03 Cobra missing, backfiring, and sputtering below 3k Rpms. Need Avice

[FoxBody Curves]

As stated in the title, my cobra is sputtering and backfiring below 3 to 3500 rpms then smooths out, it seems to me like its missing fairly bad. Its hard to tell during idle since it has stage 3 cams installed and i'm fairly new to this car so I cant say for sure. It's also worth mentioning that during WOT I haven't noticed the backfiring/hesitation and it takes off like a rocket. I pulled the plugs and cylinder 1 and 2 plugs were fairy foul but not terrible. I cleaned them all up and re-inserted them and it seemed to noticeably help for a while but not eliminate the problem. I do plan on doing a compression check, using a code reader, as well as checking the coil packs these next days off. Is there anything else I should be looking into? Any imput would be appreciated, Thanks.

EDIT: Also if it means anything to anyone. I am able to gently accelerate without any popping/backfiring or hesitation fairly well, but as soon as I give it to much throttle it starting showing those mentioned behaviors.

 

[olympic]

Since the car has cams it's safe to assume it has been tuned. Has it always been this way for you or did it start suddenly? Perhaps it is tune related? First thing I'd do it clean the MAF sensor with electrical contact cleaner or brake cleaner. Sometimes they get fouled with oil from a cone filter. Then pull the vacuum line off the fuel rail pressure sensor, if there is fuel in the hose then the FRPS needs to be replaced. Since the issues occur mainly at part throttle it makes me think it's related to the MAF or oxygen sensors but it could be many other things.

After checking the codes and other obvious items the most useful thing would be a datalog so hopefully you got a tuner with the car. Post here if you need help setting up and reading the datalog.

 

[FoxBody Curves]

Since the car has cams it's safe to assume it has been tuned. Has it always been this way for you or did it start suddenly? Perhaps it is tune related? First thing I'd do it clean the MAF sensor with electrical contact cleaner or brake cleaner. Sometimes they get fouled with oil from a cone filter. Then pull the vacuum line off the fuel rail pressure sensor, if there is fuel in the hose then the FRPS needs to be replaced. Since the issues occur mainly at part throttle it makes me think it's related to the MAF or oxygen sensors but it could be many other things.

After checking the codes and other obvious items the most useful thing would be a datalog so hopefully you got a tuner with the car. Post here if you need help setting up and reading the datalog.

Thanks Olympic, I have not had the car even a week. However the previous owner stated this has been happening since he got the car tuned last at HPP Racing in Texas but now i am starting to doubt it's a tuning issue ( I could be completely wrong) I will be sure to clean the MAF sensor while im attending to the others on the checklist.
As far as a tuner I am still in the process of getting my hands on one, however i will be sure to come back with my results.

 

[FoxBody Curves]

I was able to check the coil packs today using a multimeter. They all seemed fine and within spec however I haven't completely ruled them out. I plan to hook up a code reader tomorrow and see if it throws some codes to direct me in the right direction as well as clean the maf sensor and compression check.
I also checked the plugs after 30 minutes of driving or so and 1 and 2 were foul again. 1 was dry and black while 2 was black with moisture which seemed like it had a hint of gas but I wasn't 100 percent sure.
I'm thinking the next thing to look into might be the injectors??

 

[MG0h3]

After ensuring the mechanics are good, I’d contact a tuner and datalog.

If it’s missing and fouling plugs you should have codes at least telling you some info.


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[FoxBody Curves]

After ensuring the mechanics are good, I’d contact a tuner and datalog.

If it’s missing and fouling plugs you should have codes at least telling you some info.


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MG0h3, I agree completely. I wanted to be sure I could check everything I can before I drop it off somewhere. I'm in hopes someone has experienced what I am and could give me some better information. I'm not to mechanically inclined, but know enough of the basics to look for.

 

[BlckBox04]

Datalog and tune it.

 

[FoxBody Curves]

Unplugged the maf sensor today and the backfiring came to almost a complete stop. I didn't not drive with it like this, but just reving the engine, I didn't notice any popping or hesitation. Im going to clean the sensor tomorrow with MAF cleaner and take it for a drive. If the cleaning and replacement of the MAF does not remedy the problem, what else should I be looking at??

 

[FoxBody Curves]

Also worth mentioning that the wideband was reading 13.8 to 14.8 while idiling, but if I stabbed the throttle, the wideband was reading 17s for a split second. Could this really be a tuning issue?

 

[MG0h3]

It’s normal to have a momentary lean spike when you crack the throttle.

And yes, all of
This could be a tuning issue.




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[03cobra_keek]

If you unplugged the maf and it smoothed out, it went into speed density in the tune which is preset table like open loop. Take a scan tool and check your long term fuel trims and see what it says. If it was tuned its possible someone disable the codes so the check engine light doesn't come on. Its definitely running rich so check or replace o2 sensor, clean maf, air filter, NEW plugs and clean injectors then look at messing with the tune if it's still running rich

 

[BlckBox04]

I’m surprised the car stayed running and didn’t throw a CEL when you unplugged the MAF

 

[FoxBody Curves]

If you unplugged the maf and it smoothed out, it went into speed density in the tune which is preset table like open loop. Take a scan tool and check your long term fuel trims and see what it says. If it was tuned its possible someone disable the codes so the check engine light doesn't come on. Its definitely running rich so check or replace o2 sensor, clean maf, air filter, NEW plugs and clean injectors then look at messing with the tune if it's still running rich

I will be sure to do that. I appreciate the input. I will attend to all of those as soon as I can. I can't get the car into a reputable shop until mid June unfortunately. I'm seriously hoping I'm narrowing down the issue, still getting a dyno tune regardless.

 

[FoxBody Curves]

I’m surprised the car stayed running and didn’t throw a CEL when you unplugged the MAF

No cel came on, however I did see a MAF code appear on the reader when I unplugged the MAF. The engine dropped rpms at first but came back to life and idled fine and I was able to rev the engine without any hiccups. The second time I unplugged it, it was running very rough.

 

[FoxBody Curves]

It’s normal to have a momentary lean spike when you crack the throttle.

And yes, all of
This could be a tuning issue.
Thanks for clearing that up, ive never had to mess with a A/fF gauge so it had me a little worried seeing it was leaned out for a split second.



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[FoxBody Curves]

One last mention. The car is fully built, ported heads, cams, etc. There isn't much that hasn't been touched on this car. Previous owner gave me the dyno sheets for pump gas and it was around 650 . It's also been set up for E85 with all the supporting mods and made 750 to the wheels. Is it possible this car is running this rich for a reason or would that have nothing to do with it?

 

[03cobra_keek]

That will do it, I would still check your ltft and see what it's doing if it hasnt been disabled. The pcm does all the guess work for you. Tuning a car when only only half the sensors are working properly is like going for a run while you're eating a cup cake

 

[01yellercobra]

Might be dumb, but since you have two tunes are you sure you're running the proper tune for whatever fuel is the tank?

 

[FoxBody Curves]

Yessir. Switching the two is as simple as flicking a switch in the glove box. I'm running pump gas now and that's what the switch is set to.

 

[FoxBody Curves]

That will do it, I would still check your ltft and see what it's doing if it hasnt been disabled. The pcm does all the guess work for you. Tuning a car when only only half the sensors are working properly is like going for a run while you're eating a cup cake

My scanner tool must not have this option. I could not find anything related to fuel. Is this something a SCT tuner is needed for?