loose Distributor CAP = Perfect idle

[ira]

7 hours ago, Mike said:

I haven't read your whole thread because I just don't have the effort to scroll through 7 pages.  But, just curious if you've already swapped out the cap and rotor for a genuine Nissan product?  I've seen stuff like this happen with the cheap Chinese knock offs.  I'd hate to see 7 pages of debugging information only to find out that your cap/rotor combo are poor quality or maybe even the wrong part?  Just throwing ideas, again apologies if this has already been asked.

I've done a lot of work on engines in my lifetime to know that cheap parts only cost you money (and time).

Hey Mike, appreciate the thoughts..

so yes, car in past has always been services with good quality parts.   in the past 7 pages i swapped plugs, cables, rotor,, cap, fuel pump, filter, and confirmed distributor is the correct one for this model.  today it ran again for more than an hour with out choking or dying.  the blimps and misses are still there but engine is truly running healthy.  i can tell just by standing next to it.  as i pull car out of garage, its moves very smooth and responsive.  i have to put new tires before doing more road tests. 

before replacing the TPS, id like to know what to test or look for to rule it out.  

[ira]

FSM said the TPS should cut off around 900 RPM (Give and take 20) but most people on the net say 1400 rpm.   Mine Cuts off about 1250, should i go up or down?

 

Also do i make the adjustment on the actual TPS or on the AFM?

[siteunseen]

Have you read this? 

https://www.atlanticz.ca/zclub/techtips/tps/index.html

[ira]

18 minutes ago, siteunseen said:

Have you read this? 

https://www.atlanticz.ca/zclub/techtips/tps/index.html

Hey there,

 

Yup, its for years 1975 ~78.  so initially i didn't scroll down to the end, BUT now i did, so tnx for that

 

Still not sure which RPM to go off of (this link or FSM)

 

[ira]

OK folks, it looks like the issue is more on the AFM/TPS as im getting readings that don't match FSM.

so this post should be closed as the Dist Cap is no longer the cause here.  i have been getting consistent positive performance while TPS is unplugged and Dist Cap is tight.

TPS test looks good so im pretty sure its not TPS related and more AFM.

more will be posted in a new thread....

tnx to everyone who helped in past

 

[Patcon]

I would leave the thread as it is and not start a new thread. That way the final solution is with the initial symptoms

[ira]

31 minutes ago, Patcon said:

I would leave the thread as it is and not start a new thread. That way the final solution is with the initial symptoms

Fair enough..

since this is a Turbo model, i based my testing on ECCS section of the  FSM ( pages EF & EC 2~ 38).  Am i correct? 

a recap of the issue:  1) Car starts up quick. there is a little hiccup in idle for the first few min, then idle gets rougher and rougher to a point it struggles to stay on 

2) car wont go past 30 mph even if tired to accelerate gradually.  if i try to boost, it will chock immediately

i started off by using electric cleaner on ECU, harness, TPS pins, and AFM resister housing but no change in performance

Temp fix: unplugging the TPS dramatically improved the idle situation (blip remained but engine doesn't die nor idles rough) and resolved the drivability issues.  i can rev, boost and get up to 90 mph in few sec with no issues anymore

here is what im getting....
***************************************

 

** TPS testing... FSM Manual, Page EF & EC - 29

on 20-pin connector and 16-pin connector

                Pin 18 + 25 release = .5                  (Suppose to be 0 ohm)

                Pin 18 + 25 depressed= with slightest move I get infinity                 (Suppose to be infinity ohm at 30 degree if im not mistaken)

TPS Terminals..

                Pin 25 + 18 =0                                    (Suppose to be 0 ohm)

                Ping 25 + 24= when depressed almost half way I get closed circuit

                Pin 18 + Ground               =infinite                               (Suppose to be infinity ohm)

                Pin 25 + Ground               =infinite                               (Suppose to be infinity ohm)

 

** Starter Switch...FSM Manual, Page EF & EC - 31

on 20-Pin connector

               pin 9=11.5v                                    (Suppose to be Battery voltage)

 

** AFM testing.... FSM Manual, Page EF & EC -36

 

On 16-pin Connector

                pin27 to body ground = 11.5V     (Suppose to be Battery voltage)

Pin 33-26 reads OL                           (suppose to be 280~400ohm)

                pin 33-31 reads 96.7 ohm             (Suppose to be Except 0 or infinity)

Testing AFM on the 16-pin side (ECU plug side).

                pin 26 to ground= 0.6 ohm             (Suppose to be infinity)

                pin 31 to ground= 135.2 ohm        (Suppose to be infinity)

                pin 33 to ground = OL                        (Suppose to be infinity)

 

 On AFM pins Directly

                Pin 33 + 26 = 201 ohm                    (supposed to be between 280 ~400)

                Pin33 + 31 = 97ohm                        (Suppose to be except 0 and infinity)      

                pin 26 to ground OL

                pin 31 to ground OL

                pin 33 to ground OL

 

i dint open the TPS yet, i dont see a need

i opened the AFM side cover, it really looks very clean.  the carbon track looks like its brand new.  adjustments appear to be in line with the marking  

 

 

[Zed Head]

10 minutes ago, ira said:

Temp fix: unplugging the TPS dramatically improved the idle situation (blip remained but engine doesn't die nor idles rough) and resolved the drivability issues.  i can rev, boost and get up to 90 mph in few sec with no issues anymore

Unplugging the TVS would tell the computer that the engine is not at idle.  That is all.  This causes certain things to happen.  I'm not sure exactly what happens but the dramatic effect that you see suggests that your TVS is short-circuited or the wiring harness is, showing the engine at idle all the time when it is plugged in.

[ira]

14 minutes ago, Zed Head said:

Unplugging the TVS would tell the computer that the engine is not at idle.  That is all.  This causes certain things to happen.  I'm not sure exactly what happens but the dramatic effect that you see suggests that your TVS is short-circuited or the wiring harness is, showing the engine at idle all the time when it is plugged in.

Good to hear from you Zed,

 

when i saw TPS test results conform with FSM, i tested the wires back to the ECU end.  all appear healthy, i get continuity with very low resistance similar to touching leads on the Ohmmeter.  i tried to wiggle harness and connectors to see if anything is loose or shorted but all was fine.

What are ur thoughts on the numbers im getting on the AFM?

[Zed Head]

Your test results don't seem to match what happens when the engine is running.  Why focus on the AFM when the TVS has the biggest effect?

I don't know that the AFM numbers are as critical on the ECCS systems since they have closed loop control.  That's why they give a wide range in the specs.

Can't offer much help.  Your car seems to be haunted.  Weirdness abounds.  Lifting the distributor cap to fix a rough idle...unplugging the TVS makes it run right even though it tests correctly...  Mystery.

 

[Zed Head]

Have you checked all of your grounds?  Grounds are more important than most people think.  Weird stuff can happen.  Might be affecting the ECU operation.

Random internet thing about ground loops...

https://www.bapihvac.com/application_note/understanding-ground-loops-application-note/

[ira]

can it be bad ECU? is there a way to test that?