Sudden Crank, No Start After Hitting a Bump

[fatcatbestcat]

Hey, it's my dumb ass again.

So my '91 940 Turbo is still my daily. Haven't had any hiccups since I replaced the timing belt in October, which I re-tensioned some 1000 miles ago.

This morning I hope in the car to get to work, it starts up normally. I back down my driveway (which is on a hill), and I hit the sidewalk. There's a bit of a bump, which is normal. The car stalls out and won't start again.

It has battery voltage, and cranks kind of disturbingly fast, almost like it doesn't have compression. I pull the oil cap off to check if the cam is spinning, and sure enough it is. It sort of coughs when I give it throttle when cranking, so I put my foot to the floor and it fires and cold revs to 5,000 rpm. I let go of the gas and it slowly returns back to its normal cold idle.

I drive it to work and the idle returns to normal when it warms up. I did notice it was perhaps a little sluggish in the midrange, but that could have just been me subconsciously driving it carefully. I'll see if this issue happens again this evening when I leave work.

My first thought is this is some kind of throttle position problem? My old D24 245 had a similar issue when the throttle cable adjuster broke - I had to put my foot to the floor to get it started.

Is there a way I can test the TPS to see if that might be an issue, or is this just an LH "glitch" that people have encountered before?

 

[bobxyz]

You can test that the TPS idle switch is seen correctly by the ECU, and that the IAC valve clicks - see Diag Test Modes 2 & 3 here:

Engine and OBD Diagnostic Codes<

Volvo Engine and OBD Diagnostic Codes<

www.volvoclub.org.uk

I'd inspect the TPS connector, and the IAC connector, to make sure they're OK and fully seated.

 

[fatcatbestcat]

You can test that the TPS idle switch is seen correctly by the ECU, and that the IAC valve clicks - see Diag Test Modes 2 & 3 here:

Engine and OBD Diagnostic Codes<

Volvo Engine and OBD Diagnostic Codes<

www.volvoclub.org.uk

I'd inspect the TPS connector, and the IAC connector, to make sure they're OK and fully seated.

Thanks, I'll check my connections and try and some diagnostics when I get home. Whatever the issue is/was, it didn't seem to store any codes.

 

[dl242gt]

This seems like more of a flooded engine and weak spark. Take a look at your plugs. Maybe they need a regap if they aren't too worn.

 

[fatcatbestcat]

This seems like more of a flooded engine and weak spark. Take a look at your plugs. Maybe they need a regap if they aren't too worn.

I'll take a look at my plugs on the weekend. I didn't notice any abnormal wear on them last time I changed them in late May, and they were gapped to spec at the time but that was also before I put a chip tune in it.

I suppose the update since my no-start the other day is that the car is running fine. Nothing really out of the ordinary, and I've had no issues getting it started in near-freezing temperatures.

 

[fatcatbestcat]

Update on this, I checked my plugs and didn't notice anything terribly unusual about them. I did double check and regap them, and made sure the TPS connector was good and tight.

We're into the freezing cold weather now and sometimes the idle flare will last until the engine has warmed up a little bit. There was a brief time when it felt like I was missing a lot of power between 2,000-3,000 rpm but that seems to have gone away. My fuel economy also seems to have massively improved recently, I had been struggling to go 150 miles on half a tank of gas (as was my old average) and now it's making that happen with no problem.

Yesterday it didn't really want to start in ~-17°c weather, and the starter made some unusual noise. Today it fired right up on the first crank in closer to -20°c temps outside.

I'm deeply confused.

 

[dl242gt]

Why 940 why? Why you got to mess with dis hear car?
My next suggestion would be to stop by a home depot or lowes and buy some ox guard grease. Go over every engine compartment connector you can get to and put it in there. Seemed to help my old 93 run just a bit smoother. It's made for the aluminum house wiring but is also great for automotive use.

 

[#!rolls2]

The 2000 - 3000rpm sluggishness / mileage drop fixing itself might point to an iffy harness connection at the coolant temp sensor. Worth a check.

Throttle body clean?

Of course neither of the two points above address the starter misbehaving. I'd start with checking the integrity of the battery and its cables as well as the solenoid wire connection at the starter.

 

[fatcatbestcat]

I didn't notice any oil in the intake, and the MAF was clean (although I did clean it out again just to be sure) - I didn't take enough couplers apart to look at the throttle body yet though, nor did I even graze my eyes across the coolant temp sensor. I'll check on those on a less freezing/windy day outside.

Thanks for the tips.

 

[dl242gt]

It got cold early here this year. I mean nothing like what you deal with but we usually aren't fully into freezing in Dec and we are this time. The ground was crunchy already much earlier than usual.