Brandar77

hey guys. My 280 Z is running rich. Not exactly sure why. Here are the symptoms:
-When the car is first started (cold) it will run fine for a few min. then die if I don't rev it.
-After driving it for a while then turning it off, it floods and does not want to start back up. My mechanic thinks the injectors are bad, but I checked the plugs and they are ALL equally fouled.
Although possible, I don't see how all 6 injectors could go bad at the same time. I am thinking it could be the O2 sensor, but why would it be flooding when the engine is off?
Any feedback would be appreciated. Thanks.

BoulderZ

If it's a 280Z (not ZX), then you shouldn't have an O2 sensor (except on CA model, which might have one). More likely one of the handful of sensors went bad, or their wiring harness connections. Temp sensors are the usual culprits as it makes the ECU think the engine is cold and makes the car run rich. Alternatively, the Cold Start Valve might be stuck open, which would be like running around with a carburetor choked all the time (really rich). Your pressure regulator may be stuck, so you get way more gas than you should on each injector pulse. Use an in-line pressure gauge to see if that's at factory spec. You're definitely right, there's no way all 6 injectors went bad at the same time. Clean them up while you're servicing your fuel system anyway, but it's most likely they're just being told to do the wrong thing by the brain which is getting bad info from the sensors. If you need more detail on testing any of those individual components, let me know.
good luck,
Dave

Brandar77

Dave,
Thanks for the info. I have a strong feeling that it is the cold start valve, because it feels EXACTLY like a warm car with the choke opened up. That would also explain how the car floods when turned off. Can I safely disconnect this thing and try running the car to see if that is the problem?
Thank you VERY MUCH for your help. I've only had this car for a few months now and I am still trying to get the bugs worked out of it. I'ts pretty slow going for someone who has never worked on Z's before.

BoulderZ

Glad to help! I've been working with Bosch L-jetronic in the 280 Z cars for about 7 years, and if I can save anybody some of the learning curve then it's all worth it. No sense in repetition of mistakes! You can safely disconnect the EFI wiring harness plug from the Cold Start Valve. If the car then runs fine, you know that the CSV is wrongly getting the command to open all the time. That could be your temp sensor, thermotime switch, etc. But it doesn't rule out the CSV getting stuck open mechanically (i.e. the little solenoid in it is gummed up and stuck open). The only way to do that would be to disconnect the fuel line to the CSV.
Generally, that's not very safe to do at all. The *only* way that I know of to disconnect the CSV fuel supply safely is to buy an appropiate size brass AN fitting with a "hose barb" at one end to stick into the CSV supply line (with an FI fuel line clamp, not a worm-style band clamp), threads on the other, and a threaded brass cap to fit on those threads. That's only about $2 or so at the hardware store. Lowe's used to carry these but they ruined their hardware section, they don't even carry stainless metric pieces anymore around here.
Anyway, picking that up is an extra errand to try to fit in, which is really hard with work, holidays, school, and whatever else you've got going on, too. However, don't be tempted to shortcut on properly blocking the CSV supply line for this test. That line is at a high enough pressure at proper spec (let alone if your pressure regulator is sticky) to blow past any clamp pinching off the hose or a stopper. Then you end up with gas spraying all over a running engine, which of course is not good. The FSM maintains it's possible to keep the CSV hooked up to the fuel supply and the wiring harness, remove it from the intake and stick the end in a glass jar so you can see what it's doing. You have to try to block the hole in the manifold, then, and use a rag to try to seal the CSV in the glass jar. That never sounded like a good idea to me as it seems too easy for the CSV to vibrate out and spray gasoline vapor all over the place while you're running and testing the engine. Anyway, that's enough lawyer-type warnings. Hope that test helps reveal the problem, but if it doesn't then let me know and I'll try to post the next-most-likely diagnostics to try.
One other quick thing to check: make sure your filter and intake aren't clogged. Sounds dumb but it's easy to choke an engine that way, which could make it run rich, too.
Let us know how this round of tests goes!
Dave

Brandar77

Oh man, Oh man.
Will the problems ever stop? I was getting ready to check the CSV today, so I started the car up to move it in the garage. I let it warm up for a minute then tried to drive it in. It died. I started it, gave it a little bit of gas, and it stuttered, and died again. Sounded like it missing, and since it is running rich, I assumed the plugs were fouled (again). I replaced the plugs and just to be on the safe side, I replaced the fuel filter too. (it needed it!) I thought for sure that this would correct my problem, but alas, I was WRONG! It's acting like it's out of time now! How is this possible? I had an extra coil laying around (a Fireball PS 90 that I was going to install after I had the bugs worked out of the fuel system) and I installed it, thinking maybe my coil was fried. WRONG! I'm at a loss guys. I'm still learning the strange ways of the Z, so please forgive me for this stupid question, but can it be out of time? I drove it the other night (rather spiritedly) and all was well. When I got home it was purring, and I shut it off. Two days later BLAMO! Won't run!
**HELP, PLEASE**

BoulderZ

The starts-but-dies behavior sounds more like fuel starvation at this point, given you've ruled out spark problems by the coil replacement (you tried the arc-to-the-block test, too, I assume?). Here's a quick test:
Remove the air filter box so you can access the intake before the AFM. Try to start the car. If it starts, you may not have been getting air. Check out that air filter, could be clogged. Get a can of starter fluid. While you try to start the car, have a friend spray the starter fluid can into the intake. If the car starts, have them keep spraying for a couple of seconds after you've stopped engaging the starter. The engine ought to run fine. Then they should stop spraying. If the car dies, you're not getting any fuel.
I know it seems weird to worry about fuel starvation when it started out as a flooding problem, but there's a reason. If you were having a richness problem earlier, some of the causes could have killed off your fuel pump, or they may be two symptoms of the same problem. For example, a sticky fuel pressure reg could cause a rich mix *and* it overtaxes your fuel pump and it's supporting systems. Then the pump fails and you see fuel starvation.
So, try the starter fluid test and let us know what the results are, then we'll know where to go from there.
good luck,
Dave

Brandar77

Thanks for the advice again Dave. Turns out, it was a vacuum line! The one that goes from the throttle body to the distributor!
When I was poking around under the hood, I noticed a vacuum line hanging off the throttle body. what really gets me though, is the line had a screw going into the tip to seal it off!!! I don't know how in the world it ran in the first place. I bought the car in AZ and drove it all the way to TN!! I guess the lead going into the distributor must have been plugged up or something. Anyway I removed the vac hose from the t-body, re-connected it to the distributor, and blew and sucked, and blew and sucked (I know that sounds bad) untile I could feel the diaphram, or whatever is in that thing begin to give. I re-attached the vacuum line to the t-body and it started right up and ran fine. I don't know why it wasn't connected in the first place, and have e-mailed the guy that rebuilt the head for me asking him why. No reply yet. Not that I'm mad, just curious. And very glad it's running again. As to the CSV I diconnected the electric terminal and it continued to run rich. I then had a friend assist me in testing it. ( put in a jar and see if it's still working. You were right. It must be gummed up inside because it was still shooting out fuel with the car warmed up and the electric terminal unplugged. I'm heade up to the Z-barn this Friday to pick one up. ($25 for a used, but tested one) Beats the $100+ that MSA and Victoria British want for a new one!
Again, THANK YOU. I'd still be at square one if you had not offered your advice. I owe you big time Dave.

Brandar77

trying to post a pic...

BoulderZ

Great! Glad that worked out. And nice find on the replacement CSV. Can't wait to see the pic. Keep an eye on the distributor. They don't age gracefully and if yours was sticking like that, it may show other problems. Sounds like the head-rebuild mechanic just forgot to connect that line after setting the no-advance timing when reinstalling. At least the distributor was stuck in a good enough adjustment to let you drive home! Nice job getting the car running well again!
cheers,
Dave