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Car bogs down and dies when given gas by lafemmefiero73
Started on: 06-28-2020 06:53 PM
Replies: 15 (527 views)
Last post by: Patrick on 03-12-2022 04:55 PM
lafemmefiero73
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Report this Post06-28-2020 06:53 PM Click Here to See the Profile for lafemmefiero73Send a Private Message to lafemmefiero73Edit/Delete MessageReply w/QuoteDirect Link to This Post
My 1987 Fiero GT (stock V6 automatic) bogs down and dies when the gas pedal is pushed after being stopped for a few seconds, like at a stop sign. We've cleaned out the throttle body and replaced the spark plugs and throttle position sensor. Any ideas of where to go next? Thank you!
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Patrick
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Report this Post06-28-2020 07:57 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

I'd start with basics... such as fuel pressure.
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bootdsc
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Report this Post06-28-2020 08:50 PM Click Here to See the Profile for bootdscSend a Private Message to bootdscEdit/Delete MessageReply w/QuoteDirect Link to This Post
.

[This message has been edited by bootdsc (edited 06-28-2020).]

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Report this Post06-28-2020 08:51 PM Click Here to See the Profile for bootdscSend a Private Message to bootdscEdit/Delete MessageReply w/QuoteDirect Link to This Post

bootdsc

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Member since May 2020
After everything I went through working on the 86 gt to figure out why it had the same issue I wish I had started with simply checking fuel pressure.

Harbor freight sells two fuel pressure checker kits, the cheaper of the two is all you need and it's only $20ish.

Deleting the pulsator was the only thing my car technically needed to fix it.
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lafemmefiero73
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Report this Post06-28-2020 09:54 PM Click Here to See the Profile for lafemmefiero73Send a Private Message to lafemmefiero73Edit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you for the replies! Looking more into the pulsator issue, that sounds like what I'm running into. It looks like the pulsator connects to the fuel pump output and fuel feed line. I'm curious as to anyone who has bypassed this - is the pulsator actually inside the tank, or right outside? How easy is it to bypass in your garage with basic tool? Is it doable without dropping the fuel tank?
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Patrick
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Report this Post06-28-2020 10:51 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

The pulsator is often replaced with a short piece of submersible hose (not regular fuel line). The tank needs to be dropped.

First things first.. test the fuel pressure.
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lafemmefiero73
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Report this Post07-17-2020 07:10 PM Click Here to See the Profile for lafemmefiero73Send a Private Message to lafemmefiero73Edit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you! I tested the fuel pressure with the Harbor Freight kit. Right when the fuel pump turned on, it went to 40 psi and then sat at 38 psi. The Haynes manual says normal range is 40.5-47 psi. Is mine close enough to in range that it's probably not causing the issues?
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Patrick
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Report this Post07-17-2020 07:21 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by lafemmefiero73:

40 psi and then sat at 38 psi. Is mine close enough to in range that it's probably not causing the issues?


That should be fine.

As a test, try temporarily unplugging the electrical connection of the MAP sensor and see if that makes a difference.
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lafemmefiero73
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Report this Post08-15-2020 11:20 AM Click Here to See the Profile for lafemmefiero73Send a Private Message to lafemmefiero73Edit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you! I tested for vacuum leaks and didn't find any obvious ones. I used a scanner, and the voltage on the MAP sensor read at 3.76 whether the car was at idle or given throttle. It never changed. I replaced the MAP sensor with a new one, and it still had the same problem bogging down and reading exactly at 3.76, no variation between idle and throttle. It sounds like the next step in testing would be to unplug the wire to the MAP sensor to see if the reading changes, and if it does that would indicate the wiring is fine? Thank you!
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cebix
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Report this Post08-15-2020 12:25 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
Is your EGR good? On the duke it seems to be a common bogging source, not sure about the V6.
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Patrick
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Report this Post08-15-2020 04:18 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by lafemmefiero73:

It sounds like the next step in testing would be to unplug the wire to the MAP sensor to see if the reading changes, and if it does that would indicate the wiring is fine?


Possibly.

Here's my thoughts on doing this with low fuel pressure. I don't know if/how it applies to normal fuel pressure, but heck, see what happens.

 
quote
Originally posted by Patrick Here:

With the MAP connected, it appears the ECM reduces the amount of fuel that the injector is spraying... even though the end result (due to the low fuel pressure) is that the engine starves. I suspect the ECM is designed to work within a defined range of fuel pressure, and can't correctly cope when the pressure falls below a minimum level.

This is all conjecture on my part as I understand very little about EFI.


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Steel
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Report this Post08-15-2020 05:08 PM Click Here to See the Profile for SteelSend a Private Message to SteelEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'd rule out a plugged catalytic converter.
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lafemmefiero73
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Report this Post08-16-2020 09:05 PM Click Here to See the Profile for lafemmefiero73Send a Private Message to lafemmefiero73Edit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you! It has a newer CAT. I took apart the EGR valve, and the diaphragm and springs seemed in good shape and held the spring tension when I plugged the outlet line. Also, I started the car with the MAP sensor unplugged, and it started and immediately died. Next, I started the car with the MAP sensor plugged in, but the vacuum line to the sensor disconnected. The car idled very rough for about 10 seconds and died. Does that mean the MAP sensor is ok, even though the voltage readings weren't changing? What do you all think next?
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lafemmefiero73
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Report this Post08-17-2020 09:22 PM Click Here to See the Profile for lafemmefiero73Send a Private Message to lafemmefiero73Edit/Delete MessageReply w/QuoteDirect Link to This Post
I put an extra ground strap from the engine to the chassis because the resistance was around 175 ohms, which was way too high. The original one was very corroded. After that, all of the engine codes I was getting (throttle position sensor too low, MAP sensor voltage too high and too low, and EGR failure) were cleared, and just the EGR code remained. I put the original stock EGR back on, and that seemed to help. Then, when I pulled out of the garage, the oil pressure dropped and it died. I added oil, and that helped, but the oil pressure kept dropping to like 5 psi every time the car bogged out. I didn't notice that when the car bogged out before, but that may have been because the engine wasn't grounded well so the gauge wasn't as accurate.

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Visigoth87Fiero
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Report this Post03-12-2022 04:27 PM Click Here to See the Profile for Visigoth87FieroSend a Private Message to Visigoth87FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
Torque convertor clutch solenoid on a 3 speed automatic .
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Patrick
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Report this Post03-12-2022 04:55 PM Click Here to See the Profile for PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

We last heard from the OP on 08-17-2020. I guess we'll never know the eventual outcome.
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