Need a little diagnostics help

[Barrnone]

Usually I can just search the forum and find what I need, but I am a little unsure about this one.

Picked up a 1988 Turbo A/T, no mods and seems to run OK. Went to get it smoged and it failed.

Here are the numbers:

Test | RPM | %CO2 | %O2 | HC Max| HC | %CO | NOX Max | NOX
15 MPH | 1651 | 13.7 | 0.6 | 106 | 182 | .52 | 762 | 898
25 MPH | 1755 | 13.7 | 0.6 | 81 | 168 | .53 | 701 | 755

After the test I checked for codes and did not have any. Checked the Vf voltage without the T1 E1 jumper and it showed 5 volts at idle and 3.5 volts at 2500 RPM. If I understand this correctly this means that it is running lean. Am I correct so far in my thought process? Am I also correct in thinking that the NOX is probably high because the car was getting hot during the test?

Thanks

 

[Kevin]

what were the limits? and you failed nox only?

 

[Barrnone]

Sorry, edited to add the HC Max and NOX max numbers. I failed both HC and NOX.

 

[jetjock]

Emissions problems can be difficult to solve from afar. Having said that:

Lambda = 1.007 for both tests and your numbers are consistent with an engine in fuel control. The HC could be ignition, valve stem seals, worn turbo, rings, leaky valves, or a malfunctioning EVAP/PCV system. I'd also check the EGR to confirm it's operating and the passages are clear. Since lambda is unaffected by combustion it's also possible the converter may simply be tired. Normally I wouldn't suggest this without first knowing the feed gas composition (to determine converter efficiency) but if you just want to pass replacing the catalyst will get you there.

 

[Barrnone]

Thanks for the answer. I think I was trying to be a little lazy and hoping it would pass. I have gone ahead and started going through everything just like I have with the other Supras I have picked up in the past. A couple of things I have found so far: it had BCPR5 plugs and a leak where the EGR attaches to the intake plenum.

 

[Poodles]

Fix the EGR leak (and while it's off, clean the passages out).

Also, did you get the car hot before you took it to be inspected? Catalyst needs to be warm to function correctly.

 

[Barrnone]

Finally got a chance to get back on this. Fixed the EGR leak and checked that it functions properly.

After this I kept hearing what sounded like a vacuum leak still. After checking what seemed to me obvious locations, it seems to be from around the edges of the freeze plug on the intake plenum. I can put my finger over a section and the noise diminishes.

First is there a more proper way to prove this other than the finger test.
Second, if this is the problem it seems like the only fix is to pull the plenum and r&r the plug. Is this correct?

Thanks for all the ideas so far.

 

[TurboStreetCar]

You could try spraying the leaky plug lightly with carb cleaner and see if the idle/noise fluctuates or changes.