I have a friend with an S70 that has an apparent intermittent fuel cut (and engine dies)

The car re-started right away with no problems after sitting 10 min. the other day. It started a month ago and has been happening more frequently since.

Not too familiar with the S70 of those years, It's a '99 S 70 with the electronic throttle/ gas pedal.

The engine cut's out, leaving no OBDII codes, and there are no stored event data either. Then re-starts again without problems, maybe 20 min later. All systems AFIK are running OK (or at least what I can see supported by my OBDII tool)

Today the car runs fine, didn't reproduce the probelm.

The engine rev's upon giving it the pedal, but the car doesn't go while in gear (drive), tach'ing out, then dies.

It sounds to me like there's a communication error in the transmission control unit and the ECU, and the ECU cuts out when it can't go, then re-sets after it's been off for a while.

I know on these early drive-by-wire cars, there were issues with the throttle body switch, but it doesn't sound like this is that probelm.

Anybody have thoughts on it? Had similar experience?

Thanks,
Pete

Sounds like the fuel pump relay:

http://www.brickboard.com/AWD/index.htm?id=1265592

The relay is #103 in the fuse tray and usually gets worse with hot weather.

Klaus
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The more I learn, the more I forget. So why learn?

That was my initial thoughts, but in this case the engine runs, and tach's out, and does not engage the transmission drive at all, then afer a few seconds the engine cuts out completely.

It's not like it looses power with no fuel pressure. Wheh it happens, you can press the pedal, the tach climbs, then the car slows (no forward motion from the drive line), and then the engine dies.
It really acts like the transmission is disengaged at first, like it's put into neutral, then the ECU cuts out the engine.

If the tach doesn't work, it is a wonder the engine even runs. The ECU and TCU both need to know engine speed.

Perhaps your code reader isn't picking it up?

Klaus
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The more I learn, the more I forget. So why learn?

So why would you say that?

Nomenclature: "and tach's out", means that the engine runs to redline. Tach indication that the engine is working just fine, it 'Rev's Out'.

That doesn't mean the tachometer stops working.

The fact that you say the ECU & TCU need to know what the rpm's are doing is exactly my point.

Sorry, I am not an NHRA member. To me, when the "tach's out" it means that the tach is not working.

So you can rev all you want to so long as the car is in N or P? Everything is normal until you put it into D or R?

Klaus
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The more I learn, the more I forget. So why learn?

No this happens while the car is in drive, driving along on the road.

If it happens when coming to a stop, then it is the lock up converter that is not releasing. The converter lockup is a known problem and requires new software download from the dealer. No codes are produced for this problem.

Klaus
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The more I learn, the more I forget. So why learn?

Now that makes more sense. Thanks

Although I've never driven the car and had it happen to me, it always happens as she is pulling away from a stop or slowing down from high way speeds.

So it is not an engine problem. Have her flush the tranny and make an appointment with the dealer to have the new software installed for the TCU.

Klaus
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The more I learn, the more I forget. So why learn?

With those symptoms and no OBDII codes, my knee-jerk thought is Fuel System. Those symptoms are very similar to the troubles I had with a '94 850. Replacing the fuel filter helped, but only after replacing the fuel pressure regulator (FPR) and pump did the problem go away.

When the car dies and won't restart, does the fuel pump run? If you can't hear it for a few seconds when the key is turned to position 2 I suggest checking the fuel pump relay. If that checks out go on to fuel pressure anomalies.

A TCU or ECU problem of that magnitude surely would log a code.

-Will
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854 - 244 - Mini

BTW an easy way to check for this is to listen - the pump is surprisingly loud. If you can't hear from the cabin you can have a friend cycle the key to II position and listen from under the rear of the car or in the trunk.
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1998 V70 AWD Turbo 195k+