[davets]

2005 Maxx with 3.5. 99,000 miles. Just started where when I give it 3/4 throttle or better there will be a severe hesitation then the car wakes up and takes off. Odd thing is that when the hesitation occurs the RPM's still go up as if the engine was responding correctly to the throttle input.

 

[Starship]

It sounds like a transaxle problem (low on fluid or low line pressure). You'll need to get it scanned for DTCs. The PCM keeps track of shift performance and thus troubleshooting has to start with the stored code(s).

 

[White Lightning]

2005 Maxx with 3.5. 99,000 miles. Just started where when I give it 3/4 throttle or better there will be a severe hesitation then the car wakes up and takes off. Odd thing is that when the hesitation occurs the RPM's still go up as if the engine was responding correctly to the throttle input.

Do you mean accelerating from a complete stop or while your driving?? If it's while driving I have the same problem, the motor revs, growls and then suddenly lurches forward...

 

[davets]

Thanks for the quick replies. It looks like I wasn't very clear in my description. The engine will hesitate. I mean it falls flat. The tach indicates the RPM's rising as if the engine were responding correctly to my throttle input but the engine totally drops off. It's exactly like a carb would act if it had accelerator pump issues. It gives me the impression that the tach indicates RPM's based on the gas pedal position rather that actual engine rotation speed.

It doesn't matter if the engine is warm or cold. If the RPM's are lower, like below roughly 1,800 or so it will flat spot if I mash the throttle then it will recover quickly. If I'm on the freeway and the RPM's are up and I mash the throttle there will be no hesitation.

 

[Starship]

2004 is when they went to the throttle-by-wire in which the PCM does what it wants to do. One scenario is, the PCM keeps track of shift performance and adjusts the line pressure by the pressure control solenoid. It's possible that the fluid pump inside the transaxle is not generating sufficient pressure at low input shaft speeds even with the PCM commanding maximum pressure. The shifts are then being delayed.

 

[davets]

I'll have to get it checked I guess. It really doesn't feel like a transaxle or shift issue. When I hit the gas the engine falls flat then kicks in. Yes the tach shows the RPM's rising at that time but the engine is not revving with the transaxle slipping. I don't think the tach is accurately reflecting the engine RPM while this is occurring. It is exactly what happens when a carb'd engine has a flat spot due to the accelerator pump not giving a shot a fuel off idle.

 

[DrivenDaily]

I have a question that might help (I hope). Since this is a drive-by-wire setup, is it possible that the PCM is telling the throttle to open AND advancing the spark timing? If so, then the tach would respond by deflecting upward even if the engine is mechanically not responding.

I know this is a stretch, but I'm looking for a way to explain the evidence thus far presented in a way that can be logically understood.

(Again, I don't understand the entire operation. I'm just offering ideas.)

 

[Starship]

Fake tachometer? That's too spooky. I actually have a Tiny-Tach for small engines (don't laugh). I wonder what I'd see if I were to hook it up. Anyway, the transaxle was what popped to my mind based on the age and mileage of the vehicle but who knows?

 

[DrivenDaily]

Fake tachometer? That's too spooky. I actually have a Tiny-Tach for small engines (don't laugh). I wonder what I'd see if I were to hook it up. Anyway, the transaxle was what popped to my mind based on the age and mileage of the vehicle but who knows?

Since our engines have COP (coil-on-plug), how does the Tiny-Tach pick up the signal?

 

[Starship]

It has a flexible pickup cable that's normally wound around the ignition wire. I think it picks up the RF spikes and thus will work if I get it around or near the ignition coil. I actually haven't tried it, of course.

 

[davets]

Now you're talkin' guys. You guys are understanding what my impression of the problem is. I've never had a DBW equipped vehicle before and I'm just now starting to read about a hesitation associated with DBW. I would be content if this was my issue but it didn't do it when I bought it this summer. I could borrow a scanner that shows operating perameters but I think the digital readout would not reflect the drop in RPM clearly like an analog tach would.
I haven't come across any common problems with this model car related to the tranny. Are there any? Thanks.
I just noticed my details listed a 2004 green Maxx. That was the car I was looking at when I registered to do research before buying. I ended up with the '05 white Maxx.

 

[Starship]

There aren't any common transaxle problems per se. The thing is, DTCs may be set but the CEL will not turn on unless there's a problem with the emission control system. As I've posted before, it'd be best to get it scanned for any stored DTCs. In addition to the current codes, often historical or pending codes tell a story as well.

 

[davets]

seems to be getting worse. Took it to a tranny shop. 1st guy test drove and said it seemed like normal hesitation while downshifting. 2nd guy hooked it up to scanner and drove it. said all looked good.