Have u changed the fuel filter? And have u checked ur injectors?
New TB and CAI - Stumbling / Small Backfire - HELP
- Thread starter Ninety3Coupe
- Start date
Okay guys, what about the EGR and O2 sensors? I keep seeing a ton of information saying the to unplug the EGR (he still has all his connected since he's in the smog Nazi capital of the world) and I guess cap it off and run it to see if the stumbling stops. Not sure as I have no experience on EGR stuff.
I have also been researching and see a ton of people say after 80k miles you should change the O2's and his is past that, and they appear to be original. So even changing them out at this point seems like the logical thing to do anyhow.
The O2's really make a lot of sense to me since the car stumbles in lower RPM's, but at WOT there is no issue. Since the O2's are shut off at WOT because the car goes into Open Loop, and since in normal driving conditions it's in Closed Loop, a bad O2 would could cause this stumbling issue, right?
I've know Ninety3Coupe for 25+ years and I'm trying to help him out, but I'm 1300+ miles away and there's not much I can do physically to see or hear what's going on with this thing.
He's cleaned the MAF replaced the fuel filter, fuel pump, TPS, checked for all vacuum leaks, plugs, plug wires, timing, distributor, yada yada yada. We're just kind of stuck and the more research I do lately keeps pointing to a bad O2 or the EGR.
Plus from what I've been reading it seems that bumping the fuel pressure kind of masks a bad O2 when it's in Closed Loop. Can anyone confirm that?
The issue with the bad gas/varnish smell he's been getting seems to be a more intermittent thing and not related to this stumble. He's only had that happen a few times, so we now think the Charcoal Canister and related parts may be the culprit with that (especially since this car was all stock when he got it; well essentially stock compared to most), but we're still looking for opinions on that too.
Really appreciate everyone's assistance and thoughts on this. This is his toy and it's no fun playing with a toy that doesn't work right, ya know?
Oh yeah, one other thing he's got a MAF out of a Crown Vic to swap in and right now he's running a 73mm C&L MAF with his stock 19lb injectors. We were under the impression he could swap in the Crown Vic MAF with the 19's, but now he's thinking the Crown Vic was meant for 24's (seems he found some conflicting info on this). Anyone got an definitive answer on that too?
Sorry for the long post and mountain of questions, just trying to help my Bro out!
I have also been researching and see a ton of people say after 80k miles you should change the O2's and his is past that, and they appear to be original. So even changing them out at this point seems like the logical thing to do anyhow.
The O2's really make a lot of sense to me since the car stumbles in lower RPM's, but at WOT there is no issue. Since the O2's are shut off at WOT because the car goes into Open Loop, and since in normal driving conditions it's in Closed Loop, a bad O2 would could cause this stumbling issue, right?
I've know Ninety3Coupe for 25+ years and I'm trying to help him out, but I'm 1300+ miles away and there's not much I can do physically to see or hear what's going on with this thing.
He's cleaned the MAF replaced the fuel filter, fuel pump, TPS, checked for all vacuum leaks, plugs, plug wires, timing, distributor, yada yada yada. We're just kind of stuck and the more research I do lately keeps pointing to a bad O2 or the EGR.
Plus from what I've been reading it seems that bumping the fuel pressure kind of masks a bad O2 when it's in Closed Loop. Can anyone confirm that?
The issue with the bad gas/varnish smell he's been getting seems to be a more intermittent thing and not related to this stumble. He's only had that happen a few times, so we now think the Charcoal Canister and related parts may be the culprit with that (especially since this car was all stock when he got it; well essentially stock compared to most), but we're still looking for opinions on that too.
Really appreciate everyone's assistance and thoughts on this. This is his toy and it's no fun playing with a toy that doesn't work right, ya know?
Oh yeah, one other thing he's got a MAF out of a Crown Vic to swap in and right now he's running a 73mm C&L MAF with his stock 19lb injectors. We were under the impression he could swap in the Crown Vic MAF with the 19's, but now he's thinking the Crown Vic was meant for 24's (seems he found some conflicting info on this). Anyone got an definitive answer on that too?
Sorry for the long post and mountain of questions, just trying to help my Bro out!
Thanks DT - I was away from the computer. DT is correct (he can always speak on my behalf).
I don't want to jinx it, but it seems like bumping the FP helped a bit. I set it at 52. That seems way too high to me, but it helped.
The smell of bad gas (varnish) is really getting bad now. I mean, really bad! When it warms up I can smell it just idling at a light and when I park in the carport it is overwhelming to say the least. It's almost embarrassing, I have had other people roll up there windows at a light now.
I have read (with DT's help - thanks Dave!) that bad O2 sensors can cause some of these issues, a bad EGR, charcoal canisters being bad, gas caps, cracked vacuum lines to and from the charcoal canisters, the valve on top of the charcoal canisters,, etc.
I am not convinced the problems (stumbling and the smell of bad (varnished) gas) are exclusive and separate. I read that bad O2 sensors can be masked by bumping FP to a higher level. This would possibly be what I have done?
That is $400-500 in parts I think if I add it up right. I am not in a place to spend that right now, so some info would be great! Anyone?
I don't want to jinx it, but it seems like bumping the FP helped a bit. I set it at 52. That seems way too high to me, but it helped.
The smell of bad gas (varnish) is really getting bad now. I mean, really bad! When it warms up I can smell it just idling at a light and when I park in the carport it is overwhelming to say the least. It's almost embarrassing, I have had other people roll up there windows at a light now.
I have read (with DT's help - thanks Dave!) that bad O2 sensors can cause some of these issues, a bad EGR, charcoal canisters being bad, gas caps, cracked vacuum lines to and from the charcoal canisters, the valve on top of the charcoal canisters,, etc.
I am not convinced the problems (stumbling and the smell of bad (varnished) gas) are exclusive and separate. I read that bad O2 sensors can be masked by bumping FP to a higher level. This would possibly be what I have done?
That is $400-500 in parts I think if I add it up right. I am not in a place to spend that right now, so some info would be great! Anyone?
Let's back up here!!! It was running good before the parts so let's go back to stock and add a performance part at a time and find the issue... I for one think it's the 19lbs injectors I have never heard someone upgrading there cars without first upgrading the injectors... With more air movement you need more fuel....just a thought ... If it was o2 sensors u would probably get a code
Well, I was going to begin swapping parts one at a time but folks began pointing towards fuel pressure regulator and a fuel pump so I did that. The TB and CAI is when the stumbling issues arose, the bad gas / varnish smell happened when I replaced the H pipe to a catted one. I have since removed the aftermarket piece (and sold it - P.O.S. rattled) and now have the stock one back on. That means a couple times the stock O2 sensors have been pulled and replaced in the past month. Contamination or damage by the mechanic? Maybe...
A lot of my friends (non-Fox fans) ask me why I haven't upped the injectors. Everything I have read says that you need to match the MAF to the injectors. I have a 70mm MAF and sensor off eBay here on my desk that I wanted to install but got conflicting info saying I would need 24# injectors to run it. And furthermore, the online calculators show I am still within the HP levels of a 19# injector. I would LOVE to be wrong and replace them. Thoughts anyone?
James - Your reply to the thread came, and I am not kidding, 2 minutes after I hit Buy It Now on eBay for 2 new O2 sensors. They say they last for 60K-ish so it couldn't hurt I guess. The smell began (as best as I can recall) after the initial swapping of the pipe.
I'm going for another drive in a bit, but earlier it did not hesitate with the bumped FP. It did start to have that bad gas / varnish smell however as soon as the engine got hot. That is what is really bugging me, and O2 sensors seem to be a culprit that causes all these issues, no?
Thanks again James and all others for any and all input and comments!
A lot of my friends (non-Fox fans) ask me why I haven't upped the injectors. Everything I have read says that you need to match the MAF to the injectors. I have a 70mm MAF and sensor off eBay here on my desk that I wanted to install but got conflicting info saying I would need 24# injectors to run it. And furthermore, the online calculators show I am still within the HP levels of a 19# injector. I would LOVE to be wrong and replace them. Thoughts anyone?
James - Your reply to the thread came, and I am not kidding, 2 minutes after I hit Buy It Now on eBay for 2 new O2 sensors. They say they last for 60K-ish so it couldn't hurt I guess. The smell began (as best as I can recall) after the initial swapping of the pipe.
I'm going for another drive in a bit, but earlier it did not hesitate with the bumped FP. It did start to have that bad gas / varnish smell however as soon as the engine got hot. That is what is really bugging me, and O2 sensors seem to be a culprit that causes all these issues, no?
Thanks again James and all others for any and all input and comments!
The gas smell could Also be from from running super rich!! Which is better than lean any given day... I had the same issue with my notch when I first started adding performance. It's would stumble all over itself come to find out I had the wrong size in there I though they where 24s but they where like 40 somethings. As soon as I put the right size in boom ran like a champ and I had at the time already upgraded my heads, cam, maf. Upper and lower intake etc.., so ur issue I feel is injector to MAF match up and getting enough fuel to feed your motor... Where are you located?
---
I am here: http://maps.google.com/maps?ll=29.033583,-95.434867
---
I am here: http://maps.google.com/maps?ll=29.033583,-95.434867
I'm in Anaheim, Ca.
I'm a bit confused. The stock 19# injectors I have are are too small or I have too much fuel in your opinion? I appreciate you taking the time to work through this with me as I have seen many posts by you and value your input.
The gas smell is not a smell of fresh, normal gas - like what is in the tank when I had it out the other night. It is a very, very strong varnished / bad, rotten gas smell. As bad as I have ever smelled. If anything, I smell it under the hood more strongly on the passenger side by the charcoal canister. I could be wrong on that, but I seem to notice it more there.
I'm a bit confused. The stock 19# injectors I have are are too small or I have too much fuel in your opinion? I appreciate you taking the time to work through this with me as I have seen many posts by you and value your input.
The gas smell is not a smell of fresh, normal gas - like what is in the tank when I had it out the other night. It is a very, very strong varnished / bad, rotten gas smell. As bad as I have ever smelled. If anything, I smell it under the hood more strongly on the passenger side by the charcoal canister. I could be wrong on that, but I seem to notice it more there.
I'm confused about the matching of your MAF with the injectors. What if you try swapping the original MAF. The car should run fine with it. You may be down on HP due to the size of the MAF, but otherwise it should be good. At least you could cross that off the list of the potential problems.
Sadly, the car came with the C&L 73mm and I don't have a stock 55mm unit to try. I only have the C&L and the refurbed 70mm Ford unit from eBay. I have only used the C&L that is in there now, I have never swapped it.
It ran fine when I got the car with the C&L on it. It ran fine with the intake manifold upgrade, etc. It is only when the TB and the CAI went on that the stumbling occurred. As I bumped up the pressure with the FPR, and now again with the new pump it progressively gets better running, if not running almost perfectly now - I consider myself a somewhat happy camper with the stumbling being mostly (if not completely) fixed. Which leads me to...
The varnished gas smell happened only after the H Pipe was installed (IIRC). I removed the BBK H Pipe and went back to stock after it was rattling. The smell is still there and now getting worse if I am not mistaken. Worse after the latest (this morning) bump in fuel pressure, again, if I am not mistaken.
I bring the varnish up in the same thread as the stumbling because I am not sure if they are related problems or not. I look to you fine (and more well versed) folks for help. Doesn't seem right to me to hold back info I may think is not pertinent...I could be wrong. I provide as much detail as I can (maybe too much, sorry guys).
It ran fine when I got the car with the C&L on it. It ran fine with the intake manifold upgrade, etc. It is only when the TB and the CAI went on that the stumbling occurred. As I bumped up the pressure with the FPR, and now again with the new pump it progressively gets better running, if not running almost perfectly now - I consider myself a somewhat happy camper with the stumbling being mostly (if not completely) fixed. Which leads me to...
The varnished gas smell happened only after the H Pipe was installed (IIRC). I removed the BBK H Pipe and went back to stock after it was rattling. The smell is still there and now getting worse if I am not mistaken. Worse after the latest (this morning) bump in fuel pressure, again, if I am not mistaken.
I bring the varnish up in the same thread as the stumbling because I am not sure if they are related problems or not. I look to you fine (and more well versed) folks for help. Doesn't seem right to me to hold back info I may think is not pertinent...I could be wrong. I provide as much detail as I can (maybe too much, sorry guys).
More info the better when u get a mustang that is not stock that means someone has already caused you a headache.... 
....so let the car warm up to normal temp then tell us what u have ur fuel pressure set at with the vacuum line on and off then with a flash light not a lighter... Check each injector for leaking fuel.. It is not uncommon for a o-ring to become brittle or rip from removal and reinstallation u should always replace the o-rings anytime u remove them and then reinstall...It only takes one bad injector to make ur car run like crap....stumble and get really bad MPG...
Now does the exhaust have cats on it? Does the smell ur smelling... smell like rotten eggs/sulfer smell mixed with gas?
Have u done a compression check on each cylinder yet? Easy to do... Takes very little time...
---
I am here: http://maps.google.com/maps?ll=29.036740,-95.426767
....so let the car warm up to normal temp then tell us what u have ur fuel pressure set at with the vacuum line on and off then with a flash light not a lighter... Check each injector for leaking fuel.. It is not uncommon for a o-ring to become brittle or rip from removal and reinstallation u should always replace the o-rings anytime u remove them and then reinstall...It only takes one bad injector to make ur car run like crap....stumble and get really bad MPG...Now does the exhaust have cats on it? Does the smell ur smelling... smell like rotten eggs/sulfer smell mixed with gas?
Have u done a compression check on each cylinder yet? Easy to do... Takes very little time...
---
I am here: http://maps.google.com/maps?ll=29.036740,-95.426767
When he changed the upper and lower intake manifold he put all new o-rings on the injectors.
The car ran great when he changed the U&L intake manifold. I know because I personally drove the car and there was no stumble or anything. The car pulled hard all over in ever RPM and idled perfect. The car came with the 73 C&L MAF and ran great before the U&L intake manifold was put on and after, so I don't believe the C&L is the culprit to the stumble issue. And his injectors are the stock yellow/orange ones that from what he and I can tell are Ford's 19lb injector that came on these cars.
The bad gas/varnish smell started to occur when the new h-pipe was installed (a BBK high flow catted version) and the stock 4 catted h-pipe was removed. It only happened one time, but it left us stranded because the car would not start. A mechanic looked the car over the same moment this happened, as we happened to have it happen as we were looking for a shop to gut out the cats in the BBK h-pipe because the ceramic inside them was loose and causing a loud rattle in his exhaust. The mechanic hooked up his vacuum gauge and checked the fuel pressure and he determined it was the fuel pump. Well fast forward 20 minutes after we called AAA to come tow it (this was just right around Christmas and this shop was closing for 2 plus weeks, so we couldn't leave it there) and "I" said, "hey lets try it one more time," and to our surprise the car started and ran perfect again.
So fast forward a couple weeks. He decides he's had enough of the ****ed up BBK h-pipe and removes it and puts the stock h-pipe back in the car, but the bad gas/varnish smell keeps happening and causing the same scenario of not starting again and leaving him stranded.
Now here's where I'm going to lose some of you. In that time he also added the new CAI, 70mm throttle body and spacer to his already installed U&L intake manifold and THIS is when the stumbling issue started occurring. Remember the injectors have new o-rings, the MAF is still the same 73mm C&L that came on the car and ran perfect before and after the U&L intake manifold swap, but the only difference is he's added the new TB with spacer and CAI.
The only other thing done to the car to that point was the h-pipe being swapped out several times, and we all know the O2's had to be removed and installed several times, so it's entirely possible these O2's got damaged in some way. The h-pipe swap was done by a mechanic shop also, but the rest of the performance mods were done by Ninety3Coupe.
I'm not saying the O2's are the sole cause of the stumbling issue or the bad gas/varnish smell. But the MAF and O2's are somewhat related since the MAF tells the computer how much metered air is coming in and the O2's monitor the burn of the fuel and with all the times he's bumped up fuel pressure and the fact that the O2's have been pulled multiple times lately (not to mention they have over 90k miles and almost 20 years on them), it's entirely possible they are overly saturated, damaged or just not holding the proper voltage any longer, which in conjunction with the increased air flow the car's getting now, plus all the extra fuel that's being thrown at it now, the O2's could be skewing the readings and the computer is trying to compensate.
Now I know the 5.0's computers are very adaptive (unlike my Cobra and most any new car out there), so with that said, it's that fact that leads me to think if nothing else replacing the O2's to this point certainly can't hurt.
I mean the engine should be getting more than enough fuel (and yes it's probably very rich now), now that he's swapped out what he indeed did find was a failing fuel pump with a Walbro 255lph and he's added the FPR and gauge to assist in fueling.
Also from everything I've read and calculated those stock 19lb injectors should be more than enough injector for his power level with the fuel pump upgrade plus the FPR. It certainly couldn't hurt to go to a bigger injector and trust me he and I agree that some larger ones would be helpful, but unless one went bad (which we understand it could of) I don't think it's the injectors. Especially since the car pulls great at WOT and only stumbles in the 2-3k RPM range in normal driving conditions.
If anything I've said is way off, please someone correct me. I'm just stating the facts of what I personally know and have personally seen with this car.
Also the only mods this car had on it when he bought it were the 73mm C&L MAF, shorty headers, cat-back exhaust and a short shifter. That's it, it still had the stock U&L intake manifold all the way down to the stock paper filter in the stock air intake. Other than that, that's it, so this was not a highly molested Fox body. But now it sure the **** is! lol that's for you N3C!
The car ran great when he changed the U&L intake manifold. I know because I personally drove the car and there was no stumble or anything. The car pulled hard all over in ever RPM and idled perfect. The car came with the 73 C&L MAF and ran great before the U&L intake manifold was put on and after, so I don't believe the C&L is the culprit to the stumble issue. And his injectors are the stock yellow/orange ones that from what he and I can tell are Ford's 19lb injector that came on these cars.
The bad gas/varnish smell started to occur when the new h-pipe was installed (a BBK high flow catted version) and the stock 4 catted h-pipe was removed. It only happened one time, but it left us stranded because the car would not start. A mechanic looked the car over the same moment this happened, as we happened to have it happen as we were looking for a shop to gut out the cats in the BBK h-pipe because the ceramic inside them was loose and causing a loud rattle in his exhaust. The mechanic hooked up his vacuum gauge and checked the fuel pressure and he determined it was the fuel pump. Well fast forward 20 minutes after we called AAA to come tow it (this was just right around Christmas and this shop was closing for 2 plus weeks, so we couldn't leave it there) and "I" said, "hey lets try it one more time," and to our surprise the car started and ran perfect again.
So fast forward a couple weeks. He decides he's had enough of the ****ed up BBK h-pipe and removes it and puts the stock h-pipe back in the car, but the bad gas/varnish smell keeps happening and causing the same scenario of not starting again and leaving him stranded.
Now here's where I'm going to lose some of you. In that time he also added the new CAI, 70mm throttle body and spacer to his already installed U&L intake manifold and THIS is when the stumbling issue started occurring. Remember the injectors have new o-rings, the MAF is still the same 73mm C&L that came on the car and ran perfect before and after the U&L intake manifold swap, but the only difference is he's added the new TB with spacer and CAI.
The only other thing done to the car to that point was the h-pipe being swapped out several times, and we all know the O2's had to be removed and installed several times, so it's entirely possible these O2's got damaged in some way. The h-pipe swap was done by a mechanic shop also, but the rest of the performance mods were done by Ninety3Coupe.
I'm not saying the O2's are the sole cause of the stumbling issue or the bad gas/varnish smell. But the MAF and O2's are somewhat related since the MAF tells the computer how much metered air is coming in and the O2's monitor the burn of the fuel and with all the times he's bumped up fuel pressure and the fact that the O2's have been pulled multiple times lately (not to mention they have over 90k miles and almost 20 years on them), it's entirely possible they are overly saturated, damaged or just not holding the proper voltage any longer, which in conjunction with the increased air flow the car's getting now, plus all the extra fuel that's being thrown at it now, the O2's could be skewing the readings and the computer is trying to compensate.
Now I know the 5.0's computers are very adaptive (unlike my Cobra and most any new car out there), so with that said, it's that fact that leads me to think if nothing else replacing the O2's to this point certainly can't hurt.
I mean the engine should be getting more than enough fuel (and yes it's probably very rich now), now that he's swapped out what he indeed did find was a failing fuel pump with a Walbro 255lph and he's added the FPR and gauge to assist in fueling.
Also from everything I've read and calculated those stock 19lb injectors should be more than enough injector for his power level with the fuel pump upgrade plus the FPR. It certainly couldn't hurt to go to a bigger injector and trust me he and I agree that some larger ones would be helpful, but unless one went bad (which we understand it could of) I don't think it's the injectors. Especially since the car pulls great at WOT and only stumbles in the 2-3k RPM range in normal driving conditions.
If anything I've said is way off, please someone correct me. I'm just stating the facts of what I personally know and have personally seen with this car.
Also the only mods this car had on it when he bought it were the 73mm C&L MAF, shorty headers, cat-back exhaust and a short shifter. That's it, it still had the stock U&L intake manifold all the way down to the stock paper filter in the stock air intake. Other than that, that's it, so this was not a highly molested Fox body. But now it sure the **** is! lol that's for you N3C!
Last edited:
I may have missed it, but what brand of CAI? Does it put the MAF in the fenderwell?
The CAI is the BBK BlackOut version and the MAF stays in the engine bay in essentially the same position as stock.
Here's a few pics of it and the entire engine bay. Maybe you guys can see something we're missing.
Mobile Photobucket
Mobile Photobucket
Mobile Photobucket
Here's a few pics of it and the entire engine bay. Maybe you guys can see something we're missing.
Mobile Photobucket
Mobile Photobucket
Mobile Photobucket
Last edited:
I actually had a stumble and idle issue when I switched to a fenderwell intake. It seem to help clocking the maf but i just went back to the open filter which fixed the problem. This was a h/c/i car with a 75mm Pro M maf.
The thing with the CAI is, he's been running the intake with the filter in the engine bay up until this past Saturday (the 28th) when he finally ran the rest of it into the fenderwell and the stumble was there with a direct path of air to the MAF.
Any luck guys have u pulled ur intake off at the throttle body you installed and see if your.... I am going blank with my vocabulary ... The flapper ... And see if it's closed or open or opened to much and have you rechecked your all your settings under the hood like your throttle position sensor and what not...
---
I am here: http://maps.google.com/maps?ll=29.036726,-95.426903
---
I am here: http://maps.google.com/maps?ll=29.036726,-95.426903
I checked and the TB opens just fine - I can't picture it opening too much, it is perfectly perpendicular - is that right? I bought a new TPS because mine looked funny and I installed it, set it to .975ish.
Again, the bump in FP seems to have helped the stumbling but the smell of varnished gas is much worse. I still think the bump in FP masked the true issue at hand.
I am waiting for the new O2 sensors to show in the mail. I have high hopes, but I think I know the true answer (no dice). We will see.
I have subscribed to another forum and I just finished posting my question there. It is a little more "fox-centric" and I am hoping for more input there. I have seriously spent (and so has DT - THANKS DAVE!) dozens of hours researching this. The info is just not out there. Just when I get to a similar issue the thread dies and I don't know what the answer is.
I will update as I get info. I very much thank all that have helped so far! You guys rock.
Again, the bump in FP seems to have helped the stumbling but the smell of varnished gas is much worse. I still think the bump in FP masked the true issue at hand.
I am waiting for the new O2 sensors to show in the mail. I have high hopes, but I think I know the true answer (no dice). We will see.
I have subscribed to another forum and I just finished posting my question there. It is a little more "fox-centric" and I am hoping for more input there. I have seriously spent (and so has DT - THANKS DAVE!) dozens of hours researching this. The info is just not out there. Just when I get to a similar issue the thread dies and I don't know what the answer is.
I will update as I get info. I very much thank all that have helped so far! You guys rock.
Dude I think I have figured out my issue I believe It's a 16dollar part called a fuel pump relay get one and change it out I am ordering one today make sure it's motorcraft I heard the knockoff brands don't last
---
I am here: http://maps.google.com/maps?ll=29.936538,-95.448192
called a fuel pump relay get one and change it out I am ordering one today make sure it's motorcraft I heard the knockoff brands don't last---
I am here: http://maps.google.com/maps?ll=29.936538,-95.448192
Users who are viewing this thread
