Quick vacuum question
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Melting Slicks
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From: What did the 5 fingers say to the face? SLAP!!
Quick vacuum question
Having just installed the SuperRam, my '86 runs like a turd. Anything over half throttle and it starts sputtering. When the motor is cold it's not as bad. Thinking it might be a vacuum leak I put a vacuum gauge on it. It holds rock steady at 14 1/2" of vacuum. The only variance is when the idle changes slightly. Then it moves between 14 and 15" slowly with the idle. Wouldn't the needle be bouncing around if I had a vacuum leak? Or am I just getting too excited at the prospect of ruling out the famous SR vacuum leaks?
On another note, I had a mechanic ask me if my TV cable was out of adjustment. He said something about it "loading up". He didn't really seem like the sharpest tool in the shed, but my cable IS out of adjustment due to having the wrong throttle bracket installed. Anyone ever heard of this?
Thanks
[Modified by flyersfan1088, 8:37 PM 5/11/2004]
On another note, I had a mechanic ask me if my TV cable was out of adjustment. He said something about it "loading up". He didn't really seem like the sharpest tool in the shed, but my cable IS out of adjustment due to having the wrong throttle bracket installed. Anyone ever heard of this?
Thanks
[Modified by flyersfan1088, 8:37 PM 5/11/2004]
Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
Re: Quick vacuum question (flyersfan1088)
Someone just posted about the dramatic improvement in his car's performance once he properly adjusted the TV cable.
I don't have any personal experience on how the car performs with the cable out of adjustment, I always adjust mine before driving the car.
14-1/2 vacuum reading: Depends on the cam you're running. If it's anywhere near 220 @ .050, then that's a good number. If you're running a stock cam, then it's too low.
Take a vacuum reading with the trans in gear (that is if you have an auto). Set the emergency brake and chock the wheels if you're doing it alone; that's how I do it when no one's around.
You can use an unlit propane torch to search for any sign of a leak. The idle speed will change if the propane gets sucked into a leaking spot. I just use my garden hose and plenty of water.
Forgetting to plug a vacuum port, like the one under the TB can create a lean condition which may not show up as a flucuating vacuum gauge. The reading would most likely be steady, but lower than it would otherwise be if the port was blocked off.
What FP and TPS setting are you running now?
You may need to check and/or raise your fuel pressure if the vacuum continues to check okay. You also may need to hook up a fuel pressure gauge, tape it to the windshield and see if the pressure holds when the engine reaches the point where it has sputtered on you.
Jake
I don't have any personal experience on how the car performs with the cable out of adjustment, I always adjust mine before driving the car.
14-1/2 vacuum reading: Depends on the cam you're running. If it's anywhere near 220 @ .050, then that's a good number. If you're running a stock cam, then it's too low.
Take a vacuum reading with the trans in gear (that is if you have an auto). Set the emergency brake and chock the wheels if you're doing it alone; that's how I do it when no one's around.
You can use an unlit propane torch to search for any sign of a leak. The idle speed will change if the propane gets sucked into a leaking spot. I just use my garden hose and plenty of water.
Forgetting to plug a vacuum port, like the one under the TB can create a lean condition which may not show up as a flucuating vacuum gauge. The reading would most likely be steady, but lower than it would otherwise be if the port was blocked off.
What FP and TPS setting are you running now?
You may need to check and/or raise your fuel pressure if the vacuum continues to check okay. You also may need to hook up a fuel pressure gauge, tape it to the windshield and see if the pressure holds when the engine reaches the point where it has sputtered on you.
Jake
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Melting Slicks
Joined: Jan 2003
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From: What did the 5 fingers say to the face? SLAP!!
Re: Quick vacuum question (JAKE)
14-1/2 vacuum reading: Depends on the cam you're running. If it's anywhere near 220 @ .050, then that's a good number. If you're running a stock cam, then it's too low.
What FP and TPS setting are you running now?
You may need to check and/or raise your fuel pressure if the vacuum continues to check okay. You also may need to hook up a fuel pressure gauge, tape it to the windshield and see if the pressure holds when the engine reaches the point where it has sputtered on you.
Jake
Fuel pressure is 45 psi
TPS hasn't been set. I won't bother with that until the new throttle bracket comes. With the stock bracket it won't fully open the butterflies under WOT, so I know the TPS isn't reading WOT.
Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Re: Quick vacuum question (flyersfan1088)
[SNIP] TPS hasn't been set. I won't bother with that until the new throttle bracket comes. With the stock bracket it won't fully open the butterflies under WOT, so I know the TPS isn't reading WOT.
[/SNIP]
The TPS is critical to proper performance of the engine.
That's how the ECM knows the throttle body butterfly position and rate. Without it, the ECM has no way of knowing what you're doing with your right foot. So the ECM doesn't know the correct fuel and timing to use.
You can forget about properly tuning the engine until you set the TPS correctly.
Your vaccum reading is about right too.
Jake
[Modified by JAKE, 11:16 PM 5/12/2004]
[/SNIP]
The TPS is critical to proper performance of the engine.
That's how the ECM knows the throttle body butterfly position and rate. Without it, the ECM has no way of knowing what you're doing with your right foot. So the ECM doesn't know the correct fuel and timing to use.
You can forget about properly tuning the engine until you set the TPS correctly.
Your vaccum reading is about right too.
Jake
[Modified by JAKE, 11:16 PM 5/12/2004]
Thread Starter
Melting Slicks
Joined: Jan 2003
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From: What did the 5 fingers say to the face? SLAP!!
Re: Quick vacuum question (JAKE)
[QUOTE
The TPS is critical to proper performance of the engine.
That's how the ECM knows the throttle body butterfly position and rate. Without it, the ECM has no way of knowing what you're doing with your right foot. So the ECM doesn't know the correct fuel and timing to use.
You can forget about properly tuning the engine until you set the TPS correctly.
Your vaccum reading is about right too.
Jake
[Modified by JAKE, 11:16 PM 5/12/2004][/QUOTE]
I hadn't touched the TPS, so I didn't think it could be that far out of whack. But now I'm curious about the whole not going to wide open thing. I noticed the TV cable keeps the butterflies from fully opening. If I put enough slack in the TV cable for the throttle body to fully open, the car shifts like a slushbox. I wonder how many other cars don't open the butterflies fully? I wonder how many people have even checked?
By the way, I don't have any vacuum leaks. The sputtering was a spark plug with a small crack in it. Must have done that when I was pulling the boot off.
The TPS is critical to proper performance of the engine.
That's how the ECM knows the throttle body butterfly position and rate. Without it, the ECM has no way of knowing what you're doing with your right foot. So the ECM doesn't know the correct fuel and timing to use.
You can forget about properly tuning the engine until you set the TPS correctly.
Your vaccum reading is about right too.
Jake
[Modified by JAKE, 11:16 PM 5/12/2004][/QUOTE]
I hadn't touched the TPS, so I didn't think it could be that far out of whack. But now I'm curious about the whole not going to wide open thing. I noticed the TV cable keeps the butterflies from fully opening. If I put enough slack in the TV cable for the throttle body to fully open, the car shifts like a slushbox. I wonder how many other cars don't open the butterflies fully? I wonder how many people have even checked?
By the way, I don't have any vacuum leaks. The sputtering was a spark plug with a small crack in it. Must have done that when I was pulling the boot off.
