'95 Pathfinder Automatic Transmission Issue of Something Else?

[tlgrimmy]

Hello guys, I have a 1995 Pathfinder auto 4x4 with 158k miles. I recently did a transmission service (new oil and filter) and added a transmission gauge. It shifted fine before and after the service. Oil hadn't been done in a long time and was dark. It shifts quickly and smoothly into drive, reverse, park, 1, 2, etc. However recently, only after warming up for ten miles or so, it will occasionally not want to downshift/accelerate. I will slow down a bit and then hit the gas and the engine will just bog like when you try to accelerate in a manual if you're in too high a gear at a low speed. I could usually just come to a stop and try again to fix the problem, but it recently got a bit worse. It was driving along and shifting perfectly fine and then the issue started and wouldn't quite. When I got home, I noticed a mild idle surge when in park. It was consistent and just jumped up a few hundred rpms then back down very rhythmically. The transmission temperature stayed low the whole time (140-150 F). The idle surging issue actually made me feel a little more hopeful that it may not be a transmission issue, but I'm trying to prepare for the worst. What do you guys think. Bad/dirty IACV? TPS? I know those could cause some engine surging, but do you think they would mess with your shifting?

Edited May 7, 2013 by tlgrimmy

[Precise1]

I can't give you a good answer, but I can tell you where to find them...

 

Go to the Garage section and download the FSM in the pinned thread. In that are some pretty good diagnostic processes, including for the auto tranny.

 

Three things I would check right away is the ECU for fault codes, vacuum lines under the hood for cracks and proper connection and give the wiring for the TPS, MAF and engine coolant temp sensor (top front center leftish sticking out of the right side of the coolant passage, 2 in a row, it's the rearmost one) a wiggle when it is running to see if any of those affect the idle.

 

B

[Alkorahil]

Based on the symptom description, this sounds more like a MAF sensor harness issue/loss of engine power issue than transmission issue.

 

But ....DO THIS

 

 

• 1. check that there is the proper amount of fluid in the transmission. Do this after it is warmed up with the vehicle still running to get a proper reading.

 

 

• 2. Get in the vehicle and start it. As soon as it starts look at the Power/AT switch next to the mirror control on the left side of the dashboard.

 

IF the orange light on the Power/AT switch flashes several times (5-7) when the vehicle starts you have an error code stored in the AT control unit.

As Precise said, download the FSM for how to read the AT codes and fid out what it is saying.

[tlgrimmy]

I can't give you a good answer, but I can tell you where to find them...

 

Go to the Garage section and download the FSM in the pinned thread. In that are some pretty good diagnostic processes, including for the auto tranny.

 

Three things I would check right away is the ECU for fault codes, vacuum lines under the hood for cracks and proper connection and give the wiring for the TPS, MAF and engine coolant temp sensor (top front center leftish sticking out of the right side of the coolant passage, 2 in a row, it's the rearmost one) a wiggle when it is running to see if any of those affect the idle.

 

B

 

 

Based on the symptom description, this sounds more like a MAF sensor harness issue/loss of engine power issue than transmission issue.

 

But ....DO THIS

 

 

• 1. check that there is the proper amount of fluid in the transmission. Do this after it is warmed up with the vehicle still running to get a proper reading.

 

 

• 2. Get in the vehicle and start it. As soon as it starts look at the Power/AT switch next to the mirror control on the left side of the dashboard.

 

IF the orange light on the Power/AT switch flashes several times (5-7) when the vehicle starts you have an error code stored in the AT control unit.

As Precise said, download the FSM for how to read the AT codes and fid out what it is saying.

Thanks guys. I will check out each of the parts mentioned over the next couple of days. It has definitely gotten worse at this point. It only takes about 1 mile of driving before it starts to bog down when I try to accelerate. Always gets worse when I try to give it some gas after the symptoms have started, often refusing to go past 1200-1500 rpm. Then it will suddenly work fairly normally for a few seconds and shortly return to bogging. The Power/AT switch doesn't blink when I start the truck, it just goes solid for a second and shuts off. I'll download the FSM as well and see what I can do. Feel free to post any other ideas you might have and I'll be sure to post in a few days after trying some of these options.

[WyKi]

Have you checked the corrugated pipe that connects to the intake? that tends to break/crack and suck air in thru that. Mine was doing something like that aswell.... Ias a temp fix i put duct tape around it until i found another good one.

[Alkorahil]

You mention twice that it starts acting up 'after it warms up' and and 'about 10 miles'.

I am thinking this may not be a transmission issue.

 

This symptom has me thinking of the engine coolant sensor and the O2 sensor both of which start giving signals to the ECU after the vehicle warms up.

I would start with the engine coolant sensor. When they go bad they will cause hell with the engine as the ECU doesnt know what to do. IT is a very simple to replace part and very important for the engine to run correctly and get good gas mileage and they do nee to eb reaplced from time to time.

Many here can attest to this.

[tlgrimmy]

Have you checked the corrugated pipe that connects to the intake? that tends to break/crack and suck air in thru that. Mine was doing something like that aswell.... Ias a temp fix i put duct tape around it until i found another good one.

Looks like mine is ok, but definitely worth checking. Thanks!

[tlgrimmy]

You mention twice that it starts acting up 'after it warms up' and and 'about 10 miles'.

I am thinking this may not be a transmission issue.

 

This symptom has me thinking of the engine coolant sensor and the O2 sensor both of which start giving signals to the ECU after the vehicle warms up.

I would start with the engine coolant sensor. When they go bad they will cause hell with the engine as the ECU doesnt know what to do. IT is a very simple to replace part and very important for the engine to run correctly and get good gas mileage and they do nee to eb reaplced from time to time.

Many here can attest to this.

I'm starting to lean that way as well, which has me very relieved. I haven't found any obvious cracked parts/hoses or loos wires/connectors, so I'll have to look into how to test each of these components. I never thought about an engine coolant sensor causing such an issue, so I'll have to check that out as well. Thanks!

[Precise1]

Most of the sensor stuff is just checked with an OHM meter, but it can be a little deceptive where they test right cold, but don't work right hot or something. Also, sometimes the issue isn't with the component, but rather the wiring or connector, so be patient and thorough when checking things out or you risk running yourself in circles.

When you get this worked out, you may want to consider a tranny cooler and/or filter; the tranny is about the most expensive thing to replace.

 

Also, don't forget to search the forums for key words, almost everything that can be done has been discussed here and don't be shy about posting if you get stuck.

 

 

You mention twice that it starts acting up 'after it warms up' and and 'about 10 miles'.

I am thinking this may not be a transmission issue.

 

This symptom has me thinking of the engine coolant sensor and the O2 sensor both of which start giving signals to the ECU after the vehicle warms up.

I would start with the engine coolant sensor. When they go bad they will cause hell with the engine as the ECU doesnt know what to do. IT is a very simple to replace part and very important for the engine to run correctly and get good gas mileage and they do nee to eb reaplced from time to time.

Many here can attest to this.

^ What the parts pimp said, he knows his stuff.

 

My buddy was over 2 weeks ago with his 91 and we worked on a lot of things. I showed him the temp sensor and described the problems people have had and while doing so, I wiggled the wiring. As he went to leave, when the pathy warmed up it died as if the ignition was shut off. I've never seen a pathy just die like that, and when we got it started after much cranking, it ran like crap with a mis and blew out black smoke when throttled. After checking a bunch of things, we tweaked the wiring and connector and it ran perfectly again. When he got home, he disassembled the connector cleaned out a bunch of corrosion, lubed it with di-electric grease and it's running flawlessly and reliably.

The ECU really wants good input from that sensor!

 

B

[tlgrimmy]

Wow! That took awhile to get fixed, but I'm pretty sure it's all finally squared away. I'm not sure if i mentioned this already, but I found a vacuum line that had fallen off between the firewall and the intake manifold, so I replaced all of the vacuum lines. That helped, but the issue simply took longer to creep up and wasn't quite as bad. I got tired of spending hours trying to diagnose the issue, so I finally took it in to a mechanic to have him diagnose things for me. A transmission specialist said that it was a definitely an issue under the hood and not the transmission (whew!). The mechanic had a code reader that could deal with the OBD 1 port on my truck and he ended up finding a stored code despite no engine light present. I guess the distributor has a camshaft position sensor built into it and the code was an error for that. I went ahead and replaced the distributor and gave things a whirl (that's an expensive little distributor!). Things went much better and I thought I was in the clear, but after about a half hour of driving the issue came back only not as bad as before. I still had the engine bog and no acceleration. I kept going back to fuel pressure because it really felt that way in the pedal to me. I could even back off of the pedal and gun it a bit and usually get a bit of a response. I then realized that I never changed out the fuel filter, which I thought I had taken care of when I did the timing belt. After changing that out, all symptoms seem to be gone. I drove around for a little over an hour and tried letting it sit an idle, driving on the freeway, driving around town, and I even did a little offroading, so it seems that she's good to go (knock on wood). I wish I had remembered the fuel filter earlier, but it was definitely a compound issue with all of the improvement after each part was fixed. Thanks again for all of the help guys. Much appreciated!

[Slartibartfast]

Sounds like an expensive fuel filter! Good to hear you got it running right though.

[enkrypt3d]

Thats strange I have similar symptoms where it feels like the transmission doesn't want to downshift into 3rd or 2nd depending on the speed... which is tough when entering the freeways... I've already replaced the fuel filter, spark plugs, wires, distributor cap & rotor etc ... one thing I haven't done is clean the MAF or replace the engine temp sensor - can someone point out where that thing is?

[Slartibartfast]

Your upper radiator hose hooks to a pipe going to the engine. Mine's got two sensors on it (IIRC one is for the dash gauge). Looks like the rearmost one is what the computer looks at.

 

Mine doesn't always want to downshift either. There's nothing wrong with the engine or trans that I'm aware of, it's just that the TCU just doesn't know that the truck is underpowered, so it goes for overdrive when I'm trying to drag it up a mountain pass. Next thing I know I'm making a parade, and then it drops to second and howls at me. I've found that it works much better in power mode (which I leave on at all times now). It downshifts earlier and more easily, I swear at it for doing stupid things less often, and I've noticed no impact on fuel economy.

[tlgrimmy]

Well, it looks like things went south again...It seemed like all was cleared up, but after a couple of trips the symptoms came back again! Engine bogging and even quitting at times. I gave the air flow meter and the throttle body a really good cleaning and the truck ran much better, but still starts to bog from time to time. This time I discovered something that got me worried. It used to be that the engine would still bog when I switched it into neutral. Now the symptoms go away when switching into neutral. I can usually back off the gas a little and then punch it to get past the engine bog, but I noticed the transmission switch light came on just before switching gears and stayed on for a 30 seconds or so. I watched the switch the next time it bogged down and when I tried to accelerate out of it, the light came on again just before switching gears. It doesn't come on during the bogging, just when I try to accelerate out of it. The tranny guy I went to said the bogging wasn't due to the transmission, but now I'm really starting to wonder. Nothing else seems to cure the problem and now with the transmission light coming on, I'm begging to thing that it must be the tranny. Any thoughts? Getting sick of dealing with this thing and am contemplating selling it. I'm already into in for a grand and am loosing the desire and wherewithal to troubleshoot this thing. It looks like it would be a royal PITA to put in another auto transmission and I'm not willing to shell out the $2000 to get a properly rebuilt one. Anybody want my pathfinder;)? I'll let it go for $1000. Ton's of new parts and lower miles. Could make a great rig for somebody who feels like dealing with the tranny.

[Slartibartfast]

When you try to accelerate out of it, are you pushing it to the floor? That light comes in on power mode, which you can do with the switch or which IIRC it goes into automatically if you floor it. That may be why the light is coming on. It's also possible that the bogging engine is confusing the trans computer.

 

Put the switch on 'auto' and turn the ignition on without starting the engine. The light should come on for two seconds and then go off again. If it doesn't, or if it flickers for several seconds afterwards, the trans computer thinks there's something wrong. If not, I agree with your mechanic, this sounds like an engine issue.

 

The fact that it stops bogging in neutral is interesting but IMO doesn't necessarily point to the trans, unless your current issue is unrelated to what it was doing before. If the transmission was somehow binding up and slowing the engine I would expect it to make all kinds of bad noises in the process.

 

I'd start by checking the electrical plugs in the engine bay, especially any you may have jostled when you did the fuel filter. Open them up, look for corrosion, clean them up if needed, see if the wires are buggered. If a plug is making a lousy connection, bumping it may have made it connect again briefly.

 

One other possibility is a gummed up fuel pump. Mine gave me issues a while back when I ran it down way past empty and apparently sucked crud into it. It bogged horribly and barely ran, and that's when it would start at all. When we took it to a mechanic, it started right up, ran fine, made it a block, and then cut out again. If a clogged fuel filter caused part of the problem, then maybe there was enough crap in the gas to gum up the pump as well. (The mechanic cleaned mine out and it was back to its old self.)

 

I know the feeling of thinking it's fixed and having it act up again. Good luck!

[Towncivilian]

I don't understand how any "crud" can get sucked in from the bottom of the tank. The fuel pump pickup is at the bottom of the tank. What is there to suck up? There's also a sock over the pickup and the in-line fuel filter to catch anything. I suppose it's possible for the pickup screen to become clogged but most new cars have just that filter and I've never read of a case where it *needed* to be replaced - it's basically a lifetime filter (oh how I hate that term) and is to be replaced with the fuel pump assembly. The in-line fuel filter becoming clogged is certainly a possibility, I'm not sure they have bypass valves.