Lacking power from 0-20(1st gear) LT1 need help
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5.0 and 5.7 Discussion, Lacking power from 0-20(1st gear) LT1 need help in Cadillac Engine Technical Discussion; The thing is that ever since i replaced my intake manifold gasket there was a slight power loss in the ...
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    Lacking power from 0-20(1st gear) LT1 need help

    The thing is that ever since i replaced my intake manifold gasket there was a slight power loss in the 1st gear when it shifts to 2nd gear teh engine roars and it just feels like there is more power there but when I step on it from a stop It does NOT hesitate or anything bad like that but the tires don't spin at all it'll just start going forward.

    I was thinking of replacing my egr valve but I took it off today and it seems fine the valve goes in and out pretty easily although its a little slow to go back out I think its normal.

    In park and neutral the throttle response is great no stumble or hesitation.

    How would I know if my 1st gear is messed up causing the less power to be transferred to the wheel? I searched and there were a coupel mentions of the 1st gear being bad sometimes causing power problems.

    i do have a slight buck/hard shift from 1-2 gear its hardly noticeable but its there.

    I'm sure the hoses are routed correctly the fuel filter and wires/plugs have been replaced my car has 53000 miles. 02 sensors replaced last year

    Is it possible for the cats to be plugged with such low mileage? the previous owner drove it daily but only for about a 10 mile drive so she put very few miles on the car and I drive it only about 3 times a week average 150 miles total a week.Is there any other way to know if they're plugged besides the cat rattling?

    Why would a leaking exhaust cause a power loss I've read this a couple times but dont understand why?

    One of my exhaust bolts broke that was also attached to a bracket going to the back of the alternator I wonder if this has anything to do with it.

    I'll probably replace my egr valve but I would prefer not to replace anything that is still working. An autozone guy tested the valve 2 weeks ago and it still held suction so can it still be defective?

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    The EGR valve won't cause a problem like this, so I would leave it alone. Unless it has some large vacuum leak, it is likely fine.

    Do you have anyway to monitor short term fuel trim? It strikes me as you have a vacuum leak. Can you check idle vacuum? There is enough bandwidth to make it idle ok and drive, but yet still have short/long term fuel trim way off.

    The EGR is a negative backpressure EGR. So possibly it is opening too early. Plug it off and drive, see if there is much change. I wouldn't bet there is, but good to check.

    1. Check EGR by plugging it off and don't use it.
    2. Check for idle vacuum, is it low? If the leak is under the intake you won't hear it, and the LT1's ECM can compensate, but can't respond well to changes like accelerating.
    3. You might check PCV and also, try to see if you are seeing a vacuum in the PCV system. Try to plug off the air into the PCV and hook a gauge to it. If you are seeing vacuum, it might be a sign. Also, if it is leaking under the intake, you may (not sure how much baffling there is) see some oil loss and maybe some oil smoke. The spark plugs would see it. Again, longer shot here, this is hard to detect.

    I have seen cats melt and be plugged that way, but often that is only due to abuse with lean mixtures. If you are stock and haven't messed with it, I doubt it. plugged cats typically show up as rich plugs. But the ECM will be compensating with short/long term fuel trim.

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    what do you mean by


    Do you have anyway to monitor short term fuel trim? It strikes me as you have a vacuum leak. Can you check idle vacuum? There is enough bandwidth to make it idle ok and drive, but yet still have short/long term fuel trim way off.

    what do i need to check the vacuum and where could i hook up a gauge I believe I have a gauge around in my garage i can use.

    any idea of what the vacuum should be?

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    I'll check mine, but I would expect it to be fairly high, like 20 inches or so. If you are seeing much lower, might be a problem.

    You can hook it up in place of the Optispark vent vacuum source on the drivers side of the intake in the middle. Do it direct to the manifold.

    I'll check mine tonight and let you know what mine does for a comparo. Anyone else with a 94-96 LT1 can give some idle vacuum readings for a good comparisson?

    Short term fuel trim is the new name for the Integrator (look for my posts for it on the 4.9L forums and Deville FWD). The Long Term Fuel trim is the Block Learn value.

    Basically the STFT is the digital A/D representation of the O2 sensor output, digitially interpreted. So it is a combo of O2 cross counts and O2 voltage in an value the computer understands, 0-255. The LTFT is the same type reading, but it is the offset for the STFT. So if the STFT is running an average of say 155 (lean adding fuel) all the time, (leaking intake gasket, etc) the LTFTwill correct for it by coming up to 155 or so (lean adding fuel), and the STFT should return back to 128 average. These numbers fluxuate, so it isn't like you do this to one and the other does this, they vary, so you must look at them and do some good averaging in your head on where you see it the most.

    So this will give you a clue on if there is leak or not.

    It is normal to see the STFT go high under acceleration (150-160) and low under decel (80-90), as the ECM struggles to compensate. As it gets ahold of the corrections, it will start to return to 128.

    The one that tells the most of the LTFT, as it shows what is being corrected, if all is being corrected, the STFT should look close to 128.

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    thanks i appreciate the help i am going to buy a vacuum gauge or something today ill check my vacuum later or tomorrow.

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    well i have narrowed my problem down to a leaking exhaust on the passenger side i can hear a lot of air being sucked in and the front passenger side bolt is broken so im going to get this fixed soon and post the results of my cars performance short after.

    the cats arent plugged

    ive been busy lately so not too much time to fix the car at the moment

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    If I measure vacuum at the Optispark vent vacuum line I get 15 psi. Seems low for this low of cam engine. I will try to get a better place to measure.

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    Quote Originally Posted by N0DIH
    If I measure vacuum at the Optispark vent vacuum line I get 15 psi. Seems low for this low of cam engine. I will try to get a better place to measure.
    ive been so busy i havent had a chance to buyt he vacuum gauge but since im probably going to spend about 100 on the broken exhaust bolt im going to do that first and if the power comes back im leaving it as is.

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    Wink Re: Lacking power from 0-20(1st gear) LT1 need help

    Quote Originally Posted by ocjmakaveli
    ive been so busy i havent had a chance to buyt he vacuum gauge but since im probably going to spend about 100 on the broken exhaust bolt im going to do that first and if the power comes back im leaving it as is.
    Can you get to a Pep Boys or other automotive shop? They usually will scan your engine (electronically) with a SnapOn tool or similar for very little money. That way they can tell you if you have a vacuum leak or if your MAP sensor reads high, you may have clogged cats.

    Most likely, you have a vacuum leak caused by the bad manifold bolt on that particular side, but still, I don't think that would affect your 0-20 so much.

    Maybe your trans is going on the 1-2. Are you getting any check engine lights?

    Brian 96 Impala SS / 96 FWB

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    Silly question, it isn't starting in 2nd gear is it? I think I read on the Impala sites that GM disabled the 2nd gear start, but my 94 FWB has it still (V4P might have a different program that kept it).

    With 3.42's and 2nd gear start the car would respond like a Powerglide car with 3.42's.

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    Quote Originally Posted by N0DIH
    Silly question, it isn't starting in 2nd gear is it? I think I read on the Impala sites that GM disabled the 2nd gear start, but my 94 FWB has it still (V4P might have a different program that kept it).

    With 3.42's and 2nd gear start the car would respond like a Powerglide car with 3.42's.
    how would i know what gear its starting out in?

    now that i think about it that makes sense because it does feel as if it starts in 2nd gear because the engine sounds fine but its like the power isnt transferred as well and its lugs forward. then again this might be because of the engine not giving the power output

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    1st, drop to 1st gear on shifter, any change?

    2nd, leave in first gear and step on it, the rev it and see if it screaming at 40 mph or can go all the way up to 70 mph. You won't be able to do 70 mph in 1st. But easily in 2nd.

    Note carefully the shifting during normal driving too, mine is somewhat harsh (firm, hard, a shift that means business) in shifts (V4P car), I don't know if all FWB/Impalas/RMs are.

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    Question Re: Lacking power from 0-20(1st gear) LT1 need help

    Quote Originally Posted by N0DIH
    1st, drop to 1st gear on shifter, any change?

    2nd, leave in first gear and step on it, the rev it and see if it screaming at 40 mph or can go all the way up to 70 mph. You won't be able to do 70 mph in 1st. But easily in 2nd.

    Note carefully the shifting during normal driving too, mine is somewhat harsh (firm, hard, a shift that means business) in shifts (V4P car), I don't know if all FWB/Impalas/RMs are.
    Manually shifting it and starting in 1st is a great idea to check that!

    But, manually shifting should not raise shift pressures (if I'm understanding you correctly) and it should shift as hard/soft as you would feel normally.

    But, again, but if you see a real difference manually shifting it through the gears and you see that it IS starting out in 2nd when you select D, then what is causing that????

    Brian 96 Impala SS / 96 FWB

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    It does start in first i checked it today and besides feeling the same when i manually have it in 1st i also feel the 1-2 shift which is a little harder than it used to be.


    nowadays if i ride the gas through the 1-2 shift it shifts harsh this started last summer when i was drag racing on an in ramp to the expressway not too harsh but more noticeable than when new

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    Re: Lacking power from 0-20(1st gear) LT1 need help

    You don't have a stuck PCV valve or something do you? It would make it doggy until you get going. The ECM would be showing a way off long term fuel correction, and once long term gets set, short term should get back around 128. But it will be fluxating much more wildly than with no vacuum leak.

    Sounds like something got put together wrong, connected wrong, or is leaking.

    Fuel pressure regulator do anything like this? (I can't imagine it would, but...)

    I haven't read up on the flow charts on the 4L60E, but on the THM350/400 manual shift does increase fluid pressures across the board. The flow circuits change a but.

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