While jumping right into this, I would like to start off by saying that I’ve been chasing an ongoing issue with my manual 2003 Mach 1 for months and I’m reaching the point where I’m ready to give up on diagnosing it myself and take it to a shop.
For some insight, the car currently has approximately 117,600 miles, a K&N intake, stock manifolds and H-pipe, and Borla ATAK mufflers.
The original recurring code was P0172 (System Too Rich Bank 1). It came back roughly once per month in March, April, May and July. Then in August, instead of P0172, I received P0420 (Catalyst Efficiency Below Threshold Bank 1) twice within five days and only 164 miles. The car is my daily and mainly drive it with highway miles considering a 60 mile round-trip commute, so this is pretty concerning for me.
I’ll attach the freeze-frame reports separately so everyone can see the fuel trims, speeds, RPM, load and fuel-pressure data for themselves.
The main symptoms have been:
- Uneven and slightly shaky idle
- Car sometimes rocks at idle almost like it has very mild cams (very Lumpy Tone)
- Passenger-side exhaust is consistently sounding a bit louder, and bubblier/poppy
- Driver-side exhaust sounds noticeably cleaner/smoother/growly (best I can explain it)
- Occasional pops/backfire around 2,500–3,000rpm when having a little bit of a light heavy foot and switching gears from 1st to 2nd
- Constant popping like popcorn while holding the revs at 2,000–3,000 rpm’s
- Low-rpm acceleration can feel heavy or sluggish
- Occasional difficult restarts after the car sits for approximately 5–30 minutes (found this out by the car struggling to turn on after consistently turning it off and on in a long drive through line)
- Cold starts are usually stronger than hot starts, but can still give me issue when cranking over before starting
General Occasional weak starting
- In the past, the engine occasionally stalled after high-speed driving and throwing it in neutral, or while coasting downhill in neutral
- Fuel economy has been approximately 14–15 mpg, even though MOST of my driving is on the freeway in 5th gear with my stock 3.55 Gearing (I know this because I daily the car lot and consistently top off the Car in gas and measure it EVERY TIME by resetting the trip meter)
- Full tank of premium (15.7 Gallons) Last me 230 miles MAX (Mainly Highway Miles)
- The codes always appear while the engine is fully warm and I’m steadily cruising on the freeway (not while idling in my driveway)
This is everything I’ve done trying to fix or narrow down the problem:
- Installed eight new NGK iridium spark plugs
- Gapped the plugs approximately .050–.053 inch
- Replaced the coils with a complete set of used Edelbrock coils off a 99 Cobra That WAS Working
- Swapped the Bank 1 injectors with used set of Bank 1 injectors from another 2003 Mach 1 (24Lb)
- Installed a new fuel pump
- Installed a new fuel filter
- Replaced all four O₂ sensors with new sensors (NTK)
drove around a bit got the code again Swapped the upstream O₂ sensors left-to-right
- Also moved the other O₂ sensors left-to-right during diagnosis
- The problem continued to remain associated with Bank 1
- Swapped the CCRM with one from another 2003 Mach 1
- Cleaned the original IAC then noticed no change also with my idling issue so I ended up, replacing the IAC with a used Lincoln Mark VIII IAC I got from the Junkyard
- Cleaned the MAF using proper MAF cleaner
- Used fuel-system treatment TWICE! (3 month Gap between uses)
- Sprayed brake cleaner around the intake manifold looking for a vacuum leak (Did not notice an obvious idle change during the brake-cleaner test)
- Replaced the passenger-side radio noise suppressor (advice from a friend)
- recently swapped in the MAF from other other 2003 Mach 1 (That WORKS)
The most recent MAF swap happened after the second P0420 just yesterday (August 31st), so I don’t have enough driving time yet to know whether it changed anything, but then again, I’m not sure if it will because if it really was the MAF, then it would be affecting both banks, but we will have to see, it’s more of a why not I guess. But for the most part it has still sounds and feels the same at idle.
The plugs greatly improved the original weakness of power and sluggish starts and cleaning/replacing the IAC from the Lincoln MKVlll helped the stalling, but the uneven idle noise from the passenger-side exhaust end is still noticeably different with occasional popping more consistent condensation, and smoke on cold starts from that side (Bank 1)
I own a set of BBK long-tube headers and a matching BBK catted X-pipe, but I have not installed them yet. I don’t want to install new catalytic converters and possibly damage them if the engine is still running super rich.
At this point I really don’t know what else it could possibly be besides a vacuum leak or some sort maybe but considering that this car is my daily and deeply need to find out what’s wrong with it, I’m willing to spend some money (Nothing Crazy) for a genuinely deep diagnosis from a shop. I don’t want to pay someone just to scan the codes and recommend a MAF or catalytic converter based on the code description. I want somebody to test the fuel pressure mechanically, check pressure after shutdown, inspect the EVAP purge system, evaluate the MAF data, test the injectors and compare the Bank 1 O₂ signals before and after or generally just whatever the procedure might be to crack down on this shit that’s making me go insane!
I would still 110% rather diagnose and repair it myself if possible. I’ve considered buying a smoke machine and compression tester, especially because I can use those tools again. However, I don’t want to keep spending money on tools or parts that won’t actually narrow this problem down.
Based on these symptoms and everything already replaced or swapped:
- Would buying a smoke machine meaningfully help with this specific problem?
- Is a full compression test justifiable?
- What should I test next before paying a shop?
- If I take it in, what specific tests should I require for a proper diagnosis? And how much am I looking at$?
- Could the original rich-running/misfire condition have damaged the Bank 1 catalytic converter and caused the two recent P0420 codes. And how badly do I need to get this fixed before anything else gets fucked up?
- Is there anything else to the 2003–2004 Mach 1 or Ford fuel systems that commonly causes this combination of symptoms?
I’m attaching all six freeze-frame reports along with the list of work completed. I’m looking for a proper direction. The car still runs strong (from what I know) but I’ve always been wanting to overthink everything and not ignore a problem before it turns more severe (talking from experience) so I’m a bit paranoid and just want to fix it as soon as possible so I can make sure that my Mach is not only being as efficient as it possibly can but at its best potential.
I’ve put a lot of time, effort and money into trying to solve this, and I’m honestly reaching the point where I don’t know what else to do. I really love this car and I’m willing to keep it for the long run. I’ve made it to be everything that I’ve ever wanted and I’ve been trying so hard to keep it running correctly, please help me and keeping my baby alive and healthy. I’m more than willing to communicate about any questions or concerns!
Thank you all!
