I have a 91 gt with 168,000 on the speedo that I recently refreshed the motor. The bottom end is stock with molly rings. I did some minor porting and gasket matching on the cylinder heads, and cut 30 off the bottom. I had a valve job done with new valves and trick flow valve spring upgrade kit. It has a E303 ford cam, 190 lph fuel pump, professional products intake, edelbrock 65mm throttle body, C&L mass air and elbow, holley fuel regulator set at 39psi, 24lb injectors, superchips multi tune chip and dyno tuned, stock base timing 10 degrees, the 4th tune is set for 150 shot pulling 6 degrees of timing, accel coil,module,and plug wires, new ford pick up coil, one step colder motorcraft plugs with 38 gap, nx wet system with wot switch. After being tuned the 150shot worked perfectly for a full bottle of nitrous, but now backfires through the intake and explodes the air filter housing. I have tried new plugs, checked for vaccum leaks, and had nx rebuild both solenoids and still the same results. The total is 7 air filter housings, 4 mass airs, and 2 IAC. Does anyone have any ideas?

 

what fuel are u using? i would go colder plugs, i went 3 steps colder with a 125 shot.

 

try running a plate setup. Their much less likely to produce a backfire.

 

Stupid question but, did you purge it before you hooked up the second bottle? Other than that Im thinkin fried a valve.
-P.

 

+1 fried or stuck valve.

 

I am using 93 octane sunoco gas just like before and nx told me not to run any additives because it was hard on the solenoid's seats. The weird thing is it work perfectly for 5 months before I freshened the engine and for a month after. No unfortunely I do not have a purge but never seemed to matter before. I was thinking maybe a valve but the compression is 165-175 psi and it runs so good otherwise. I was wondering if anyone has used superchips multi tune chip and maybe had a problem of it switching from tune to tune. Its to hard to tell if it is really doing anything.Thinking maybe the timing is not being retarded 6 degrees like it should. But I will try colder plugs and see what happens, whats the worst that can happen blow another air filter housing. thanks for the help.

 

its too fat. its raw fuel. is it doing it while your on the throttle or after you let off? whats your a/f? was the tunes done with the current engine and injectors.

wide open switch might not be turning off nitrous before throttle plate closes. this is what i think it is. seen it happen before. people dont recheck it after working on the car. and it lets the nitrous activate at 60-70% throttle instead of wide open. so when you let off the pedal the tb closes before nitrous cuts off and boom.

 

I havent changed anything since the tune. I am using a wot switch with a switch on the shifter so the wot switch is just a safety thing, and I checked it, it seems to be right a wot. But I am going to do away with the wot switch and go to a rpm window. When I hit the button on the shifter, it comes in and really starts to pull but then blows half way through the pull. The a/f on the dyno when being tuned was 10-11, witch they said was do to the spark droping out because the plugs were gaped at .054 so they told me to gap them at .038 to even it out. I had not had it on a a/f meter since, until today and it went from 13.4 down to 11.2 but did not backfire today for the first time in two months. This time I did not let the bottle fully heat, the pressure was in the yellow 800-900 psi. Since I still have the meter I am going to try again tomorrow, so we will see.

 

So gapping the plugs a bit tighter seemed to help? i just installed a nitrous kit and i am having small backfires and cutting out when on the gun. i have the original plugs in the car, but im only spraying a 75 shot through her. sound like a plug problem? i plan on getting a plug thats atleast 3 steps colder.

 

Well it seems like gaping the plugs took care of the rich condition according the the readings I got from the meter yesterday. But I had changed the plug to .038 the day after being tuned and the system worked fine until after the first bottle which was for a month. Make sure the bottle is turned on all the way I have heard of it causing something like that. Before doing the motor runing a 75 shot I went one step colder on the plugs and one degree of timing.