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Catastrophic Consequences of Vacuum Line Leak on Turbo PT

 
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Old 08 Oct 2014, 10:07 am
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Default Catastrophic Consequences of Vacuum Line Leak on Turbo PT

This morning I was at work and was running late for an important meeting several miles down the road. I needed to get their fast. So instead of taking the "Safety Clown Car" (Ford C-Max Hybrid), I decided my trusty PT GT would get me their quicker but still safely. Boy, was a I wrong.

I had just left and office and was about 500 feet down the road when suddenly the engine went full throttle and the brake peddle went all the way to the floor. Luckily (or "sadly" depending on how you look at it), this is not the first or even second time I had a car go inexplicably full throttle while driving down the road. So I just instinctively grabbed the key and turned the engine off.

There was still a few minutes to my meeting so I ran back to the office and grabbed the "Clown Car" leaving my PT next door in a back parking lot where I pushed it. Even with an engine problem, she still looks awesome.




While in the meeting, I diagnosed the problem in my head. I had seen no check engine light. And the most likely way a PT engine would run away and brake loss occur at the same time would be if there was a fairly large leak in the manifold between the throttle body and engine. That would let the engine think the throttle was open and cause a loss in vacuum disabling the brake booster. The engine may have not run long enough for the PCM to decide the loss in vacuum was chronic and not just due to open throttle. Thus no check light.

After the meeting I returned to the office and then walked next door to my PT. Being "Handy", I almost always have my tool bag on board with just about anything I could need. So it was time to find and fix this problem. And it did not take long. It appears that the hard plastic vacuum line running to the top of the throttle body had rubbed the wire loom above it and that created a small hole. For an expedient "field" fix, I pulled out the trusty electrical tape and rapped it up very well. Then I hit the key and the engine purred with normal throttle response just the way Mr. Chrysler intended.




The permanent fix will be to replace the line with one from a salvage 04 Platinum Edition PT that I've already identified as a great source of spare parts for my GT. Of course, I will also add some extra protection for the replacement line so another hole does not get rubbed in it.

At work one of the things I do is review designs for new production machinery. I always like to look for features that would cause a catastrophic accident during failure. And I suggest ways that might be avoided. It's okay for machines to fail. They just shouldn't create highly hazardous conditions when they do. Too bad Chrysler didn't have somebody looking for this on the turbo PT engine. It's a shame to think one small hole in one vacuum line could cause the car to race down the road uncontrollably. Imagine what might have happened if a vacuum leak like this occurred when an inexperienced teenager was driving their PT down the road. Somebody at Chrysler should be ashamed.
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Last edited by Handy_Cruiser; 08 Oct 2014 at 10:12 am.
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Old 08 Oct 2014, 10:28 am
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

Glad you are so HANDY--- you knwo some one actually should be held accountable this could and most likely has cause a accident and at WOT that is not GOOD
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Old 08 Oct 2014, 11:02 am
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

Had anyone ever have moved things to the point that this could have occurred. I get you are upset. But with the milage and age it could have been moved around to cause this issue. Lines should be inspected on accession to determine if a problem with chafing is possible and corrected. Witch I'm sure your going to do on you new pt. Glad you didn't have any lasting affects of your adventure.
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Old 08 Oct 2014, 11:09 am
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

maybe a little exaggerating on the full throttle comment?
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Old 08 Oct 2014, 11:19 am
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

When the line from the brake booster over to a "T" junction came loose, mine, instead of going full throttle, when up to about 2K and down to idle and back up and down. Continued that way along with a rock hard brake peddle that wouldn't depress at all. Luckily it happened in the garage just as I started to go out. Just tracing the lines and finding where it came loose at the "T" fixed it.

Glad you didn't run into anything and was able to find and fix your problem.
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Old 08 Oct 2014, 12:05 pm
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

My engine doesn't not appear to have ever been touched. Everything looks original from the factory best I can tell including battery and plugs.

If you look in the photo you will notice that the wire loom looks somewhat deteriorated. These things happen over time with any older car.

My main issue was that the car did go full throttle. After I stopped. I started it back up and it rev'ed back up fairly quickly. I was surprised such a small hole in one vacuum line had done that. When I first opened the hood, I was looking for a much bigger leak. I thought maybe the large vacuum line to the brake booster had come loose. I was surprise that it was just that little plastic line. But patching it did fix the issue.

The effect I experienced may be due to where this line is located right at the throttle body. I haven't had time to research what that line is for. But it obviously pulls a constant vacuum.

And I am not angry, but just surprised that the engine would do that. You would assume that it would just increase in RPM's as CREWZIN experienced since the amount of extra air coming in must be limited.

Strangely, my son experienced the same thing once with a 1989 Chevy pickup truck except without the brake loss. I found the problem to be a very small twig that got into the throttle body and held the butterfly open just a few millimeters. When started, the engine would rev up fairly quickly and climb until what could be considered full throttle. When you add the loss of the brake booster on the PT, you get a very interesting experience to say the least.
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Old 08 Oct 2014, 12:26 pm
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

sooooooo I guess VE and CFM calculations don't exists and why have a 49mm TB when a 8mm ID hose can flow the same CFM to create a full throttle condition? And the TIP and MAP must have "punked" out as well to be ignored by the PCM? I really like the "like" example of the mechanical linkage carbureted fueled engine comparison to the PT Cruisers cable controlled air flow TB. Now how did the PCM adjust the FI for the correct pulse rate and duty cycles as well the ignition timing control?
All that from that 8mmID hose with a small hole in it !? ....awaohawow! I gotta get me one of them!
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Last edited by NitroPT; 08 Oct 2014 at 12:29 pm.
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Old 08 Oct 2014, 02:20 pm
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

Unless it was you that put the zip tie on the base of that line as well as the tape, it would fair to say someone has been else has played with that line in the past.
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Old 08 Oct 2014, 02:43 pm
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

Quote:
Originally Posted by Handy_Cruiser View Post
For an expedient "field" fix, I pulled out the trusty electrical tape and rapped it up very well.
I saw the zip tie as well and just figured Todd did that as well? But it is a good question! Well see what he says?
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Old 08 Oct 2014, 03:01 pm
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Default Re: Catastrophic Consequences of Vacuum Line Leak on Turbo PT

Full throttle
Helped brother do a Neon timing belt/water pump/tensioner, his first time,
I warned him about getting the duct between the air cleaner and throttle body on and tight. Car started right up and he drove it home, next day about 20 miles from home--> full throttle. He had it towed to my garage and the duct end attached to the air cleaner had folded on the very bottom leaving a gaping hole for air. Loosened the clamp and carefully sliped it on the air cleaner and back to normal, no more problems.

(It happened to me on my neon, 01, I left the clamp loose a day latter it went full throttle..) what a way to learn.
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