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2.8L Hesitate under part throttle. by stinky817
Started on: 11-08-2014 07:11 PM
Replies: 4 (154 views)
Last post by: stinky817 on 11-09-2014 08:24 PM
stinky817
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Report this Post11-08-2014 07:11 PM Click Here to See the Profile for stinky817Click Here to Email stinky817Send a Private Message to stinky817Edit/Delete MessageReply w/QuoteDirect Link to This Post
Hello everyone. I've got an 86 SE with a 2.8 and a getrag trans.

here's my problem.

I start the car, it idles fine. i go to drive it, and when i put it in gear and hit the gas, the car just stumbles, if i go WOT, it runs fine..... so basically anywhere between i'd say 15% and 50% throttle it just doesn't want to go.

I was thinking it's the EGR system, because that runs on vacuum when the throttle is open, but the EGR passages are clear and the EGR valve opens and closes properly, and the valve isn't plugged..

The car has new:
Plugs
Wires
Distributor (with cap and rotor)
TPS
MAP Sensor

I checked the normal stuff.... Timing, Fuel Pressure..

The only thing I haven't done yet is get my hands on a scanner to make sure all of the senors are reading correctly

anyone have any ideas?
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phonedawgz
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Report this Post11-08-2014 09:48 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
1 - Check your fuel pressure when this problem is happening. Connect up a gauge and have a second person watch it while you drive. Target fuel pressure 42 - intake vacuum in psi.

2 - Reset your ECM by disconnecting the battery for 15 seconds to clear the fuel trims. Then disconnect the O2 sensor and leave it disconnected. Running on the stock ECM fuel trims does it run normal? If so suspect a bad O2 sensor.

3 - Purchase one of my OBD1 to USB scan cables and see what your actual fuel trims are (BLM (learned/remembered long term) and INT (short term)) 128 means it is running as GM expected it to. A higher number indicates the ECM is adding fuel compared to the base programming. Lower means the ECM is taking some away.

----
WOT and Idle are both conditions where the ECM runs the engine richer than at part throttle cruise. I SUSPECT that the engine is running lean. Suspect means this is where I would start looking at it. It does not mean for you to then assume this is what is happening. Test with the above procedures and see if you confirm or deny that it is indeed running lean.
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stinky817
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Report this Post11-08-2014 09:56 PM Click Here to See the Profile for stinky817Click Here to Email stinky817Send a Private Message to stinky817Edit/Delete MessageReply w/QuoteDirect Link to This Post
I forgot to say that I did disconnect o2 sensor and it didn't make a difference. I'll check running fuel pressure during the issue.

What software should I use with the usb to aldl connector? I have one, but Last time I tried to use it on an Indy, it didn't work with winALDL on a Windows 7 laptop
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phonedawgz
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Report this Post11-08-2014 10:49 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
TunerPro RT.

My install disk in on the bottom of this page - http://reddevilriver.com/aldl.html

It will work with your cable. Included on the disk is the 'free' version of TunerPro RT. It runs 100% after a 10 second nag screen. You can purchase a license and avoid the nag screen however that is never required.

Also on the disk is the .adx data acquisition file for the 85-88 2.8 Fiero ECM.
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stinky817
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Report this Post11-09-2014 08:24 PM Click Here to See the Profile for stinky817Click Here to Email stinky817Send a Private Message to stinky817Edit/Delete MessageReply w/QuoteDirect Link to This Post
Ok. So here's what I've found out. Fuel pressure is normal all the time.

When the problem is happening the rpm in the ecm (and the dash) fluctuate pretty heavily (I was holding a light load at 2500 rpm) the data list on the scanner I was using (solus) was fluctuating between 4500, and 2500. The needle on the gauge was only jumping between 2500 and 3500. I think I found out what the problem is, but what is the fix for it? Tach filter? I already have a new module in the distributor.....

I took some screen shots with my phone of the graphs on the scanner if you'd like to see them

Edit to add: when I got home I turned all of the lights off in the garage and don't see any arcing with the wires anywhere

[This message has been edited by stinky817 (edited 11-09-2014).]

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