Flat spot at 3400 to 4000

Shaun @ Tru6 · 05-05-2003, 05:27 AM

Last week my 84 Targa with 215K developed a serious soft/flat spot in power between 3400 and 4000. Runs fine otherwise, and after 4, good power is being produced. I put in a bottle of Valveline injector cleaner and a fresh tank of Sunoco 94, which cleared it up for about 100 miles, now it's back. It feels like it's running on 4-5 cylinders during this (lack of) power band.

OEM wires 10K old, checked connections. Valves done 3K ago, new air filter and plugs with valve adjust. Pulled cap off, cleaned the terminals and rotor, which are only about 10K old.

Any ideas?

Thanks

Shaun

BGCarrera32 · 05-05-2003, 06:46 AM

First guess...fouled injectors (or injector). Check your plugs. If one of them is black with excessive fuel (not oil) could be time to service or replace injectors. I had an injector go bust and it kept squirting excessive fuel into the engine, and limted power a lot.

My second guess is the throttle position sensor...its on the passenger side of the throttle body atop the intakes. There is a plug with 3 connections...I don't have a Bentley manual on hand to tell you how to check this, but often they crap out in a portion of the rotation of the switch while stepping on the accelerator...they can often be tested with a digital mulitmeter that has a bar graph. Once you have the switch pulled off the throttle body and the meter hooked up in resistance mode, you can sloooooowly turn the switch through its rotation and watch the graph move, and perhaps you will hit a small area where the bar graph drops out or "dead spots".

Also check the 4 pin fuel injection harness connector located on the bulkhead, behind the heater blower motor on the drivers side of the engine.

Good luck-
BG

Shaun @ Tru6 · 05-06-2003, 06:24 AM

Thanks for the very very thorough response BG, looks like a good combo weekend between this and a new front lip.

Best

Shaun

Dan Owens · 05-06-2003, 06:40 AM

Shaun,

When did you last replace the O2 sensor. Same exact symptoms with my 84 when the O2 sensor was due for replacement. They're suppose to be replaced about evry 50K, I think. Ran fine at idle and up to 3500 RPM under normal throttle. Once I got to 3500 and up to about 4500 it was like it was flat and then back to normal after 4500. If I put my foot into it, it ran pretty good through that RPM range but I could still feel the hesitation there. Once I put in a new O2 sensor and had the AFM recalibrated it ran great again.

Dan O