away even with the gas pedal down. It was at 300-500 RPM, sounded like misfiring and stalled again.

The cranking and starting car with low RPM's went on for another 5 minutes until I turn the key and again, all the car is getting power but theres no crank. I wait 15 minutes this time in the 40C degree weather and start the engine. It starts perfectly, with a very small hiccup at the start. I drove home, 30 minutes, without an issue.

The car is at home right now, and whenever I try and start it, it starts right away without an issues.. Don't want to drive it anywhere

I am now completely stumped. I ruled out all of the things I could think of, and have no clue what it is now.

TLDR: Car started to not crank at all, waited 15 minutes and starts. After that, car cranks but wont start, and when it did would idle 300-500 RPM for a few seconds and turn off. Waited 15 minutes and drove home without a problem..

 

You are probably having a combination of a couple of things that fail intermittently and rightly can confuse you. Hard to give you an exact answer without laying of hands but the areas to be addressed are: starter, ignition switch, fuel pump or relay, crankshaft sensor or Hall sensor (not sure what the '89 has, it is a on the cusp year). I know, not a lot of concrete help but not so overwhelming to solve if diagnosed right--none of the problems mentioned are expensive unless you start throwing parts at the advice of some self interested mechanic. Do you have a reliable Volvo shop?

 

No I don't have any reliable volvo shops here.. I'm really thinking that the cranking and losing power issue is caused by a clogged fuel filter. I looked under and sort of took it out and it looks really old so I'm going to replace that. I'll see tomorrow if that does anything.

 

I guess your RPM sensor is flaking out.

 

It's definitely NOT the fuel filter. The Crankshaft Position Sensor is where I'd start.

 

Let's see if this Two-Poster resurfaces or not....


If not, blah blah blah, talking to spambots....



Inspect rpm sensor for frayed wires.


That is all I have to say unless he shows back up.

 

Don't worry I'm back, don't plan on leaving for now lol. I did some research and that sensor definitely fits the symptoms I'm getting. Now I just need to find the part. I went through the wiring and didn't see anything out of the ordinary

 

https://www.fcpeuro.com/products/vol...0-940-271949oe

but, first, you should inspect test rather than just replace. a bad CPS will have frayed or rotted wiring as the sensor itself doesn't fail, its too simple.

 

Bad cps can look ok, can't go by looks. No way to test, has to replace it.

 

How would YOU test your crank sensor?


There is a test.

 

1) ohm meter. unplug the sensor, and measure the resistance. center pin to either side should be about 160 ohms, there should be no open or short circuits. the center pin is the ground shield, the two outside pins are the signal.

2) hook digital multimeter across two outside pins, set for low AC volts, crank motor, pulses of a small voltage (a few 10ths of a volt?) should be apparent.

 

Well, OK, but the problem is intermittent! Which means that under some conditions the sensor fails, heat, moisture, whatever. So, when you test it it may be OK, then, not... Therefore, it CANNOT be meaningfully tested.

 

yeah, intermediate problems are a bitch to diagnose.