Mod Tech or OEM? Stroker fails CA smog check

[cbremer]

Not sure if this should be Mod or OEM.. but it involves a modified engine, so here it is

'87 XJ 4.0L stroked & bored to 4.6, AW4 auto.

I miserably failed my smog test today. Readings were:

HC PPM@15mph: Max 133, GP 321, Meas. 143
HC PPM@25mph: Max 104, GP 271, Meas. 139

CO %@15mph: Max 0.89, GP 2.19, Meas. 2.51
CO %@25mph: Max 1.12, GP 2.42, Meas. 2.78

NO PPM@15mph: Max 1090, GP 2057, Meas. 710
NO PPM@25mph: Max 1130, GP 2114, Meas. 689

So I failed HC, and exceeded GP (gross polluter) for CO. NO is not too bad.

I put on a brand new cat yesterday, so that's not the problem. I'm installing a new O2 sensor this weekend as well. Cap, rotor, plugs & wires are less than a year old, and this is not a DD, so they have maybe 8-10k miles on them. I drove around for 45 minutes, mixed city & freeway driving to warm everything up right before the test.

A big question mark for me is: I currently have 26 lb/hr injectors installed (got a great price on them). Should I install 24 lb/hr injectors (or even 20 lb/hr)? Of course I can't find my stock 19 lb/hr injectors, or I'd try retesting with them installed :rattle: It appears to be running very rich, but I don't know how much to scale back on the fuel injectors.

Last problem: they failed me on the visual portion of the test since I don't have a 'thermostatic air cleaner', which I removed when I installed the stroker with the Mopar performance header (with EO sticker, so that's legal). Anyone know where to get a universal-fit TAC, or how to fab one up?

thanks as always-
chuck

 

[5-90]

Most strokers are happy with the 23# injectors, but you may need to build a MAP adjuster to "dial them in." The 23# units are close, but I'm wanting to think the trypical stroker likes just a touch less fuel.

Since it's HC and CO that are failing you, I'm inclined to think it's a fuel mix problem - which is why I'm thinking your injectors are too big, and you may need the adjuster. It's a fairly simple voltage divider - but you'll have to Google it, since I don't have links handy. Try a search here for "MAP Adjuster" and see what you get as well - that will likely turn up a link.

The "thermostatic air cleaner" (what rot!) is little more than the "choke stove" - the sheetmetal around the exhuast with the air tube going into the box. Are you RENIX (1987-1990?) It's possible to fail the smog if you don't have that air tube installed - but they don't seem to look to see if it's connected at the other end up here. Hell, I've gotten smogged without even having the airtube - and all my reports say "not present." I keep one with me when I go to get smogged again - just to show 'em. So far, they've done that every time.

Running with your stocker injectors - 19-20#/hour - is likely to decrease your HC and CO, but increase the NOx emissions - due to a lean fuel mix and the resultant elevated combustion chamber temperatures. Probably not much help.

You'll eventually want a MAP adjuster anyhow (keeping the right AFR also helps to cut fuel consumption,) so you might as well build it now.

5-90

 

[SDXJ]

Make sure the smog tech runs your xj in 1st and 2nd gear on the dyno, NOT in Drive. I don't have a stroker, but a failure turned into a passer with flying colors. Oh yeah, good idea on the injectors too.

 

[Dr. Dyno]

The 26lb injectors are definitely too big and that's why your engine's running rich but rather than swap in smaller injectors (Ford 24lb'ers are the most common on '87-'95 based strokers), you can build a MAP adjuster and turn down the input voltage below the stock 5.0v to shorten their duty cycle. This will correct the richness and the MAP adjuster will only cost you ~$10 in Radio Shack parts. If you're handy with a soldering iron, making one is easy. Here's my MAP adjuster write-up:

http://www.angelfire.com/my/fan/MAP_adjuster.html

I also have a 4.6 stroker but it's a HO version and my XJ is a '92. I'm using Ford 24lb injectors, stock fuel pressure regulator, and MAP adjuster set at 5.15v. I pass emissions with flying colors.
My guess is that you'll need to set your MAP adjuster at ~4.5v (a 10% enleanment from stock). This should get you very close.

 

[cbremer]

Follow up for reference sake:

I installed Ford 24 lb/hr injectors, did a tune-up (new plugs, air filter & oil change), replaced the O2 sensor (which tested bad- no continuity in the heating element), repaired a couple of cracked vacuum lines (which fixed my wandering idle), tested various other sensors, and installed a heat stove/"thermostatic air cleaner".... and passed! Readings were a bit above average, but well below the maximum limits.

New readings are:

HC PPM@15mph: Max 133, Avg 43, Meas. 95
HC PPM@25mph: Max 104, Avg 32, Meas. 60

CO %@15mph: Max 0.89, Avg 0.16, Meas. 0.66
CO %@25mph: Max 1.12, Avg 0.15, Meas. 0.70

NO PPM@15mph: Max 1090, Avg 406, Meas. 112
NO PPM@25mph: Max 1130, Avg 349, Meas. 54

Still a bit higher than average on HC and CO, and well below average on NO. I've had the parts to make an adjustable MAP sensor in my garage for a while, so I may (finally) do that and lean it out just a bit more (higher NO, but lower HC and CO, right?)

Thanks guys... now I'm just waiting for my sticker