280z Running Rough

[Z Tyler Z]

Hey everyone, need some advice for my 1976 280z. It’s been running very rough lately, to the point where I need to give it gas at stop lights to keep it from dying on me.

Here’s the symptoms

RPMs drop 200+ when I brake at idle, sometimes kills the engine. (vaccum leak?)

Engine misses a lot at lower rpms, generally under 2k, but occasional above2k. Gets jerky at times because of this.

Sometimes when I stop than restart it sounds like not all the cylinders are firing but eventually goes away. This is accompanied with very low oil pressure; it could just be my sensor but idk for sure.

After it’s been driven for a while all these symptoms go away. Generally after being driven a bit then stopped for a bit then restarted. I always let her warm up a couple of minutes before driving.

I’ve already done basic things like cap & rotor, ngk wires and plugs. Zs-ondabrain (Dave) is going to help me clean all the EFI components and replace all my Fuel injector connectors with some we got off a Gm and Audi at a Pull a part. *btw Dave I picked up some cleaner stuff at Autozone tonight* (not de-oxit but the guy said it does the same thing)

Any advice is highly appreciated.

Thanks,

~Tyler

Edited January 21, 2010 by Z Tyler Z

[Zs-ondabrain]

Come on guys, we need a little help on this one, BLAKE!!! hint hint

He's gonna bring the car over on Saturday and we're gonna work together to try and figure this out. ANY TIPS from you FI guys would be great.

I'm a carb guy and the best I can do is swap out his FI connectors for better ones, de-oxit the connectors and terminals, and listen for air leaks.

Anyone? Please!

Dave

[Pomorza]

I'm new to Z's so I may not be correct on this one. For what I understand from your post you Z is running rough enough that it plain dies on you occasionally. Since you say it feels like (sounds) that your running on less cylinders than normal continue with the ignition system. Check the coil and the dizzy. Make sure you are getting nice clean readings (steady) and not ones that are all over the place. Also make sure that all the injectors are indeed firing and not just a few at a time or non at a time. If only a few pistons are firing at a time it has to either be fuel spark (or air in cases) but start from there mate.

Secondly I would pull the valve cover and inspect under there. Possible something is loose in there or isn't where it should be. Just get a nice good long look and see if all is good.

Thirdly. Vacuum leaks as you said. I've had one in my old Jeep that cause very similar dying issues. Took me weeks to finally figure out that it was a vac leak. (spend $$ in the process). Also check that the timing is steady. I've seen a car that had loose nut and the timing kept changing on him.

My best advise to you though would be to get a FSM off the net and start trouble shooting. FI systems are fairly complicated when compared to carbs so a good understanding of how they work and a good manual goes a long way. I know that's not exactly "help" but its fairly hard to diagnose over the net.

Jan

[Z Tyler Z]

I'm new to Z's so I may not be correct on this one. For what I understand from your post you Z is running rough enough that it plain dies on you occasionally. Since you say it feels like (sounds) that your running on less cylinders than normal continue with the ignition system. Check the coil and the dizzy. Make sure you are getting nice clean readings (steady) and not ones that are all over the place. Also make sure that all the injectors are indeed firing and not just a few at a time or non at a time. If only a few pistons are firing at a time it has to either be fuel spark (or air in cases) but start from there mate.

Secondly I would pull the valve cover and inspect under there. Possible something is loose in there or isn't where it should be. Just get a nice good long look and see if all is good.

Thirdly. Vacuum leaks as you said. I've had one in my old Jeep that cause very similar dying issues. Took me weeks to finally figure out that it was a vac leak. (spend $$ in the process). Also check that the timing is steady. I've seen a car that had loose nut and the timing kept changing on him.

My best advise to you though would be to get a FSM off the net and start trouble shooting. FI systems are fairly complicated when compared to carbs so a good understanding of how they work and a good manual goes a long way. I know that's not exactly "help" but its fairly hard to diagnose over the net.

Jan

Thanks for the input we'll be sure to give that all a try on Saturday.

With the running on less then 6 cylinders issue, it's only seemed to do that to me twice. Each time I drove the car a short distance (less than 2 miles), parked it while I went into he store. Then when i started it back up she sounded awful, as if not all the cylinders were firing.

When I first start the car up, it never seems to have a problem with possibly running on less than 6 cylinders. It's always been happening the second start up after a short drive. It also never had any of these problems during the summer time, they all should up during winter. It isn't that cold in Washington but it isn't always warm either. (and generally rainy )

But yesterday when I drove to Autozone with a friend, it drove like crap getting there. Did the whole idel at 600 and missing thing. Did the not firing on all cylinders when I started it back up, then drove absolutely perfect after I got out of the parking lot. Idled perfect, drove like a Z should.

We'll probably look at the TPS too, I read on Atlantic Z car that this could be possible causing the weird idle problems. We should have a better understanding after Saturday of what it could possible be.

I'll probably pick up a timing gun too, last time I adjusted it, it was by ear, so I'm sure that's off a bit too.

On a positive note, it does start up without any problem. Which is nice when it dies in the middle of a busy street.

-Tyler

[Pomorza]

That pretty much seems like the problem I'm having. On the second start up it idles like crap and misses occasionally. But after a minute or two it acts normal. Please let me know what you find. I'm having a look at it with a friend this up coming weekend so hopefully between the two of us we can figure things out.

Jan

[FastWoman]

The missing with the second startup might relate to burning oil. Maybe the valve guides are worn? The smoke with initial startup might foul the plugs for a short while until all the cylinders start firing again.

You can test for a vacuum leak with the power booster by pulling a vacuum on it and seeing if the vacuum holds. It's quite possible for this component to leak. I had a '75 with an asthmatic, semi-leaky power booster at 15 years of age. Ignore any rebuilding instructions in your FSM, as parts weren't even available back then.

The best thing you can do with your EFI system is to pull the big harness off of the ECU (just beneath the driver kick panel), and work through it with a multimeter and the FSM. You can measure just about everything on the entire system at that one connector.

In general, the most common problems with EFI systems are stray vacuum leaks, resulting in unmetered air (and improper fuel/air ratio). Does the exhaust smell lean? Do the plugs look lean? If the vacuum spaghetti is old, it's good to replace it for good measure. You'll probably find several leaks. Don't forget to check for cracks in the big rubber boot between the airflow meter and the throttle body. Check that the airflow meter vane moves smoothly. Lubricate it for good measure.

I'm like Jan: I still have a few issues, including missing at idle and a sometimes-rough re-start. I'd love to hear what you find. I've decided my next step is new injectors, but I just haven't gotten enough free time or good weather to do that.

Peace,

Sarah

[Z Tyler Z]

Ok, so on Saturday Dave and I (Ok mostly Dave ) worked on my Z. It seems to be running much better; knock on wood.

I ended up driving there and it drove rough for a few miles then pretty well the rest of the way to his house (about 8 miles away). When I got there and I tried to restart the car and it wouldn't fire.

It ended up being a loose fusible link, we ended up replacing all the fusible links to a newer maxifuse system, following the guide below.

http://www.atlanticz.ca/zclub/techtips/fusiblelinks/index.html

Then we replaced all my 34 year old Datsun EFI connectors with ones taken off a GM at the local Pull A Part and cleaned all the green off of the female Datsun connectors. There was quit a bit of green oxidation on the old connectors.

Then Dave gave the AFM and the TPS a good solid cleaning. He also cleaned up the engine bay ground. Now my car idles fine, rpm's don't drop when I brake, and there is a lot less engine missing (didn't miss once when I drove home and on my short drive yesterday)

I'm going to let the car sit a few days then give it anther drive and see how it runs. Next time I head over we plan on adjusting my valves (there's a little chatter) and replacing some of the wiring the PO duct tapes together.

Thanks for everyone's advice, and a big thanks to Dave. Now I might finally be able to finally start on the interior of my car. Interior has been stripped for a good 4 or 5 months now.

[WingZr0]

Congrats bro . Must of been a tricky one to solve. Had the same similar symptoms but from a whole nother problem. Read the 'Fuel Injector Port Blocked Solid' or 'The State of Things' threads for a funny read.

Edited January 26, 2010 by WingZr0

[lbpdz]

if it persists, check to see if the distributor is getting "sticky".. I've had that happen

[Zs-ondabrain]

The only problem is that we did so much (FI connectors, fuse block upgrade, cleaning the AFM and TPS, Checking vaccum hose and other inspections) that we're not real sure where the real problem was.

But as long as it works like it's supposed to, we're (HE's) Happy.

Next step is to truly inspect and repair vaccum hoses, fix or replace connectors that have Duct tape on them, etc, ect. You can only do so much in a day when I can't shut up. I have a problem of describing everything I'm doing and why. But with any luck, he'll catch on and remember my mumbling and put it to practice someday.

Ain't it fun?

Dave

[Zs-ondabrain]

So while installing Tylers carpet kit yesterday, I popped open the AFM cover to inspect the meter because it was seriously back-firing when a little throttle was pushed. AND I MEAN SERIOUS SPUTTERING AND BACKFIRING!!

So I've never adjusted one before, nor have I even looked at the FSM to figure it out. BUT I took a whack at it and loosened the small screw and pushed the black notched wheel forward by about 1/8" and retightened the screw. The car is now responsive, smoother idle and most importantly, No more backfiring.

Hopefully, this little screw has been the issue the whole damn time and it's been fixed, finally. Time will tell though. This car is slowly becoming a decent first Z for Tyler and you can see it in his eyes. He's happy.

My job here is done,

Dave