Strange stalling issue. - Defender Source
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  #1  
Old September 6th, 2009, 04:17 PM
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Strange stalling issue.

Hello all,

I know there are many threads on stalling. I have read them. My truck stalls only under very specific conditions, so I hope this description will help with the diagnosis.

It happens when I am going down steepish hills at low speed with the brake applied. More rarely it will occur when I charge up to the top of my steep driveway and brake at the top. It happens regardless of how much fuel is in the tank, or whether the engine is warm or cold, or whether it's hot or cold outside. It never happens on level ground. I have a '97 SW with an automatic. Does the automatic transmission use vacuum to shift? I have a nagging suspicion that the combination of brakes and transmission shifting is robbing the engine of vacuum and hence the stall. It always starts right back up and doesn't throw a code. Sometimes after the restart it will run rough for a few moments, while other times it runs like nothing happened.

Thanks in advance for your help, and your patience with yet another stalling post.
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Old September 6th, 2009, 06:22 PM
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I would guess more a fuel issue. Have you changed your fuel filter lately? How many miles are on the truck? How long have you owned it?
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Old September 6th, 2009, 07:55 PM
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Quote:
Originally Posted by woldd90
I would guess more a fuel issue. Have you changed your fuel filter lately? How many miles are on the truck? How long have you owned it?
Thanks for the reply.

I've had the truck for about 4 years. It has just over 108k miles. The fuel filter has been changed since this problem began.

I've spoken to my mechanic about it . He was unable to reproduce the problem. I can't make it happen either. It's sporadic.
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Old September 6th, 2009, 10:28 PM
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I've never worked on the ZF automatic, but most automatics that I have dealt with that aren't computer controlled all use some kind of vacuum solenoid to vary the shift pattern.

But I'm more thinking that the vacuum situation is causing the issue. Not only do you increase the vacuum in a long downhill (vacuum does go up on a downhill, right?), but you're also at low throttle, so you're probably over-fueling the engine. The fuel pressure regulator is also vacuum controlled. Doesn't the pressure RISE with a high vacuum? This would further increase the over-fueling issue.

Just guessing, but that's my thought.

-Hans
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Old September 9th, 2009, 11:55 AM
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Quote:
Originally Posted by Hans
But I'm more thinking that the vacuum situation is causing the issue. Not only do you increase the vacuum in a long downhill (vacuum does go up on a downhill, right?), but you're also at low throttle, so you're probably over-fueling the engine. The fuel pressure regulator is also vacuum controlled. Doesn't the pressure RISE with a high vacuum? This would further increase the over-fueling issue.
I was totally unaware that the fuel pressure regulator was vacuum controlled. I'm going to look into this.

Thanks everyone for your thoughts.
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