Engine making pops out of the intake

[ValdostaFiero]

Hello everyone,

I few months back I bought an 1985 GT V6 2.8.  One thing I've been struggling to figure out is a pop that comes out of my air intake.  When then engine is under load, mostly is 1st and 4th, with low RPMS on acceleration the engine will pop several times over my left shoulder.  It seems to occur once the engine has heated up.  It won't do if you give it a lot of gas and power through all the gears.  But slow casual driving with not so much gas and lower rpms seems to trigger it.

I checked all the cylinders and they are all firing to some degree. (noticeable shake and sound on ever unplugged plug).  I have not done a compression test.
I've changed: Plugs, Wires, Cap, Coil, Oxygen sensor between engine and cat, fuel filter, air filter.
I also discovered two vacuum hoses on the throttle body that were unplugged and one on the ECM.  The hose on the ECM is rotted out and I plan on replacing all the vacuum lines here shortly.
I've also run two bottles of Gumout through the tank and just last week a bottle of Seafoam.  I've also tried running ethanol free gas through the tank.

After doing all the above the engine purrs and runs really smooth.  I've noticed significant power increase and it no longer feels like its struggling.  I wasn't noticing the pop anymore so I was intentionally trying to get it to do it by slowing down to 30 in 4th and giving it gas.  It would not pop for me.  Even in first on a very slow casual start (right on red), it would not pop.  It popped once then entire 45 minute ride and it was unexpected, in first after a stop sign.

My two thoughts on the matter are either a vacuum problem or possibly a semi clogged injector still.  I ran the Gumout through the engine about two month ago and the seafoam just last week but perhaps the seafoam finally did the trick in mostly unclogging an injector? I've heard arguments for both, or even for a bad Valve.  However none were from Fiero owners. 

[TopNotch]

If you are unsure of the condition of your injectors, take them out and take or send them to Fuel Injector Connection. They can clean and restore them to like new.

[Fierofool]

I'm going to interpret your statement about the ECM to mean the EGR.  The ECM doesn't have vacuum lines going to it.  The EGR system is comprised of 2 basic parts.  The EGR Solenoid that is located just below the thermostat housing and the EGR Valve that's on the crossover pipe, just to the left of the distributor and ignition coil.  There is a vacuum line running between these.  A crack in the hard plastic line probably wouldn't give you the symptoms you describe, but maybe the unplugged lines on the bottom of the throttle body might.

To me, it sounds like it could have been a sticky valve or lifter.  I once bent a pushrod in my AMC Javelin and it did the same under acceleration or load.  Coming back through the intake would indicate that it would be an intake valve, of course. 

SeaFoam can be used in a variety of ways.  In the tank or through the intake.  When used through the intake, some people inject it through the throttle body.  I like to disconnect the vacuum hose on the passenger end of the upper plenum and let it be pulled in through that port.  It really doesn't do much for the injectors but it will help to clean the inside of the plenum and the valves.  It can be used in the crankcase, but some have reported disastrous effects, so I'd be very careful with that application.

Techroline (sp?) is a good product for cleaning the fuel system and injectors.  Just dump a bottle into the tank once a month for a couple of weeks or months, depending upon how much you drive the car. 

It appears that you've found a solution.  Hope it's the correct one so you can enjoy the car.  BTW, did you ever make contact with oldbikeracer?