Erratic Run on a 2001...

My Copilot Zip

New Member
Aug 23, 2022
Was asked to help on this. Not my car and not at my place, so it's a back and forth process (small town tho) and also a big school for me, having never worked on a Mustang (but almost everything else - from B-52's to Bowling machines... and lotsa cars) SUBJECT: 2001 Base coupe - 3.8 / auto. Reportedly has a replaced fuel pump (no documentation). Original complaint: Starts, runs smooth until operating temp is reached, then begins stumbling and within a few minutes it slows and dies & would not restart until cooled. I put a Think scanner (didnt understand I could scan for live stream data - was only looking for codes) on it and it first showed only an EGR issue. Replaced EGR. Cleared code, started cold and did the same routine, then only showed the FRPS was at fault. Replaced that. Started cold and the same issue prevailed. It was then I learned about live stream and saw it was only getting a pretty steady 11.6 PSI. R&R Fuel filter and while disconnected did a FP squirt test momentarily. Seemed to be putting out a lot of fuel. With new filter, the live stream was erratic. Pressure at one point jumped 4 PSI to 66 then to 5 then 30 to 4,3,2, then died. Removed shrader cap and found the valve core leaking. Replaced that. Engine seemed to be progressively running worse. Now key-on shows no pressure on scanner or mechanical gauge. Cycling key several times starts engine repeatedly and engine will idle for a long period and not die but if revved more than a minute will die and require cycling again.
At this point I know the pump is running, but am wondering if the pressure regulator (if that's what it is) is a/the problem. The part I see is inline from the main fuel line to the rail (passenger side and is round disc shaped 3" diameter with in/out nipples. The odd thing is Carquest says they see the part, but O'reilly's and the old NAPA say they don't see a FPR for that application. So... I'm becoming frustrated... The part is stamped Ford, has these identifiers on it. FIZE-AA 001020A. Because it's the long weekend, I can't check with Ford on it. I've seen many posts with similar symptoms, but most seem to end in a replacement pump. Thought I'd write you young gunz and see what your thoughts are...I'm a 75 year old guy who's been wrenching since my first erector set at 4 years old... Tho many of my 350 rigs have been flat head Fords and straight sixes, so digging into computers and electronic engine controls this deep is a bit like Alice jumping into the rabbit hole...:bang: THANKS for any ideas, suggestions, or butt-kicks!
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Active Member
May 17, 2005
San Diego, CA
I had a similar issue with my Bullitt Mustang. When my brother had it, it would start and idle fine but after a bit of driving would start to stumble under acceleration above about 2500 rpm. A lot was done to the car including replacing the fuel pump, plugs, and "gutting the cats"... still didn't fix Once I had the car, was able to replicate his problem and also found that it would only stumble under heavier load on the engine. Turns out that even though the fuel pump was replaced (determined by the date code on the fuel pump when I removed it), the new fuel pump was also bad. Once I replaced the fuel pump the issue was resolved and I'm able to boot it like it should be.