I need a little help from some of the Fiero system experts here.

On page 6E2-C2-2 of the 1986 service manual, the first paragraph discusses the acceleration mode. It says, “The ECM looks at rapid changes in throttle position and manifold pressure, and provides extra fuel.”

Can you tell me exactly what happens in the acceleration mode? Does it hold the injectors open longer or are they pulsed faster?

I’m having trouble with my ’86 GT. It runs like it has a carburetor without a working accelerator pump.
I have replaced the Throttle Position Sensor (TPS) and the Manifold Absolute Pressure sensor and neither makes a difference. In fact, I think that I have replaced all of the sensors by now.
Here is a link to the previous post;
https://www.fiero.nl/forum/Forum2/HTML/135335.html

Thanks,

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Jim Martin
White '86 GT
Monterey, California

I read your other post. Take a compression tester and thread it into the 02 sensor bung on the exhaust. I think the number was no more than 4lbs pressure to test the exhaust flow.
Also, what are the fuel pressure numbers like? Specifically first key on, ignition off and then idle. The last is full quick revving.
Post your findings.

My thoughts are plugged cat, or weak fuel delivery.

[This message has been edited by f85gtron (edited 07-14-2015).]

I agree sounds like plugged cat. Also check plug wires for excessive resistance.

I built a back-pressure test kit using an old O2 sensor, pressure hose, and a low pressure guage (0-5 psi).

I measured the back pressure and it did not go above 1.5 psi until I reved the engine to about 3000 rpm. I did manage to get it to 3 psi but I had to rev it to about 4000 rpm.

the cat is only a couple of years old and is a Magnaflow unit.

I tested the fuel pressure with a fuel injection test kit from O'Reilly's Auto. I don't remember the exact numbers (they are in my shop log at home) but the pressure was well within specs according to the shop manual.

Fierofinder, as mentioned in the previous post, the ignition system has been completely replaced and tested, new distrubuter, coil, plugs and cables. Also, the TPS, MAP, IAC, O2, and Incoming Air Temp Sensor have all been replaced with no change. (I decided to just replace all of the 30 year old sensors).

The car starts fine with no hesitation and runs fine at low speed without miss-fires or stumbling, although the idle did seem a little rougher this weekend and was not as smooth when downshifting (it's a manual trans). It's when I try to accelerate hard, like getting on the freeway or passing, that I have real problems.

When it was running correctly I could beat my wifes Audi up the on-ramp. Now I have to put the throttle peddle all the way on the floor just to get on the freeway at 50 mph.

An EGR valve that's not closing properly (and/or opening too soon/too long) can cause some weird symptoms.

With it being relatively easy to do, how about blocking the EGR tube (I'd do it at the manifold end to also rule out a possible leaking tube) and see if temporary elimination of the EGR valve changes what you've been experiencing.

quote Originally posted by Jim_Martin29: replaced the EGR valve and the EGR solenoid

Installation mistakes can be made, parts can be faulty. Temporary elimination of the EGR system might shed some light on the issue. If nothing else, it eliminates a variable.

[This message has been edited by Patrick (edited 07-14-2015).]