I think we're going backwards???

[onesexZcar78]

Hello all, I own a 1978 280z with the stock L28...my fiance has replaced some parts recently and it seems to be getting worse...doesn't make sense to me. Don't get my wrong my fiance knows Z cars like the back of his hand but he's been kinda puzzled and very cold as we have no garage to work on it in. So here's what we did...had an oil leak and replaced the valve cover gasket, had an exhaust leak and replaced the intake/exhaust gasket. It also sounded like a subaru before we started...had a miss and replaced the #5 injector but we put this and all other injectors which are not even a year old into a different intake that we had wanted to try which is from a 280zx. With the new intake we also put the throttle body that came with it but left my mass airflow sensor. We got it all put back together and it started but idled around 1500-2000rpm! We realized that my MAFS was bad anyway so we replaced that with the one that came with the intake...fixed the idle and now it has a bad miss...so we replaced the injector plugs because they were old and crusty and coming apart...now it misses worse! So he thought about it and some how came up with coolant temp sensor? Replaced that and now it wont start at all. It turns over and fires every so often but no start. If you take the idle adjustment screw out it fires more but still no start??? Any ideas? Please help!

Thanks,

Kat

[sblake01]

Don't get my wrong my fiance knows Z cars like the back of his hand....

That's not the feeling I get reading your post. You've got a lot of mis matched components in that car from what you're saying. A P79 intake on a N42 head, an AFM from a ZX with the stock 78 ECU (I'm assuming), and the later throttle bodies use a TPS that's not compatible with a 78. Couple that with the fact that there are different water temp sensors and the one you use must be matched to your particular application. Now, please don't take this the wrong way, this is just my opinion. I'll have to defer to someone else on this one because with all that extra drama that has been introduced into a car that apparently already had existing problems, I can't even hazzard a guess.

[onesexZcar78]

Thank you for your input. So, you said that the AMF isn't compatable with the 78 ECU? Is the tps also not compatable with the ECU? And out of curiosity if the intake matches up to the head just fine what problems would it cause being from a zx? I don't know enough about the specific parts I just know that the L28 was in both the 280z and the zx so other than different sensors I'm not sure what's different about the intake itself. Again thank you for any help you can provide us! :stupid:

[onesexZcar78]

Ok I just talked with Joe (fiance) and he put my '78 tps on the newer throttle body. He also said that the only difference between the two AFM is that the one from my 78 has a air temp sensor in it which he took out and put into the newer one...So, would all this end up working together? I also forgot to mention we have spark and fuel we've checked the plugs and wires both good and the new coolant temp sensor is for my 78. Any ideas on other things we can check? Could a coil cause this or maybe something in the ignition system?

~KatROFL:paranoid:

[zbane]

This statement has me worried.

It turns over and fires every so often but no start. If you take the idle adjustment screw out it fires more but still no start???

You have fuel. You have spark. You have (I assume) vacuum and everything connected nice and tight.

Do you have compression?

The statement I quoted describes what I was going through just a couple weeks ago. It turned out that I had a blown head gasket.

A compression test will help to determine if this is the case or not.

Also, regarding poaching parts off a ZX, what year ZX did the manifold and other parts come from?

If it is from a 79 model year (build date @ 8/78-5/79) I don't think you would have much trouble. After the 79 model year, things changed ever so slightly (from what I've seen)...

This is all pure conjecture, of course.

[onesexZcar78]

We do have compression and everything is hooked up nice and tight. We also replaced the fuel pressure regulator for the specific intake we put on it. unfortunately I can't remember what year zx those parts came off of because we go them at a u-pull-it yard. What I was getting at with the idle adjustment screw was that it seems almost like it's idle is to low to start. Sounds wierd because how can it be too low to start but that's what it seems like to me.

[Maddos]

Might want to check the manifold gasket he replaced has the cutouts for the injectors. If it's the carby style will be restricting fuel flow. Someone else on this forum I think had the same issue.

[ktm]

Your fiance needs to slow down and think about the problem, possible causes, solutions, and methods of determination before he throws any more parts at the car.

You say you have compression....what are the compression numbers?

What block and head does the car have (I am not assuming at this point that it is stock)? I know Steven stated N42 (as that is the stock block).

You need to verify fuel pressure. Buy a fuel gauge and install it before the fuel pressure regulator. You may have fuel, but it may not be at the correct pressure.

Verify your timing, never assume it is correct. Verify that when the crank pulley is showing TDC, that the distributor is pointing to #1 and that the cam lobes are in the correct position.

Verify that the plug wires on installed in the correct order.

Check your spark plugs and see if they are fouled. Wet plugs will keep the car from firing, as well as a "flooded" cylinder. This will happen if you keep cranking and do not get any ignition. Once that happens, you either have to wait or pull the plugs and dry them out as well as the cylinder.

Check all sensor connections to make sure they are in good condition. You stated your injector clips were in poor shape. The rest of your connections could be in similar shape. Clean all electrical contacts with electrical contact cleaner.

Verify that your injectors are working by putting a mechanics stethescope to them (buy from Autozone or just use a long screwdriver).

Verify that your fuel pump is working and that your fuel filter is in good condition. Again, you say you have fuel but if the pump is dying or the filter clogged, you may not have the pressure.

Verify that the distributor cap is in good condition and that the terminals are free of corrosion. Verify the rotor to contact gap is within spec. Verify that the rotor is in good condition. Verify that the distributor cap terminals are in good condition.

I typed all of this up in 3 minutes off the top of my head and covered about half the topics. You have to be methodical.

[onesexZcar78]

Thank you very much for all your suggestions. We do have good/correct compression and fuel pressure. My fiance is a mechanic and has all the correct tools to check things like fuel pressure. There are however quite a few suggestions you gave me that we can try so again thank you very much. I will pass these ideas on to Joe(fiance) and with fingers crossed maybe one of them will be the problem. As far as electrical connectors I know we've replaced a few of them including the one to the coolant temp sensor and all the parts we did put on my car were not thrown on in hopes of fixing it they were parts that were not working properly and were replaced. If anyone else can add to Bo's list of things to check it's very much appreciated although we do have quite a list of new ideas to try now thanks to Bo.

[onesexZcar78]

I will also verify that we did get the correct gasket although I believe he checked it against the one we pulled off which was working just fine minus the exhaust leak which is why we decided to replace it.

[onesexZcar78]

I have another question/concern that Joe was talking about yesterday when we were working on my car...he said that it had 12v on both sides of the injector plugs but it was supposed to drop some on one side. Does it drop after it starts or should we not have 12v on both sides? If we are not supposed to have 12v on both sides what may cause this? I read in another forum I was reading that it could be caused by a bad ECU? is this true?:surprised

[onesexZcar78]

We figured out what was wrong! Thank you to all who replied. It ended up being a bad AFM, a bad cold start valve, and a bad thermistor. Thanks again

~Kat