I know, high NOx = check EGR function

[ccarley]

But I've got some questions on this subject.

'89 V1500 Suburban, stock 350 TBI but with a throttle body spacer, and a salad bowl. Passed Smog! But, the NOx was high (a couple of points from failing) at 15 mph and 25 mph.

I am missing the snorkel from the air filter to the grill, so it's sucking hot air. I'm sure that is not helping. Also, with the larger tires, my speedo is about 10 mph off at 60 mph; that's pretty significant. From what I understand, the computer controls the EGR valve according to road speed?

If I get the snorkel installed, and get the correct speedo gear, I'm wondering if that will lower my NOx output at all.

The engine is otherwise running great. New plugs, wires, cap & rotor (Accel super truck tune up kit, I know but...) air filter, and the oil change was done a few months ago. I had run Lucas fuel system treatment in the tank a couple of tanks ago. Running regular 87 octane fuel.

The cat is original too; with over 170,000 miles on it at this point. The HC and CO numbers were pretty reasonable, and the smog tech in the past has said that the cat is probably fine. Of course, here in CA, they pretty much rape you to replace a cat; you can't even mail order one anymore!

Anyway, I'm good for another couple of years. I'd like to fix whatever I can before I go in again though.

Thanks for any suggestions!

 

[eagle mark]

On that truck should be the 1227747 ECM and EGR is controlled by TPS% and MAP. VSS or speed comes into play in newer ECM/PCM.

If your that good on smog and from your avatar and tire comment I'd say it is the tires without a gear change causing a lower MAP reading and higher TPS value to maintain speed then the origanal calabration was designed for.

For the speedo off contact sweetk30 for a modified DRAC. It's a little white box that plugs into EFI harness and makes adjustments to VSS signal to Speedo, Cruise control and ABS. Will have an effect on TCC lockup but not EGR operation.

So if you fail for Nox next time and it is because of EGR operation put back the stock tires or change gears... HTH!

 

[ccarley]

Thanks Eagle Mark,

That helps, more info the better. I'm going to get the cat changed before I smog again... it's too bad that out here in CA they won't let you do a smog test just because (where I live anyway); they will only do a smog test if it's required on your registration. I'll see about another set of rollers too, they should be pretty cheap to come by!

Clay