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Old 03-02-2011, 07:04 PM   #1 (permalink)
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Default Engine Revs flaten at 2800 rpm

I think I'm gonna lose my mind.... too late, that left years ago.

Anyways my Sami is running like I have a malfunctioning rev limiter which I can't find. What I mean by that is, if I step on the gas hard the rpm/rev just flatten, and the car bogs down. It drives around town at 20-40mph just fine. It's just when you want to take it on the highway, or anywhere you might need a little more power, it sounds like a 747 taking off and acts like a limp noodle. I can't get up a decent hill to save my life, unless I want to do it at 15mph in 2nd gear, and that's just a normal road with an incline, not even a steep mountain road.

And this after all the TLC I given it... bummer. We've replaced the O2 sensor, every check valve, etc. rebuilt the carb, new muffler etc. We even passed California emmsions like it was a new car. Problem with that is that it never has to go above 35mph to pass the test.

Even repleaced the catalytic converter, although I'll admit to canibalizing it from a dead dodge neon which had it new for only three weeks before it died of catastrophic transmission failure. I don't know if there is such a thing as a converter being too large for a car.

I've also adjusted the valves, three times at this point, but I'm still getting a ton of slap/clatter, and it seems to be worse after a longer trip. It also sounds like my exhaust is ratteling, only it's totally tight and I can't even budge it. I couldn't really care about the noise, if she would just go.

Anyway, it feels like I'm driving around with a potato in my tailpipe, and I promise there isn't one there.

Much pouting...


H.E.L.P. Please
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Old 03-02-2011, 11:45 PM   #2 (permalink)
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This might be a silly question and I don't claim to be a great mechanic, but have you checked the lobes of the camshaft? If you're adjusting the rockers and still getting the tapping noise and it has no power you might want to take a caliper after it! Of course there are a lot of other guys here that know a lot more about these things than I do, so just an idea...
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Old 03-03-2011, 08:34 AM   #3 (permalink)
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My first guess would be something is not right with the carb secondary vacuum system, or, fuel enrichment circuit. The bogging when you mat the throttle usually means the fuel/air mix is out of whack. How's your fuel pump? Fuel filter new? My old Toyota PU wouldn't climb the mountain passes in high gear, when the filter started to get plugged. I think the problem is fuel system related. Did this come on gradually, or, all of a sudden?

My experience with cam lob wear is that it usually shows up on one cylinder first. You get one cylinder that has an off, "flat", sound when firing as a lobe wears and things get worse from there. You might check the screws that hold the rocker assembly to the head. That might explain why your lash adjustment wont stay tight, but, you would also have a loss of oil flow to the rockers and low oil pressure. Your cam will be toast in a hurry, if that's what's going on. I've had engines with both flat cams and skipped timing. They will still rev just fine. They just don't have any high end power, or, sound right.

I don't think cat size would matter. Since you passed emissions, I would think it unlikely that it's plugged up already. Maybe, it fell apart inside and is causing restriction? I know pulling the converter is a PITA, but, it might be worth it to eliminate it as a cause of trouble, after you explore the other possible causes.

Exhaust noise could be just a bad donut between the manifold and the head pipe.

Hey, I'm just guessing here on what might be happening. Best of luck to you in your trouble shooting.

Last edited by Azelgin; 03-03-2011 at 08:39 AM.
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Old 03-03-2011, 12:24 PM   #4 (permalink)
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I got the car with a rebuilt engine, as far as I am aware the compression is fine.

As for the fuel system... yeah that's a bit of a trick. My mechanical won't work due to cam wear, so it's been replaced with a low pressure electronic, coming off of that is a fuel filter with a return nozzle/spigot, to release the pressure to the tank, and then it's going into a fuel pressure regulator which has been turned down to 1 psi so it doesn't overwhelm the carb float. Now normally I would have thought that no car can run 1 psi, but it behaves the same whether its 1psi or 7psi. I stomp on the gas and BLAAAAHHHH.

Though I have not checked the screws going to the rocker assembly. I will do that. Timing is dead on though. Mind you it revs fine in the driveway, but not in motion.

Here's another question... What if I straight pipe the cat for now, I wont have to do the emissions thing for 18 months yet, how will that affect the engine and gas milaege, not that that's great anyway.

I replaced the donut between the minifold and the head pipe, twice.

And I'm perfectly fine with your guesses... so keep 'em coming.

P.S. I did get the heater valve unstuck, your lube trick worked great. Of course I still have no heat, but the valve works.
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Old 03-03-2011, 12:26 PM   #5 (permalink)
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Quote:
Originally Posted by Dwcarr1 View Post
This might be a silly question and I don't claim to be a great mechanic, but have you checked the lobes of the camshaft? If you're adjusting the rockers and still getting the tapping noise and it has no power you might want to take a caliper after it! Of course there are a lot of other guys here that know a lot more about these things than I do, so just an idea...
Does that mean I have to take the whole head off?
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Old 03-03-2011, 12:39 PM   #6 (permalink)
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The 747 sound is probably a stopped up cat convertor. remove your o2 sensor and try it if it improves the cat is stopped up.
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Old 03-03-2011, 06:53 PM   #7 (permalink)
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Quote:
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The 747 sound is probably a stopped up cat convertor. remove your o2 sensor and try it if it improves the cat is stopped up.
Should I just disconnect it, or actually take it out so that there is a hole in the manifold (won't it sputter?)?
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Old 03-03-2011, 08:30 PM   #8 (permalink)
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Quote:
Here's another question... What if I straight pipe the cat for now, I wont have to do the emissions thing for 18 months yet, how will that affect the engine and gas milaege, not that that's great anyway.
I'd give it a try. Shouldn't make mileage any worse, as there are no sensors downstream of the cat.
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Does that mean I have to take the whole head off?
No. You can use a dial indicator to measure lift on the rockers. If they are all the same, (intake compared to intake, exhaust compared to exhaust)the cam is fine. Since you say the mech. fuel pump wont work because the cam is worn, you could have a cam that's going flat. I know a skipped timing belt/chain will register low intake manifold vacuum, but, I'm not sure if a worn cam will, too.
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Should I just disconnect it, or actually take it out so that there is a hole in the manifold (won't it sputter?)?
I think he's saying to pull it out and see if the extra hole improves performance. I think removing it might confuse the smog system and you'll be dealing with more symptoms to complicate the issue.

Last edited by Azelgin; 03-03-2011 at 08:39 PM.
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Old 03-03-2011, 08:50 PM   #9 (permalink)
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Quote:
Originally Posted by Azelgin View Post
No. You can use a dial indicator to measure lift on the rockers. If they are all the same, (intake compared to intake, exhaust compared to exhaust)the cam is fine.
Okay... that's a bit outside of what i know... not that I'm not willing to do it, but would you mind pointing me to the pages in the FSM which might guide me through such a measuring procedure. I'm real good with directions. The good thing is I have another head.

Thanks again
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Old 03-03-2011, 09:10 PM   #10 (permalink)
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Quote:
Originally Posted by Evesgird View Post
Okay... that's a bit outside of what i know... not that I'm not willing to do it, but would you mind pointing me to the pages in the FSM which might guide me through such a measuring procedure. I'm real good with directions. The good thing is I have another head.

Thanks again
I'm not even sure they would have that method in there. They probably get into things a little deeper by pulling the rocker assembly and measureing lift directly off the cam. It's more of a backyard, shade tree, okie type thing. You could set up a cheap (Harbor Freight) clamp on type dial indicator over the same point in each rocker, crank the engine over and record the lift you have on each one. A bad cam is not going to wear out evenly, so, there's going to be noticeable deviation in lift from one to the other, if, it is indeed getting flat. I use my cheapo dial indicator for all kinds of stuff I never thought of measuring.
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