Can't get my L24E to pass smog

[xlr8r]

I'm baffled. I know enough about engines to get in trouble & will eventually figure this out, but maybe someone with more fuel injected Datsun experience can help point me in the right direction rather than me continue to check every little thing.

 

The car has low CO (good) but high HC (Hydro Carbons) in the 800 range when they do the steady RPM test at 2000rpm because it's missing. I'm clearly not burning all the fuel. You can hear it miss quite obviously while it idles. It seems to only be during low load that it runs crummy, ie at idle and cruising. However, at WOT this L24E seems to pull & run just fine. It pulls hard if you ask me, like I'm getting all it's horses. When cruising it's hard to modulate a steady cruising speed because it's missing/sputtering along and slows down, then when I give it the slightest bit more gas it wants to leap forward.

 

Car is a 79 810 with the standard L24E & manual trans. It does not appear to be a California model, the 78 I am parting out and have spare parts from does appear to be a California model.

 

Here's what I've checked:

1. Compression- Good, they are all just shy of 150, I'm at 4300ft. above sea level, with cylinder 5 giving me a slightly lower 140. The spark plug on cylinder 6 was wet (I assume fuel, didn't seem to be oil) when I pulled it after warming it up to do the compression check, so this may be my problem cylinder, not sure if just one cylinder can make the HC's as high as they are?

2. Valve lash- was a little on the loose side, but I've tightened it up.

3. When idling if I pull each plug wire individually it does effect the engine's running, so each cylinder seems to be sparking & getting fuel.

4. Plug wire resistances (Taylor brand) are good, Plugs are NGK's & all have a good color to the tips, gaps are good.

5. Ignition Coil resistance measures at 2ohms on my cheapo multimeter. Manual says it should be between .84 to 1.02. Assuming my multimeter is accurate is this enough of a difference to screw everything up? I'm just assuming my multimeter isn't accurate enough to really tell me what it is.

6. Checked the throttle valve switch. If there is a FAQ on how this operates and effects the tune I'd love to see it. It's odd how it's basically on or off, no in-between. I'm wondering it this has to do with how twitchy cruising along is. Anyways, the switches position was originally such that it was always sending the same signal. I adjusted it so it switches between on/off at just a little bit of throttle, per the manual if I understood it correctly. This adjustment did not improve things.

7. Water temp sensor seems to be ok per ohm readings

8. AFM seemed to be faulty. I wasn't getting any resistance measurements, so I swapped the one in from the 78 that did have proper readings. It does have a few extra prongs but I assume the needed prongs for my 79 are in the same position, I'll double check the manuals (I have a 78 & 79 manual). It still runs poorly.

9. Timing, was set to 10 advance. Idle RPM's go up if I give it more advance but it's still missing.

10. Distributor- Cap looks good internally. The rotor seems to mainly be firing on the back end. Meaning if looking down at it, the wear it shows is all on the left side. The pickup coil has 400 ohms of resistance as it's supposed to. Haven't looked at the points because I just barely learned about them.

11. Fuel pressure was good at around 35-36 psi. If I lightly grip the the hose I can feel it pulsing. Not sure if the damper does completely take out all pulsing or not. So would a bad damper be enough to cause what I'm experiencing?

 

I'm wondering about many things but I think my next step is to pull out the injectors/rail & pressurize it to see if any are leaking.

Any ideas?

[Skib]

Iv never had to pass smog in my life lol

 

but I do have an L24e ECU laying around if you need it.

[datzenmike]

Maybe someone can comment on this: I heard that running the tank low and adding a gallon of alcohol will get you through emissions. Something like this.

[Laecaon]

Or if it has a Cat, run the car very hard prior to getting it checked to make it very very hot. Burns everything out of the exhaust.

[Z-train]

Change the oil.

Change the airfilter.

Pull the timing back a few degrees.

Run the lash to a 11 thou.

Run the highest octane you can find.

Excessive blow by MIGHT be getting ingested.THe alcohol might work(don't drink it).

If you have a wet plug with fuel or oil,this needs to be addressed before testing

 

A borrowed MSD box MIGHT get you thru.

[DanielC]

A low CO and a high HC to me means suspect a lean misfire. The misfire is not caused by anything wrong with the ignition system, there is simply not quite enough fuel to fire in the cylinder after the spark occurs.

 

Part throttle cruise is when the engine is tuned to run the leanest. Going to WOT makes the mixture richer. so under those conditions, the engine runs fine.

[xlr8r]

Yeah, the lean misfire is what my friends at the shop & I have kind of concluded given the emissions readings. I just wanted to see what ideas experienced Ratsuners had.

 

What is the best way to enrichen the low load situations? Any ideas as to why it would be running lean?

 

I know there is a screw on the AFM that can be adjusted to effect how lean or rich the car runs. The manual makes it seem like this method should be used as a last resort though. I need to get my 800 HC down to 500 or below, which shouldn't be hard at all if I can rid of the misfire.

[Skib]

 

I know there is a screw on the AFM that can be adjusted to effect how lean or rich the car runs. The manual makes it seem like this method should be used as a last resort though.

 

thats because its spring loaded and if you let it go..... well lol good luck ever getting it back to where it was.

 

 

but I have a how to on tuning AFM's I can email you. its a word document

[Sealik]

I know there is a screw on the AFM that can be adjusted to effect how lean or rich the car runs. The manual makes it seem like this method should be used as a last resort though. I need to get my 800 HC down to 500 or below, which shouldn't be hard at all if I can rid of the misfire.

 

8 mill screw, upper left in pic.

 

 

Mark wheel/clock position before adjusting.....you can see where I marked either side of the tab with a felt pen.

Hold onto wheel....loosen screw. Adjust...re-tighten screw.

Doesn't take much to change AFRs...try 1 or 2 notches

Wheel moved CCW-rich.... CW-lean

 

 

You can also shift the elec board for the wiper arm to have a new 'path'

[xlr8r]

I adjusted the AFM (also put the 79 AFM back in, it's actually operating correctly, the 78 is not a suitable replacement) to the richer side. It looks like it had been adjusted before about 8 clicks to the lean side. I adjusted a little at a time and basically ended back up where I believe it was from the factory. I may need to play with it one more time now that the spring has settled into it's new position.

 

The car still runs poorly at idle, low load, & tip in. If I back off the timing it does seem to miss less but is an absolute slug from a stop. I checked the emission control system last night. The fuel check valve seems good, it does take a lot of effort to get a little bit of air through it from the tank side though. I never managed to get air to move through the canister from the gas tank to the intake side, and yes I did apply vacuum to the control valve. So maybe that valve is not working correctly.

 

I'm beginning to suspect injectors more. I put a fresh tank of gas in it because it's earlier tank was a mixture of old & fresh gas. I also put in some injector cleaner.

I think I'm in that dreaded situation where if this were someone else's car, as an outsider I'd immediately figure out the problem. Since this is my car & I've been dealing with it for weeks I'm blinded & can't figure it out.

[Sealik]

All the spark plugs the same colour???

 

If one is different......<...........could be an injector...or...

 

Someone just had a set 4-sale, although they are pretty cheap at Rockauto

[xlr8r]

Plugs have all been the same color. #6 was wet last time I checked them, so I'll run the engine again & see if #6 is wet. If so I'll know something is definitely going on in that cylinder.

[xlr8r]

OK, I think I finally figured out the problem. It was my Distributor. I had to order a new dizzy, so I won't know for sure until it arrives.

 

So basically the reluctor & stator weren't playing nice. It appears that the magnet under the stator has become so brittle that it cracked in a few spots, allowing the stator to shift over enough that the reluctor wasn't centered anymore & the 2 were making physical contact on 2 cylinder points while being too far away on the opposite cylinders. I took it apart to clean out all the metal, put it back in, & the car wouldn't start. I took it apart again to see what I did wrong at which point the magnet broke up into too many more pieces, so I ordered a new dizzy. I'll have this thing on the road sometime next week hopefully!

[Z-train]

I have a 79 distributor sitting around.

[xlr8r]

I should've thought to ask you. I have a 78 dizzy sitting around, want to trade? If so pm me.