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Guest Message by DevFuse
 

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Really Freaking Annoying Drivability Problem-Cause found!


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16 replies to this topic

#1 Snowman

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Posted 03 November 2003 - 09:16 PM

I have posted about this in the past, but still have not found the answer.

The problem: My car absolutely refuses to go over about 75 (actually around 80 because my tires are slightly oversized). I can get up to 75 without even opening the secondary on the weber, but if I mash it to the floor, it doesn't go any faster. I don't think it's a dragging U-joint or anything because shifting down to 4th doesn't seem to help. Also, the fuel economy has not been great recently. This problem basically appeared out of nowhere. All of a sudden my car just wouldn't go as fast and the fuel economy dropped off.

What I have tried:

-weber carb: gets up to 75 much faster but still won't go above it

-cap, rotor and plugs, inspected disty: no ascertainable difference

-set timing to 14 degrees BTDC: no ascertainable difference

-hollowed out cat thinking it was fried from previous rich running condition: again, it gets up to 75 a bit faster, but still won't go above it

-re tensioned timing belts: runs smoother, better drivability in general, still won't go above 75

What I think could be the problem:

-Do vacuum advance modules go bad? Maybe mine has a leak in the diaphragm and is no longer giving full advance. I have a disty from an automatic-tranny engine that I could steal the module from if it's the same.

-Something is seriously fubar-ed internally
Is it possible that the extended periods of high-speed driving I had this summer messed somthing up? But this problem did not appear immediately. It showed up after about 1000 miles more, which was driven at normal speeds. However, if this is the case, I do have my old engine still around which could be resealed and put back in if the current one is messed up beyond help.

Any suggestions would be great. I am starting to get angry with my car.

#2 Forkspear

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Posted 03 November 2003 - 09:38 PM

Did you gut the cat in the Y pipe?

#3 Snowman

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Posted 03 November 2003 - 09:50 PM

yes

#4 Setright

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Posted 04 November 2003 - 02:01 AM

If it can get up to 75 faster, then surely it has more power, and should be able to pass 75. Unless it's an electric thing, like the ghost of a cruise control??

#5 Snowman

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Posted 04 November 2003 - 02:44 AM

I should have mentioned this in the first post. I sort of hinted at it with the shifting-down thing, but didn't actually say it.

It would appear that it is RPM-related. In gears 1-3, it really doesn't take a whole lot of power to turn over 4000 revs, but in higher gears with greater load, it takes more power, and for some reason, the engine just isn't making power above that speed, which must be around 3500 rpm to do 75 in 5th gear. That's why I would think it is something like the vacuum advance, which is supposed to increase as more air is sucked into the engine. I'm just not sure how to test this, or if other things could cause this problem. Could the coil be weak, causing the spark to get blown out in this situation?

#6 Meeky Moose

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Posted 04 November 2003 - 08:04 AM

maybe the speedo is stuck.. got something wrong with it when it hits 75??

#7 Meeky Moose

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Posted 04 November 2003 - 09:25 AM

heh my lifted webered hatch got 26mpg in 4low drvin from jersey to virginia, lol


i did notice it gettin worse after i figured out the futzed linkage and got it into 2wd..

even tho the speedo says i'm goin 10mph slower than what i really am. i can still peg it at 85.. which is about 95 really..

so somethings wrong with yur guy's soobs fer sure.. i did notice hookin up the emissions tubing, it ran worse.. so i left it vented.. which it is a suction anyways, so not really polluting..

#8 calebz

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Posted 04 November 2003 - 09:50 AM

Originally posted by Meeky Moose
heh my lifted webered hatch got 26mpg in 4low drvin from jersey to virginia, lol


i did notice it gettin worse after i figured out the futzed linkage and got it into 2wd..

even tho the speedo says i'm goin 10mph slower than what i really am. i can still peg it at 85.. which is about 95 really..

so somethings wrong with yur guy's soobs fer sure.. i did notice hookin up the emissions tubing, it ran worse.. so i left it vented.. which it is a suction anyways, so not really polluting..



Meeky, they have different cars than you. Different engine, different rules

#9 Meeky Moose

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Posted 04 November 2003 - 09:53 AM

yeah.....:banghead:

#10 northguy

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Posted 04 November 2003 - 09:56 AM

Kelly, I'm not much of a whiz on engine dynamics, but it sounds like a distributor problem/ electrical, although I doubt it has to do with your coil. I'll ask the local pro where I work and get back with you.

#11 Guest_taprackready_*

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Posted 04 November 2003 - 10:57 AM

Originally posted by Snowman
That's why I would think it is something like the vacuum advance, which is supposed to increase as more air is sucked into the engine. I'm just not sure how to test this, or if other things could cause this problem. Could the coil be weak, causing the spark to get blown out in this situation?



Basically, in all vehicles with a vacuum module and weights and springs in the distributor your advance is maxed out to the most it will be at about 2800 RPM. Your vacuum advance does not continue to advance timing all the way up to 6000. The vacuum in your engine drops off at higher RPMS. You can verify this with a handheld vacuum gauge hooked to the manifold. You can with no harm to the engine unhook the vacuum adance and cap the line in the carb or manifold and drive it to check and see what effect it has on driveability.

Essentially, vacuum advance is for part throttle, just off Idle, driveability and economy.

Bill

#12 viceversa

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Posted 04 November 2003 - 12:35 PM

Did 80's carbed models come with an O2 sensor? I know it can be a real acceleration/mpg killer. Same for EGR valve.
Probably not the case here. The fact that it runs rich should be an indication of something.

#13 Snowman

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Posted 04 November 2003 - 12:57 PM

viceversa: No, mine doesn't have an O2 sensor, and the rich condition existed with the previous Hitachi carb (which was just worn out), not the weber.

taprackready: It's my understanding that the ported vacuum source the disty has will actually pull more vacuum at higher rpms, unlike manifold vacuum, which drops off.

I tried sucking on the line going to the disty with the engine idling, and the rpm increased a little, but not nearly as much as if I were to just turn the disty and advance the timing a few degrees.

Could the disty bushings be worn out, causing it to move around at certain speeds, giving innacurate timing?

#14 viceversa

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Posted 04 November 2003 - 01:22 PM

Maybe you could try asking on alt.autos.subaru? rec.autos.tech is another good one.

#15 northguy

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Posted 04 November 2003 - 01:45 PM

Snowman, I asked the local pro here, and as he hasn't read the entire thread -he only got the boiled down version I had a couple of minutes to relate - he suggests that it sounds like carburation problems; maybe an air leak around the adaptor plate or incorrect alignment of bolt holes? His suggestion - pose the situation to redline. Hope that helps.
Matt

#16 MilesFox

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Posted 04 November 2003 - 02:49 PM

having oversize tires, the speedo might read 75, but the car is actually going 5-10mph faster

#17 Snowman

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Posted 04 November 2003 - 06:09 PM

The answer: Yes, it's fubar-ed internally. A compression test today indicated that the rings on the #1 piston are bad. All the others consistently read 150, whereas that one was 75 dry and 145 with oil in the cylinder.

I am not in despair, however. Next semester I am taking an engines lab at UAA, so I will bring in my old 140k engine, totally rebuild it and maybe hop it up a bit, then swap it in. My current motor will last that long, since the only thing it won't do is go fast.

If you have any suggestions on where to buy a rebuild kit from or what modifications can be done during the rebuild process, please see my other post.




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