Hesitations, sputtering & backfiring on 84 Carrera

[squelch]

Took my 84 Carrera out for a drive today and noticed that throughout the rev range, when getting on it, it is hesitating and sputtering a bit, especially when adding throttle after a shift and up around 5-6k rpm. When getting off of the throttle, it tends to pop, like small backfires.

It has absolutely no problem starting and runs fine when cruising.

The only thing I have done to the engine recently was add a Fabspeed premuffler. I assumed the popping and backfiring sounds were just a result of the new sounds of the premuffler, but it definitely is not running as smooth as it was.

I don't know if the premuffler caused the change or if the timing is just a coincidence.

Any thoughts?

Thanks,
Chuck

[Steve W]

Many 3.2 with pop and backfiring after removing the cat and installing a bypass or Euro premuffler. This is because the already lean stock programming has become worse with the reduced exhaust backpressure. Evidence this by how it backfires when you let off the gas on decel. The mix goes lean so fast, not even the O2 sensor is fast enough correct it - and you don't want to be depending on the O2 to bandaid the mix anyways. The only correct way to fix this is by installing the matching chip program to match. Fortunately Pelican has just this chip in their catalog.

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_FULmot_pg1.htm#i

[PatrickB]

Originally Posted by Steve W

Many 3.2 with pop and backfiring after removing the cat and installing a bypass or Euro premuffler. This is because the already lean stock programming has become worse with the reduced exhaust backpressure. Evidence this by how it backfires when you let off the gas on decel. The mix goes lean so fast, not even the O2 sensor is fast enough correct it - and you don't want to be depending on the O2 to bandaid the mix anyways. The only correct way to fix this is by installing the matching chip program to match. Fortunately Pelican has just this chip in their catalog.

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_FULmot_pg1.htm#i

+1!

[squelch]

Thanks Steve. One of your chips was on my wish list anyway, so I will go ahead an order one soon.

I have an '84 Carrera ROW model without an O2 sensor. I am not very familiar with the chips yet, but I know I want one of yours. Everything is stock except for the pre-muffler and I don't plan on changing the muffler anytime soon. I don't see anything on the Pelican page that specifies one for a Euro model car. Do I need to have a custom one made, or do you have one already tuned for a car with this set-up?

I ask the question here for other's benefit, but will also likely give you a call to order if Pelican doesn't have what I need.

Thanks,
Chuck