ZX Turbo and the AFM of secrets

[vectorsprint]

1983 280ZX Turbo. Stock setup.

 

My other topic was a bit old and named for a distributor question that you guys helped solve months ago. Now, I have a whole new and interesting set of issues.

 

So as was seen in the video I posted, the car idled low, and was near stalling. I have the digital dash, so have no idea what my actual RPM is, and don't know how to measure it. But I bypassed the VCM, as I had replaced the vacuum lines on it, and when I applied vacuum to the AAC with a pump, the car wanted to die. SO the AAC is on the car but not connected to anything, the EGR is not being actuated.

 

Car runs much better at low speed. Doesn't pop and buck at low and part throttle anymore. Now my bucking and popping is in boost near the top of the boost gauge. I have yet to put a fuel pressure gauge on it, but the popping is coming from the intake. Wisdom I've seen on other Z boards indicates an intake pop is a lean condition. So that leads me to the next question I have, and it regards the AFM.

 

I spoke to the person who owned the car before I did. As we talked, it came out that he'd had the AFM open. And now I have a suspicion that the screw in the afm was turned, and the spring sproinged. Now the flap is not at the proper tension.

 

I know running down this path is probably a red herring, but the fuel pump, FRP, and injectors are all pretty straightforward. And since I can't find a Z31 turbo computer around me, I'm left using the 1983 ECCS, so that means using the afm. Reading about afm tuning, it looks like if the flap has the wrong tension, it can cause rich and lean conditions. Any suggestions on how to recover the afm? Or am I better off trying to find a known good used one?

[datzenmike]

Tight intake valves or worn valves and seats can also allow the firing cylinder to ignite the fuel spray inside the intake port.

 

True the EGR is not active at idle BUT if it's dirty wiith crusty deposits it won'r seal properly and leak inert exhaust into the intake diluting it.

[Slowpoke]

You need some more hard data, AFR, Vacuum, fuel pressure, plug color...If you have a multi meter you could use the FSM to test the AFM. That should give you and indication of how it is working.

[vectorsprint]

You need some more hard data, AFR, Vacuum, fuel pressure, plug color...If you have a multi meter you could use the FSM to test the AFM. That should give you and indication of how it is working.

Hard Data Get! Well, it's more firm, than hard. AFR eludes me. I have no good way to measure it. AFM, I looked in the 83 manual. I might be blind, but I wasn't able to find an AFM test procedure in the 83 ZX FSM. Is that in the FI bible instead? Anyway, plug color. All plugs look.. A little lean. Not scarily so, but I've also jumped off of it every time it pops. Cyl's 1 and 2 had kinda rich-looking crusty plugs. I hope the head gasket is not eroded between cyls 1 and 2. From what I understand though, that's rare on these cars, and a blow to an oil gallery or coolant gallery is much more likely. But, I also grabbed fuel pressure and vacuum data

 

Fuel pressure jumps a bit, seems to coincide with a slight lifter tick I have (P90A head). But it's bouncing between 36-38 PSI with the FPR unplugged. And since I had the FPR unplugged, I have a manifold vacuum of 17-17.5 Inches of mercury./ I have no idea what an ideal vacuum is, though thats in the green on my gauge. I do know that a ZX turbo wants at least 36 PSI at the fuel rail stock.

 

I may try loosening the spring tension in thew AFM to richen it a bit, but seeing these numbers, and the disparity in plug reads, I'm kind of leaning towards my issue being injectors. Guess it's time to build an injector tester and get a noid light.

[datzenmike]

What video are you referring to??? and does it demonstrate the 'popping' under load???

 

 Have your timing checked, it's probably too advanced. It's probably just pre ignition or pinging under load. It would explain the poor idle.

[vectorsprint]

What video are you referring to??? and does it demonstrate the 'popping' under load???

 

 Have your timing checked, it's probably too advanced. It's probably just pre ignition or pinging under load. It would explain the poor idle.

This one I put in my last thread:

 

It doesn't demonstrate the popping. That's new. After I plugged all of my vacuum leaks, replaced the CHTS with the correct size unit from Nissan, made sure all of my injector harness clips were secured, replaced the belts and timed it, it still runs like garbage while cold, and will pop out the intake under boost.

 

I put the timing at 24 BTDC ad indicated in the manual, but I'm willing to take my skills as suspect. Right now, it feels and sounds like its running lean, and given that it sat for a while, I'm kind of leaning towards the injectors being varnished and not giving me good flow.

[Slowpoke]

From the 81 turbo supplement. I don't have the 83 manuals or know if the 81 AFM id different from the 83. 81 timing is 20 +or- 3deg. Fuel pressure should be 30psi at idle, 37 pedal fully depressed.

 

You may need to find these numbers in the 83 manual to verify.

 

[vectorsprint]

 

From the 81 turbo supplement. I don't have the 83 manuals or know if the 81 AFM id different from the 83. 81 timing is 20 +or- 3deg. Fuel pressure should be 30psi at idle, 37 pedal fully depressed.

 

You may need to find these numbers in the 83 manual to verify.

 

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Oh man. Thanks both of you. Other sources I'd found, 83 manual included, said 24 BTDC, I cranked it back to 20,and verified my AFM is within the spec of the turbo supplement, and she purrs now. Makes boost, doesn't hesitate or pop or stumble. It's like a whole new car.

 

I know I can come off as a noob on this stuff, but sometimes, I don't know what resources I don't know I have.

[datzenmike]

Try removing each plug wire one at a time and see if one cylinder is causing the popping under load.

 

If one cylinder is doing this, swap the injector with another cylinder and see if the problem moves. If it stays on that one cylinder then it isn't the injector. This, to me, might be a bad valve not sealing.

 

 

 

There is the real possibility that the head gasket is blown. One cylinder is firing through and lighting an adjacent cylinder which pops out the intake.

 

You might also have a cross fire from one wire to another on the distributor cap. Have a look at the cap after dark. Give it  a few hard blips and see if there are any blue flashes.

[Bleach]

1981 and 82 say 20 before, 1983 says 23 (or 24?) . I think either will work.

 

I ran premium fuel and moved the timing up to 24 for the most power.

 

I had the same thing and even though my tests for vacuum leak didn't show anything, it ended up that my fuel injector seals were tight at idle, but pushing up under boost. It caused a lot of popping and wouldn't keep pulling hard. I had to remove all the injectors and coat the new o-rings in a thin layer of gasket sealer. I also switched away from the metal 280Z injector holders and went with the correct plastic 280ZX injector holders.