Cold weather start but won't stay running...CTS ?

[abscate]

Both the fuel pump relay and the main system relay have shown to have temperature related failures/ hot and cold

[SonicAdventure]

Both the fuel pump relay and the main system relay have shown to have temperature related failures/ hot and cold

It’s 28 in the sun and now it started on the first try and ran fine.

I can bring my extra fuel pump relays in the house and warm them up and test again tomorrow as it’s going to be just as cold. What is the best way to test the fuel relays so I have some baseline?

Where / what is the main system relay? Not sure if I have an extra one of those but I might.

[erikv11]

Best way to eliminate the fuel pump relay as a problem is to just use a jumper wire. If the problem occurs with the jumper then that relay isn't the issue.

The main fuel system relay on an 850 is the gray one up at the radiator. Under that little black shelf or cowl.

Temperature dependent relay failure is much, more more commonly the other way around: failure when hot, OK when cold. This is true of any electrical part.

[SonicAdventure]

Best way to eliminate the fuel pump relay as a problem is to just use a jumper wire. If the problem occurs with the jumper then that relay isn't the issue.

The main fuel system relay on an 850 is the gray one up at the radiator. Under that little black shelf or cowl.

Temperature dependent relay failure is much, more more commonly the other way around: failure when hot, OK when cold. This is true of any electrical part.

I’ll watch RSPI’s video on fuel pump relay jumper. Isn’t the grey relay above the radiator to fuel injection relay or are there two up there?

It’s Wierd - this car consistently performs the same way in temps less than 25 degrees F or so...starts right up and then stalls. Ambient temps above 25 and it has no issues. This is the first winter I’ve had the car. I’ve replaced the ECT, the cam and crank sensors and all ignition components in the last 2-6 months.

Never getting a CEL for any of the cold weather no start issues.

What else can I check? Any chance a 1:1 Motronic ECU swap might clear this up?

[erikv11]

You have it right on the relay by the rad. On abscate's cars there is no fuel injection relay, so he refers to "main system relay" because that's how fuel injection is handled in a 98. On your 850 the main system relays are the three J relays next to the fuel pump relay.

It is a stumper, I'm not coming up with any good reason for the cold problems. Worth looking at relays though, especially if you figure out that the fuel pressure is too low when it is not starting in the cold. I guess that would be a useful troubleshooting route, figure out what the fuel pressure is when it is not starting.

It's basically never the ECU. I wouldn't hesitate just swap in another one to rule it out though. No harm in that if you have one known to be good for the car.

[abscate]

Erik, thanks for doing the 1999 to 1996 transcription of information

[erikv11]

Transcription, translation, it's all centrally dogmatic ...

[SonicAdventure]

Merry Christmas everyone -

Well, the problem continues...haven’t been able to do much diagnosis over the past week. Was curious how the fuel pressure could be measured. I know the fuel pump is priming I can hear it loud and clear.

I guess what frustrates me the most is the fact that this error produces no CEL...ever.

The fact that they went to such effort to put all these sensors on the car yet when something this dramatic happens (no start) there isn’t an obvious trigger to alert what the problem is.

One other item I’ve noticed is that when it does eventually start up and stay running, it’s usually accompanied by a strange buzzing sound from under the drivers side dashboard. It sounds like a small electric drill running with the chuck on a very light setting. After a about 10-15 seconds this whirring/buzzing sound stops. Is that some sort of clue? Could a relay under the dash be causing the issue?