Jump to content
Email logins are now active ×

IGNORED

My 1978 280 Z car


argniest

Recommended Posts

I have a nice 280z car, blue 510 color. Too bad its sick and not running correctly. I have been reading these forums, and see lots and lots and lots of things that could be causing it. I have 3 separate mechanics talking to me about it, and some of them are not in agreement about what the problems are. Some say fuel injectors, wiring connections, fuel pump, low compression (and therefore need new piston rings, so they say they might as well rebuild it while they are at it)...etc .... I am in a tug of war here...stuck in the middle of all this. I am not complaining, but would like to get moving in the right direction.

I owned a 300 zx for 10 years. And drove a blue 1984 Z back in 1990. Oh yeah, I also test drove a 1976 260z car, that someone in my town was selling. It had dual carbs on it. So I do have some experience driving a few different z cars, but never had the pleasure of driving a different 1978 280Z car. So I have nothing to compare my poor running engine too.

Well anyway I am so glad I found these forums. They look extremely active!!!!!!!!!!

Edited by argniest
Link to comment
Share on other sites


So here are some of the issues...Im sorry this list is long, but if someone wants to read it over, it will get you up to speed on my baby's condition.

Overall, I still feel like the car should give 25% more power at least, and maybe 35% more. Just a gut feeling based on what I think it should be able to do, if it was running correctly. It has 182,000 miles on the engine. The body is in good/great shape. 95% rust free. I have had lots of mechanical work done to the car (by a shop that fixes high end cars and restores them too), all new suspension pieces, new rubbers everywhere, new shocks, brakes, transmission rebuilt, differential rebuilt. Drive shafts, half shafts all ok. Exhaust in good shape. Custom frame rails/pieces were welded onto it to make it a lot stronger. All this work was done by a relative of mine. He wanted to make sure I was going to be safe in it. :-) Well at least safer than the condition it was in. I have had several other people see that work, and compliment the people who did it.

(per suggestions) I did a 100 mile spark plug test and plugs 6,5,4 are all somewhat black and goopy, but 3,2,1 are all sort of powder greyish/brownish (I have been told by 3 mechanic friends those look normal). I did a longer mileage test, and the plugs showed the same conditions. I also just put some new plugs in myself this time (instead of a mehanic friend), and gapped them to .40. They are the BP6ES-11. The mechanic said they didnt need to be gapped. But I did anyway when I replaced myself.

The car is sucking down gas too much. Gets about 11-18 mpg from normal driving. When spark plugs were new, and driving mostly on highway, it got 17 or 18 mpg. With the fowled up plugs (now that I know about them getting fowled up in the first place) it gets 11/12mpg or maybe a little less.

I stink like exhaust (or gas???) after being in or around the car while its running and with windows down. It almost makes your stomach churn. If windows are up, 99% of the time I dont smell anything unless its really windy outside, or I drove for a while like a few hours. Its cold here in the midwest, so I let it idle with the back of the car sticking out of the garage, with the door mostly open. Boy did it stink once I got out of the car. I didnt smell anything in the car, but outside, oh yeah. It stunk up the garage real good.

Its hard for me to say if its exhaust or gas smell. But I am leaning towards that its a rich fuel smell and not exhaust only.

When I first start the car after a few days, I think there is a cloud of white or grey smoke. Its so hard to tell what color it is. But the guess is that there is oil leaking down past the rings, and its gets burned up when idling and goes away. Except for that smoke, I never see any smoke coming out of the car, no matter how much I accelarate.

One of my 3 mechanic friends, says its only running on 5 cylinders. He drove car for like a minute, and that is what he said!!!!!!! And also because of it only running on 5 cylinders, it gonna burn more gas. He figures number 6 fuel injector is not working correctly. And is therefor causing a vaccum problem, and pulling down effectiveness of #5 and #4 cylinders, but not 3,2, or 1.

I also wonder, if because fuel injector isnt working on #6, that its causing a no fire in the cylinder. And then shooting the gas out the tailpipe. Which is causing this exhaust/gas smell that is very noticable?? I mean it stinks up your coats and clothes when you walk inside...its like peeeeeeeeew what stinks. Oh its you. Were you out by the z again. Yup.

Car was checked for vaccum leaks, mechanic friend says it has none. He has been working on BMS, mercedes, jag's, volov's, Z's, etc since late 1970's. And he checked for vaccum leaks right away after fixing all the mechanical stuff. But he still doesnt know exactly what is wrong with my Z car!!!!!!! We are working through a process of elimination.

We replaced the AFM, but then it seemed to run worse then before. So I am going to change it back to the older (looks original) one. Just for now. Cant be changing too many variables at once. It has the adjustments turned all the way down as far as they can go. For whatever thats worth.

The car idles at 800/900 rpm or so, but it seems a little rough to me. You can see a mirror vibrate when its idling.

I also ran a few cans of sea foam through it, and some Starbrite too (another cleaner product). I cant say that stuff really made much of a difference that I noticed. But it must have done something good!!!

When the spark plugs are new, it definately has a lot more power. Starkly noticable.

Another mehanic friend adjusted the timing back to stock settings he said, or something very close to it. He also ran an AFR meter with a sensor hooked into the tailpipe. And after tweaking the timing and turning the Air flow meter screw all the way in....got it running as good as I had seen it. I could even burn out and lay some rubber. He said the AFR numbers looked OK. Maybe not perfect, but OK anyway.

But he said I had low compression. Only 125 in two of the middle cylinders, and 135 in the others. He says thats too low. Another mechanic told me that is fine for an engine of this age???? Another different mechanic of Z cars, told me it should be more like 150 or 155 at a minimum and I think he said they were 165psi or so....new.

What is the correct psi for cylinders for a 1978 Z car with 180,000 miles on it? Someone surely knows :-) a good guess. he he

My mechanic #2 says the rings are bad and need to be replaced, and he feels I need to rebuild the engine to, in the process of fixing the rings. Mechanic #1 and #3 say that is the last resort and there are way too many other things to look at. And I agree with #1 and #3. I dont want to rebuild the engine until all other problems are resolved.

When I changed the spark plugs a few days ago...I noticed a small pool of oil in the pit under the spark plug hole. Each these pits right under where the spark plug plugs into (on the outside of the engine I mean of course) had a small amount of oil in there. At least that is what it looked like to me. I mostly wiped it up, and I dont know if it has been there for years or not. So I will watch that closely.

Mechanic #2 pulled the valve cover off and I think what he said was the cam and valves seemed ok. not too tight. I guess he was worried they were too tight or too loose? But he said that wasnt the problem. The timing chain is in good shape too. He looked at it.

Oh yeah, all the snow melted and then it rained and got up to 60 degrees, one day. Then back below freezing. So that gave me a chance to drive my car. Welllllllllllllll it made some noises (like bucking or hesitating like no fuel was coming in), and actually stopped dead in two out of 3 test drives. I had been driving for an hour, pulled into a gas station, and BOOM. It just stopped running. Then I cranked it over 3 or 4 times and it wouldnt start. Mind you, it was about 9 degrees out at that point of the night. I sat there about to cry I think and waited 5 minutes. THen it started.

The next day I drove and it bucked and chugged (slowed down for a second or two and then back to normal speed/power), but it never died. So right after that I drove back to my garage. The third day, the same thing happened when going up a big hill. It bucked/chugged like BAM, and then it kept running. I headed for home after that happened. It died while driving down a side road thank goodness. Then same thing happened. It cranked and cranked 4 or 5 times. Nothing. Waited 5 to 7 minutes, and it started right up.

None of this happened while driving over a 1000 miles in the summertime this year. Something in the cold weather seems to be effecting this. I think the fuel pump is going bad. But I know it could be plugged up fuel tank, plugged up screen in the fuel pump, and electrical connection. I am going to buy a fuel pressure guage, and also hook up a test light to the fuel pump wires under the back passenger seat. And the next time it happens I want to see if the test light is on or off, and what fuel pressure says...

Im just trying to list some of the main symptoms I know about.

I could write more...but this thing is getting crazy long now.

Edited by argniest
Link to comment
Share on other sites

So here are some of the issues...Im sorry this list is long, but if someone wants to read it over, it will get you up to speed on my baby's condition.

But he said I had low compression. Only 125 in two of the middle cylinders, and 135 in the others. He says thats too low. Another mechanic told me that is fine for an engine of this age???? Another different mechanic of Z cars, told me it should be more like 150 or 155 at a minimum and I think he said they were 165psi or so....new.

What is the correct psi for cylinders for a 1978 Z car with 180,000 miles on it? Someone surely knows :-) a good guess. he he

In my opinion, a 1978 280Z car with 180,000 miles on it should be getting 125-135psi. You're fine and your compression numbers report that there's nothing wrong with your engine mechanically, aside from normal wear and tear. If you're ultimately going to build a fast Z or race your Z, you'll want cylinders all in perfect health and with compression numbers 95-99% within range of each other. That is, your lowest cylinder is 95% the compression of your highest.

The oil outside your spark plug holes could be mess caused by the mechanic that they didn't clean up after doing your compression test, or doing your compression test incorrectly. It's common for mechanics to drop a little oil into the hole to determine if the now oil-sealed rings will create any additional compression in the cylinder. If so, then your rings are worn. If not, the reasons for low compression will be elsewhere.

An L28 turbo wants to see 135-140psi. An L16 or L20 like are in other Datsuns want to see closer to 180psi. You have an L28 non-turbo, so might vary from the later model L28ET slightly but I'm not sure to add to those numbers or subtract.

Edited by Jennys280Z
Link to comment
Share on other sites

If you're ultimately going to build a fast Z or race your Z, you'll want cylinders all in perfect health and with compression numbers 95-99% within range of each other. That is, your lowest cylinder is 95% the compression of your highest.

hmmmm I heard that it can go down to like 75% of the value, and not 95%. I think I read that in the EFI manual from 1975 for these cars. But who knows where I heard it or read it. I cant remember for sure. Sorry.

The oil outside your spark plug holes could be mess caused by the mechanic that they didn't clean up after doing your compression test, or doing your compression test incorrectly. It's common for mechanics to drop a little oil into the hole to determine if the now oil-sealed rings will create any additional compression in the cylinder.

I was there when mechanic #2 did this test, and I didnt see him do that with the oil. However, that doest mean someone else didnt do it. :-) Because mechanic #1 also did a compression test like a year ago. And I wasnt present when he/they did that. So they could have squirted some in there. I wiped it all out of there and will be noticeable if it comes back when I drive on another test drive.

If so, then your rings are worn. If not, the reasons for low compression will be elsewhere.

I just have to believe with 182,000 miles on it, that the rings have to be getting worn down. Im assuming no one ever replaced them. Can the rings be replaced without rebuilding an engine, and is there any downside to doing that without a rebuild?

Link to comment
Share on other sites

with a compression test, you are looking more at the variance between cylinders, rather than the absolute number. They aren't terribly accurate. If you want to know for sure if you need new rings, do a leak down test. That said, I don't think this is your main problem. Sure, the motor may be a little tired and a little down on power, but it should run smooth regardless.

Do the fuel pressure test as you said. If you have rust in your tank or a fuel flow problem, the car wont run right. The fuel pressure has to be in spec.

2nd, test the water temp sensor. If you are getting too much resistance in the water temp sensor it will run rich.

if one and two test ok, send your fuel injectors off to get cleaned and flow tested. My suspicion is that you have a bad injector, or a couple of injectors leaking.

4th, do a proper valve adjustment. If the valves aren't adjusted, the compression will be low. Was the compression test done hot? A proper compression test should be done hot, and with the other plugs pulled so that the motor turns easy. Missing this step alone along with a proper valve adjustment could be worth 15psi.

Link to comment
Share on other sites

with a compression test, you are looking more at the variance between cylinders, rather than the absolute number. They aren't terribly accurate. If you want to know for sure if you need new rings, do a leak down test. That said, I don't think this is your main problem. Sure, the motor may be a little tired and a little down on power, but it should run smooth regardless.

Mechanic #2 did do a leak down test, right after he did the compression test. He said several of the cylinders compressed faster than others. He called it like fast-fast-slow, or slow-slow when it was compressing. I also was in the car with my foot on the brake when he was doing this. So I witnessed all this first hand. The car wanted to move ahead when he was donig this, so I held down brake, and also turned over the car when he said to do that.

I really dont know what the exact output of this test was (was there a psi reading he was looking at too?). However, after doing these tests, and playing with the AFR meter (with the sensor in the tailpipe, and after he looked at the valves, he surmised I need an engine rebuild. That the piston rings were all bad. And might as well go through the engine at that point. He said the valves looked OK. And he put the valve cover back on at that point of the diagnostics he was doing.

Do the fuel pressure test as you said. If you have rust in your tank or a fuel flow problem, the car wont run right. The fuel pressure has to be in spec.

I am just trying to find a local source for a fuel pressure guage I can hook up with a fuel hose, inline, right after the fuel filter. So far, they all look like they are meant to be used directly on the fuel rail. And not inline, like I want. I suppose that is because the car stores, dont expect an older car like this to need something from them. And good quality is what I want too, not some piece of junk. I dont care if I pay 5x more for it, if its reliable.

2nd, test the water temp sensor. If you are getting too much resistance in the water temp sensor it will run rich.

We replaced water temperature sensor. Mechanic #1 told me it was bad. So that was replaced about 1000 miles ago. So I will assume that isnt a problem anymore.

if one and two test ok, send your fuel injectors off to get cleaned and flow tested. My suspicion is that you have a bad injector, or a couple of injectors leaking.

I bought new(refurb) fuel injectors from a datsun mechanic that has been working on these baby's since 1978. He has 3 warehouses of parts. But because of the snow (and my lack of wanting to drive on the bad roads) I have not been able to have them installed yet. I got the new injectors, rings, and quick disconnects just sitting here waiting....

4th, do a proper valve adjustment. If the valves aren't adjusted, the compression will be low. Was the compression test done hot? A proper compression test should be done hot, and with the other plugs pulled so that the motor turns easy. Missing this step alone along with a proper valve adjustment could be worth 15psi.

Well, mechanic #2, did check the valves and thought they looked OK. This guy has worked on Z cars before. They had 50 of them at one point in time. So I definately have to trust his judgement. I watched him check the valve clearances...and he was like hmmmmmmmmm they look OK. So he buttoned it back up, and that is when he got out the AFR meter to run more tests.

And yes, the compression test was done hot, within 15 minutes of when I rolled in there I believe it was.

TO ME, THE BIGGEST PROBLEM IN ALL OF THIS, IS THE EXHAUST/GAS SMELL. IT HAS FACTORY INSTALLED DUAL SUN ROOFS, AND IF YOU LEFT THOSE OPEN IT WOULD CHOKE/GAS YOU OUT IN 5 MINUTES....BUT AS LONG AS ALL WINDOWS ARE UP, YOU DONT REALLY SMELL IT AT ALL, OR NOT UNLESS YOU ARE IN THERE FOR A LONG TIME DRIVING AROUND

THE OTHER THINGS IS THAT I FEEL IT HAS MORE POWER TO GIVE. AND MECHANIC #2 SAYS IT HAS 25 TO 35% MORE POWER TO GIVE TO ME. THE OTHER THING IS THAT IT SEEMS TO BE BURNING UP MORE OIL THAN TYPICAL. I DONT HAVE EXACT DATA ON IT. HOWEVER, I THINK BECAUSE OF THE FUEL ADDITIVES, AND THE POSSIBILITY OF FUEL LEAKING DOWN PAST THE RINGS, THAT THINNED OUT THE OIL AND MADE IT BURN MORE THAN IT SHOULD HAVE BEEN THIS SUMMER, WHEN I WAS DRIVING IT AROUND.

IM SAYING IT BURNED UP MAYBE 3 QUARTS OF OIL IN 1000 MILES. AND MIND YOU, I AM NOT DRIVING AROUND LEAVING A PLUME OF SMOKE. NO MATTER HOW HARD I ACCELARATED, I NEVER SAW ANY SMOKE. THE ONLY TIME IT SMOKES IS WHEN IT FIRST STARTS IN THE MORNING, AND AFTER A FEW MINUTES IT GOES AWAY. I FORGOT TO MENTION THIS IN MY ORIGINAL POST (ABOUT THE OIL BURNING). SO I FIGURE I AM DONE ADDING ANY SEAFORAM, SO I WILL MONITOR HOW MUCH OIL IT CONSUMES THIS NEXT BATCH OF TEST DRIVES. HOPEFULLY IT WONT BURN UP AS MUCH WITHOUT ALL THOSE ADDITIVES POSSIBLY LEAKING DOWN INTO THE OIL.

Link to comment
Share on other sites

Get the factory service manual. There is on available online, (someone here will need to chime in and get you a link). That will give you a starting place. You can have a lot of little things that all add up. Personally, I'd put in a new fuel filter and check the fuel pressure first. Then I'd check the timing. Check to see that the dist plate moves with vacuum (even sucking on an attached tube) and I'd spray wd all over the thing (inside, including the cap). Cozye is correct, a bad temp sensor, or one that has a poor electrical fitting will mess things up. My personal experience is that so long at the compression between the cylinders is 10% variation, it should run along fine.

You didn't say how long you've had the car-more specifically, how long it has been setting. Rotten gas and a sludged up tank are big issues with these cars. When you replace the filter, tap the "in" side gently on a white paper towel and see if little fragments of crud come out. Could be a sign.

Let us know what you find.

Leonard

Link to comment
Share on other sites

Hi Argneist! Another '78! ;)

Your compression is a bit low, but I don't think that should make it run as badly as you're experiencing. You might be burning some oil, but that's another issue. The guidelines I'm familiar with say that the lowest compression should not be less than 90% of the highest compression figure. Having two adjacent cylinders with low compression might suggest head gasket leakage in those two cylinders. Are those two plugs the goopy ones?

Oil pooled up in those spark plug pits could be from oil leakage around the valve cover gasket overhead.

The sudden behavior changes that you describe (fine one minute and running badly the next, and then suddenly clearing up) suggest electrical issues to me. I think it would be a good idea to pull off every electrical connector on the engine, inspect it, clean it, apply some silicone dielectric grease, and reassemble. I'll caution you that the connectors are a bit crumbly at their age.

An even better approach would be to replace all of the connectors you can. Here are the most common type on Ebay:

http://cgi.ebay.com/ebaymotors/Datsun-280z-280zx-6-NEW-Fuel-Injector-Connectors-EV1-_W0QQcmdZViewItemQQhashZitem4cf2851c25QQitemZ330486324261QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

You will need 6 for the injectors, one each for the air bypass heater, cold start valve, thermotime switch, and coolant temp sensor. The 3-wire connector on the throttle position switch is available off of other more modern cars in wrecking yards. The big connector at the bottom of the air flow meter is not exposed to as much heat and probably stays in much better condition (at least on my car). The enormous connector on the fuel injection computer (ECU) behind the driver's side kick panel is very protected and should be in perfect shape, but it would be a good idea to remove it, clean, grease, and reinstall. Make sure the ignition is OFF when you do this!

Do you solder and know how to use heat shrink, or do you know anyone who does? (You can also use crimp connections, but solder is better.)

There's a little spring clip that holds each of these connectors on -- like a squared off letter "C". To undo a clip, you'll need to lift either the top or the bottom of the "C" with a tiny screwdriver, and then rotate the clip around the connector to free up the other side. You don't have to remove the spring clip entirely before pulling the connector off.

After cleaning up the electrical connections, I'd put in a fresh set of plugs, drive the car a couple hundred miles, and then read the appearance of the plugs. They should all look about the same. If they don't, then you might have injector issues.

Anyway, I would think you'll know a lot more if you just clean up the electrical.

Link to comment
Share on other sites

Mechanic #2 did do a leak down test, right after he did the compression test. He said several of the cylinders compressed faster than others. He called it like fast-fast-slow, or slow-slow when it was compressing. I also was in the car with my foot on the brake when he was doing this. So I witnessed all this first hand. The car wanted to move ahead when he was donig this, so I held down brake, and also turned over the car when he said to do that.

So what was the leak down percentage ?

Also, oil burning after startup. That sounds like valve guide seals.

fwiw, you probably could use a a rebuild, but again I don't think it's your main issue of running how it is now.

Link to comment
Share on other sites

Argneist, 3 quarts of oil consumption per 1000 miles is a LOT of oil! I'm starting to think mechanic #2 is right that you need a rebuild.

That said, you might have other problems too. You need to sort through the entire fuel delivery/intake system to get everything right.

The fuel smell in the exhaust is either from rich running or from misfire. It's not the problem, but the symptom. The fix for the problem is probably electrical, IMO.

Link to comment
Share on other sites

His post 7 came up while writing my post 8..... 3 quarts of oil in a 1000 miles is over the top. Something is wrong inside. 180K miles on these motors isn't a big deal when properly maintained. For all we know, it hasn't had much in the way of oil changes, etc etc. I'd still check the basics discussed here and would be looking for a known good used engine ($200 to ?? -wouldn't pay over $600 and there are 100's out there) or pony up and spend $2000 if the rest of the car warranted it.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.