Backfire....

[roadster]

Recently I´ve noticed symptoms of backfires or rather loud pops, coming from back of exhaust. This seems to occur when engine rev is above 2000rpm and I engage the clutch....pop...Anyone had this experience? You should think this is an ignition problem, spark advance etc, but I´m not sure.

I inspected vacuumlines and find out that my pump recycled on and off. Checked Map sensor line no leak so the leak must come from underneath the plenum. Connected a vacuum tool and it confirmed my theory I had a leak. I then connected another checkvalve in serie up at LH plenum and the leak almost disappeared. The vacuum tool now show slowly decreasing vacuum, but backfires still occures. Can this be the source of my backfires?

I also took a look at my secondary actuators with a tiny flashlight, and the lever don´t seem to move a bit at wot ,warm engine ignitionkey on, full power. Is there a way to check the actuator without pulling the plenum, cause it takes me about 2 weeks to get all seals and tubes from dealer here in Sweden. I´ve read Rob´s vacuum diagnoses, "great help there" and applied vacuum to the connection going to the "differential sensor ECM" but no luck, the secondarys don´t open. Strange thing is I defenitely feel difference in normal and full power operation, but it doesn´t make any difference if I disconnect the electric vacuum pump, the "king"pulls strong whichever. To me the car runs smooth except for the pops.

Would be nice to gain some horsepower!!!! Plenum will be pulled this winter. Feel free to comment....
http://www.zr1.net/gifs/vacuum.jpg

Patrik 90 zr1

 

[Rob]

Partrik,

The vacuum pump can be disconnected and the secondaries will still work under most normal operating situations. The secondaries will operate off the vacuum created by the engine itself. The pump helps to keep the level of vacuum up under extended periods of WOT.

I would first fix whatever vacuum leaks you have under the plenum first and insure that the secondary port vacuum system is leak-free and the actuators are operating normally. That would be the first thing I'd do.

 

[roadster]

Shouldn´t I get a code 61 if my secondarys don´t operate normal or vacuum is lost? Tried to apply vacuum through the line going to the ECM, but seems that the line is open at solenoid so the actuators wont open. I will connect a vacuum gauge at this connection and se if there is vacuum when I drive.

Where can I buy plenumgaskets and other vacuumparts,solenoid etc. in the US?

thanks
Pa

 

[Rob]

You should get a code 61 if the secondaries fail to open.

As for plenum gaskets, and parts, talk to Kurt White at
http://www.whiteracingproducts.com I don't know if he'll ship international or not, but it's worth a shot.

 

[roadster]

Thanks for the info Rob......Hope it´s that vacuumleak causing the backfire....Guess it´s time to pull that famous plenum..