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Very sluggish take off power. by Rezol
Started on: 07-21-2013 09:23 PM
Replies: 7 (304 views)
Last post by: Gall757 on 07-29-2013 02:20 PM
Rezol
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Report this Post07-21-2013 09:23 PM Click Here to See the Profile for RezolClick Here to Email RezolSend a Private Message to RezolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hello folks, new here (and to fiero's) but not to auto's (mechanic by profession for 10+ years). Recently purchased an 86 GT, automatic. Have been doing some work to it and have run into a roadblock of sorts. I have very low to none take off power. Sounds/feels like low its starving for fuel, however after getting up to speed, right before it shifts into 2nd and after that it runs and has, what I imagine, normal power for the small 6 cyl with an auto. I do not have fuel pressure reading at this time because I can not find my guage, but will get those numbers asap. I do keep getting a code for the MAP sensor but it checks out good (using voltmeter and vacuum pump). I have removed EGR and made block off plates for the exhaust and intake and plugged vacuum lines for it. Vacuum canister is rusted out so I have the line that feeds it plugged. PCV is good, and can find no other vacuum leaks. Transmission seems to shift fine, but firm. Have messed with TV cable and while it does change the shift points (as intended) it doesn't affect my problem at all. I have checked and set the timing, as well as the TPS just to make sure. Any help, ideas, or general things to check or eliminate would be greatly appreciated. Thanks, Mark
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Kevin87FieroGT
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Report this Post07-22-2013 07:27 AM Click Here to See the Profile for Kevin87FieroGTSend a Private Message to Kevin87FieroGTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Maybe plugged cat.

Edit: possible O2 sensor.

[This message has been edited by Kevin87FieroGT (edited 07-22-2013).]

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Slow6
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Report this Post07-22-2013 08:52 AM Click Here to See the Profile for Slow6Click Here to Email Slow6Send a Private Message to Slow6Edit/Delete MessageReply w/QuoteDirect Link to This Post
I'm having the same issue and have done a little looking on here, so I'm looking forward to reading responses. I did come across a thread related to adding a ground that eliminated that issue for a quite a few on here. I will be doing this to mine in a few days and hope that it resolves the same issue.
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Rezol
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Report this Post07-22-2013 10:38 AM Click Here to See the Profile for RezolClick Here to Email RezolSend a Private Message to RezolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Sorry, I forgot to mention, I have removed the cat because I thought that was a possibility. No difference. Could the O2 sensor be bad without throwing a code?

I also just read the post about the ground wire. Will also be doing it, if for no other reason than piece of mind.
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AL68
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Report this Post07-23-2013 12:04 AM Click Here to See the Profile for AL68Click Here to Email AL68Send a Private Message to AL68Edit/Delete MessageReply w/QuoteDirect Link to This Post
Check the fuel pressure at idle and while driving/accelerating. You can have enough pressure at idle & reving the engine but not enough fuel volume under a load while driving to keep the pressure up - bad pump or plugged filter. At low throttle opening/high vacuum there's less load on the motor so it needs less gas. The pressure should go up a little under a load - lower vacuum makes the regulator increase the fuel pressure.

Drive the car on flat ground and accelerate to a point where it starts to bog/lose power, then let up on the gas a little and see if you feel a little surge of power, usually a sign of low fuel volume/pressure.
I get this all the time at work - power surge is usually a fuel problem, no surge = plugged cat/exhaust, timing,etc.

You might have a bad map sensor but it could be reading too low vacuum from accelerating harder because of low fuel pressure.

[This message has been edited by AL68 (edited 07-23-2013).]

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Rezol
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Report this Post07-23-2013 12:31 AM Click Here to See the Profile for RezolClick Here to Email RezolSend a Private Message to RezolEdit/Delete MessageReply w/QuoteDirect Link to This Post
I do get that little "surge" of power, everything smooths out and seems normal when I left of the throttle a little. I will get fuel pressure readings tomorrow to check/confirm your advice. Will also go ahead and change fuel filter since I have no idea when it was done last and has been sitting for a "few" years, per previous owner. Thanks for the input and idea's. Will report back what I find.
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Rezol
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Report this Post07-29-2013 02:04 PM Click Here to See the Profile for RezolClick Here to Email RezolSend a Private Message to RezolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Figured it out finally. Mostly my fault for trusting a previous owner's actions. First time I went to look at the car, it started hard and after about 3 minutes the manifolds were glowing BRIGHT red. Told him the timing wasn't right, etc. So when I went back it started better and no more glowing. He said he set the timing and it was all good. Obviously when I purchased car, that was one of the first things I checked. However, I was going by his marks... they weren't right and it was causing the engine to fire during a partially open valve (which was giving me the loud ticking sound, which I thought was just an exhaust leak). SO much better and more fun to drive. Except now I realize the brakes on this fiero aren't to good for slowing down fast Still get a little bit of that ticking sound under acceleration though. The valve may have buildup on it, not allowing it to close all the way. Luckily I have another complete engine that I'm going to tear down and rebuild.

Went through and did some other things as well. Changed all vacuum lines, cleaned throttle body, IAC, checked injectors, MAP, TPS, checked fuel pressure with key off, at idle and also under load, did a compression check. Overall I'm a lot happier with the car! This could turn into my favorite car to drive ever!
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Gall757
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Report this Post07-29-2013 02:20 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rezol:

This could turn into my favorite car to drive ever!


Fieros can do that.... Welcome to the Forum!
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