280ZXT ignition timing

[russ in va]

I posted this on the L6 forum a few days ago and have had no replies, so lets try a different audience.

 

I'm trying to get the timing set up on my L28ET. It's a stock 83 drivetrain transplanted into a 1970 S30. It has been in the car for years and the swap was done two owners ago.

 

I've got the base timing set to 20 degrees as per the FSM. My concern is that as I watch the timing and bring the revs up from idle to 4000rpms, the timing stays at 20 degrees advance, it does not increase. I know this distributor has neither vacuum or mechanical advance, but I would expect the ECCS to add timing as the revs come up. I've scoured the FSM and can find no mention of the factory timing curve. It has occured to me that MAYBE, the ECCS is smart enough to know that I am free reving the motor and only adds timing under load (using input from the AFM combined with the CAS.)

 

Can anyone provide info on what the timing should be doing as rpms incresase?

 

I am very fortunate to have access to a dynojet, so my next step is to check the timing through the rev band on the dyno under load.

 

After that, I'm down to ohm-ing out the wires, though electrical work is not my forte so I'm a bit hesitant to start down that road.

 

Any input is appreciated!

 

PS If anyone has a spare distributor and/or ECCS I can swap in, I'd love to try it! I'm more than happy to pay for the UPS store to box and ship it to make it easier on anyone willing to help.

[cygnusx1]

It should advance. Something is wrong in the computer, wiring, or distributor. Unfortunately this does not look like a mechanical problem. It is electrical or electronic in nature. The best thing to do is to swap out a dizzy and then an ecu with known working ones. If the problem persists, its a wiring or signal issue.

[Tony D]

I'd agree. I think I saw this other post, and replied there as well. If a CAS was suspect, I'd more figure it would be a miss, not a failure to advance. That is the sole function of the ECU's Programming.

[russ in va]

I could get an ECU (and a distributor) from this guy http://www.zcar.com/forums/read/12/1838425

-OR- I could spend that money on MS ... but then it would take me months to get the car running again ... unless someone wants to make/sell me a harness??? http://forums.hybridz.org/showthread.php?t=112504&highlight=ms+downtime

[Tony D]

It took me 8 hours to make a harness from scratch. You can buy it 95% completed save for terminations for $65... I know what I would do.

 

There is no reason the MS would take you 'months' to get running again. Unless you did something like me, and use a bad Laptop, solder the joints cold a few places, and...oh yes, have a car with an intermittent early-model CAS that would go for 45 minutes before going out intermittently...

 

If the car is running, MS will make it better. If it's not, chances are itwon't solve your issues if you are using the same electrical system causing you problems now. If you have verified the ancillary components, and it's down to the ECU, then a replacement MS will take a few hours of installation and another couple on tuning. Drivability will be like night and day compared to a new functioning ECCS system.

[cygnusx1]

Actually, the car drives pretty darn well with the stock ECCS/injection in a fully functional state and an FMU tuned properly. You would be surprised. However, the MSII is definitely not the right place to learn basic electrical. If you are not electrically inclined, it will take you longer. My advice is to pick up another ECU, heck, I can mail you mine for shipping$ to test. I think I have three of them.

 

My prediction for the culprit is 60% wiring flaws and 40% ECU. PLEASE: make sure all of the ECCS inputs and sensors work. It's VERY easy to do so.

 

TPS - on off switch move the throttle by hand while reading the pins.

Head Temp - simple resistance reading

O2 - voltage output 0-1volt while running

Air Temp - simple resistance measurement

AFM - read resistance while moving the flap manually.

[russ in va]

OK, I went through the ECCS Electrical System Inspection from the FSM Pgs 96-109 of the Engine Fuel and Emission Control System setion AND played with the car on the dyno tonight. Lots of info.

 

First of all, my ECCS does not appear in the chart I have ??? It says on it "Nissan Genuine Remanufactured Engine Control Unit" (ECU not ECCS ... does this mean it is not a turbo ECCS ??? that would explain why I'm not getting any advance with RPMS!) A18-602 045K Then it also says 0307 (but the first digit is faint, could be C307)

 

Then the results of my probing with the Fluke (I'm not afraid of the harness anymore):

-Throttle Valve is working properly

 

-Air Flow Meter Tests

- - pins 33 to 26 slightly out of range at 202 Ohms (FSM states 280 to 400)

- -pins 33 and 31 good at 129 ohms

- - the FSM does not say to do this, but I pushed the flap through it's range of motion (it moves freely and steadily) while watching the resistance ... it's all over the board! It continuously ranges up and down while moving it through its range of motion .. it will track with the flap for a while then jump up or down and track again, then jump again! This seems like a bad thing to me but I'm outside the scope of the manual here so input is appreciated (weird thing is that air/fuel on the dyno runs seems fine???)

 

-Air Temp Sensor reads 1.903 K ohms at approx. 80 degrees F, that's OK per the FSM (over 68 F should be less than 2.9 K ohms)

 

-Cylinder Head Temperature Sensor - fails the factory test but I'm puzzled

(note: infared pyrometer reading at CHTS = 95 degrees F at the time of these tests)

-pin 23 to body ground is infinite resistance (shoud be less than 2.9 K ohms at 68 F or above per FSM)

-BUT (this is not a factory test, I just looked at the wiring diagram and figured out where the other lead from the CHTS hooks up) pin 23 and 26 together read 1.237 K Ohm (why doesn't the FSM have you take this reading instead of the 23 to body ground reading?)

-Reading right off the sensor itself was 1.240 K ohm

-Also, if you unplug the CHTS with the engine at full operating temp and running, it misses badly BUT there is not a noticable spike on the dyno's wide band 02 sniffer?? (does this sound normal?)

 

-Control Unit Ground Circut Tests

- - Pins 28,26,107,109,112 and 113 are properly grounded BUT...

- - Pin 108 does not have continuity with ground (when the 15 pin connector is NOT plugged into the ECCS), nor does it have continuity with the connector to the Air Regulator which as far as I can tell should be the other end of this wire, is that right?

 

-Air Regulator and Fuel Pump Relay Tests

- - I'm not sure if you are supposed to have the 15 pin connector plugged into the ECCS when performing this proceedure .... with it unplugged it fails (same test as last step), 108 does not have any continuity to ground .. with it plugged in it has 0 resistance, it is grounded ... either way it fails, it should be in the range of 25 to 90 Ohms per the FSM

- - Checking the air regulator ... clamping down on the vacuum line (per the FSM) when the engine is cold does slow the idle speed (that's good per the FSM) ... I could not get the hose off to do the specified visual check because the hose is so hardnend I would have had to cut it off so this will have to wait until I can get a new hose to replace it with but I think this step is irrelivant at this time since the air reg does NOT have continuity between it's poles so according to the FSM I need to replace it too!

- - Air regulator power circut test - fails (note I did not disconnect the starter motor as directed in the FSM, instead I pulled the coil wire and performed the test by actually cranking the motor, I assuem that my short cut is not the reason it fails) I only get .14v at wire 108 when cranking, zero if you plug the coil wire in and start the car

SO .... should I run a new wire from pin 108 to the air regulator?? ... is that the correct routing? (I'm still not good at reading a wiring diagram)

 

I did not do the rest of the tests on the fuel pump relay and injectors since the car does run cleanly on all 6 cylinders it did not seem neccessary. My concern is still with the ignition timing.

 

My dyno results, posted below, were good considering I am still not getting any spark advance (base timing set at 20 degrees, and it falls back a couple of degrees as you run it up through the revs on the dyno under load); 149 hp and 180 ft lbs with a decent air fuel curve (a little lean up top)

 

ALL INPUT IS APPRECIATED!!

[Bernardd]

- - the FSM does not say to do this, but I pushed the flap through it's range of motion (it moves freely and steadily) while watching the resistance ... it's all over the board! It continuously ranges up and down while moving it through its range of motion .. it will track with the flap for a while then jump up or down and track again, then jump again! This seems like a bad thing to me but I'm outside the scope of the manual here so input is appreciated (weird thing is that air/fuel on the dyno runs seems fine???)

 

 

That is normal. The afm has small resistors that change the voltage to the ecu with the varying resistance to provide throttle enrichment.

 

The only time the ecu holds the timing at base (20deg's) is when the tps sensor is shorted between the center terminal and the reference terminal. This forces the ecu to use the idle timing map. Have you checked the tps at the ecu to see if is opening?

[russ in va]

-Throttle Valve is working properly

 

Yep, it works. Pins 18 and 25 have continuity when the throttle is closed and the circut goes open from the moment you crack it open all the way to the floor.

[cygnusx1]

It sounds like the AFM is working ok. I actually cleaned the contacts inside the AFM on mine once. Maybe you should try that anyhow. Just spray clean it and lube the slider contact with some dielectric grease.

[racerx260]

base timing on an 83 turbo is 24 btdc. 81 and 82 had 20 btdc. I have an 83 and the response between 20 and 24 is very noticeable.fyi

[Tony D]

The key to the AFM Readings is it doesn't go to 'infinity or zero'. Jumping around may make the ECU go intermittently up or down, but only in a very steady state condition---like right at highway cruise. My 75 does that, right at cruise the engine will 'shut off-turn on-shut off' if I approach an open spot in the AFM Trace reeeeealllly slowly on the open road. I can do it free rev by bringing it up slowly as well...right about 2275rpm it will go into an oscillation because the wiper arm has worn through the resistive trace right at that point and when the ECU sees 'zero' it shuts off pulsewidth. Conversely is can go 'full fuel' going to the other extreme. But unless I am cruising very conciously at that speed, it won't do it. The car runs so damned well otherwise, I simply sped up 3mph at cruise, and it never effects the car. So even with an 'open' in the sweep, the car will be functional unless the AFM flap is held right at the trouble point. Usually it's sweeping so fast it's more of an averaging thing. The ECU in the car is like 8mhz, while even most cheap DVOM's are 100mhz in scan time, so many times while you may 'see something' on your meter, in practical terms the stock brain will not register it at all becasue it's so much slower. The important thing is 'not zero or infinity' on the tests.

 

A Diagnostician gave me a tip that has panned out well: If you have a FLuke with Min/Max/Record, hook up piercing probes in the lines you want to test, start the car, turn the meter on and set it up for Min/Max/Record, and just go for a drive. On many of these components, a "Zero" or "Infinity" reading is out-of-range and indicates a failed component. After your drive, before you shut the car off, take the meter out of the Min/Max/Record mode and recall those values. If you see "Zero" or "Infinity" you have a bad component, period. Replace it. The 100MHZ Scan rate of the Fluke 87 is faster than all of the Stock ECUs out there (was at the time at least) and will pick up very small defects. While my example above of my AFM is technically a component that I know 'is bad' and should be replaced...this kind of test will reveal an 'intermittent non repeating failure' while driving the car that may not show up during bench testing. When I did the test on my AFM it indeed 'failed' by showing the "Open" (Infinity) reading, but the car did not buck or stall at the time because I swept across it so fast the ECU didn't pick the glitch up that time. The Fluke recorded it, though.

[russ in va]

OK, I installed the known-to-be-good ECCS that Dave lent me (THANKS DAVE!) and found no change ... I still get no advance as I bring the revs up. Rats!!! What now? I'm at a loss. Based on the knowledge that Bernardd shared about the TPS signal triggering the ECCS to not advance, I'm going to triple check the TPS, though I already did. Any other suggestions?

 

I'm trying to get this straight in my head. On an old school dizzy, when the weights spin and crank in the advance they make the point plate turn. But since the ECCS is doing the job of the points and the advance plate with computer magic, there are no moving parts like this in my dist, right? So since it's not the ECCS itself, that MUST mean that some input into the ECCS is causing this, right? Other than the TPS, what could possible do this? My ignorance is killing me!

[cygnusx1]

I kind of had a hunch that it was not the ECU because typical failure of an ECU results in a cold black box. They either work or don't. Hang onto it until you feel like you have a resolution. The next step would be the guts of the distributor. Although, TonyD does not think it's the distributor...we now know that the ECU is OK and what else is there in the timing circuit besides wires and distributor guts? It's a very strange problem and the timing could be locked at full advance or idle advance we just have no idea. Maybe you should also try a different coil while you are at it.

 

BTW do you know if the timing advance ever did work for sure?

 

Another thing, my car ran well with or without the TPS connected, and with or without the knock sensor so I doubt timing is effected by the TPS and knock sensor (unless there is knock).

 

There might be ONE signal that the ECU is looking for in order to advance timing. Trouble is, what is that signal and why isn't your ECU getting it.

 

When you checked all your ECU sensors and inputs, did you read the values through the harness at the ECU connector? You should. This will include all wiring in the diagnosis.

 

Is there any way to know if the injectors firing frequency is increasing with revs? This would indicate that the ECU knows that you are reving the motor. Listen to the injectors with a screwdriver tip against one of them and the handle pressed against your ear while you rev.

[russ in va]

Dave, thanks for the input. And thank you for your generousity with the ECU loan!

 

I replaced the coil itself (the old one was leaking oil), but not the power transistor. I had ordered a coil from the local import autopart store, but when it came in it was a coil only ... and made in China. They had a Bosch blue coil on the shelf, so I got that instead for the same money. I did not think this could effect timing advance so I had not mentioned it. Do you agree?

 

No, I don't know if the car was ever getting advance. So this problem could date to the time of the swap 6 or 8 years and 2 owners ago, or it could be recent. At this point I should problable bring up some info I originally posted in another thread. The day I bought the car, it ran pretty well (about like it does now). A couple of days later, it lost all power. Actually dynoed it and it made 85 RWHP. On Dave's advice, I checked the timing and found base set at about 0 degrees. I twisted the distributor to full advance and got about 20 degrees. Car now runs like it did when I got it. I'm now begining to think these problems are related .... but I have no idea how?

 

When I did my diagnostics, I did check everything at the harness under the dash.

Note: The CHTS testing did not check out per the FSM, I'll paste those results in here now from post #7 above in italics for easy reference ... could this be the problem? And what's the right way to fix it?

-Cylinder Head Temperature Sensor - fails the factory test but I'm puzzled

(note: infared pyrometer reading at CHTS = 95 degrees F at the time of these tests)

-pin 23 to body ground is infinite resistance (shoud be less than 2.9 K ohms at 68 F or above per FSM)

-BUT (this is not a factory test, I just looked at the wiring diagram and figured out where the other lead from the CHTS hooks up) pin 23 and 26 together read 1.237 K Ohm (why doesn't the FSM have you take this reading instead of the 23 to body ground reading?)

-Reading right off the sensor itself was 1.240 K ohm

-Also, if you unplug the CHTS with the engine at full operating temp and running, it misses badly BUT there is not a noticable spike on the dyno's wide band 02 sniffer?? (does this sound normal?)

 

The only other bothersome result from my probing was the ground/air regulator wire at pin #108 (see post #7 for details). Can I just run a new wire to fix this?

 

I'll have to try the listening techinque to be sure, but since the air fuel stays in line on the dyno, I'd certainly expect the injectors are firing in the right time. I would not think they could supply enough fuel at 800 cycles per minute (idle speed) to feed the motor when it's running 5000 rpms and makeing 150 hp. Doesn't the fact that the car runs and revs up at all indicate that the ECU knows the right RPMS and is sending spark signals? Just trying to think this through.

[cygnusx1]

...Doesn't the fact that the car runs and revs up at all indicate that the ECU knows the right RPMS and is sending spark signals? Just trying to think this through.

 

You would think.

 

Another potential problem...Are all the parts from the same year L28ET? There were differences between the three turbo years. In particular, the distributor electronics were different. Not sure exactly how different, but they were.

[russ in va]

I know the 81's had the CAS down on the crank pulley while the 82 and 83 had the CAS in the distributor. I'm not aware of any other differences. At any rate, I know my distributor does have the CAS in it. I don't know what year my ECU is from as the part no. does not appear on the ECU part number list I have. Do you know what year the ECU you loaned me is from?