90 NA Auto Trans issues, any input ASAP would be great
 

Hey guys, just wanted to start out saying that I love the site, being new to the Z (I got both my z32 and z31 in the last few months) there is so much great info on here. So here is my problem that I'm wondering if anyone else has run into. Randomly the trans won't shift into fourth, or it will be in fourth and fall out into third. Now when this happens, there is no "engine braking" in third as well. If you're going down the highway at 4k in third and let off the gas, the revs drop to idle. The third gear concern only happens when fourth isn't working. At first I was convinced the clutches were done, but then it worked fine for a few weeks, and now it's doing it again. Because of the lack of consistantly working or not, i've assumed that it's an electrical problem. I've checked the dropping resistior and it's ranging from 1.78v to 2.9v, the AT control unit ground is only showing .014v of loss to chassis ground, the ohms are almost 30 when the key is on, but like i said, I'm only seeing a .014v loss. It holds in everyother gear, and doesn't seem like ambient or trans temp is a factor. So there you go, as much info as I think is relevent to the situation. If there are any follow up questions, I'd be glad to answer them or run any kind of tests. If anyone has any information or suggestions, please don't hesitate to contact me. e-mail is Aaronkrider@msn.com Thanks guys, hope we can figure this one out.

Aaron

Considering how much work you've done trying to figure it out, this may be dumb to ask, but have you checked the fluid level? A low fluid level can cause problems of that sort.

The fluid was drained and refilled to the correct level a few weeks back, the level is still the same now, no signs of leaking or fluid consumption. And the fluid still seems new, no signs of accelerated deterioration. still reddish/pink and still has the normal ATF smell. I apprecate the insight tough, the only dumb question is the one we don't ask. Especially with me working on the car! (I've forgotten the basics a few times and it's led to lengthy repairs that could have been solved by a fuse... damn 550s....)

I know the feeling - I'm going through something similar right now with respect to "if I had just done this simple thing before, I wouldn't have these other problems now."

As for your problems though, I really hate to say this but I can't be of much more assistance. Not only am I more of an engine guy (I've never worked directly on transmissions before), but I'm more of a manual guy, so an automatic transmission and its diagnostics are jibberish to me. Sorry.

You might want to post in the technical forum on twinturbo.net though, they have some of the brightest Z32 techs in the world posting over there.

I'm in the same boat as Zlover...automatic trannies are a mystery.

This may soudn really lame, but I'll throw it out there....Since it sounds like it's an intermittent electrical problem, have you tried cleaning the electrical connectors around the tranny, or looking for a wire that's been pinched?

..... and on top of that, your speed sensor, TPS and, iirc, one other fuel injection control device is tied into the A/T ecm. They need to be in proper working order too. Have you run the A/T ecm diagnostics?

The A/T ECM diag gives me no codes at all, TPS doesn't appear to have any spikes in the range of operation. I'm going to go through and add some grounds to the AT wire harness as per a nissan bullitin I've dug up. And I'm going to look for and poor connections or pinched wires while I'm at it.

Not a bad idea....a grounding net can only help.