Topic: Backfiring through the TB after TB and injector install

[MYSTANGT]

Hey guys,

I just swapped my TB and a set of injectors on my 97 2.5L and it is now backfiring though the intake  

I hear a loud pop from the filter but ONLY when i am on the throttle at high rpm. The first time it happened it was as i was shifting into 2nd gear at about 4500 rpm. After that it would do it sporadically if i was standing in place and keep revving it up and up and up and then i'd hear a loud pop from the throttle body ...  

I did swap all the sensors from my 2.5L onto the 4.0 TB and the injectors are a fresh refurbished set from precisionfuelinjectors.com

Could it be that the computer is still relearning or is something wrong here?  

[dwtaylorpdx]

Did you hook the regulator back up? If it has one on the rail?

Mine backfires when it runs out of gas....

Dave

[MYSTANGT]

my regulator is on top of my tank so i dont get a chance to come near it.

The truck runs great though with these mods but this backfire is kinda making me worry...

[sharpxmen]

Hey guys,

I just swapped my TB and a set of injectors on my 97 2.5L and it is now backfiring though the intake  

I hear a loud pop from the filter but ONLY when i am on the throttle at high rpm. The first time it happened it was as i was shifting into 2nd gear at about 4500 rpm. After that it would do it sporadically if i was standing in place and keep revving it up and up and up and then i'd hear a loud pop from the throttle body ...  

I did swap all the sensors from my 2.5L onto the 4.0 TB and the injectors are a fresh refurbished set from precisionfuelinjectors.com

Could it be that the computer is still relearning or is something wrong here?  

1. how did it run with the injectors and original (2.5L) t/b? - just so i know if it's your t/b or still your old problem or could be the t/b and the new injectors.
2. this symptom is usually experienced when running lean - did you test your fuel pressure?
3. i don't think this is the case, but just going to mention it - make sure that you hooked the map correctly and you have no check valves on that line (not sure if your map is mounted on the t/b or not, if it is then disregard this).

[Jeffy]

You should have done one install at a time not both together in the same day.  If the fuel leak was your main concern then you should have left the 2.5L TB on the engine and tried to solve that problem first.

Two conditions usually cause backfires.  One is the engine is running lean.  The other is timing is advanced too much. Since the timing is computer controlled, you usually don't have to worry about that.  Did you reset your computer?  How many miles are on the engine since the swap?  Did it ignite the fuel that was already in the intake from before?  Did you fix the preexisting fuel issue or did you throw everything on and hope of the best?  If you still have a fuel leak then it could be the fuel igniting in the intake.

[MYSTANGT]

I swapped the injectors first started her up and it solved the poor idle and it had more power as i was hoping. I dont have plates on the car yet so i literally drove up the street and back without opening it up. I took it to 2500-3000 rpm once or twice and all seemed well. Assuming it was i went ahead and swapped the TB.

Once again, idle is perfect, more power and it drives great. I ran it up and down the street and it was great. Same thing at 2500-3000 rpm. I then let it fully warm up in order to really open it up. Once it was upto operating temp i took it down the block fast, shifting at 4500 rpm.

First frw passes it was great and maybe on the 5th pass as i was shifting from 1-2 at 4500 i heard a loud pop. I stopped and checked everyrhing out. All was well. Still idles perfect, drives well, powers there, but if i stan in plave and keep revving up and down and up and down (like ricer type revving) it would pop every 5 or 6 time. The more i dd it, the less frequent it became. 

I drove a total of maybe a 1/10th of a mile and had to leave.

I did reset the comp

[MYSTANGT]

UPDATE:

Drove around for 10-15 minutes and puled the plugs. All dry and seemed fairly good. Maybe a little whitish but nothing unusual, so that checks out OK.

I did however figure out EXACTLY when it would backfore. ONLY when the throttle is wide open while in low rpms. (below 3K) so basiclly when i really load it up.

If i rev it out to 4500 exponentially everything is fine, only when i fully mash the throttle earlier will it backfire, so i guess the tb is too big. Plus i do have 3" piping as an intake with a large K&N (home-brewed)   

Also, when driving upto 4500 rpm in first and shift fast into 2nd it will pop BUT only if i mash the throttle fully down. If im through the floor in forst and then shift at 4500 into second but only have the throttle half-way, no pop, drives fine.

I dunno...what do i do? Do i drive it as is, maybe a bad/weak tps, or is the TB too big + the filter?

[Jeffy]

UPDATE:

I did however figure out EXACTLY when it would backfore. ONLY when the throttle is wide open while in low rpms. (below 3K) so basiclly when i really load it up.

Your causing a rich situation as your dumping all that fuel into the cylinder then letting off.  The incomplete burn is exiting into the exhaust and exploding in the exhaust.  This is not good for the catalytic converter though.

[MYSTANGT]

I am 99% sure that the pop is in the intake manifold not the exhaust...but from what this sounds like you think that im running too rich?

What can cause this? Will the computer recalibrate with time?

[Jeffy]

I am 99% sure that the pop is in the intake manifold not the exhaust...but from what this sounds like you think that im running too rich?

What can cause this? Will the computer recalibrate with time?

If it's on the intake side then are you sure you fixed that leak?

[MYSTANGT]

Well the car runs great, idles perfect, plugs are dry, intake and tb are dry so i feel like i did solve it but... This is really odd. When i open it up abruprtly it pops...

[sharpxmen]

reset the computer and drive it for about 2 weeks - it takes 50 starts and few miles city drive to relearn the fuel trims - i think that's what you experience,  the fact that you flood the engine with air it makes it lean since the computer does not have the new air/fuel curve narrowed down - it will compensate right after via o2 feedback but on the initial wot that's the result... my guess

[dwtaylorpdx]

To reset the computer disconnect the battery then turn the key on.
Let it sit about 10 minutes then turn the key off and reconnect the battery.

I found that if I drove to work and turned the key off at each light then
back on it seemed to count as a cycle.

Roll on the throttle to WOT once during each cycle. I do it in second and let it get to about 5000 before I lift.
Or 3rd up a freeway on ramp. Keep an eye on your speed!

Worked for me after I did my rebuild, injectors, TB header installs.

Dave

[MYSTANGT]

I will certainly do so!

And ypu had the same backfires that i did and it solved them?

By the way, step on it WOT at 2,000 and rev all the way to 5,000 and keep doing it over and over even if it does backfire and buck?

THANK YOU dwtaylorpdx!!!!

[MYSTANGT]

IN ADDITION TO THE PREVIOUS POST:

could this be my maf sensor? As i was swapping the TB and the sensors i did spray a good amount of carburetor cleaner directly into the little rubber elbow that later goes over the vacuum port on the TB.

Would a bad maf sensor give me these rando
 backfires at WOT but have the car run well otherwise?