Questions about loss of low end power.
03-13-2006, 07:56 PM
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Questions about loss of low end power. Hi everyone,
Recently my Z has been acting up on me. I am unable to spin the tires from a STOP. Bad sign huh..
I am an A4, 1997 Z28, and only seem to "get up and go" after ~2000-2500RPM. I think I have narrowed down my problem to this list:
Injectors stuck
Fuel Filter
O2 Sensor(s)
EGR Valve Malfunction
Coil
ICM
Opti (hear some people have a reverse of the usual loss of top end power when their opti is crapping out)
TPS
PCV Valve Stuck
All together this adds up to around ~$500 in parts if I want to fix everything and do installation myself, so I was wondering if anyone else had any insight or simliar experiences instead of me playing process of elimination. The car has 90k on the clock and has never had the opti replaced to my knowledge. Could their be something else at work against my car? Belts? ANYTHING? Lol, any help would be great guys.
P.S. There are no codes being thrown at all, not even blinking ones.
Recently my Z has been acting up on me. I am unable to spin the tires from a STOP. Bad sign huh..
I am an A4, 1997 Z28, and only seem to "get up and go" after ~2000-2500RPM. I think I have narrowed down my problem to this list:
Injectors stuck
Fuel Filter
O2 Sensor(s)
EGR Valve Malfunction
Coil
ICM
Opti (hear some people have a reverse of the usual loss of top end power when their opti is crapping out)
TPS
PCV Valve Stuck
All together this adds up to around ~$500 in parts if I want to fix everything and do installation myself, so I was wondering if anyone else had any insight or simliar experiences instead of me playing process of elimination. The car has 90k on the clock and has never had the opti replaced to my knowledge. Could their be something else at work against my car? Belts? ANYTHING? Lol, any help would be great guys.
P.S. There are no codes being thrown at all, not even blinking ones.
03-13-2006, 08:38 PM
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I'm thinking sensors because people have told me that their O2s caused similar conditions without throwing a code :-/ I plan on changing the fuel filter tomorrow, but when I got it today, the guy at the register kind of smartassingly (new word?) said it was probably the fuel pump. Would the fuel pump cause this issue? I had the wires/plugs changed about 3 months ago, so they should be fine. Where can I check for a vaccum leak?
03-13-2006, 08:44 PM
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A fuel pump could yes. When you pull your filter, blow through it to determine how clogged it is. If it was very clogged and it was your stock one, a fuel pump is a possibility. Do you run the car out of gas often? Like take it down so it has half a gallon in it?
O2s will usually cause horrible gas mileage before anything else. How is your mileage? Did you have a shop scan your computer? It can set codes, but not turn on the SES light. If your O2s are malfunctioning, a scanner will reveal this on an OBD2 car.
It's unlikely it's the opti. Signs of optispark failure usually include horrible misfiring upon acceleration. At 90k yours should still be okay, unless you got some sort of liquid on it.
Grab a can of carb cleaner, turn on the car, and spray your vacuum lines. If you see bubbles coming out of one, you've found your leak.
O2s will usually cause horrible gas mileage before anything else. How is your mileage? Did you have a shop scan your computer? It can set codes, but not turn on the SES light. If your O2s are malfunctioning, a scanner will reveal this on an OBD2 car.
It's unlikely it's the opti. Signs of optispark failure usually include horrible misfiring upon acceleration. At 90k yours should still be okay, unless you got some sort of liquid on it.
Grab a can of carb cleaner, turn on the car, and spray your vacuum lines. If you see bubbles coming out of one, you've found your leak.
03-13-2006, 09:01 PM
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Thanks urban!
Where are the lines I should spray with cleaner? I was going to seafoam or whatever the TB to see if it would clear up the injectors in case they were bad. My milage isn't stellar but it isn't crappy either, I guess averagish since I've been doing more city driving since my last fill up. In the city I got about 15mpg which I dunno how good/bad that is. Will a Snap-On scanner be able to read the codes if they don't set off the light? One of my dads friends will be in the garage part of a station tomorrow and has one he could use. I'm just confused where to spray I guess..if you know of a write up/detailed way to do this that would be great. I'm just afraid of what it could be if it isn't a leak/filter/fuel pump.
Where are the lines I should spray with cleaner? I was going to seafoam or whatever the TB to see if it would clear up the injectors in case they were bad. My milage isn't stellar but it isn't crappy either, I guess averagish since I've been doing more city driving since my last fill up. In the city I got about 15mpg which I dunno how good/bad that is. Will a Snap-On scanner be able to read the codes if they don't set off the light? One of my dads friends will be in the garage part of a station tomorrow and has one he could use. I'm just confused where to spray I guess..if you know of a write up/detailed way to do this that would be great. I'm just afraid of what it could be if it isn't a leak/filter/fuel pump.
03-13-2006, 09:42 PM
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Here's where you'll find lots of diagrams and schematics for your car:
http://shbox.com/1/4th_gen_tech1.html
If you look through the component location views you'll find all of the vacuum lines.
http://shbox.com/1/4th_gen_tech1.html
If you look through the component location views you'll find all of the vacuum lines.
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03-13-2006, 09:46 PM
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Ah, I know about shoebox, I'm just confused where I spray exactly. I'm still a newbie to the LT1, so I don't know if I should spray it into the box, on the wires or what..I'm assuming on the wires since the cleaner will react..but maybe I'm wrong. Worst comes to worst I'll just ask my dads friend to do it since he's working on 350s before I was born and can hopefullly help diagnose the problem.
03-13-2006, 09:59 PM
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All I did to find my vacuum leak was I sprayed all around the vacuum check valve and as much of the hosing as I could see. The leak was immediately apparent, and now my dashboard vents work lol
You can also remove hoses from the vacuum check valve and use a vacuum tester on them.
Honestly I think your problem may be a fuel issue, or maybe a spark issue. Did you replace the coil at the same time as the plugs/wires? Have you replaced the ICM and done the cooling mod to it?
It's also possible there's nothing wrong with your car other than it needs a little maintenance. My '94 A4 car didn't spin the tires much off the line either depending on the pavement quality. Can you drive another LT1 for comparison? Maybe you could explain the lack of low end power better. Did it used to feel faster than you had a SUDDEN drop in performance, or was it a slow drop over time?
You can also remove hoses from the vacuum check valve and use a vacuum tester on them.
Honestly I think your problem may be a fuel issue, or maybe a spark issue. Did you replace the coil at the same time as the plugs/wires? Have you replaced the ICM and done the cooling mod to it?
It's also possible there's nothing wrong with your car other than it needs a little maintenance. My '94 A4 car didn't spin the tires much off the line either depending on the pavement quality. Can you drive another LT1 for comparison? Maybe you could explain the lack of low end power better. Did it used to feel faster than you had a SUDDEN drop in performance, or was it a slow drop over time?
03-13-2006, 10:55 PM
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Originally Posted by urbanhunter44
All I did to find my vacuum leak was I sprayed all around the vacuum check valve and as much of the hosing as I could see. The leak was immediately apparent, and now my dashboard vents work lol
You can also remove hoses from the vacuum check valve and use a vacuum tester on them.
Honestly I think your problem may be a fuel issue, or maybe a spark issue. Did you replace the coil at the same time as the plugs/wires? Have you replaced the ICM and done the cooling mod to it?
It's also possible there's nothing wrong with your car other than it needs a little maintenance. My '94 A4 car didn't spin the tires much off the line either depending on the pavement quality. Can you drive another LT1 for comparison? Maybe you could explain the lack of low end power better. Did it used to feel faster than you had a SUDDEN drop in performance, or was it a slow drop over time?
You can also remove hoses from the vacuum check valve and use a vacuum tester on them.
Honestly I think your problem may be a fuel issue, or maybe a spark issue. Did you replace the coil at the same time as the plugs/wires? Have you replaced the ICM and done the cooling mod to it?
It's also possible there's nothing wrong with your car other than it needs a little maintenance. My '94 A4 car didn't spin the tires much off the line either depending on the pavement quality. Can you drive another LT1 for comparison? Maybe you could explain the lack of low end power better. Did it used to feel faster than you had a SUDDEN drop in performance, or was it a slow drop over time?
03-14-2006, 12:36 AM
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Oh, and it never has burned serious rubber, but only recently have I tried to get it to. I also thought about clogged cat(s) but the car passed emissions today, so I guess that shuts down that theory?
03-14-2006, 11:58 AM
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If it starts acting up when it gets warm, try doing the cooling mod (you are correct, you can check shoebox's page for a good walkthrough) to the ICM and getting a new coil on there will help her out too. The stocker might be shot. I've seen them die at 50k.
If it passed emissions, the cat doesn't rattle and it doesn't smell like sulpher, your cat is probably fine.
If it passed emissions, the cat doesn't rattle and it doesn't smell like sulpher, your cat is probably fine.
03-14-2006, 12:36 PM
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Yeah, no sulphury smell, no rattling so I guess the honeycomb inside on both is fine (I'll be replacing with a no cat Y soon anyways), and I'm going to change the fuel filter and coil tomorrow (got both total for $25 with lifetime warranties). I'll try to find a cheap ICM and put that on at the same time, too. If it isn't those do you have any other suggestions urban?
03-17-2006, 02:43 PM
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Replaced the fuel filter and noticed a pretty good gain, but it still lags some. I have the rear intake leak, could there be a crack in my intake (drawing in air/letting oil escape from the lifter valley - which would result in loss of power/lean condition?) Or should I keep trying smaller things?
