TA76

Hi all, I posted a few weeks ago regarding my freshly built LT1 in my 94Z28 (6spd). To make a long story short I had a LT4 Hotcam & LT headers installed (used) and 24lb SVO injectors (new) during the rebuild. After getting the car back it was backfiring, mechanic thought it might be a bad O2 and need the ECU reprogrammed. OK, so I sent the ECU off to MadZ28 and Ion reprogrammed the car for my specs. I then got the correct extention for the O2 wire and replace the makeshift one I had with my original 63K mile O2.

Started the car up this afternoon and it seemed to run fine for a while, once it got warmed up it started to backfire thru the exhaust again. This seems to occur when you put the car in gear and move it. It revs fine although a little choppy when cold. I found one plug not plugged in and also the AIR lines are not connected (see photo for both items).

BTW-The check engine light is not on.

Javier97Z28

That purple connection is your MAF sensor connection.. unless it's an AIR connection that has the same color weatherpack seal...

speed_demon24

TA76

Thanks but the MAF is plugged up correctly and it has a purple weatherpack too. I can't seem to find a place for this connection.

Injuneer

The AIR pump has a 3-pin connector. Could that be unplugged? Is it possible the plug in the MAF sensor is not the correct one?

Javier97Z28

The AIR system has two connectors if I recall correct also.. btw. The 3 pin as Fred noted, and possibly another red/blue looking connector.

TA76

Thanks guys, I'm pretty sure the MAF is correct. Plus, I don't think this connector would reach it anyway. Does the AIR system need to be connected? Would any of this cause the backfiring?

Javier97Z28

No, it would not cause any backfiring or improper running conditions. On 93-95 cars it would throw a silent code (no ses light).

Backfiring could be caused by an improperly installed opti.

I don't know what year your car is though or whether you are running vented or unvented.

1racerdude

What do ya mean by your defination of backfire?
If it revs pretty good without going BANG,BANG,POOMP, with flames out the TB or exhaust,I don't consider it a backfire

Check plug wires,opti install,valve adjustment. All can cause my kind of backfire.

TA76

It is a 94 non-vented opti and... it was the one item I skimped on. I purchased a supposed low mileage unit trying to save a buck. What the car does is POP. It sounds like it is right under the floorpan. I don't know about flames out the back but I could have someone look. I'm pretty sure the car was running rich because I changed the plugs out and several of them looked fouled out and had a strong odor of gas. However, that was before ECU tune and O2 replacement.

Would a bad O2 throw a code? Anyway to tell if my Opti is bad?

itzkwik

wait for code or take it apart

Injuneer

Not even a "silent" code on OBD-I, as long as there is a good fuse in the circuit. The lack of AIR system is not the problem.

How tightly sealed are the caps on the header AIR connections? If they are leaking, it will cause the engine to run rich, and then provide excess air to burn the fuel in the exhaust system.

Sweetred95ta

Clean all the (fouled) plugs and see how it runs.

curly

Crossed plug wires can cause exactly what you are talking about.... I learned when we installed my LT's. That might be worth double-checking.

TA76

Again thanks guys, I will check all of that. I did replace the plugs with brand new ones (even though the ones I took out were new too).