Only stumbles at close o full throttle....

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Togglehead
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Only stumbles at close o full throttle....

Post by Togglehead » Mon Apr 30, 2007 3:15 pm

Well..i know there was a thread about this already....but i have another question or two before i go ahead and check my timing....

1. Can your timing just...go out? I mean..if you were running fine one day, then the next it was all wacky....is that logical?

2. The bucking i get is really only noticable in 1st and 2nd....but it wont do it at ALL if i dont have the pedal down to 3/4 or more. Meaning..if i leave the car at 1/2 throttle or a little above.....it pulls as half throttle should. But as soon as i push the pedal down to 3/4 or more...i start to stumble....

Could it be the TPS?
1985 944
89' XR

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Maurice S
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Post by Maurice S » Mon Apr 30, 2007 3:33 pm

have you done the tune up thing yet as previously suggested? Cap, rotor wires etc.

Did you squirt those CV joints yet? How'd that work out.
85 XR '" Lightly Street Massaged"

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Post by Togglehead » Mon Apr 30, 2007 4:53 pm

Actually no, i havent done that stuff yet. I guess i should do all that before trying to hunt stuff down. Gotta rule out the simple stuff first.

And no...i have NOT squirted the CV joints...although i ordered that needle nozzle thingy. Honestly....they havent made a single peep for three days now....and the last time they made a sound...was in the rain. Im almost thinking this might be an e-brake thing....

Does the e-brake run to the right rear wheel?
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tvissoc
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Post by tvissoc » Tue May 01, 2007 9:26 am

I've had similar issues with my XR in the past. These four things made progressively significant difference.

1. Get NEW PLUGS and WIRES! No fancy platnum crap. Autolite 764. If you've not done a cap and rotor in a while, go ahead and do that.

2. After the above tuneup, unplug the knock sensor. Take it for a spin and listen for pinging under load.

3. Throttle position sensor. I had other symptoms that required me replacing it, but it also affected full throttle response.

4. I also had to replace my fuel pump at one point when it seized up. After the new pump install, almost all of my full throttle hesitation was gone.

Hope that helps.

Tony
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John Brennan
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Post by John Brennan » Tue May 01, 2007 10:34 am

The VAM can be associated with symptoms like these also, especially if there are wiring problems. If there's another one nearby, try swapping it out an seeing if it still happens. But check all your wiring.
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John R. Rowlands
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Only stumbles at close o full throttle....

Post by John R. Rowlands » Tue May 01, 2007 10:51 am

Togglehead,

Like Tony says. Plus you are probably reaching at lease 5000RPMs in 1st and 2nd, which would lead me to believe that you may not be getting full ignition advance. Check your PIP signal and the TFI! Also wouldn't hurt to check your cam timing if it doesn't idle right. Run KOER.

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Post by Maurice S » Tue May 01, 2007 11:18 am

Another thing you may want to check for is VAM to turbo inlet hose condition as it may be collapsing under full throttle...if it appear weak or in your case with the mods, unreinforced (the factory hose had a wound springlike metal to keep it open) bend a wire hanger into a "W" and force it into the hose...make SURE it's a tight fit as you dont want it getting sucked into the compressor...take it out and see if it stops...if so get a proper strong hose to replace.
85 XR '" Lightly Street Massaged"

Togglehead
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Post by Togglehead » Tue May 01, 2007 2:08 pm

John...actually i dont think i am hitting 5 grand....but it might be around there. If i floor it from the bottom of the RPM band up....it wont start bucking until i get up there....but im not entirely sure at what exact RPM...i'll test today.

Car idles perfectly.

PIP signal and TFI. Things to read up on...as i dont know what they do...

KOER?

Maurice...that i DID check, and the original stuff is in there..and its NOT collapsing. I can barely squeeze it with my hand.
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Post by Togglehead » Tue May 01, 2007 9:21 pm

The first of several stumbles comes btw 3500-3800 RPMS invariably.
1985 944
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Reno3133
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Post by Reno3133 » Mon Jun 04, 2007 3:26 pm

Have you fixed this problem?

I started having this EXACT issue on the way to carlisle. So i'm gonna take the advice was given and see what happens.

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Post by DSPXR4ti » Mon Jun 04, 2007 8:00 pm

Have you try to replace the MAP sensor ( BPS) I had one go bad and could not get the car to rev. pass 3500 rpms replace it and it went past 7000 rpms, let us know how it go's.

Ben DSP XR4ti

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Post by Rocky Leitch » Tue Jun 05, 2007 12:39 am

Togglehead, I have a similar issue with
Karmann. But her idle got out of wack.
We took her on a road cruse, let her sit for a day,
got in to drive and the idle was all messed up. Steve
did something to her and this stumble is not in our face.
I remember telling him the idle was feeling (like in your foot
feel) off in cycle. We too need to replace the simple things.
Bottom line it happens in axt as well as mxt.. that's next on
the to do list.
Keep us posted, please.


Rocky
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Post by Reno3133 » Tue Jun 05, 2007 8:37 am

I changed the spark plugs and wires and it solved my 3500-3800 studdering issue. Thank you.

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Post by worked_xr » Tue Jun 05, 2007 4:50 pm

I have a similar issue but I noticed it only does it when the gas tank gets below half full. After doing a bit of research, apparently this is a common indicator of a bad in-tank fuel pump. So go fill your tank to absolutely full and see if you have the same problem, then see if it gets worse as the tank gets lower. If so, it may be time for a new fuel pump.

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