Hello all,

I have a 1991 740T sedan. It has 177k on her. I have been driving it for 2 years now, I bought it with 137k. It has been a good car. I drive it daily to work about 80 miles round trip. It was running fine and the next morning I started it up and get in it to go and it dies. Right after I back out of the garage. Took about 5 minutes to fire back up. Then I drove to the gas station (about 2 miles) and it died pulling in. Filled up and spent another five minutes cranking until it started. At this point I decided to just get it home and use another vehicle. So I then wait until Saturday to check it out. It was a little warmer out (probably 35-40) and it started up fine and did not die. I took it for a little spin and then changed the oil. All seemed fine. Go to start it Monday morning and it does the same thing. Starts up, then after about 3-5 minutes it dies. Then no start or very hard start. So I figured I would check the plugs. They were the originals. I changed the plugs, wires and the cap and rotor (all orig). This was last night. Started it up and let her idle for a few minutes. Hop in for a spin and back out and it dies. Then another 5 minutes to get it started to get back in the garage, same problem. So, any thoughts? Coil? It runs fine when starting cold. I tried swapping the radio relay from left to right (under the hood on strut towers), did that when I changed the oil, didn't do anything but maybe they are bad? Or coolant sensor? Or? I have not had this problem with car before now and it ran fine when parked the day before it started doing this. Any input appreciated.

Thanks,
Mike

 

I have changed the crank sensor, fuel pump relay, and cleaned out the IAC. This was all done within the first year of ownership. Also some vacuum lines. I can hear the fuel pump when I turn the key to on, and it starts when cold. Seems like something is failing after it gets a little warmed up. Could it be the fuel pressure regulator? Can I test this out somehow? I also changed the alternator about a month and a half ago, it was original as well. But did not have any problems after that was changed.

 

ambient temp at your location?

 

It is 20ish today. But the car is in a garage, so probably 25-30. Usually though it is not affected by the temp, always started in the cold. It will start, just dies after a few...thanks

 

have you checked the condition of the plugs,cap,rotor?

 

Brand new. I thought that was it because they were the originals on it, date coded 1990!lol..

 

pierce? Any ideas? Does this car have the code check box under the hood? I have not noticed it, but will have a look tomorrow when I get back into it.

 

hmmm.. think if i were you i would be checking the CTS<br />meantime, did you actually pull a plug to see the condition/if was fouled? edit: i now saw your first post that you changed them .. just wondering if you pulled one after the no starts were happening.

 

They were not fouled, just worn. They are now all brand new, plugs, wires, cap and rotor. The car has run maybe 5 minutes since I put the new ones in so no way they could be fouled.

 

CTS...is there two or just one? I will research if there is a way to check them, ohm meter?

 

there is one CTS that has two thermistors in it (of which one goes to the ECU and the other goes to the ICU), then there's another coolant sensor which goes to the dash gauge.

they are a high resistance when cold and a low resistance when hot.

 

https://www.volvoclub.org.uk/faq/EngineSensors.html

This has lots of good info. I am going to check the crank position sensor for resistance. I will visually look at coolant temp sensors under intake.

 

Really no way to check resistance with out pulling the sensor out then? Or just undo wire plug and check at plug connection on sensor? Temp gauge works good, so I would think that sensor is ok?

 

the wiring is as likely of an issue as the sensor itself, so the best way of doing it is to unplug the ECU, and ohm-meter test the sensor wire on the ECU plug, being careful not to damage said plug with your meter probes. I suggest getting the engine up to full temperature, then unplug and measure it, wait a few hours for the engine to cool down and measure it again. that FAQ page you linked has the values. I believe the CTS is ECU pin 13, and ICU pin 2

 

Roger, check the plug end correct, not the sensor. I don't know if it will run long enough to get it up to full temp, but have to try.

 

another thing, will the engine stay running with the MAF (AMM) unplugged? (unplug/plug back in with ignition off)

 

You may well have a bad crankshaft sensor. What brand did you use when you replaced it a year ago?
You do have OBD1, any codes?
Important when replacing crucial parts to use quality parts. These days, cheap Asian parts fail way too much...

 

Welp, I think that was it. I kept my old/original CPS and fuel relay. I put both of the old parts in and she is running great! Starts in barely one crank, new plugs and cap and rotor seem to help as well, Now though after sitting two weeks the master cylinder has developed a leak...so time for a new master cylinder....

Thanks for all the replies everyone, glad I kept the old parts.