Strange Get-Up-And-Go Problem
 

Well, having a little bit of a wierd problem for a while now. I'll describe it as best I can.

Basically, the car is a complete dog from off idle to ~3000-3500 rpm. When you hit the gas, the car acts like it's pulling up a long, steep hill. However, when you reach between 3000 and 3500 rpms, there is a point at which the power immediately comes on. It's almost like someone flipped a switch, it's that sudden. So from a stop, it goes: bog...bog...bog...bog...bo/POWER.

As near as I can tell, I really began noticing this after the tranny rebuild. Also, above 85 mph, the car vibrates like crazy, and it is definately speed related and definately not the tires/wheels. My theory is that the vibration is coming from the drive shaft...gotta get a new aluminum one sometime.

As for the power problem, I'm kinda stumped. I almost want to think that the problem is coming from my torque converter. During the rebuild, they sent off my PI to check its balance and they polished the hub. Also, with the car at idle or in park, the converter will whine for a bit and then quiet down, and my fuel economy is absolutely in the crapper. It seems that during the period where the converter is slipping (0-3000 rpm) the car is a dog, and then when it finally locks up, it takes off. However, I don't know why the change would be so sudden. Then again, maybe it's electrical.

Any ideas?

--nathan

My car has a similar problem. There have been times when I start it up and it's still kinda cold and I kinda get on it, it's fallen on its face twice now. I've never replaced my fuel filter since I've owned the car in 99. I kinda wonder if that doesn't have something to do with it... In my case anyways. Also I have a similar vibration problem. Sometimes the problem is there, sometimes it's not. Weird.

tough one, just remeber always start with easy things first, check your filters and fluids before looking at a major issue. Fuel Filter trans fluid all the easy stuff GOOD LUCK!

Yeah, the vibration problem is always there. I've replaced the U-joints on the driveshaft and it helped just a tiny bit. I think the shaft is out of balance.

Anyway, the power problem is also fairly consistant, but the rpm at which it occurs can vary by 500 rpm or so. The fuel system should all be fine. New filter, injectors, pump, regulator, etc. And the problem occured before and after the injector swap.

--nathan

Good advice, and I've checked and rechecked all the fluids a number of times. Everything seems to be ok. Anyone ever hear of a converter causing similar problems? Or maybe a coil? But I thought coils usually crapped out in the higher rpms rather than the lowers. Also, all the plugs and wires are fine.

--nathan

I would guess that it is the converter. When it is in park does it feel mushy below 3500 when you rev it?

Not that I notice. It revs like crazy in park when you hit the pedal. So I guess that would help support the idea of the converter being the problem? With the transmission in park, the flywheel/converter/input shaft are free spinning, right, and the transmission itself is disengaged.

That's kinda what I was thinking. Not too fun. Next time I'm able, I'll send the converter to someone I trust to check it out.

--nathan

Whens the last time you checked the tps volts? Have you pulled any codes? Come by, i have a code checker.

It's definitely the convertor.

Your vibration has to be something between the output shaft of the tranny and the wheels. If you're sure it's not the wheels, try turning your driveshaft 180 degrees.

Thanks for the diagnostic help.

Chris,

That's a bummer, but I guess that's what I could expect with my luck. I wonder if PI will help me out any on this one. I doubt it. It's past warranty. May just up for a new Lentech or PA converter...the're just a tad bit cheaper. As for the vibration, I'll try turning the drive shaft and see if it helps.


John,

I've got a scanner, and no new codes are showing up. TPS should be set around .95 or so. I'll put a volt meter across the tps and see how she reads throughout the throttle plate position. I'll give you a hollar this weekend to see if you want to help me wrench on this thing or if I might be able to use the lift.

Thanks everyone!

--nathan

Heck yea. Come use the lift. We are going racing at idalou tonight. I put a boost a pump on the linc. Gonna try the 28" tall tires on the 350.

FWIW, unless you've been in an accident, your TPS setting shouldn't change. What you really want to test when checking the TPS is the condition of the rheostat. The best method for doing that is to disconnect the TPS harness, and connect your test leads the same way you do when measuring volts, only set it to ohms. This works best with a DMM that has a bar graph, but even without one, it still works. Rotate the thottle slowly, and make sure the value only goes up while opening, and only goes down while closing, the throttle. If the values jump around at all, replace the TPS.

:)

Take care,
~Chris

Thanks. I learn all kinds of stuff from you. :D

Anyway, I talked to PI. They said that I could send them the converter and they would cut it open and call me back to let me know whats up and see what I want to do. At the same time, they can increase the stall speed and change it over to a lock-up converter (gas is eating me alive) and fix anything thats wrong for around $295. The tech lady says that the whining is either form a bearing in the converter or the front pump.

Question: Could a failing front pump resulting in lower fluid pressures cause a problem like I'm experiencing?? The tranny doesn't feel like it's slipping when trying to engage gears or anything, and the shifts are nice and firm.

Just trying to eliminate any other possible causes before I send the converter off. The tranny itself is under warranty, so I can get anything internal fixed at no cost. I'm personally leaning towards the failing converter....

--nathan

I don't think a failing pump would create symptoms like yours. A failing pump would act more like a bad vacuum modulator (for those of you that remember those).