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Z32 Technical Discuss all 300ZX (Z32) related Technical topics here - how do I diagnose, modify, repair etc

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Old 30-05-2017, 12:13 AM   #1
Howard
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Timing Issue

Hi everyone and thanks for allowing me on your site.
I have had 300zx's for around 25 years and they have never given me any problems.
Spoke to soon, the current car which I have had for 17 years is causing many headaches.
Basically she wont run past around 4500rpm, it feels like it is a timing issue.
I have checked the obvious and changed many parts including the cas and ecu, both admittedly second hand.
The only thing I have noticed is that by checking/setting the timing at 15 BTDC using cylinder 1 coil pack as the trigger and then comparing it using the loop wire off the series 2 ptu there is a 10 degree difference that is 25 BTDC. In both cases when revving the engine the timing retards to around 35 BTDC or 45 BTDC. Is this normal.
Any other suggestions would be much appreciated.
Fuel pressure is OK.
Wiring loom is OK.
Thanks
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Old 09-07-2017, 05:37 PM   #2
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Have done some more checks on this timing issue.
The signal to the coil pack is in the form of a pulse, the strobe will trigger at the start of the pulse but the plug will fire at the end of the pulse when the supply to the coil is interrupted.
Not sure what the pulse length is for 300zx but some cars are around 3mS.
So at 750 rpm, in 1 second the crank will turn 750/60 or 12.5 revolutions. In 3mS the crank will have turned 12.5*0.003 or 0.0375 of a revolution or 360*0.0375 degrees, which equals 13 degrees.
In other words the strobe will flash 13 degrees before the plug fires at a pulse width of 3mS. So setting the timing like this will mean the car is retarded by 13 degrees. Which is basically what I was getting.
The best way to set the timing is therefore to remove the coil pack from No 1 cylinder and put the strobe trigger in the link wire to the spark plug. Can only assume that when Nissan use the link wire on the ptu that the strobe has a delay time set in it based on the pulse width at tick-over.
Perhaps the above is rubbish but it does make some sense to me.
Anyhow it doesn?t help me with my problem that still exists on the car. One thing I forgot to mention is that I?m pretty sure that the problem started when I had some welding work done on the car. The welding was to the driver?s side ? right hand side as you sit in the vehicle: inner sill area.
Any help or comments would be much appreciated.
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Old 09-07-2017, 06:05 PM   #3
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Have you checked the ECU for error codes?

Have you tested whether the misfire/breakdown is load dependent or just a flat rev limit? Try revving out in first with just a little throttle and see if it revs further than full load.
When it stops revving, is it a complete cut out or does it just sort of hold there and stop accelerating?
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Old 09-07-2017, 06:41 PM   #4
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Thanks for your comment.
The fault has been on the car for sometime and the obvious has been checked.
ECU for engine and autobox are both clear.
The problem is load related the car drives perfectly up to about 5000rpm and then just stumbles, the turbo boost is maintained as normal, the car wont accelerate further and the power is not as it should be that's why I thought it was timing.
Have fitted gauges in the car to monitor fuel pressure and tps and both are fine.
The problem started after some welding work and I cant relate the welding to the problem. The car is very rarely used due to my overseas work.
I think the problem may be very simple to cure and I may be looking for something complicated.
Thanks anyhow.
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Old 09-07-2017, 11:16 PM   #5
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Have you put conzult or datascan on it? What does that say.
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Old 10-07-2017, 12:45 AM   #6
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Does the timing advance 10 degrees when you move it from park/neutral to drive?

I'll assume you've done the spark plugs by now? It could be something as simple as tired coilpacks running out of power at peak torque, does it blow smoke when it hits the wall?

Only other things that come to mind are blocked cats or the timing belt has skipped.
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Old 10-07-2017, 06:39 PM   #7
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The timing retards when going from neutral to drive i.e. 15 to 25 degrees BTDC. New plugs correct type, replaced coil packs admittedly second hand, doesn't smoke but it is running rich. New SS exhaust with no cats. Have changed the cambelt recently but the fault was there on the old cambelt, but saying that it could be a possibility to consider. Putting it on Conzult is definitely a good idea but finding time to take it to a dealer is the problem. Many thanks for the suggestions.
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Old 10-07-2017, 11:13 PM   #8
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Had a look at the air flow meter?

It's possible the PTU (ignitor) is the problem but would be unusual for one to show such a consistent fault rather than just running like a dog or stalling hot.

Since it started after some welding have you had a look over the earth straps and alternator wiring? Checked charging voltage isn't dropping or too high at revs?

You can get cables and software for DIY consult diagnostics although getting it to work with laptops often has hiccups. There's blue tooth connectors and software for phones too if that suits better.
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Old 11-07-2017, 12:37 PM   #9
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Quote:
Originally Posted by Howard View Post
Have changed the cambelt recently but the fault was there on the old cambelt, but saying that it could be a possibility to consider..
While you have it apart have a look at the dowels on the intake cams. They can shear off and then the intake sprocket won't be accurately located. I've seen it happen a few times before which can cause some rough running.


It's very normal to see 40deg+ of ignition timing when revving it, don't be concerned with that. Sounds to me like a cam timing or CAS issue.

I'd be checking (in order) the CAS drive pin in the cam and in the CAS, then the cam belt timing, then the locating dowel on the intake cams.
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Old 17-07-2017, 11:23 PM   #10
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Just an update. Got hold of an ECUTalk cable and software and installed on PC bit of a job on Windows 10 but now appears OK.
Only fault I could find was LHS O2 sensor was not working due to a wire off on plug and socket. Both O2 sensors now fluctuate during revving.
On driving nothing showed up.
This time the engine started to splutter at about 4800rpm on load. Noticed that after reducing the engine speed the engine continued to run rough.
Typical readings.

Meters at tick-over 2000 (no load)
RPM 760 2000
Water Temp 81 81
Battery 13.92 13.92
Timing BTDC 15 37
AAC % 15 47
Inj mS LHS 2.25 2.04
Inj mS RHS 2.41 2.13
Air Flow 1.20 1.65
Fuel Temp 33 33
A/F % LHS 107 89
A/F % RHS 117 96

Any comments would be much appreciated; otherwise it looks like the cambelt is the next check.
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Old 18-07-2017, 07:38 AM   #11
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Those figures generally look ok to me.
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Old 18-07-2017, 06:44 PM   #12
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Check all the under bonnet connectors for corrosion and fit. Clean them with contact cleaner. Make sure to do the cas - ptu - injectors - coils - temp and afm meter connectors also clean the air flow meter. Also have you ever had a new cas connector put on because they can get interference if they don't have the sheaf in the connector.
Good luck
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Old 19-07-2017, 10:32 AM   #13
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Quote:
Originally Posted by TWIN TERROR View Post
Check all the under bonnet connectors for corrosion and fit. Clean them with contact cleaner. Make sure to do the cas - ptu - injectors - coils - temp and afm meter connectors also clean the air flow meter. Also have you ever had a new cas connector put on because they can get interference if they don't have the sheath in the connector.
Good luck
Dave
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Old 19-07-2017, 06:51 PM   #14
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Quote:
Originally Posted by TWIN TERROR View Post
Check all the under bonnet connectors for corrosion and fit. Clean them with contact cleaner. Make sure to do the cas - ptu - injectors - coils - temp and afm meter connectors also clean the air flow meter. Also have you ever had a new cas connector put on because they can get interference if they don't have the sheaf in the connector.
Good luck
Dave
What sheath are you referring to there dave, im about to swap my cas plug to series 2 and that might be handy to know
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Old 19-07-2017, 09:10 PM   #15
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Sorry for not being more specific but I had a brain fart and couldn't get my head around the correct wording on some decent pain killers at the moment and not thinking real clearly so will do my best. Inside the outer cable sheath between it and the inner conductor cables on the cas there should be a braided sheath that protects against interference. I was told when I replaced mine a few years ago to be very careful to make sure it stays intact as best you can or you can get electrical interference on the signal to the ecu and it can cause some funny things to happen with the timing signal .
If any one can give a better description please add to this.
Cheers
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Old 22-07-2017, 11:31 PM   #16
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Checked out the ECUTalk display whilst driving the car today. At tickover the timing shows 15 BTDC at idle, when revving the engine - car on stop; it rose to about 35 BTDC, when driving under load at around 4000rpm the timing was swinging and went from about 10 BTDC to 45 BTDC. Tried another CAS and it was even worse with the timing permanently around 10 BTDC and no engine power whatsoever. So a possible CAS issue????
Should the timing remain fairly consistent at all revs???.
The only other meter that showed some fluctuation was the voltage 14 +/- 0.3.
Thanks for any comments suggestions.
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Old 23-07-2017, 08:59 AM   #17
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Quote:
Originally Posted by Howard View Post
Checked out the ECUTalk display whilst driving the car today. At tickover the timing shows 15 BTDC at idle, when revving the engine - car on stop; it rose to about 35 BTDC, when driving under load at around 4000rpm the timing was swinging and went from about 10 BTDC to 45 BTDC. Tried another CAS and it was even worse with the timing permanently around 10 BTDC and no engine power whatsoever. So a possible CAS issue????
Should the timing remain fairly consistent at all revs???.
The only other meter that showed some fluctuation was the voltage 14 +/- 0.3.
Thanks for any comments suggestions.
No - timing will be up and down between 10deg and 40+deg. That is normal.

Interesting you tried one that stayed on 10deg. Either that CAS is stuffed or you have a wiring issue. Moving the plug or wires around might have shown a short/break in the wire. Did ii show revs on the dash when you were getting a steady 10deg?
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