Stalling out when going over bumpy road or shaking intake boot.

Post by **amblerman** » 08 Mar 2021, 14:18

Hi Folks.

Today driving my trusty 1999 s70 NA 5 speed was.... interesting.

while driving through a bumpy construction zone, the engine shut off. Thankfully it was a 5 speed so I could put the clutch in and coast while I cycled the key to restart the engine.

It happened 5 times and then stopped occurring on smooth roads.

I made it to a parking lot and thought about the issue. It only happened when the car was on bumpy roads. I decided to debug the issue by shaking everything under to hood.
I was able to reliably reproduce the issue quite easily.

see attached video.
In case anyone can't view it, here are the steps to reproduce.
1) car idles fine.
2) grab intake boot and start wiggling it .
3) the intake boot, airbox and related pieces start moving...
4) car stumbles and stalls

My current thoughts are either an air leak or electrical.
I'm going to start investigating tonight but wanted to get this out there .

Any thoughts?

D18DD179-3CCD-4339-8304-96D0EAE601D9.mov: (7.79 MiB) Downloaded 113 times

Post by **abscate** » 08 Mar 2021, 16:07

Have a good look at the battery cable where it feeds into the fuse box, and also the positive terminals. If you need to replace you can spend $60 fir the one year model or $90 for the Volvo

Probably a main bus feed fault if everything goes dark with no codes

Post by **RickHaleParker** » 08 Mar 2021, 16:22

1. Take the intake hose off. Stretch it and look for cracks in the bellows. A crack maybe opening creating in rush of unmetered air.
2. Clean the MAF connectors and sensor.

Post by **amblerman** » 08 Mar 2021, 17:36

abscate wrote: ↑08 Mar 2021, 16:07 Have a good look at the battery cable where it feeds into the fuse box, and also the positive terminals. If you need to replace you can spend $60 fir the one year model or $90 for the Volvo

Probably a main bus feed fault if everything goes dark with no codes

I rebuilt all my cables two years ago with large gauge multi-strand welding wire and marine grade terminals. I shook all the cables and no stalling with those. Assuming there isn't an internal failure with the cables (which of course is possible) I think they are probably good. I will of course check further.

It was only stalling when shaking the intake boot which also shook the air box. I couldn't get it to stumble with the battery cables although I have barely begun to debug this.

Post by **amblerman** » 08 Mar 2021, 17:38

RickHaleParker wrote: ↑08 Mar 2021, 16:22 1. Take the intake hose off. Stretch it and look for cracks in the bellows. A crack maybe opening creating in rush of unmetered air.
2. Clean the MAF connectors and sensor.

I definitely plan on doing a detailed inspection of the boot.

does anyone have any idea if bad connection of the MAF plug while the engine is running would cause it to stall out?

I know you can run the engine without the MAF plugged in but I don't know the behavior one would see if the MAF was making intermittent connection while the engine runs

Post by **abscate** » 08 Mar 2021, 17:50

You can definitely stall out with a flaky MAF connection

Post by **RickHaleParker** » 08 Mar 2021, 22:08

amblerman wrote: ↑08 Mar 2021, 17:38 does anyone have any idea if bad connection of the MAF plug while the engine is running would cause it to stall out?

There would be a period of confusion as the ECM switches from Metered airflow to Calculated airflow.

Post by **amblerman** » 10 Mar 2021, 16:24

Well, I finally got a chance to start debugging the issue.

1) started car without MAF connected.
Idled fine.. I could not replicated the issue. No amount of shaking the intake boot would cause it to stall.

2) turned engine off, reconnected MAF, started car and shook intake boot.
Idled fine.. I could not replicated the issue. No amount of shaking the intake boot would cause it to stall.

Ugh.. while in the parking lot of my orthodontist, I could replicate the issue at will.
Now I can't. That's a shame. I was really hoping to be able to replicate it again.

I have a car that runs well..... until it doesn't.

I did notice two things though.
1) my car still passes the glove test.. almost sucked the glove in.

2) My coolant temp sensor is frayed.

After running with the MAF disconnected, it threw two codes.
P0102: MAF related . totally expected
P0113: Air intake temp sensor: not expected as mine is a non-turbo. Currently thinking that this is related to the MAF being unplugged?

Post by **abscate** » 10 Mar 2021, 17:17

Obviously the solution is avoid the Orthodontist

Post by **RickHaleParker** » 10 Mar 2021, 18:00

amblerman wrote: ↑10 Mar 2021, 16:24 P0113: Air intake temp sensor: not expected as mine is a non-turbo. Currently thinking that this is related to the MAF being unplugged?

You are think Intake Manifold Pressure which a turbo ECM needs but a NA ( Naturally Aspirated ) does not.

Air intake temperature is used to calculate air density. Air density is used to calculate air/fuel mixture.

Older cars had a separate Air intake temperature sensor. Then they figured out they could use data from the MAF to get the Air intake temperature. Saving the cost of a sensor, some copper wiring and labor.