New owner, couple of small issues

[Destrto]

Hey guys, I'm a new owner of a 1990 2+2 N/A Auto. I've always been a fan of these cars, and I've finally found myself one. However, this one has a couple of issues that I'm hoping you guys on the forum can help point me in the right direction to getting diagnosed and fixed.

The first one, is a slight hesitation when coasting. It seems to be intermittent, but once it decelerates to about 1000-1200 RPMs, it will sometimes pulse a few times. This has happened a few times so far since owning it. it happens whether I have my foot on the brake, or letting off gas or brake. It's very slight, but still noticeable.

The second issue is a bit more concerning. I currently have a small oil leak coming from what appears to be the rear of the engine, where it hooks up to the transmission. It only drips for a few minutes after the car has been driven, and then stops. And if I use stop leak, the leak goes away for awhile. Now, to me, this says a gasket is leaking, or a bolt is loose. But the couple of times that I tried to look, I couldn't find or reach any that seemed to be loose.

I'm familiar with basic troubleshooting, but I am new to these cars in particular and how they work. So, any tips or a good direction to take would be very appreciated.

[centralcoaster33]

Hey Destrto, welcome to NICO Club!

Congratulations on your new Z ownership.

I think you could check for a vacuum leak on the brake booster hose or somewhere around the intake that may affect your idle on deceleration... that or maybe your idle air control valve (if your run ac all the time, maybe even your auxiliary idle air valve) might need a cleaning. Maybe plugs, O2 sensor, fuel pressure, bad fuel injector, etc., others will know better than me. Sorry about the maybes. I'm guessing in order of suspicion. You can do some diagnostics with the ECU to narrow stuff down. I really recommend the following...
http://www.nicoclub.com/archives/nissan ... ostic.html

For the oil leak, I guess you could tell if it's transmission fluid or oil. It sounds like it's coming out of the bottom edge of the bellhousing, so I'd guess rear main seal. Not too tough to do and usually paired with a clutch job, but since you're auto and converter jobs are rare, it's probably just the seal never being replaced or looked at. Wipe the area clean, drive a bit and try to pinpoint the leak source. You don't want to do a main seal if it was your oil pan!

I don't have a Z. Lot's of the members do, so stay tuned for more experienced feedback. Until then, check out our FSM resource! (this link is to each chapter, we don't seem to have the table of contents page, you can download the PDF to your device)

http://www.nicoclub.com/FSM/300zx/1990/

[Destrto]

Hey Destrto, welcome to NICO Club!

Congratulations on your new Z ownership.

I think you could check for a vacuum leak on the brake booster hose or somewhere around the intake that may affect your idle on deceleration... that or maybe your idle air control valve (if your run ac all the time, maybe even your auxiliary idle air valve) might need a cleaning. Maybe plugs, O2 sensor, fuel pressure, bad fuel injector, etc., others will know better than me. Sorry about the maybes. I'm guessing in order of suspicion. You can do some diagnostics with the ECU to narrow stuff down. I really recommend the following...

For the oil leak, I guess you could tell if it's transmission fluid or oil. It sounds like it's coming out of the bottom edge of the bellhousing, so I'd guess rear main seal. Not too tough to do and usually paired with a clutch job, but since you're auto and converter jobs are rare, it's probably just the seal never being replaced or looked at. Wipe the area clean, drive a bit and try to pinpoint the leak source. You don't want to do a main seal if it was your oil pan!

I don't have a Z. Lot's of the members do, so stay tuned for more experienced feedback. Until then, check out our FSM resource! (this link is to each chapter, we don't seem to have the table of contents page, you can download the PDF to your device)

Thanks for the welcome!

And thank you for the tips on where to start my search.

With the oil leak, it is definitely oil. Dark brown in color. Smells more like oil than what trans fluid normally smalls like. I'll check on your suggestion about it being the rear main seal.

I appreciate the extra links. I've been looking for different sites with more information and decent parts list for replacement.

I also need to look up what a few of the electrical connectors up near the firewall are for. I found one that had been disconnected due to having a broken wire. I fixed it and reconnected it, but haven't noticed any difference in anything. It wasn't throwing any codes for anything, so I'm not sure if it was important.

[Destrto]

The other thing that I have seen so far, is that the oil pressure on the dash shows close 0 all the time. When I first test drove it, oil pressure showed normal levels, or what I would expect to be normal. But now, whether its cold, warmed up, idling or driving down the road, oil pressure reads nearly 0. I don't notice any issues with idle due to this. I'd just like the gauge to show correctly, if at all possible.

Is there anything that I can check to prove or disprove the stock gauges reading as accurate? I have heard that the stock oil pressure gauge is not very accurate.

[elecfus]

at the points you describe, low RPM and taking your foot off the throttle, are the points at which the cam phaser activates. it is switched electrically but operates by oil pressure. leaking oil and low oil pressure will cause it to malfunction. if it's leaking around the bell housing then it's most likely the rear main seal. the seal that stops oil leaking from where the crankshaft protrudes into the bell housing. on a manual car this tends to destroy the clutch.

do a transmission fluid and filter flush to stop the trans from heating up so much and replace that seal. do a few oil and filter changes to clean up the engine.

you should never use stop-leak in the engine oil. its job is to chemically melt all the rubber seals. it's great if you just want to keep a bomb running for another 6 months.

[Destrto]

Sorry for not getting back here sooner. Thanks for the input on those issues. I'm definitely going to get started on that one of these weekends.

Another issue (could be normal for auto) is that it seems like it hesitates a bit when shifting up. Is there anything short of fluid and filter change, or a valvebody rebuild, that I could try to stiffen or tighten the shift points? I know on my old 3000GT auto, you could adjust the line pressure within the valvebody to get harder shifts.

The car seems like it makes good power, but it has that hesitation to upshift when getting up to highway speeds. Like it's waiting too long to shift.

[elecfus]

pretty normal behaviour for burnt transmission fluid. a fluid and filter change should fix it

[Destrto]

pretty normal behaviour for burnt transmission fluid. a fluid and filter change should fix it

Thanks for that. I see that they make a shift improvement kit (Shift kit). And I'm familiar with those, as I put one into my 3000GT that worked wonders.

A couple other questions, instead of making new threads for them. This car had the factory Bose system. But after removing the front dash, it looks like it's been cut out. Was there a factory amp anywhere?

Also, does the passenger seat not have any tilt/recline? Or am I just looking in the wrong spot.

Is there a thread about tightening the gas pedal? It feels loose.

[elecfus]

get a copy of the manual. the instructions are all in there.
http://diyservicemanuals.com/nissan-300 ... r-manuals/

not sure about modifying the transmission.
some came with electric seats with buttons on the side, some came with manual dials.
gas pedal should be adjusted as per the service manual. the distance between the pedal arm and stop needs to be a certain distance, the cable can be adjusted by a bolt on the throttle body as well. the throttle position sensor also might need adjusting. the cables do rust as well which will make them sticky.
you should get a consult cable if you plan to work on it. there are a number of items that need fiddling.

[Destrto]

get a copy of the manual. the instructions are all in there.
http://diyservicemanuals.com/nissan-300 ... r-manuals/

not sure about modifying the transmission.
some came with electric seats with buttons on the side, some came with manual dials.
gas pedal should be adjusted as per the service manual. the distance between the pedal arm and stop needs to be a certain distance, the cable can be adjusted by a bolt on the throttle body as well. the throttle position sensor also might need adjusting. the cables do rust as well which will make them sticky.
you should get a consult cable if you plan to work on it. there are a number of items that need fiddling.

Kool. Thanks for the information. I'll read through the manual and see if everything makes sense.

[Destrto]

Oh! Also, reading about what transmission fluid to run, I always seem to have a hard time finding the right kind. Anyone have a good recommendation for transmission fluid on an auto?

[elecfus]

Dexron 3. in Australia the only reasonable choice for me over the years has been penrite due to the cost and quality. the have a product selector on their website as well.
http://www.datateck.com.au/Lube/PenriteAus/
I'd go with the fully synthetic because it burns at a higher temperature.

you can use anything that says Dexron 3 on it. it's not like the Fords that needed special friction modifiers which limits you to lower quality more expensive fluid.

[Destrto]

Dexron 3. in Australia the only reasonable choice for me over the years has been penrite due to the cost and quality. the have a product selector on their website as well.
http://www.datateck.com.au/Lube/PenriteAus/
I'd go with the fully synthetic because it burns at a higher temperature.

you can use anything that says Dexron 3 on it. it's not like the Fords that needed special friction modifiers which limits you to lower quality more expensive fluid.

Anything that says Dexron III. Got it. That should make it easier to find some fluid. I had to hunt around for days to find out that my Mitsubishi could only take ATF+4.

[DCaff300ZX]

Thanks for that. I see that they make a shift improvement kit (Shift kit).

Do NOT buy the ALC2 shift modulator for anything other than a brand new, or known-rock solid Nissan AT unless you want to replace that trans ASAP. Ask me how I know...uh-huh.

[Destrto]

Thanks for that. I see that they make a shift improvement kit (Shift kit).

Do NOT buy the ALC2 shift modulator for anything other than a brand new, or known-rock solid Nissan AT unless you want to replace that trans ASAP. Ask me how I know...uh-huh.

Haha. I think you either know somebody or are that somebody.

The kit I'm looking at claimed to be from Transmaxx. It doesn't mention being the ALC2 kit.

It worked very well on my 3000GT auto. But that's the only vehicle I have any experience with.

I've gotten a list full of parts for general maintenance.

I seem to be getting pretty poor gas mileage as of late. First tank was around 20Mpg with mostly out of town, highway driving. But every tank after that has been about 18 or less with the same driving. I have purchased a new fuel filter and spark plugs to try and remedy this, but does anyone have any other recommendations?

[elecfus]

it will run with the oxygen sensor disconnected. but it runs very rich. 200km/tank sort of mileage.
get a consult cable.

[Destrto]

Could a bad oxygen sensor possibly be causing my issue with poor mileage?

To me, it seems like I should be getting a bit better mileage than this.

[elecfus]

sounds normal. it's an old heavy 3L turbo engine so i wouldnt expect it to drink like a prius. NRMA(australian insurance company) found in their tests for the 1990 model that it did 16L/100km while you're getting 12L/100km. USA EPA gave it MPG 16 city 22 highway. so that fuel economy seems pretty normal. you can get a drop in fuel efficiency just from having the wrong oil level or bad oil. friction turns engine power into heat, enough clean oil not getting to parts or just dirty or burnt oil not flowing properly reduces the efficiency of the engine. similarly, the transmission wont transfer power properly if the hydraulic fluid and lubricant that is ATF has degraded.


yes it could be caused by an O2 sensor but so could a number of other things. And a consult cable is cheaper than an O2 sensor. so i'd get that before replacing random bits. it will save you quite a bit of time.

anything to do with fuel efficiency can be anything at all involved in the woosh, spray, boom, fart cycle. cylinder compression, ignition coils, ignition wiring, ignition transistor unit, fuel injector wiring, leaking vacuum hose, fuel injector, ECU, a bad sensor. but you're also reporting typical mileage with a typical variation that could be caused by something like it being a slightly hotter day so the aircon had to work harder.

[DCaff300ZX]

I agree, 18-20 mpg is the higher end of the Z32 mileage range, typically I got 18 when both cars were running right...yep, TT is really about the same unless you drive like a maniac all the time, but that goes for anything really.
Never hurts to check the hoses and electrical connectors though!

[z.Leinbach]

truee that, i just ran a 220 in town tank on 89, and this tank... I'm sitting at 140 at , now idk if it's my exhaust switch up?? or time for more maintenance..

[Destrto]

sounds normal. it's an old heavy 3L turbo engine so i wouldnt expect it to drink like a prius. NRMA(australian insurance company) found in their tests for the 1990 model that it did 16L/100km while you're getting 12L/100km. USA EPA gave it MPG 16 city 22 highway. so that fuel economy seems pretty normal. you can get a drop in fuel efficiency just from having the wrong oil level or bad oil. friction turns engine power into heat, enough clean oil not getting to parts or just dirty or burnt oil not flowing properly reduces the efficiency of the engine. similarly, the transmission wont transfer power properly if the hydraulic fluid and lubricant that is ATF has degraded.


yes it could be caused by an O2 sensor but so could a number of other things. And a consult cable is cheaper than an O2 sensor. so i'd get that before replacing random bits. it will save you quite a bit of time.

anything to do with fuel efficiency can be anything at all involved in the woosh, spray, boom, fart cycle. cylinder compression, ignition coils, ignition wiring, ignition transistor unit, fuel injector wiring, leaking vacuum hose, fuel injector, ECU, a bad sensor. but you're also reporting typical mileage with a typical variation that could be caused by something like it being a slightly hotter day so the aircon had to work harder.

I appreciate the information there. Never hurts to learn something new about these cars. Like I said, I'm used to a mitsubishi. It'll take a while to get used to what all this car does and how it reacts. The climate control threw me off at first. I couldn't find any settings for changing air flow, and then I found out that it's automagic. Haha.

Do you happen to know a good outlet for these Consult cables? Are they similar or the same as one of those obd1 readers?

Since I've been looking around, I'm seeing that my mileage is about normal for the car.

Now, I'm seeing my alternator is going out. Battery warning light shows up all the time while driving now. Looking through the forums, it seems like it's a pretty easy job. So that shouldn't be too difficult.

[centralcoaster33]

You can go online and find obd1 to obd2 consult cable adapters. Most auto parts stores will have obd2 scanners to plug that cable into. Some, may have the adapter cable. You can, however, not buy anything and use the flashing lights on the ECU to read codes. Here is a link on how to do that. The article describes a different car, but the codes, and turning of the screw and such are the same.
how-to-read-obd1-trouble-codes-for-1993 ... 17489.html

If you get any codes, feel free to post them up for us to review.

[elecfus]

it's just a standard serial cable with a funny plug on the end. I made my own. cost like $2 for the usb>serial breakout board and i just spliced it into the ECU wiring.
otherwise brand doesnt really matter, you cant really go wrong since its such a simple cable. there are free programs online that let you just plug a laptop into the car with the cable and read the codes. you cant reset the codes without one and there are some codes and sensor readings that wont give light flashing error codes.

also, if you just want to go cheap and read the light blinks, the ECU is hidden under the floor kick panel and a bugger to get at so you can just bridge two pins on the consult port which does the same thing as the potentiometer on the ECU.

[Destrto]

Oh ok, nice. I'll check that out. I have an obd2 bluetooth module from my mitsubishi, but it obviously wouldn't register the car.

I have a few issues with my audio, as well.

I went through and discovered the horrible hack job on all the speakers. The Bose system has been bypassed and cut out on every one of them. Bummer. I've fixed the wiring to the speakers, and replaced the rear deck speakers, but now, for some reason when I turn the volume on the head unit passed a certain point (3/4 volume on the unit doesn't sound very loud, either. For some perspective, I could keep my old head unit at volume 15 and it would be loud enough to hear with the windows down on the highway. Volume 15 on this one is barely audible at idle) it distorts pretty bad and sounds like all the speakers have blown.

My initial thoughts are that the head unit is just crap. Or that I may just need to run all new wiring straight off of the head unit. The only part that's strange is that it only started doing this when I replaced the rear speakers.

Is this car picky or particular about having speakers wired backwards or anything?

[Destrto]

Alright, update on things. I fixed the sound problem. It was not nearly as serious as I originally imagined. It was simply a speaker wire being shorted.

Now, on to a more technical issue. I'm getting the Battery light on the dash. I had the alternator tested, and it came back saying that a diode is failing. I also notice that when I'm idling that the lights will eventually start to dim, And when I hit the throttle a little bit, the lights will brighten up. Fairly certain this points me to the alternator being bad.

I'd like to get the upgraded alternator, the infinity one. Has anyone used one, and could offer some insights on installation, or specifics to which model to look for?

[DCaff300ZX]

The OEM alternator is by far good enough for the car, my Z guy laughed at me for considering otherwise saying that the only way you need more alt is with some stupid-big sound system...so just get a quality OEM replacement. Failure is common, whether from age or being doused with ATF from a bad PS hose/connector- both of mine have tossed their stocker LONG ago.
BTW, the fsm has a section regarding troubleshooting various odd issues and such, hopefully you've done this (download fsm) and use it for your work? I have been able to do about 95%+ of my necessary work from the fsm and combined with a few choice questions here, it's an invaluable resource for tests and numbers such as codes, voltages, etc. and will help YOU become a Z32 guru!
Good Luck with the rest of your work!

[Destrto]

Good to know about the alternator. You bring up a good point too, about the PS hose. Gives me something to check for.

I have been looking through the fsm. I like to get feedback from other members as to what works and what doesn't. Tips and tricks, and opinions from those that have done it and tried different things.

[Destrto]

Another question I had. About the trunk hatch seal. Is there an easy way to tighten the latch down, or a good replacement for the rubber seal? Mine currently seems loose, rattling audibly and visibly when going over bumps

[DCaff300ZX]

Yes, you can loosen the two bolts and sort of force the catch latch down further and retighten to gain a little more hold downwards, or even bend it slightly as needed but usually this means the hatch seal has worn too much and needs replacement...did that with my NA for a spell but it always comes back as the seal flattens further given the stupid-heavy hatch (have you removed the heavy counter-weight under the middle cover, this helps some), so both of mine have had new ones from CZP installed and aren't really that expensive, and fix that problem every time.

[Destrto]

Yes, you can loosen the two bolts and sort of force the catch latch down further and retighten to gain a little more hold downwards, or even bend it slightly as needed but usually this means the hatch seal has worn too much and needs replacement...did that with my NA for a spell but it always comes back as the seal flattens further given the stupid-heavy hatch (have you removed the heavy counter-weight under the middle cover, this helps some), so both of mine have had new ones from CZP installed and aren't really that expensive, and fix that problem every time.

I have not checked the counterweight, but I will check that before anything, to see if it helps at all. Thanks for the tips. I appreciate them.