how to stop the backfires

[Beachbum3478]

i have an 89 lebaron gtc TII/5spd with a full 2.5 mandrel exhaust with no cat and an ultraflo muffler at the end. and when i let off the gas in any gear, esspecially third it keeps backfiring, it just keeps on popping real loud. what is causing this and how can i muffle it a little without changing my setup, would adding a little resonator tip help at all?

[minimopar]

It's caused by a misfire, which from what I have seen on my A/F guage, is from the ECU cutting out too much fuel.

[88_Pacifica]

Unused gas is popping in the exhaust which means you may be running rich. Check all the fuel settings and then go from there. DOn't try and cover it up as this may be a problem later down the road. Plus the emissions moster will kill you on that one..

[william]

My GLH did the same thing... no cat, no muffler. It got progressively worse. I found that my ignition timing was not correct, it was retarded by a couple degrees. The hold down was not tight enough, and the distributor was retarding itself over the miles. It wasn't loose by any stretch (could still turn the dist by hand, but not easily). Might be worth double checking.

[tryingbe]

Put a catalytic convertor on it.

[iTurbo]

Have you checked codes? If the speed distance sensor is faulty, it will really make the popping worse on decel.

[Runner]

I remember reading about this once, not sure how much of it applies to our turbo cars, (i.e. reduced valve lap with a turbo car, effect of reduced back pressure *after* the turbo) but I think enough of it applies that if you put your old exhaust back on it'll stop.

http://www.flowmastermufflers.com/backpressure.html

I don't mind it myself, but then it is a pop and not a backfire like a gunshot. It just broadcasted "I got a friggin' huge, free flowing exhaust!" (3", behind door exit) Thinking about it now, I wonder if I don't have a bit more popping than average because of my 88 TBI cam.

Another thought...

Quote:

Originally Posted by tryingbe Put a catalytic convertor on it.

x2. adds a little backpressure, cleans the air, there's little or no performance penalty with a high-flow cat and it keeps Smokey off your case.

[minimopar]

The popping occurs if you are too lean or too rich. Too lean causes a misfire which deposits the unburned fuel into the exhaust system just like running too rich does.

[Beachbum3478]

whats this hold down on the distributor and how do i tighten it

[tryingbe]

Quote:

Originally Posted by minimopar The popping occurs if you are too lean or too rich. Too lean causes a misfire which deposits the unburned fuel into the exhaust system just like running too rich does.

Or if you run an open exhaust.


I have a 3 inch downpipe with cut-out and a stock exhaust system.

No pop whatsoever if I use the stock exhaust. If I use open the cut-out, it'll pop when the car decelerates.

[minimoparking]

same here. It comes with the territory. If you run a free flowing exhaust, it's gonna pop, bark and spit.

[xrattiracer]

chrysler computers dont completely shut off the fuel in an overrun (decel) condidtion, which loads up the exhaust and causes backfires. it is completely normal and nothing to worry about, you just cant hear it with the stock exhaust. most other manufacturers computers shut off the fuel 100% during overrun, not sure why chryco chose not to.

[Beachbum3478]

so at night would those backfires be little flames

[scott_s]

If you want to get rid of it, get a cal with the fuel adjusted at your high vacuum level. Though I like the popping and farting from the car on deaccel, I found that when I turned off the fuel for my high vacuum (deaccel) the popping and farting is no more.

[desertsnake1991]

I chased this demon as well! I went on MY GTC TII cabriolet, with a free flowing exhaust, Hi-flow cat, and Bossi/DTM exhaust, and it was popping like hell at first (was due to my then extreme small plug gap) that became pronounced or noticeable when I put more efficient Magnacores on. I then widened the Gap out to .40 roughly, and it quieted down a lot, but its still there, just not as pronounced. I went round and round and round with Timing issues, spending 4 Hrs Garage/Shop time at a real Mechanics place , just to find out that the Timing was all spot on. Frustrating! So, summary is, for me, it was a combo of wrong spark gap, and that almost straight thru exhaust...you just hear it more vs a stock exhaust!