Can you figure this out?

[Nismorunner182]

Hey guys see if you can figure this out

My z has been hesitant lately. It's increasingly getting better. So see if you can figure this out.

Things I've done that have improved;

Timing 15 degrees TDC
Coolant sensor
Knock sensor
both O2 sensors replaced
fuel filter
correct NGK spark plugs
New TPS connector
New MAF
Compression Test- results; 1-190, 2-185, 3-155, 4-190, 5-185, 6-190. So not bad except for cylinder 3.
I replaced the PTU with a used one. The subharness was bad. If you moved it slightly it would affect the car.
As far as I know injectors are good.

Now,

There is a bit of smoke coming from the back of the engine bay. Not a lot but enough to be noticeable. Also, There is still a code for both O2 sensors even though they were replaced. There is also a code 21? I think that is the Ignition signal circuit if I remember correctly, yet the PTU is good. Its a series 2 by the way.

The car is still slow, but definitely running better, however even though it's older it should still have some sort of pep in it's step right???


Thanks guys

[evildky]

Throwing O2 codes could be a misfire or a bad cat. Either could cause the car to feel hesitant. The PTU is fired from the ECU, could be a bad ecu. Just because it doesn't throw an ecu code doesn't mean it's not bad. You need to check the 6 trigger signals in the input side of the ptu, snap on logic probe, oscillator or other suitable tool.

[Nismorunner182]

Thanks man. I'm sure there is a slight misfire. I checked the continuity of all connections on the PTU. As far as a bad ECU i never thought of that. What would cause that? Everything seems functional codes read as designed. Also a bad cat car would cause hesitation?


Thank you sir!

[Rubyz32]

I knew a guy who spent lots of time and money chasing similar demons only to find that the original problem was the ecu. Don't be like my friend. He picked his up for $100 bucks and she ran beautifully for six months until he decided to tear it all apart and start an endless build.

[Nismorunner182]

Well thanks man. I'll look into that.

[elecfus]

did you replace the wiring for the PTU? is it a gen 1 or 2 ptu? the gen 1s have these wires joining to the dies that burn up when they overheat. diagnosing them is pointless because they can test good but just be floating. a gen 2 ptu is 50$ on ebay.

you can also just check the plugs, if one is dirty then you know there's an ignition problem. if one is burnt theres a fuelling problem. what did the original spark plugs look like? notice anything odd about any of them?
check the coil packs,
a wiring continuity test will only show a broken wire not one that is shaking around slightly connected.

[evildky]

A bad cat can clog from the build up of the crap it would be burning off if it worked.

[Nismorunner182]

did you replace the wiring for the PTU? is it a gen 1 or 2 ptu? the gen 1s have these wires joining to the dies that burn up when they overheat. diagnosing them is pointless because they can test good but just be floating. a gen 2 ptu is 50$ on ebay.

you can also just check the plugs, if one is dirty then you know there's an ignition problem. if one is burnt theres a fuelling problem. what did the original spark plugs look like? notice anything odd about any of them?
check the coil packs,
a wiring continuity test will only show a broken wire not one that is shaking around slightly connected.

I did not replace the wiring. What I did was replaced the PTU with a series 2 one that had a subharness with it. The origingal is a series 2 as well. However I did splice off the main signal circuit connector (harness side) and clean it thoroughly due to terrible corrosion. I spliced it all back in and now at least when you touch or move the PTU harness, the car won't die, stutter, or have really unreliable idle. But it is still hesitant.

The spark plugs on the drivers side bank are in pretty good shape. About how there are supposed to look. What's weird is according to my compression test, that is the side with all perfect 185 psi scores. The left side plugs are mostly sooty, not all the fuel is being burnt. but that is the side where 2 cylinders had 195 compression and one just had 150. Most likely a piston ring. But still, the car should have enough power to at least be fun to drive.

I replaced both O2 sensors and it's still throwing both codes. I figured that would fix the problem on the left bank thats running rich. I did reposition my TPS and I think I did it correctly but not 100 percent sure so that might be part of it but it is not the source of the issue.

I think my left bank ignition coils are going bad, or the coil pack connnectors are getting corroded too. That's all I can think off because everything else on the car that could cause this issue has been replaced or fixed. Except I need to clean and install new harness connectors for the IACV.

Anyway sorry for the rant. I appreciate anyones input

[Nismorunner182]

Oh and as far as the cat, there seems to be good flow coming from the exhaust. It is very visible. But I don't necessarily know if that confirms that cat is backed up or clogged. I just don't think that is the issue.

[elecfus]

when you positioned the TPS did you measure its values after tightening both screws? were the measurements the same on a voltmeter and the consult? I've seen people adjust them properly but only to tightening one screw then tightening the other moves it out of adjustment.

you can just measure the resistance of the coils. old coils can still work perfectly fine with double the maximum ohm reading but still good to replace. if the measurement of the coilpacks is good then they dont need to be touched.

your compression is fine. one bank with clean plugs and one with sooty plugs just means it's out of balance. one bank is running lean while the other runs rich. you can only really tell lean from knocking and in the long run the spark plugs will burn up, melt and fall apart inside the engine.


when you say you need to replace the connector for the IACV do you mean that the valve is hunting? you can check it in consult and a vacuum leak will make it flop between wide open and shut. I test for vacuum leaks with a propane blowtorch. where its sucking in air, if you spray propane at it or starting fluid it will suck it in, raising the idle and sound of the engine. so i just go around all the hoses and joins seeing if it changes the sound of the engine.

[DCaff300ZX]

RE- IACV:
The IACV possible problem beyond a vacuum problem is two-fold- first, the two connectors are notorious for corrosion and breakage issues (which you have just addressed with the PTU) that cause idle and hesitation issues, and second- the IACV itself locks up inside from 20+ years gunk and will not operate correctly, or at all. Sometimes a fouled IACV can be freed up with blasts of WD-40 through a hose opening, but often not as in both cases with my NA and TT. New-only IACV and harness replacement was the only option with my TT, while the NA recovered with just new connectors and PCV hoses and PC valve replacement. The brittle old PCV hoses split easily on the bottom where you can't see it from removing the balance tube and were my problem with the NA, plus corrosion and a broken connector.
DO check over your PCV setup and IACV carefully, at minimum cleaning/replacing the IACV connectors and PCV hoses if necessary and trying WD-40 blasts of the IACV itself, or recommended: replacement of the harness with upgraded heat and moisture-proof version (CZP, Z1, etc.), and possibly complete IACV replacement if the old one doesn't recover (common). The IACV isn't cheap however (DON'T buy used, won't work!) so be SURE before buying a replacement- there are tests for the IACV in the osm.
Good Luck!