Engine Popping Deceleration

[Stevo]

1980 Spider has some popping during deceleration in the exhaust. I noticed the the exhaust is a rather small ANSA muffler and the resonator appears to have been removed. It does have a catalytic converter. I have adjusted the entire fuel system using Artigue's manual. Items I replaced, fuel tank, fuel lines, fuel filter, fuel pump, plugs, wires, cap, rotor, O2 sensor, auxiliary air regulator. The car has plenty of power and runs great. I notice a small amount or pop hear and there during idle. Some articles mention that this is normal for a free flowing exhaust when people change their exhaust out for performance. They say it is normally suppressed sound resonation in stock exhaust systems. I adjusted the throttle position sensor which is supposed to cut off the injectors during deceleration. I will be checking the color of the plugs soon to verify.

If any of you have noticed the same issue when going to a ANSA exhaust and can confirm this, I would appreciate this.

Thank you for any help or advice.

[RRoller123]

Check the connections of the TPS, but do it back at the ECU under the glove compartment, to be sure the wiring is intact.

[GeorgeT]

I noticed that mine would do this if the ignition timing wasn't within spec.

[Stevo]

Thanks, I will try the TPS at the ECU. The timing was set to spec.

[rridge]

On FI cars, decal popping often indicates a TPS that is out of adjustment or simply not working. It has a switch which changes the fueling schedule when the throttle is fully closed. When its not functioning properly the mixture goes too rich on the overrun. A continuity check on the three TPS contacts will tell you whether the switch is opening and closing as the throttle plate moves off rest.

Any change in idle position of the throttle plate requires an adjustment to the TPS. Often the fine machine screws that hold the TPS in position on the throttle body and allow it to be rotated for adjustment are frozen with corrosion. Let penetrating oil do its job.

Richard

[Stevo]

Thanks Richard for this information. When I used Brad Artigue's fuel injection guide, I connected an ohmmeter between terminals 2 and 18 of the TPS. Loosened the screws. Rotated the witch clockwise until the ohmmeter indicated a closed circuit. Then I tightened the TPS.

I am not sure which pins on the ECU would be to test that it reaches the actual ECU. Having replace so many items, perhaps I should swap out this TPS with a spare and see how the engine runs, and if need buy a new one.

If this is not normal for a FI engine with free flow exhaust, I sure hope to resolve it.

Thanks again.

[Stevo]

I replaced the TPS with one from my old 80 Spider and much better! Cannot hardly get it to pop at all. Now I cannot wait to see if this has an effect on the performance as far as power goes. Richard thanks for the exact "failed completely TPM" and everyone that helped! I verified the issue when unplugging the wires to the TPS. Exact same popping!

[Stevo]

After replacing the TPS and solving the popping issue there is one issue that is a bit strange. The TPS replaced, air bypass valve replaced, the car starts well on its own and runs at about 1500 RPM. Then as it begins warming up a minute or so, it starts dropping down to 300 RPM and acts like it is not doing well. Then as it warms up to 180 degrees, it idles as it should perfectly at 800 RPM. It is as if it has a dead spot there like the air bypass valve is closing too soon. Thanks for any suggestions.