Q45 late shifting? And a Warning. . . .

[richfan]

Any ideas on why a 90 Q45 shifts late from D3 to D4? Its does not seem to care whether I let off the gas or stay on it. Had the transmission built about 8 months ago without any major probs, and there is no slippage. TPS switch? Wierd. No doubt it will be expensive!!

Warning: If you go to replace your driveshaft with an aftermarket that replaces the front flexible rubber disc with a traditional U-Joint, you may run into the trouble I found. When taking off hard, the driveshaft sometimes will raise up from the torque and knock on the floorpan. It's very driveable, but pretty damn annoying sometimes.

Rich

[Q451990]

By a late shift, you mean it holds the car in D3 too long? You need to check/have it checked with Consult to see if the transmission is responding to the signal from the TCU/ECU. It may be taking a while for the pressure to get to the correct level to shift - that's the usual cause for slow shifts. If that's the case you may have a blockage in the system or leaky seals... Was this an Infiniti reman or something else? Aftermarket transmission rebuilds have a very bad track record - hopefully you got a 12 month warranty?

Any chance the drive shaft issue could be related somehow?

How many miles on your Q? Have the timing chain guides been replaced? I'd have that done before you put any more $$ in to the car if you're planning on keeping it for a while. Even a pristine car with a good transmission is essentially worthless with a scrambled engine!

Welcome to the club!

Heath

[richfan]

Thanks for replying Heath,

Yeah, it was an aftermarket reman, but I had it built about 2 years ago and its been ok ever since. Fluid doesn't smell burnt, and it never actually slips. It does stay in D3 too long though, and it reminds me of the time I steam cleaned the engine, and suffered with the exact same prob for about a week. That's why I was thinking it might be the TPS throttle position sensor.

I have the factory manual, do you think I'd be wasting my time if I went through the trouble shooting tree without the Consultant? Or should I just bite the bullet and pay the dealer to do it?

Thanks for your thoughts!!

Rich

[Q451990]

You can test the TPS with an ohm meter. If it's way out of range or has dead spots, you might be on to something... it's a rare failure, but if you've seen this before that's a good place to start.

Heath

[aaacomp]

I think your on the right track about the transmission, Just thought I'd add that after the first rebuild I had a professional transmission rebuilder here in Dallas rebuild mine and it took him an extra day because of the oem o rings. He stated he installed larger dia. to increase fluild pressure.. The transmission always shifted quick and hard into all gears. I have since had another rebuilt with the same o rings and it reminds me of a B&M shift kit , but without the cost.Level10 also sells their rebuild kit.............:thumbup

[Q45tech]

The 3 to 4th shift can occur at any speed from 25 mph to 130 mph depending on the amount of throttle in D range. In 3rd gear position the minimum upshift doesn't occur until 37 mph but the top shift never occurs.You can safely [manually] down shift to 3rd at any speed up to 135-140 mph. [150 mph with JWT ecu]

The throttle opening reads from TPS voltage [which is simultaneously sent to engine ecu and transmission ecu] is divided into 8 steps [for the transmission ecu internally] from 0/8 [closed idle] to 8/8 [WOT] roughly 0.5 volts each........not having a closed throttle voltage of 0.4 to 0.45-.49 is the usual problem.