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 10 Severe lack of power (for 15 minutes after start) (Read 5506 times)
C00lSub4ru
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Severe lack of power (for 15 minutes after start)
Dec 18th, 2018 at 12:40am
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I've been chasing this problem for almost two years.  It must have begun after a month or two of sitting in the snow, it's garaged now.

It starts pretty well, idles a bit rougher than before.  It revs all the way up in neutral just fine. When I start driving I can barely get it above 3000 rpm in any gear.  If I press the pedal more than 20% it just stops working, literally slows down.  Even in my usable rev range it has very little power, but I can struggle to get up to 30 then 45 and it's a little better.  Eventually I can use like 40% throttle and have enough power to hit the highway. After 10 minutes of highway speeds it runs fantastic in every gear at every speed for the rest of the day, even if I shut it off for half an hour to shop. By the next morning it's back to the same.

Twice now I thought I found the solution only for it to come back after a couple of weeks.  When I replaced the cables from the speed/ref sensors to the computer it ran great for a week then returned to being undrivable.  When I replaced the fuel pressure regulator I was sure it was fixed, for a month, then again it returned to being undrivable.

It has always burned/leaked a lot of oil (not sure because I don't see any oil under it.)


I have replaced the following:
fuel pump, pressure regulator, fuel filter, fuel tank strainer looks brand new
speed/ref sensors, speed/ref cables, rebuilt DME
cracked hose from AOS to j-boot
plugs, plug cables, cap and rotor a few years ago

I tested the Throttle position sensor, and one of the temperature sensors at the DME plug, and tested the AFM out of the car, all seemed fine.


I really appreciate the responses I get here, thanks for all the help so far.
  
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Cambo
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Re: Severe lack of power (for 15 minutes after start)
Reply #1 - Dec 18th, 2018 at 12:45am
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Not sure if this will help or not but have you checked for vacuum leaks? If nothing is obvious I'd spray a little brake clean around vacuum hoses/unions, intake gasket, etc and see if there's any change in idle. Of course be careful how much you're spraying and where you're spraying. You don't want to start a fire by soaking a hot exhaust manifold with a flammable chemical  Cheesy
  

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C00lSub4ru
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Re: Severe lack of power (for 15 minutes after start)
Reply #2 - Dec 18th, 2018 at 2:41am
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I'll try that tomorrow, could a vacuum leak be so severe and yet so predictably go away every time I drive?

The garage said it was running rich, not sure how they made that determination.

I read somewhere that the fuel pressure damper can fail and leak fuel through the vacuum lines.  Anyone think that's a possibility?  New ones cost $450 because Bosch discontinued them.

I'm also thinking maybe fuel injectors, fuel injector cables, bad grounds, or ignition coil
  
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Cambo
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Re: Severe lack of power (for 15 minutes after start)
Reply #3 - Dec 18th, 2018 at 2:58am
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Let us know what you come up with. Any leak past the MAF will affect how the engine runs. Also keep in mind the IAC Valve (Idle Stabilizer Valve) might be causing the issue as well.

If the damper was leaking that badly you'd have to more issues than what you're dealing with. But if you want to know if that's happening or not, inspect the hose for fuel. Also check the oil level and see if there's fuel in the oil.
  

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slinger569
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Re: Severe lack of power (for 15 minutes after start)
Reply #4 - Dec 18th, 2018 at 6:39pm
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Sounds like a vacuum leak to me too... However check your spark plugs to be sure they're not fowled.
http://www.clarks-garage.com/pdf-manual/elect-19.pdf

http://www.clarks-garage.com/
  

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Dave W
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Re: Severe lack of power (for 15 minutes after start)
Reply #5 - Dec 18th, 2018 at 6:56pm
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I would change that temperature sensor (for the DME, not the gauge).  Running rich sounds like getting too much fuel because the temp sensor is not responding properly.

Another thing that needs to warm up to work well is the O2 sensor.
  

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C00lSub4ru
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Re: Severe lack of power (for 15 minutes after start)
Reply #6 - Dec 19th, 2018 at 9:06pm
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I tried the brake cleaner method, didn't find any vacuum leaks.  I think I can barely hear a high pitched noise towards the back of the engine when it returns from rev to idle.  The vacuum leak might only be occurring under load.  I think I'm going to replace the DME temp sensor, then try the oxygen sensor.

Anybody think there's a chance it's the computer or the DME relay? My rebuilt DME is still under warranty (2 years old).  It doesn't ever stall so I don't think it's the idle control valve.  I guess nobody else suspected the fuel injectors or bad grounds.  I previously thought maybe the head gasket because there's a bit of white smoke (or condensation) when I start up, but there's none when it gets going so I don't think that's likely.
  
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Re: Severe lack of power (for 15 minutes after start)
Reply #7 - Dec 19th, 2018 at 9:53pm
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I agree with Dave.
It really sounds like a temp sensor.

I had a green fuzzy wire connection on mine and It ran similarly.

I crimped a fresh end on the wire, and she never acted up again.

Two wires. Just under the J-boot.
Very common failure..
  

Tom Simpson&&VW/Porsche freak.
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C00lSub4ru
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Re: Severe lack of power (for 15 minutes after start)
Reply #8 - Dec 26th, 2018 at 9:40pm
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Tom, what did you mean by "green fuzzy wire connection"?

I checked the wiring leading up to the temperature sensor and it looks alright.  Changed the temperature sensor, no change.  Somewhere I read that if the oxygen sensor was in need of replacement that it would run better if you unplugged it.  I unplugged the oxygen sensor, that only made it worse.  Is that accurate? Have I ruled out the oxygen sensor?  I've performed every test I can on like every sensor except for that weird test with the propane for the oxygen sensor, but my tach doesn't work so I can't really do that test.

I'm open to testing the idle control valve, but it idles fine and it never stalls so I don't see how that could be the problem.  Am I wrong? Is that still a possibility?
  
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Dave W
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Re: Severe lack of power (for 15 minutes after start)
Reply #9 - Dec 26th, 2018 at 11:34pm
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The high pitched noise could be coming from a leak in the intake manifold gasket. Try checking the tighteness of the bolts.
  

Dave - black 84 no longer exists. Sad 83 self destructed. All better now. Smiley
... Let's go hit some twisty roads! ...
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Re: Severe lack of power (for 15 minutes after start)
Reply #10 - Dec 27th, 2018 at 2:15am
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No loose bolts, I sprayed brake cleaner all over there, no change in idle.

Today when I was driving the intermittent thing happened in an instant.  In an instant it went from being undrivable (can only use 10% throttle) to pretty okay (60%) like someone flipped a switch.  I don’t think a vacuum leak would behave that way (most likely).
  
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Re: Severe lack of power (for 15 minutes after start)
Reply #11 - Dec 27th, 2018 at 9:59pm
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"Fuzzy Green" means corroded copper.
Sound like your temp sensor wiring is OK.

If she idles OK, then you can rule out IAC.

From the sounds of it, I would be looking at the AFM next. It can bench test fine, but be "noisy" like the volume knob on an old TV.

They can be re-furbished quite easily.

There is  black cover glued onto the AFM.
If you carefully pry it off (glued on), you can see the guts inside.
There is a "wiper" that runs on black carbon strip on the circuit board.

If you loosen the 2 mounting screws on the circuit board, gently pry it to one side (or the other). Then re-tighten the screws. Now the wiper should run on a "fresh" surface and work like brand new again.
Some folks slot the holes to allow more movement, but I have not found that necessary.

I also like to flush them out with "tuner cleaner" spray. That will clean the carbon strip and leave a thin layer of lube that will help it last.

Very common to do this in the Guitar amplifier world as we used to work in Smokey bars that would foul up the potentiometers. 



  

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C00lSub4ru
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Re: Severe lack of power (for 15 minutes after start)
Reply #12 - Dec 29th, 2018 at 3:31am
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Tom thanks again for the advice,

I tried what you described, my transistor plate is in there with 3 screws and every one of them is stripped.  It's like someone used Loctite and stripped them on purpose, but it definitely hasn't been adjusted before because there's only two distinct wear lines.  I'm not gonna be able to do it.

I made a tiny scrape with a pointed tool trying to get it out, doesn't look so bad, I'll probably test it before I put it back in.

I ordered an oxygen sensor, hoping I get lucky.  It may have gotten damaged when the cap blew off the extension right next to the oxygen sensor last year.  That weird thing they used in testing which no longer serves a purpose.  Caused a huge exhaust leak, mechanic plugged and welded it shut.  Maybe they burnt my oxygen sensor.
  
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Re: Severe lack of power (for 15 minutes after start)
Reply #13 - Dec 31st, 2018 at 9:03pm
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Possible you have a plugged up catalytic or muffler. With the car off knock on the muffler and listen for loose pieces of baffle or other obstructions bouncing around inside.
  
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C00lSub4ru
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Re: Severe lack of power (for 15 minutes after start)
Reply #14 - Jan 8th, 2019 at 12:50am
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I didn't hear any loose debris in the muffler or catalytic converter when I hit them with a rubber mallet.

I couldn't get the oxygen sensor off so I had the garage do it.  Just drove it back, and it's actually worse.  Took like 30 seconds to get to 25 mph, any more than 5% throttle made it slow down and cough.  As usual it gets slightly better as I drive, but it's getting worse.  It takes longer and longer to improve less and less.

I don't know if the current problem is the same as the original problem because the speed/ref harness and the fuel pressure regulator both seemed to fix it for a month.  Could there be some issue which ruined my old computer and then ruined my current rebuilt computer?
  
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