2000 GT dies once warmed up

bigred90gt

Member
Jan 24, 2022
3
2
13
41
Baytown, TX
So, I finally got my 2000 GT back together and running(ish). Cranked it up, and it cranked first try. I let it idle for a bit, but it was almost 2:00am so I didn't take it for a drive. The next day, I cranked it and once it warmed up, I tried to take it for a drive, but it died on me. After it died, it cranked right back up, but immediately died again. for a while after that, it would just turn over but not start. Then it started again, and just keeps stalling out immediately. I thought maybe the gas that was in it was no good, and it hardly had any (sitting on E), so I put some fuel treatment in it and a full 5 gallon can of gas. I messed with it again for a few hours, cranked it and held the gas down to try to burn out some of the gas, and as soon as I let off the gas it dies. I eventually got frustrated, and quit messing with it. The next day, I cranked it and it idled fine again. I backed it out of the garage after it warmed up and when I pushed in the clutch again, it died. I got it cranked and drove it, but never stopped while I was driving and it never died. When I pulled into the driveway and stopped, it died again. This happened again the next day. I can crank it and keep my foot on the gas and it wont die. I can keep it at idle RPM by with my foot barely on the gas, and keep it running no problem. As soon as I let off, it dies. Only after it's warmed up though. When it's cold, it will crank and idle fine until it warms up. Once it warms up, if I rev it or put any load on it, it stalls once the clutch is pressed again.

There is no check engine light, but I scanned it for codes and came back with P0172, Rich bank 1. I tried cleaning the MAF, IAT, replaced the IAC valve, checked all vacuum lines, checked all connections in the air intake. I've pulled the negative battery cable and let it sit for 10-15 minutes, nothing has helped. I cleared the code and it hasn't come back, but it is still doing the same thing. I tried running it with the MAF unplugged, and no change. The only thing I haven't messed with is the throttle position sensor and the EVAP canister (one of the checks for a P0172 code). I know nothing about the EVAP system, so I wouldn't know where to start with that. I do not have a fuel pressure gauge, but I did depress the schrader valve after it died and it sprayed fuel, so it's got and is maintaining pressure, I just don't know how much.

I just had the heads rebuilt with new valves, springs, retainers, seals and had them all cleaned up. Installed CMS stage 1 cams, BBK 73mm throttle body, it has a C&L CAI, BBK tuned length shorty headers, BBK catted x pipe, Magnaflow catback. It has a new fuel filter as well. The last thing I tried was swapping back to the stock throttle body, but it didn't help anything. I'm at my wits end. If anyone has any advise, I'm all ears. My next step is to take it somewhere and pay someone else to fix it, but I'd rather just do it myself if someone can point me in the right direction to try to diagnose it and fix it.
 
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manicmechanic007

Mustang Master
Sep 26, 2017
1,575
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It might just be tight and or relearning
After the mods you might be stuck with rich and lean codes forever so I would not worry about those for right now
Clear codes and retest after a long drive and new fuel
Do that at least twice and use premium fuel with no alky if you can find some
Try the stations your city shops use like gasman for the no alky fuel