I would replace the transmission computer before replacing the transmission. It's much cheaper. Remember the first rule of auto repair: When in doubt, fix the cheapest thing first.

 

I have come to the conclusion that this is not necessarily a tranny problem. It is quite likely a loss of power (hp) problem. I make this statement based on the fact that when acting up I don't get much reaction to the throttle. If I press the throttle hard it just downshifts to high rpm but doesn't seem to be much power there. Secondly, when driving and finally get to 50mph in high gear an incline will make me start losing mph. The rpms don't go up like a slip, it's more of a not enough horsepower to maintain speed on the incline. So I'd like to approach this from a engine power standpoint. So I'll recap the symptoms and then what has been done to date:

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. 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.

 

To check for a restricted exhaust hook up a vacuum gauge and hold the accelerator at about 2500 rpm. If the gauge starts to drop then you have an exhaust restriction. If it's steady then you are ok.

John

 

Latest update: Checked vacuum and idled at about 25. Snapping throttle it would drop briefly, then quickly return to 25. No drop off holding throttle at about 2500. Attached fuel pressure gauge and it held a steady 60 pounds even when driving it and it acting up (taped gauge to windshield). Paid a mechanic to put his snap on computer on it it and he said both o2 sensors bad. Front one was all over the place and rear one bounced from 92 to 98 to 100 then to 0 then repeated. Bought and replaced both o2 sensors and front one read normally. Rear one had exact same readings...92,98,100, 0. NO codes

Also, worth mentioning that if you shut the car off for even 10 minutes (still pretty warm) then the first couple of shift cycles are normal before dropping off again. Also running AC definitely makes it worse.

 

Have I lost everyone? I'm still dead in the water and no idea where to look next. Stopped at a shop yesterday and the man hooked up yet another quality OBD2 reader and said everything looked good except he was concerned the cat was at 1000 degrees. I googled around and it seems this shouldn't be too alarming. I'm assuming if it wasn't working then it would get to that temp. With new o2 sensors in place and a small vacuum leak fixed I hold 25+ pounds on vacuum no problem so could it still be plugged? Seems I have no egr valve since I've looked everywhere - autozone sells one for my car but there is no exhaust rail for it to be on and don't see one mounted on head. Doubt this would cause power loss to max 10mph. Should I try a drive with no front o2 and see if it changes anything or is that a waste of time holding good vacuum? I haven't checked compression, but thinking it runs good cold and holds good vacuum...could compression be bad? Please stick with me guys, this is a toughy.

 

Hope you don't feel abandoned but if I had anything to offer I'd be offering it.

 

Problem solved....or at least figured out. Seems the old school vacuum test is not a fool proof indicator of exhaust pressure. After running out of things to try I loosened the 4 bolts that connect the cat to the manifold. Took a drive and was flying past everyone with sheepish grin on my face. Lots of pep, shifts fine, sounded like I was running over someone's cat with the sound the leak made. I'm assuming most of the things I replaced needed to be to get the original cat destroying problem solved, so now just the cat and on the road. Thanks for all the help...it's very much appreciated.

 

Brian,

Glad to see you figured it out. I was stumped also but found it odd that your rear O2 sensor was still reading bad even after being replaced. That sort of indicated a bad cat. Sorry the vacuum test didn't show you that you had a clogged exhaust. I've been using that test for years. At least a new cat is cheaper than a transmission.

John