Dead Cylinder? Can't figure out why? Read Me! (S2 PTU Test)

Nissan 300ZX technical discussion forum: Maintenance, performance, installations, modifications, how-to's and troubleshooting.
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NolimitZ32
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Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
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MODS (Mark): This is what I was talking about, if after running all your tests we come up with different results and confirm my theory we can keep this up or maybe add it to the everything you need to know thread, if not we can always delete this, I wont be mad. I'll edit for additional content if anything becomes available or apparent.

The Long (My English teacher would be so proud) Version:
So I have been fighting an issue with my dead #5 cylinder for quite some time now, I did all of the normal procedures, tested all of the components and was left scratching my head as the New Style PTU test procedure is not listed in the FSM that's all over the internet. Hellbent on trying to find why my cylinder was not firing but had spark and fuel and compression I went a searching and here is where I have ended up. When you first discover that you aren't running on all 6 you do the Power Balance Test and discover that you have a pesky dead cylinder or two, from here you go through the usual
- Test for fuel
- Test for spark
- Test for compression
Everything comes out as it should, so you are stuck scratching your head, calling your more mechanically inclined friends, even taking the chance on trying to get something out of the techs at the dealer but nothing! well here is your fish, enjoy it. Most of the time when a PTU fries it does just that, its simple to tell. But sometimes like in my case, due to a hellatious short I had in my power wire some time ago the PTU did not fry but got just crispy enough to get out of spec and with the unavailability of a diagnosis and test page from the updated FSM you are stuck guessing and perhaps throwing down cash on a part you don't need. Well low and behold, the page that so many of us could benefit from Image

The Short Version:
Use this diagram to test your New Style PTU to make sure it is within spec if the following happens to you:

1. you start misfiring
2. you do power balance test and find the dead cylinder or cylinders
3. you check for fuel and confirm working injector/injectors and pressure
4. you pull COP and Plug and test by conventional method of grounding on manifold

A weakened/slightly burned PTU will deliver spark but will not deliver it at the strength or duration required for combustion and will cause dead cylinders to occur where by every other test there should not be.


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Shoey2
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Car: 1990 300ZX Fairlady Z Twin Turbo
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anyone else think this is sticky worthy for the people who are nervous about trying it them selves?....also i can confirm that the diagram matches our tech assist program at the Nissan dealership I'm working at...

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BigTDogg (MA)
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Stickified.

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300ZXttZMAN
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Very nice Anton!

ThisIsSparTTa
Posts: 738
Joined: Wed Sep 26, 2012 6:02 pm
Car: 91 300ZX TT 2+0

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Here's a repost I just put in another thread in case someone does something stupid like I did.:

I initially wasn't getting any results and I knew my PTU wasn't completely bad.

I was confused because one side of the PTU has numbers and the other side has letters, so i connected the numbers to each other and got NOTHING.

Then I looked closer at the diagram and noticed the 1, 2, 3 they have circled. THOSE are all the connections you need to make. So for the first test of connecting 1 and 3, you will connect "3" or 'd' to pins 1, 2, 3, 4, 5, 6. Then you will reverse the polarity and make all those connections again. The same thing follows for the rest of the tests.

If you do the math, you should be making 6*2 + 2*2 + 6*2 + 6*2 = 40 total connections. I'd recommend seeing if you can have someone give you a hand, because it was definitely laborious trying to get the probes of the DMM lined up and to stay in place on 2 sides simultaneously.

oriZnal
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Joined: Wed Aug 24, 2011 9:13 pm
Car: 1995 Nissan 300zx NA

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Sorry for bring this to life. I did my " search" and saw this sticky. I replaced my injectors (all 6) unclogged egr and make sure valve is workin fine. They are all good. I was driving home and EGR engine code came up and started noticing misfire
That's when I did egr valve test to see if it works. And it holdsas spring comes up. Needle don't go down. But that's nott my concern. My problem is I got a dead cyl#2 and umplugged clip and no response from engine. Replaced coil and STILL same thing. Replaced with #4 to see if its defect but even at that #2 dead. Pulled out PTU. And ran the testing procedure.(one u posted at top.) Its fine!!!!! Its pissing me off! I need help. PTU Is about $450 I don't have money to buy PTU unless its certain for sure. Can u guys hep me come to bottom of this? I don't think egr have to do with this one. Any more testings I should do before dropping down 450 for this PTU?????? Thanks in advance

300zxstanced
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oriZnal wrote:Sorry for bring this to life. I did my " search" and saw this sticky. I replaced my injectors (all 6) unclogged egr and make sure valve is workin fine. They are all good. I was driving home and EGR engine code came up and started noticing misfire
That's when I did egr valve test to see if it works. And it holdsas spring comes up. Needle don't go down. But that's nott my concern. My problem is I got a dead cyl#2 and umplugged clip and no response from engine. Replaced coil and STILL same thing. Replaced with #4 to see if its defect but even at that #2 dead. Pulled out PTU. And ran the testing procedure.(one u posted at top.) Its fine!!!!! Its pissing me off! I need help. PTU Is about $450 I don't have money to buy PTU unless its certain for sure. Can u guys hep me come to bottom of this? I don't think egr have to do with this one. Any more testings I should do before dropping down 450 for this PTU?????? Thanks in advance
Sounds identical to the same issue I was having. I tested the PTU (ended up replacing it with the newer style, and hardwiring the the 2 harnesses connections), checked my TPS sensor, changed the injector harness connections (the connections were corroded with green deposit), cleaned all of my electrical connections that were realated to all parts mentioned and checked for spark via timming light (should of pulled the plug and checked for spark). After doing all of that i found 2 things that made a huge diference. 1 was the gap on my plugs were way out of wack, I have no clue why, I always check my gaps when installing my plugs, I re-gapped the plugs on the side i had backfire in the exhaust. After doing that the care ran fine at idle but when I reved the motor it would stubble and misfire slightly. The 2nd thing was the cam angle sensor harness, the female side of the sensor (the part that the pins from the sensor slide into) were super loose, causeing the PTU to fire properly sometimes but then misfire at other times. I closed the openings on the harness the best I could, now the car runs great, no misfire, no smell of gas, and no backfire in the exhaust.

DEcosse
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Joined: Mon Oct 27, 2014 1:09 pm
Car: 90 Z32 TT

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Thanks for this info
I have a 90 Z32 TT with type 2 PTU
I have a problem with dead cylinder #5 - originally thought was likely the Injector, since I had swapped coils and also checked for spark with plug in end of coil in atmosphere (which appeared to be good)
But after swapping the injector it still behaves the same
I had read other internet articles that suggested that type 2's did not fail - but this suggests otherwise!

And if read correctly, suggests that it may not sufficiently fire the coil/plug under pressure, so possibly explains my symptoms/test with plug out of the cylinder?

Testing - When I check '3' (pin 4 of the 7 pin connector) to each of the '1's (1-6 of the 6 way connector) I get a different result for each one, but particularly the #5 pin which reads much lower than any of the other 5 (with polarity in either direction)
+ on pin 4 of 7-way
1 - 0.83 Mohms
2 - 3.96 Mohms
3 - 4.78 Mohms
4 - 5.02 Mohms
5 - 138 Kohms
6 - 0.83 Mohms
- on pin 4 of 7-way
1 - 5.3 Mohms
2 - Open
3 - Open
4 - Open
5 - 0.66 Mohms
6 - 35 Mohms

So definitely seems to confirm the PTU I believe and most encouraging is that indeed is output to coil 5 that has the bad readings.
Concur?

ThisIsSparTTa
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Joined: Wed Sep 26, 2012 6:02 pm
Car: 91 300ZX TT 2+0

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I wouldn't say its definitive, that's still a relatively high resistance although it does seem to line up with your symptoms. Easiest thing to do is see if you can find someone else's to borrow or grab one from a junk yard.

Also, a common problem is bad wiring from the coil packs to the PTU. You'll still have some continuity, but not enough to carry the power. Try moving the harness around that's near the PTU while the car is running and see if that changes things.

Another common thing to do to eliminate headaches like these is to delete the S1>S2 subharnesses as they are known to corrode and cause problems like this. This has solved problems on my car and a couple of friends too. There's a few guides on how to do it, but its pretty simple. Just match the wires up 1 by 1, cut them off the connector and solder them together.

Veeridian
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Car: 1990 300zx NA 2+0
2004 JEEP Liberty Renegade
Location: Boise, ID

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ThisIsSparTTa wrote:Another common thing to do to eliminate headaches like these is to delete the S1>S2 subharnesses as they are known to corrode and cause problems like this. This has solved problems on my car and a couple of friends too. There's a few guides on how to do it, but its pretty simple. Just match the wires up 1 by 1, cut them off the connector and solder them together.
So, I'm trying to see if I understand what you have written here. Are you saying to basically bipass the PTU buy matching the numbered wires with the lettered wires and soldering them together? Thus making sure you have the correct amount of power going through the wiring to get good spark?
Just a little background. I just recently had an LMU (JDM) engined placed in my 1990 300zx base model. The car has been sitting for 5 years waiting to get a newer engine. Mechanic says the reason the car feels a little rough is because the exhaust system needs replaced and probably needs new mufflers. I don't believe him as I know what the car feels like when a cylinder is misfiring. But I will indulge him since the car probably does need new pipes and/or maybe the cat needs to be cleaned out after sitting for so long. There was a lot of rust blown out of the pipes the first time the car was turned over. lol.
Anyway, please let me know. I'm new to this forum, but not new to my Z.

Veeridian
Posts: 13
Joined: Sun Apr 12, 2015 3:14 pm
Car: 1990 300zx NA 2+0
2004 JEEP Liberty Renegade
Location: Boise, ID

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and replying to my post above, found out the mechanics didn't plug in the fuel injector... idiots. Runs smoother now.

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NolimitZ32
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I didn't see the post before. No you do not bypass the PTU, you get rid of the subharness via the method SparTTa described.

ThisIsSparTTa
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Car: 91 300ZX TT 2+0

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Don't bypass the PTU, your car will not run. For the early to late style PTU conversion there was an extra unnecessary subharness in the way. Yyou should be able to cut on either side of it and match the wires up directly.
Veeridian wrote:
ThisIsSparTTa wrote:Another common thing to do to eliminate headaches like these is to delete the S1>S2 subharnesses as they are known to corrode and cause problems like this. This has solved problems on my car and a couple of friends too. There's a few guides on how to do it, but its pretty simple. Just match the wires up 1 by 1, cut them off the connector and solder them together.
So, I'm trying to see if I understand what you have written here. Are you saying to basically bipass the PTU buy matching the numbered wires with the lettered wires and soldering them together? Thus making sure you have the correct amount of power going through the wiring to get good spark?
Just a little background. I just recently had an LMU (JDM) engined placed in my 1990 300zx base model. The car has been sitting for 5 years waiting to get a newer engine. Mechanic says the reason the car feels a little rough is because the exhaust system needs replaced and probably needs new mufflers. I don't believe him as I know what the car feels like when a cylinder is misfiring. But I will indulge him since the car probably does need new pipes and/or maybe the cat needs to be cleaned out after sitting for so long. There was a lot of rust blown out of the pipes the first time the car was turned over. lol.
Anyway, please let me know. I'm new to this forum, but not new to my Z.

elecfus
Posts: 99
Joined: Mon Oct 17, 2016 4:09 am

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type 2s most certainly do fail. but the problem with the series 1 is that they are older and used an old design. its just straight silicon mounted to a heatsink and the older dies are very inefficient. combine that with 20 years of aging. try touching a T1 after its been on compared to the cool running T2 and compare the side of the heatsinks. the difference is that the T1 WILL die from overheating. a type 2 can still be killed by a poor ground connection or touching electrical connections while the battery is connected.

make sure you use the weather proof O-rings in the connectors and they are in good shape then fill the connectors with bulb grease/dielectric grease to keep moisture from coroding terminals.

dont try to infer results from measuring the resistance through a dielectric junction. transistors are tested by measuring the voltage drop across them. the test shown is to test for a dead short.

you can easily test this by swapping the connectors across banks and reading the difference in the o2 sensors through consult. or by swapping adjacent coil pack connectors and checking the plugs before and after. works on any car.

you will then want to go and check the ground tie, sand them off or solder a replacement ring terminal if the wire is shot then torque. a dead PTU2 is symptomatic of a ground fault which could be caused by a fault in the wiring harness or the ground ties. this is also why it is extremely important to never run the vehicle with the coilpacks not connected with at least one bolt to the engine or any other part for that matter with metal on the outside. I think this is what happens when people do electrical work and parts keep blowing. start testing things all over, they save time not realising a bolt here or there is necessary.


FOUR HUNDRED DOLLARS FOR A PTU? no...you can get them for less than 50$ brand new. search ebay for "22020-97E11" "22020-97E00". due to the nature of what they are, just injection molded plastic surrounding 6 power transistors with some bits to make it all stick together properly, the difference between aftermarket and nissan OEM old stock isnt going to matter.

Caramrodttz
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Joined: Sat Aug 20, 2016 1:35 pm
Car: 1991 300zx twin turbo

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wow it sounds like i have the same problem. got a dead cylinder, the s*** one under all the fuel lines and balance tube. i disconnected the plug for the coil pack and the idle didnt change. i did the same with the other 5 and it got worse so i know thats the dead one. i ordered a new coil pack thinking that was the issue. hasnt arrived yet, ordered yesterday when the problem started. and i just stumbled across this post and now i think i might have a bigger problem. really hoping its just the coil pack i ordered along with new connector and wires. but after reading this thread and not knowing what half of what you guys are talking about, kinda making me a little worried haha i guess we will find out in a day or 2 if the coil pack was the problem. fingers crossed! BTW glad i found this forum, you guys post a lot of info, thanks!


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