Vacuum leak problem

[Zed Head]

Funny, but the 36 psi with the engine running could be an indication of your FPR going bad or the vacuum line to the FPR missing or leaking. The vacuum line from the intake manifold should drop the pressure to at least ~32 psi, even with poor intake vacuum. Could be the whole problem or just one part of it but I would get the FPR working right as one "to-do". ~38 psi with hose off, ~32 psi or less with the hose on. With good intake vacuum fuel pressure can get down to 28-30 psi at idle.

Edit - changed 36 to 38 psi. The FSM calls for 36.3 but most of the FPRs seem to regulate at 38-40 psi with no vacuum hose attached.

Edited April 29, 2012 by Zed Head

[mjr45]

Zed, the vacuum line from to FPR is new, I'll be checking all this out on Tuesday, thanks again for all your help.

[FastWoman]

Edit - changed 36 to 38 psi. The FSM calls for 36.3 but most of the FPRs seem to regulate at 38-40 psi with no vacuum hose attached.

I have 2 regulators -- one from my '78, and one from an '81 ZX (same part). Both regulate pretty close to 36.3. That said, pressure gauges are often off, and I can't say for sure mine is any different. All I can say is that I have 3 gauges of different varieties that agree.

[mjr45]

I tweaked the AFM towrds the lean side and the engine ran much smoother up to about 2500, on driving it above 3000rpm there was a stumble, no power and the tach was bouncing around from 3000-5000rpm.

[mjr45]

As another note, the timing is at 17 degrees and the dizzy won't allow any less timing. The number 1 plug was moved over 1 spot to get it to run at all, when I tried putting the #1 back, it coughs but won't start.

[beermanpete]

As another note, the timing is at 17 degrees and the dizzy won't allow any less timing. The number 1 plug was moved over 1 spot to get it to run at all, when I tried putting the #1 back, it coughs but won't start.

You might need to reset the timing of the oil pump drive gear. If it is off a tooth or two it will cause the problem you described.

[FastWoman]

^^ What Pete said.

You've confirmed a rich condition. Possible causes would include your cold start injector stuck open, fuel pressure regulator regulating too high (which it seems to be?), a problem with the functioning or adjustment of your throttle position sensor, a fault with your coolant temp sensor or its connections (often an open circuit, due to a corroded connection at the sensor), an AFM out of adjustment (e.g. too loose a tension on the clock spring).

[mjr45]

Fastwoman, the I set the TPS per Atlantic Z and believe its OK, the CSV, coolant emp and FPR I will have to check. When I leaned out the AFM the spring didn't seem to have a lot of tension on it, but I'm not sure how exactly to tell or how to fix it. Yup I know that Pete is right, this was how I got it from the "mechanic" and haven't yet gotten around to pulling the oil pump to remedy the problem, but may have to in order to get the rest of it right.

Edited May 1, 2012 by mjr45

[Zed Head]

I tweaked the AFM towrds the lean side and the engine ran much smoother up to about 2500, on driving it above 3000rpm there was a stumble, no power and the tach was bouncing around from 3000-5000rpm.

That might be a sign of an ignition problem. You have a bucket full of problems.

[mjr45]

Tell me about it! I replaced the dizzy with a 79ZX and wired it per Atlantic Z and couldn't get it to turn over the starter, the "mechanic I took it to ran a jumper wire from the blue/black wire in the wiring harness directly to the starter and took off the exciter wire, it starts but I don't think thats the right way to do it but can't figure out what else to do.

[FastWoman]

When normally adjusted, the AFM vane has a bit of tension on it in the closed position. I would describe the normal closed tension as feeling "too heavy." (At least that was my perception.) The vane normally does not open up that much when the engine is idling, so this "too heavy" tension makes use of the bottem range of the vane movement, if that makes sense. If I recall correctly (might not!), the pressure needed to open the vane was on the order of 60g (about a dozen nickels at 5 g each), when pressing on the outermost part of the vane.

This is all by way of saying that if your AFM vane "feels" weak to you, it probably is. Here's how you check the spring tension and adjust it if necessary:

http://atlanticz.ca/zclub/techtips/afm/calibration/index.html

I assume you've already downloaded the Nissan Factory Service Manual. If not, you can get it free here:

http://www.xenons30.com

Go to the EF section. You'll find step-by-step instructions that will be useful for debugging your EFI. These cars are notorious for crusty electrical connections, and I suspect that might be true of your coolant temp sensor connection. The best place to test is at the big connector plugging into your ECU, as that will test both the devices AND their connections and wiring.

You can replace all of the 2-pin EFI connectors (which is most of them, including the coolant temp sensor and thermotime switch) with new. Do a search for "280Z injector connectors" on Ebay. There's a seller called f0rrest who sells a good kit. You'll need 10 of them -- 6 injectors, CTS, thermotime, AAR, cold start valve. I recommend you buy an 11th one to have on hand for testing purposes. You can get a TPS connector (3 pin) from the junk yard off of a variety of vehicles. Mine comes from a Volvo 240. You'll be keeping the same AFM connector.

[mjr45]

Fastwoman thanks for all your info, I've replaced all the 2 pin connectors and both the 3 pin TPS and the 7 pin AFM the temp and thermotine connections were cleaned up and checked per the FSM, but I'm not positive the checks were accurate so I'll recheck them, I don't believe the CSV is leaking but will recheck it as well and also the fuel pressure. The spring on the AFM moves a little about 2-3mm at idle and takes probably less than 60g of pressure to finger open which is why I said I didn't feel much tension on the spring. Today I'm going to pull the oil pump and try to get the timing fixed and go then go back to the fuel/air mixture issue. I have the FSM and the EFI Bible. Thanks for all the help.

Edited May 2, 2012 by mjr45