lighthorseozzy1

To start off with, I have a 2.8L engine, not a muscle car but i love my Firebird! I do have a couple of questions to ask, whoever answers this and maybe I will get a good mechanic to answer it. I am a mechanic but from the old school lol. I took my car to the garage and they found a bad Mass Air Flow Sensor bad and replaced it. The car runs better now but not to my standards. It will start right up but when throttle is put to it, it is rough. A little popping at acceleration but runs good pass the roughness. I took the car out on the freeway and runs fantastic. Once warm, it runs and idles somewhat smooth. Now the questions and problems. Once warm and idling and stopped at a light for a little period of time, it acts like it drops in power and comes back up to good idle. This does this but if put in neutral, it stays iding good. Possible causes is needed. Acceleration is rough at first and then smooth, even after warmed up good. Why? Where is the timing mark suppose to be at? I want this car to run jam up and jelly tight. Catalylic Converter was removed, so does make a difference? Oh by the way, this is a fuel injected system TPI. What should I do or where should I go.

KrisW

iTrader: (5)

check all of your distributor and ignition parts. Every 2.8 or 3.1 car I have had has had the ignition coil fail and the internal pick up coil fail. My best check: open the hood and run the car at night in the dark. You'll see sparks and tracks happening all over that you can't see in the day time!

My coil always shorts through to the coil bracket. The pick up coil can be checked with an ohmmeter. Good luck man!

lighthorseozzy1

I did not notice any sparking going on around coil but I did notice the spark plug wires arcing to the block, from the metal sleeves that go around spark plug wires on two cylinders. I think paper is gone on two of the sleeves. Is this possible for the mishaps? or do you have any other ideas. Thanking you so far for your help...Ozzy

KrisW

iTrader: (5)

hahahahha

If you see sparks then you have found a big problem. The paper and the metal covers are for heat shielding. If you have sparks it is not because the paper is gone, its because your plug wires are shorted and cracked through. Two cylinders out of six giving a misfire will cause all of your problems that you have described.

You must replace the plug wires. Also, you want to make sure that you pull all of your plugs, run a 14mm tap through the plug holes to clean the threads, and then put a dab of anti-seize on each plug when you put it in the head. You must also make sure that the plugs are grounding to the head and not tracking back up the outside of the plug and jumping to the heat shield.

Replace the plug with some new AC Delco plugs if they look anything but new right now.

Let us know how this turns out!

ASE doc

The arcing of the plug wires to the heat sheilds isnt the plugs not being grounded to the head. It is the plug wire boots leaking high voltage away from the plug gaps. Replace plugs wires, cap and rotor all together as a set. Apply a generous amount of dielectric compound(tune up grease) to each plug boot and spread it around the inside of the boot with a toothpick or small screwdriver before installing the wire.

The 2.8s had a common issue with the throttle shaft bushings. They wear and become loose allowing lateral movement of the shaft. This causes inconsistent airflow around the throttle which confuses the ECM as it tries to manage fuel trims. It also causes variations in base TPS voltage which further confuses the ECM. In its worst case, this can lead to severe loss of drivability.

The test for this involves using a scan tool to monitor TPS voltage while opening and closing the throttle several times. Look for TPS to change even slightly from one open/close cycle to the next. Check the throttle shaft for lateral movement. There should be no visisble movement. GM released a TSB for this issue on all 2.8s and some 3.1s.

lighthorseozzy1

I replaced the spark plug wires, spark plugs, rotor, distributor and the coil for safe measures. Runs a little better but still, When I take off, there is still hesitation and a little backfire. I know everything was running fine, before I parked it and it sat for some time. I would fire it time to time and it would fire up with no problem and idle great. I took it to the garage and they did replace the mass air flow sensor, which made it run better alot. Exactly, where is the timing mark suppose to be and a pic would help. They set it right under the tube pretruding from the timing mark plate. The throttle body shaft you are talking about, is located and again, a pic would help. I am old school mechanic lol. Something is off somewhere and it is small thing and I am going nuts all over again. Please help guys and Thanks

Sparkytfl

This is from the 85 manual (the huge official one). Looks like zero is the deepest notch not the hole.

lighthorseozzy1

I used the timing light and the mark on the damper is right underneath the probe hole. Is this correct? I thought it was more over to the left of probe hole. One more thing, Could a throttle position sensor cause hesitation and backfiring on acceleration, if it is not working properly? and if so, what is the correct postion should the sensor be in, because I could never figure that out lol. Thanks