I'm still somewhat indifferent about my 2.5 duke, but I want to take care of it until I decide which direction I want to go.
I did a basic tune-up about 4 months ago and she was running a lot better.
Rebuild the 700 throttle body.
New plugs and wires.
Replaced the timing gear cover gasket
Replaced the harmonic balancer seal and did the repair sleeve.
New belt and tensioner pulley. (the tensioner lines are lined right up to where they should be)

Now I've noticed that when you have the engine under load, it makes a sound sort of like what you would hear from a diesel engine head.
Is that pinging or just lifter clatter?

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1988 Fiero 2.5

A friend of mine once told me he though the 88 Duke sounded like a Singer sewing machine... I wonder if it isn't the additional mechanical noise from the force balancer...

That is a better description of the sound I guess.

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1988 Fiero 2.5

I don't think your lifters would care if the engine is under load or not. I'd make the same noise either way, were it them. I'd say you're pinging or maybe have an exhaust leak(cracked manifold). Check what your O2 sensor is doing.

how much of a load? Going up a long hill and I gave the car some gas (as to pass) my '87 would ping. I ran higher octane gas and that seemed to help.

It's mainly when accelerating ( to try and merge onto the highway) Or when cruising in a higher gear.

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1988 Fiero 2.5

Which plugs did you use, and did you gap them correctly?

Does it get better with higher octane fuel?

I've not had a chance to try a higher octane fuel.
For plugs, I went with Ngk as I've had good results with them.
The box said they where pre-gaped, but the site said .060 and they where all 4 spot on.
I pulled them today just to have a look and they still look like new even after 4 months.

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1988 Fiero 2.5

[This message has been edited by Zeak (edited 03-12-2014).]

I always go dealer specific. I had a 5.0 mustang with ac del co plugs and ran fine but sounded wierd... talked with a few gear heads and swapped out for motorcraft and it ran soooo quite and got good power. I dunno y but same plug base and gap, but it was like the signal was different or something. Just my experience.... thought id share after I saw the ngk. N I know thats usually for nissan or hondas.. but id try ac del co since they are gm brand. Plus 4plugs is like 20 $ or less

I agree with Zeak, the heat range on the NGK's could be a little off

DIS engine doesn't like even hates:
many "improved" plugs
Missing/bad EGR valve
Dying MAT and/or MAP
Dying spark plugs

See my Cave, DIS Ignition and 87-88 DIS Duke ECM


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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 03-13-2014).]

Try stock plugs to see if that helps.