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Loss of power when engine warmed up

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Jul 11, 2017, 8:19 AM

Post #1 of 2 (531 views)
Loss of power when engine warmed up Sign In

2003 Chrysler Sebring Sedan 2.4L DOHC 135K miles. I originally believed tranny problem but now not so sure. Drives beautifully until warmed up.

Car runs and shifts perfectly when started cold. Idles well and goes into gear smoothly to leave home. After 10-15 minutes it holds gears a very long time and I must feather off the accelerator to get it to upshift. Then I have to feather back on the gas or it will downshift again. After a long enough time it works its way all the way to high gear and doing the speed limit. Any hard accelerator is an instant downshift. To gain speed I must just slowly increase accelerator and let the vehicle speed very slowly increase. No codes. Any incline in the road (such as overpasses) there is a noticeable slow down. Pushing harder on the accelerator only downshifts and letting off gas to upshift again only slows you further. All fluids clean and clear.

Done so far:
1. Replaced shift solenoid and input/output sensors. Had TCM quick learn completed at dealer. No indication of a TCM failure and no codes.
2. Replaced plugs and wires. Did make it idle smoother and at lower rpms, but didn't solve main issue.
3. Replace TPS. No change.
4. Replaced MAP sensor. No change
5. Cleaned MAF sensor with proper cleaner. It's intact and no change.
6. Pulled IAC and it moves in and out, cleaned with spray and reinstalled. No change.
7. Pulled fuel rail, removed all injectors and used 9v battery to open and spray carb cleanerr through them to clean jets. New o-rings and reinstalled. No change.
8. Bought IR thermometer and measured temp at cat (part of exhaust manifold on the 4cyl) and it was 338 at inlet and 438 at rear. Measured at what I believe is a resonator (is this correct?) and it was the same in and out and noticeably cooler than at the cat.
9. Disconnected front o2 sensor wire to default to normal rich/lean without o2 adjustment. No change. Also wanted to see if ECM was capable of throwing a code and it did instantly. Reconnected.
10. Used IR Thermometer to measure engine coolant temp at thermostat housing (didn't trust gauge which was perfectly center on temp) and it read 194 degrees after a long stumbling drive home from buying the IR.
11. Cleaned Throttle body and replaced air filter. No obstructions. No change.
12. Removed pcv valve. Rattled nicely. Sprayed with cleaner and reinstalled.
13. Checked for vacuum leaks at all hoses with carb cleaner and no engine reaction.
Not burning oil visibly. Minor blow back at oil cap when running but not major. No coolant loss.

Could it be coil getting hot? Exhaust obstruction even though cat seems ok? Temp sensor? Fuel pump? Running out of options here. I have no means to check fuel pressure but tank is full and dropping it would be tough. I haven't explored that much because acceleration and fuel seems fine until engine is warmed up. Any advice is greatly appreciated.

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 11, 2017, 8:35 AM

Post #2 of 2 (526 views)
Re: Loss of power when engine warmed up Sign In

You need to run some tests.

First you need to have the exhaust system pressure checked at the upstream 0/2 sensor and if that stays under 1 PSI, then you need to rig up a fuel pressure gauge that you can monitor while driving to see if you are experiencing any fuel pressure drop at the fuel rail.

If you are unable to perform these tests yourself, then it is time to take it to a reputable shop for diagnosis.

If the computer is setting any codes that you did not induce yourself, post the numbers here.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

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