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I'm on the fence about recommending retarding the timing a couple degrees. Although the EGT will be slightly higher, the peak combustion temperature should drop a touch in the process though. So, I don't know what to advise on that front.
My base timing is set to the factory 6 degrees. Am I able to retard it any more and still have a decent running engine?
I'm going to spitball some ideas here which are pure speculation but...
Is it possible that carbon buildup in the cylinders is raising compression too much? Maybe do a compression test and/or borescope?
A.I.R. system working correctly, and no leaks?
Is it possible that the nylon timing gear has failed and changed the cam timing? This is a reach, and I would think it would affect performance, but I thought I'd ask.
I'm going to spitball some ideas here which are pure speculation but...
Is it possible that carbon buildup in the cylinders is raising compression too much? Maybe do a compression test and/or borescope?
A.I.R. system working correctly, and no leaks?
Is it possible that the nylon timing gear has failed and changed the cam timing? This is a reach, and I would think it would affect performance, but I thought I'd ask.
Carbon buildup could be possible since the car burned oil when I got it and I recently replaced all the valve stem seals. No more burning oil. I did a compression test on all cylinders and they were all within factory specs.
How do I test the A.I.R system? My FSM does have a section on it but I haven’t gone in depth on it.
I had the timing chain and gears replaced back in march when I had a shop replace all the engine gaskets. I think they put metal gears on it instead of nylon. I have to look at the receipt to make sure.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by mikelsuktub
My base timing is set to the factory 6 degrees. Am I able to retard it any more and still have a decent running engine?
The six degrees is just the baseline that the ECM uses to add to the programmed advance written into the software calibration. Unless your ECM fails, you're never going to actually be operating with that low of spark advance. A couple degrees of reduction (via rotating the distributor very slightly) shouldn't hurt the drivability noticeably, but might temporarily give you a bit more breathing room when trying to reduce the NOx.
The mod is free, and the testing will tell you if it helped or not.
Last edited by 69427; Sep 14, 2022 at 02:17 PM.
Reason: typo correction.
Carbon buildup could be possible since the car burned oil when I got it and I recently replaced all the valve stem seals. No more burning oil. I did a compression test on all cylinders and they were all within factory specs.
How do I test the A.I.R system? My FSM does have a section on it but I haven’t gone in depth on it.
I had the timing chain and gears replaced back in march when I had a shop replace all the engine gaskets. I think they put metal gears on it instead of nylon. I have to look at the receipt to make sure.
I'd have to look at the manual for the A.I.R. system too, but obviously look for any holes or other leaks in the system. Pull the discharge hose from the pump and see that the flow increases with RPM and, if you'll pardon the expression, suck and blow the check valve to make sure it "checks" out. After that it's electrical stuff.
I can't imagine anyone putting a nylon timing gear back on one of these things. I don't even think you could get a new one today.
So I tested the car again and it failed for the same reason. I replaced the O2 sensor and the NOx went down from being 4x higher to about 2x higher. I noticed the HC and CO numbers were lower than the average shown on the test result sheet. I compared these numbers to an old test where the car passed and the numbers were drastically different. I’m not sure what else to do to get this car to pass.
I suppose you could also confirm the harmonic balancer hasn't slipped and your timing is actually jacked up...
I replaced the harmonic balancer back in July. I actually retarded the timing a couple degrees below the factory spec. Now I’m wondering why the CO measurements are 0.01 which I read could cause high NOx.
I was a California Smog Tech for several decades, but haven't worked on cars professionally since the 90s. I used to know this stuff, but my recollection is hazy. I found this page to be a helpful refresher.
Low CO is lean, which usually causes high HC. You don't have high HC. But according to the chart in the link, lean mixture, advanced timing, and carbon build up (increased compression) are all contributors to high NoX.
I would retard the timing even more.
Check fuel pressure, raise it if possible, pay attention to fuel/air ratio. If it is lean, fix it.
Water introduced into the chambers of a running engine is effective at removing carbon. Pull a few easy to access plugs, run the piston to the top, and look at the piston tops and color for deposits. With the engine idling again, introduce water into the throttle bodies. Don't drown it out on the water, but let it ingest it. I don't know how long, how much water is needed to clear things up, but I'd probably try to get at least a gallon through it. Drive it to get it good and warm, and remove any traces of liquid water. Pull the same plugs again, take a look, and evaluate "how you did".
Just some ideas.
I'm in Torrance. I have a good test-only smog station a few minutes north of the 405 on Normandy. They will let me put a car on the machine and see how it does. I am going to go over there in the next week or so for a smog for my Typhoon. I'll ask if they would let us take a few minutes of their day to figure out your car. Let me know if interested.
Don't let your registration expire. Even without the smog cert, pay the renewal. DMV won't send you the sticker, but you won't incur penalties for late registration. Eventually you're going to get it smogged, and the sticker will automatically be sent.
I’ll try upping the fuel pressure but going to high causes the rotten egg smell and I don’t want to ruin a brand new cat. I’ve been running Lucas oil fuel additive and it seems to be helping. I’ll also try retarding the timing even more. Could I try sea foam to try and break up any carbon buildup?
I paid the registration so I won’t have any late penalties.
Is it just me ? I find it crazy having to smog test a 38 year old car.
I agree, it should be any car that’s OBDII only gets smogged. Not to get super political, but I think CAs insane smog is to try and force older cars off the road because they’re more likely to be “gross polluters” when I rarely see cars from 70s/80s ever being driven around here. That’s a reason pre smog cars are so valuable here.
I’ll try upping the fuel pressure but going to high causes the rotten egg smell and I don’t want to ruin a brand new cat. I’ve been running Lucas oil fuel additive and it seems to be helping. I’ll also try retarding the timing even more. Could I try sea foam to try and break up any carbon buildup?
I paid the registration so I won’t have any late penalties.
You can try Redline Si-1 for a tank or two. It won't work miracles(none of them do), but it does get some carbon build up removed. Only good way to tell for sure how bad the carbon is, is to pull a plug or two and look at the pistons with a bore scope.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I just got thinking, IIRC an '84 has the hot air stove that feeds the intake air during cold starts. Do you know that the air thermostat valve is properly shutting down/off the hot air getting into the air filter housing? NOx is a high combustion temperature product. Lowering the intake air temperature should be directionally correct to lower the NOx production.
I just got thinking, IIRC an '84 has the hot air stove that feeds the intake air during cold starts. Do you know that the air thermostat valve is properly shutting down/off the hot air getting into the air filter housing? NOx is a high combustion temperature product. Lowering the intake air temperature should be directionally correct to lower the NOx production.
Keep us updated on things.
How about some water injection to cool the combustion chamber ?
Spray bottle should work fine. I wonder if it has an aftermarket egr valve. Some of them had different orifices to tune them to the engine. Maybe it has a too small of one in it.
