Timing Weirdness = Emissions FAIL..1980 L20B

[Buzzbomb]

Hi Guys..I haven't posted in a while because my truck has been running awesome..Well, turns out it wasn't running awesome enough to pass the emissions test here in CO.  My numbers were great everywhere except for idle HC @ IDLE..

 

HC= Idle = 543 (limit 400) - (FAIL)

HC = 2500 RPM= 192 - (PASS)

 

CO% = 2500 = 1.27 (PASS)

CO% = Idle = .06  (PASS)

 

 

My Idle speed was about 875. Pretty wacky looking numbers to me..I went home and bumped up my idle to 1000, checked for knocked off hoses, and checked my vacuum. I'm getting around 15 hg at idle at 6000 ft altitude at a pretty steady needle. I remember from years ago that too far advanced timing can cause a high HC at idle, so I broke out the light and checked it against the V notch/tab. I plugged the hose to the distributor (which I assume is from the "air injection galley") and took my reading. My timing mark was advanced about an inch off the mark.

 

I loosened the distributor bolt and tried to adjust it back, and the best I can get is a hair less than 20 BTDC. The distributor has never been out of my truck, neither has that plate under it, and I checked timing a few years ago :o and it was about 15 or so.

 

What can cause the distributor to literally run out of adjustment space? If I advance the timing, my idle goes up, but when I lower it, the lowest I can get is a hair below 20. Only thing I've changed lately are plug wires. Any thoughts on this are much appreciated! Thanks!

[datsunaholic]

The dist has 2 adjuster bolts, though the one you can't see easily doesn't have much adjustment.  But it's also possible the advance plate inside the dist is jammed.

[izzo]

yeah wow.  Timing should be about 10.  could be a number of things. how many miles on the motor?

[datzenmike]

Vacuum advance is from a port inside the carb. At idle the throttle plate should be close to closed and the port is above it reading normal atmospheric pressure or basically zero. There is no, or should be no vacuum advance at idle.

 

Take the dizzy ca[p off and suck on the hose to the vacuum advance. The rotor should rotate about 3/4s to an inch clockwise and hold there untill you release it. As Doug said the plate may be stuck or one of the centrifugal weights or springs is off loose or jammed.

[Buzzbomb]

Hi Guys,

 

Thanks so much for the replies! I'm kind of in a pinch here because I get a free re-test for 10 days (whoop de dooo), and honestly, I'd like to get it done and not give those SOB's any more money than I already have to..

 

The engine has 184,000 miles on it, and otherwise, runs great! The plugs look great too. The only thing I've noticed lately is a little bit of pinging going up hills, and now I think I've found out why. The distributor, as far as I know, has never been R&R'ed. I'm really hoping I don't need a new dizzy. As I've checked it over the years, it's always been around "15 BTDC". Just above 10 but below 20 BTDC. As I said before, I'm now at least on the timing tab, but I'm can't retard it enough to get to the 14 BTDC that it needs to be at.Timing is on PORTED vacuum, and has been as LOOONG as I've owned the truck. As I said, Datzenmike, I DID check the timing without the hose connected.

 

I will definitely check the operation of the advance plate...That sounds like something that could be a culprit.

 

I sure appreciate the input! I will check the advance mechanism later and see what's going on with it for a good start in troubleshooting this. I'm not sure where the other distributor adjustment bolt is. I was of course using the one you can plainly see.

[datsunaholic]

The other one bolts the dist body to the plate, so the bolt is upside-down.  And usually in the back.  The normal one bolts the plate to the pedestal.

[Buzzbomb]

Ok datsunhaholic.. I will look for that thing with an inspection mirror. If I could gain maybe 1/4 inch of adjustment, I just might be able to retard that timing to around 14 BTDC. Stock is 12, but I'm at high altitude, and it always ran good around 14. I have to eliminate the sticking advance plate 1st.

 

Is this other bolt for gaining a little adjustment something Nissan did to take up the slack of a worn distributor? Just wondering. If so, pretty darned smart.

 

BTW- I could NOT kill the engine by rotating the distributor either way.

 

It's been running great since you all helped me get my head gasket repaired. The thing uses NO coolant whatsoever. This e-test crap is a drag, but it ran so good I would never have suspected the v-notch in the crank pulley was off like that. In that sense, I guess it was worth a few bucks.. However, I'm doing my best to make lemonade here, so..... :)

[datsunaholic]

Well, the bolt is there to mount the dist body to the plate, since there are different plates for various pedestal/dist body configurations and it's a VERY small adjustment.  Basically makes up for variations in machining.

[Buzzbomb]

Well, the bolt is there to mount the dist body to the plate, since there are different plates for various pedestal/dist body configurations and it's a VERY small adjustment.  Basically makes up for variations in machining.

 

Thanks datsunaholic.. I looked for it and I THINK I see it sort of under the temp sending unit on the LH side. I may have to break out Hainz's video again to see if he points out just where that is so I can be sure.

 

I put a vacuum source on the vacuum advance hose (pulling about 12 hg) as DatzenMike suggested. The advance can holds pressure as long as I have the source hooked up, BUT I get NO rotor movement and only a very slight movement from the "advance plate?" ie. the stuff with the stator and such on it. I'd say it moves less than 3/16 inch with that 12 hg of vacuum on it. If I sucked on it, I don't think it would move at all....? If I twist the rotor counter-clockwise by hand, it moves and does come back, but not as smoothly as you'd think.

 

I didn't see anything obviously broken or out of sorts in there, though. I didn't mention it earlier, but I am running the stock Hitachi matchbox distributor on the stock pedestal. Runs great otherwise, although I couldn't kill the engine by rotating the dizzy either way. I knew something was up at that point.  :P

 

One thing else I want to state.. When I put in my headgasket, I made 100% sure the timing mark on the sprockets was where it should be, and I also adjusted the valves to spec. Of course that was more than a few years ago, BUT every year since doing the HG I've passed smog with zero issues.

 

I just want to do a good process of elimination before coming to the conclusion that I need a new distributor. No sense throwing money at it if there's no need because it can be fixed. Heck, I fixed my heater control in my truck with a screw that cost less than .10, so I do have some hope for this :D .  I'm surprised it came so close to passing at all with the timing so far advanced.

 

Thanks for the input!

[Buzzbomb]

Quick update on where I'm going with this.. I did a little reading on a couple Z-car sites, and it seems like the electronic dizzys have issues later in life with the advance plate stuff getting brittle, freezing up, and/or breaking. As I said previously, my plate moves, but it is way too tough to move by hand. There is no way that vacuum can is pulling that thing enough to move it. When I first tested it, I believe it was frozen in the advanced position, hence my emissions failure at idle and not at 2500. It loosened up, but it is still too tough to move. In other words, I believe you guys are right about that plate. There just aren't a whole lot of possibilities OTHER than the distributor that can cause an off the scale timing mark.

 

Instead of trying to track down a new advance plate or tear apart the distributor to find that it's not worth fixing, I bit the bullet and bought a new dizzy. It was 20% off at Advanced Auto, shipped right to my door for free, all new parts, possibly better mileage and maybe cooler highway running thanks to a working advance, AND I get to keep MY known good Hitachi OEM matchbox for a spare. The latter is a big reason I leaned toward replacing the distributor after seeing some other stuff on what appears to be a common problem on old Nissan distributors. I just might keep the whole old distributor as a spare..I haven't decided yet if the $20 core is worth it.

 

EDIT*- I put the distributor in and it works great. This was a "Cardone" unit and it actually came with a Hitachi spark box. It's actually a nice unit, and you can't beat it for 20% off. I have around 10-12 degrees of timing now at idle whereas before it was advanced off the scale. You guys were right, and the information on the Z distributors was right. The plastic ball bearing cage in my distributor was busted. No sense trying to repair it. I had an old Standard Motor spark box laying around, so I took my known good Hitachi box off there and will get my core charge. The rest of my dizzy is just flat wore out..

 

I'll post my pass results when I get it smogged again :ninja:  ... 

[Buzzbomb]

Hi guys...Quick update for you. Datzenmike and datsunaholic were right again :D As I stated above, after their advice and my inspection, I decided my dizzy was pretty much worn out. The plastic ball bearing cage that the advance mechanism rides on was broken and the plate was binding/stuck. I put in a new distributor, and here were my e-test results today for you know whats and giggles:

 

 

HC= Idle = 135 (limit 400) - (PASS)
HC = 2500 RPM= 90.8 - (PASS)

CO% = 2500 = .35 (limit 1.5) - (PASS)
CO% = Idle = .03 (PASS)

 

The smog cartel forced me to pay for a third test because on the 1st free retest my gas cap failed. This was even after two people that worked there called the manager to see what he could do because I failed due ONLY to the gas cap. Unreal..

 

Just thought I'd follow up for those that helped and for those that search.. Thanks for the advice! Ratsun is the BEST.. You guys that have been around these cars for so long know them inside and out- PERIOD. The excellent advice from you folks never ceases to amaze me.