300ZX idling very bad, tried almost everything
 

Hello,
I'm new here on this forum. My boss is on holliday and he asked me to fix some problems with his 300ZX. So I said yes and he gave me the keys for 3 weeks and a hand full of cash to pay some parts if needed. He also said that I can take it for a ride whenever I want it to. Great deal huh!:040:

I searched the whole internet this night and I can't find a possible solution for the following problem.
The car runs quiet good. But when it's idling it is horrible. Cylinder 6 is not working properly. So recently I already get the chance to replace all the 6 injectors with connectors wich didn't kill the problem. And in this last week I tried to look for some vacuum problems but there are no problems in that section. I excluded everything. Just pulled all the sillicon hoses from the throttlebody and blocked them. On the side of the throttlebody ofcourse. After that I replaced the CHTS wich was located at a horrible place.

My boss already replaced the sparkplugs, distributor-cap with all cables and much more that I can't remember at this moment.

I'm texting with my boss while he's in Austria (Live in the Netherlands) and our final decision is that there's something wrong with the valve lifters. e.g. fast bleed down or worn inner bus/spring. So I ordered a compression measure tool that will be available tomorrow and just check all the 6 cylinders. If there's enough pressure/compression It can only be the valve lifters. If it isn't, it's a much more complicated s(h)ituation.

The problem mainly occurs at low RPM and idling. When engine is at temperature it runs very unstable but when I turn the lights on or the blower it runs al little bit better but still skipping. Below 2000 RPM with no load it's horrible. You can smell the gasoline when you hit the pedal. But as soon as you are driving there's nothing wrong but it will come back when you drive 48 mph(80KPH) in fifth gear. We already finetuned the MAF sensor but with no succes. The question now is. Does somebody recognize this or has a solution? I would be very happy if someone has the answer for this.

Sorry for bad english, Just an average school student in The Netherlands :retard:

Nobody?

Welcome to ZDriver!

Did you do this?

Have you checked the ecu diagnostic codes?

Oh my bad. The results were just fine. All cylinders got 12 bar. A little variety between 12.2 and 12.5 bar. Seems very good imo.
I've read the diagnostic codes from the ECCS but no faults except aircon. I don't no why because i got no aircon.
The fine tune of the mixture is set to a richer mixture(MAF). If we turn down the mixture it barely runs idle but it's much quicker in high rpm. So that's why the exhaust smells like pure gasoline. This whas already done by my boss couple of months ago. But I didn't tell this in the previous post.

well you could try downloading the fsm from xenon z31 site and READ IT. Or you could just keep on throwing money and parts at it. You might cure the problem that way at some point.

I already got the FSM..... and we tried almost everything if it comes to following flowcharts that are written down in the FSM...

Made a video this morning. As you can see I did something with the engine breath piping. That pipe was broken and rock hard so I blocked them both to eliminitate vacuum leak at that point. afterwards I will revert to stock setup but for no it wil stay this way. It didn't solve the ildling problem though.

just blowing away the dust of this topic. As expected the car still runs the same as before. We replaced the valve lifters of cylinder 2,4 and 6 5 months ago and we found something interesting. One top end of a valve lifter(tappet) was completely destroyed. I think it was about 2milimeter smaller than the other tappets. Maybe the previous owner ran out of oil and thought he could drive a littlebit further with empty valve lifters as result. Anyway. We changed all the valve lifters and searched for more things but eventually we found nothing. By the way, strange enough the valve rocker was undamaged.

But after changing the valvelifters still the same problem.. It runs a littlebit smoother but still shaking when idling.
We also did a compression test. All the cylinders are extremely good imo. All cylinders are 12.5 bar some are 12.4 and some 12.6.
Eventually we ended up with measuring the cam shafts.. So we had to dissasamble a lot of engine parts but finally after 8 hours it was done. We measured the cam shaft lobe of each valve and the results where not good. the lobes where to small about 0.2mm too short so we bought a seccond-hand camshaft. That camshaft was in really good condition almost as new if I have to believe the fsm.
after that we assembled everything back together and a new timing belt with tensioner. but again, as expected. No result :(
Does somebody know what to do now? I'm hopeless and it's freakin' me out.
thanks in advance.

Hi Roy
 

Have the same problem myself going to spend some of the day sourcing it. Whats happening is the injectors are dumping way too much fuel. Runs much like a Carburetor that's overloading. Beyond rich. I am thinking the Fuel Pressure REG is at fault. If you take the Vac off the REG and force air into it that would put the pressure down and see if you get a better idle. Not a fix till replaced but if it runs better replace it. I haven't had funds to replace mine as of yet but I think this is the problem. Let me know how it goes. Good Luck