gazellis

Well, I installed new cats on my 87 GXL. The engine was rebuilt 2 weeks ago. I have run 1 tank of super unleaded through with additive.



The car did not pass inspection. Interestingly, in the state of Texas they test for 3 gases. Hydrocarbons, carbon monoxide and NOx which I think is nitric oxide but not sure. The NOx is a new test this year. The inspector was really concerned that the car would fail the NOx but it passed that part easy. In fact the NOx was barely detectable. It did fail the hydrocarbons and CO.



Tonight I was trying to figure out what was wrong and I noticed that the shop that rebuilt the engine did not tighten (or maybe it loosened on its own) the lock nut for the crank angle sensor. The timing was off. I reset the timing and the car sounds and runs much better. My question is, could the timing being off cause a failure in the emissions testing? Everything else I have checked, with the help of the Haynes manual seems to be just fine. The timing was off so far that the car could not Idle below 1000 even with the air adjust screw closed all the way. Now the engine idles at 750 RPM, the popping noise in the exhaust is gone and the car has very good power.

j9fd3s

the timing being that far off could do that. also check the acv. facing the passenger side is the acv dump tube, pull that off and start the engine, no air should come out under 3000-3800rpms



mike

gazellis

It does have air coming out even at idle. Haynes manual says air should start flowing at 1500-2500 RPM. I've got air at 750. Does this indicate a bad ACV?



I also did the Haynes manual check of the EGR valve. I removed the vacuum hose from the EGR solenoid valve and I applied a vacuum. Tthe problem was that it would not hold a vacuum. The manual said that the engine shoudl run rough or stall. Nothing happened. I guess that is bad also.

bradley87se

This popping sound..its just a light sounding pop in the exhaust after a high rev? I noticed this on my car but i thought maybe a extremly leaky cat was causing it.

evilT2

its called afterburn i think. its a small backfire more or less, very common.

j9fd3s

yeah your acv isnt working right. you need to make sure the relief and switching solenoids work according to the manual. if they do make sure the vacuum lines are routed correctly, there is one in the front (theres are 3 lines there) that commonly gets swapped and the car wont pass smog. next you can take off the acv and see if it works.



the egr doesnt do any thing, but you should put something in the hose so its not a vacuum leak



mike

gazellis

I have an update here but still need help. I took the car back to the shop that rebuilt the engine. They checked everything out and found quite a few vacuum leaks but no mal-functioning parts (ACV, EGR, etc...)



They fixed the vacuum leaks. I swear the car runs better than the day I bought it brand new but it still did not pass the inspection.



The first inspection it failed hydrocarbons and carbon monoxide. This time it only failed hydrocarbons. I guess it is getting better.



The rebuild only has about 120 miles on it and the inspectors seem to think that is why it is not passing. I have not been running it hard during the break in period (keeping it under 4000 RPM and such). Maybe that is why it won't pass. I haven't got a clue. I can't really go driving around town all day every day because it is out of inspection. I guess I could risk it, it can't be that bad to get a ticket for out of date inspection.



I took it to be inspected after it had been running for a while. The engine was good and hot (up to temp that is). I have run one thing of additive through the first tank of gas. Maybe it needs another at the next fill up.



Any other ideas? I was assured that the vacuum problem is fixed. It sure does run like everything is great.

pengaru

by how much is it failing the hydrocarbons?



maybe it's just running too rich, check the sensors to see if they are within spec (coolant temp, intake air temp, o2...)

gazellis

It failed by about 90 points on both the low speed and high speed.



I think it maybe running too rich because the inspectors keep making the comment on this. How do you change the fuel mixture to lean it out?

pengaru

well it's difficult to do with only the stock equipment, but the stock equipment should run it well enough to pass the test unless you have modifications like header , porting, etc.



The ECU controls the fuel mixture for you, it uses the sensors on the engine to select which fuel maps to use, so if it's running rich it can easily be one of the temp sensors or the o2 sensor, definitely check them out.



Introducing a vacuum leak could also help it pass the test, it would help lean it out (kindof funny).

Also make sure the TPS is adjusted properly.