brand new GM Goodwrench engine fails New Jersey emissions

Bought a brand new 350 from the local dealer for only $1744 for my 220K miles '94 Suburban. The old one had barely flunked the ASTM 5015 elevated rpm "roller" test for CO (10% high) and HC (5% high). It was "using" oil; I never found a leak but had to add 2-3 quarts every 7500 miles, and the plugs never looked bad. Leaking antifreeze from freeze plugs. Plus I plan on keeping the truck for a long time, with the price of new Suburbans being what it is. The new motor shows borderline CO, NOx, and 50% high (first test) to almost 100% high (second try) HC. I've got almost 1000 miles on the motor. I'd have expected the rings to be seated by now, no?

Tomorrow I'm going in to try to get an emissions waiver, but the car still has to pass an idle test for HC and CO. My elevated rpm (roller test) HC reading this last time was 217 ppm (versus a limit of 118), and the idle limit for HC is 220. I don't think it's gonna make HC, since all of the postings I've looked at show higher emissions at idle than elevated rpm.

The plugs are new, the plug wires have 18K miles on them, catalytic converter has 100K, the O2 sensor has 20K. If not the rings, I'm thinking it's the cat. Check engine light is not on and no trouble codes (except system OK) are flashed when the appropriate wires are jumpered.

I plan to change the oil to 10W40 (from 5W30) and check the plugs tonight.

Any way to diagnose the catalytic converter without just buying a new one and trying it? Other comments?

Reply to
hillpc
Loading thread data ...

Yes, the cat can be tested with a 4 or 5 gas analyzer. Take gas readings from in front of the cat thru the O2 sensor port, compare to what you get at the tail pipe.

Gotta ask; is the cat that's on there now an OEM replacement or is it aftermarket?

What is the fuel pressure, with 220k on the TBI, I'd wonder if the fuel pressure regulator is still functioning correctly?

Make absolutely certain that the MAP sensor is connected to the correct vacuum port on the TBI.

Is the engine warming up all the way (190* coolant temperature)?

Are the injectors worn out (leaking or bouncing pintles)?

Scan data would be helpful, especially fuel trim numbers.

Is the EGR valve working as/when it should (borderline NOx) Is it leaking?

Ignition timing (set according to procedure)?

Valve lash (don't trust the engine builder)?

What does the pole piece in the distributor look like, any cracks in the magnet?

High HC and on the edge of failing CO indicates a rich condition, certain death for a catalytic convertor, especially one that spent time behind a worn out oil consuming engine.

Reply to
aarcuda69062

Lots of good stuff to check. The cat is a relatively cheap replacement ($180 installed) from a muffler shop. It looks kinda small but I don't remember what the original one looked like. Haven't checked fuel pressure in about 20K; it was fine then. (Bad plug wires with less than 20K miles on 'em had driven me me nuts checking everything else.) I'll check the MAP sensor. I'll warm it good tomorrow before the test. I couldn't tell about the TBI leaking, though I'd expect the controls would take over and squirt less fuel. Yeah, I've gotten by for 12 years without scan data; maybe it's time. The scan tools aren't cheap, as you know. EGR is behaving as the PCM expects; the EGR diagnostic trouble code disappeared when I fixed the vacuum line actuating it. PCM looks for O2 sensor response when EGR activated. I don't know what you mean by EGR leaking. I put a new gasket on it, and it doesn't sound like it's leaking exhaust into the engine compartment. As I understand it, exhaust gases cool down the combustion temp (and thus lower NOx) since there's nothing left in them that burns anymore. If leaking through, it should be lower NOx, I'd think. Base timing is OK, within a degree or two advanced at most, and the PCM sets the timing anyway, no? Valve lash, sheesh, I'll leave that one for later. Distributor pickup coil and control module new 20K ago, but I'll check the magnet. Plugs of course look brand new, as they should at 1000 miles. Sounds like the cat is what you're thinking most likely as well. Thanks for all the input.

Reply to
hillpc

catalytic converter could be a likely cause, would suggest a10w30 instead of 10w40 oil, and do you think the rings have set at

1000 miles (?) they might need a little more wear / heat to set real good.

I would think a quart of marvel oil added to the oil change in lieu of a qt. of oil would help "polish" thinks up a bit.

usually a good system will produce test results with room to spare.

fwiw - I always get the car's temperature up to normal for a given period - before getting a state test.

mho vfe

Reply to
fiveiron

Reply to
Shep

Got an emissions waiver today, sticker good for 2 years. To get I passed an idle emissions test; at least that's what they told me (didn't show me any numbers). Now I suspect flunking the elevated rpm test may have been due to the rings not being seated yet, since at higher rpm I'd expect more blowby and oil splash on the cylinder walls. We'll see how it does 2 years from now in the elevated rpm test again.

Thanks for all the good comments.

Reply to
hillpc

Those types of cats are usually only good for about 2 years and since they're only half as efficient as the OEMs, highly suspect.

Things go bad from one day to the next...

Only to a point. Adaptive fuel trim has limited control, although, when it reaches its limits, you should get a check engine light and either a rich or lean code.

the latest/greatest aren't cheap, perfectly functional for your model year truck is dirt cheap on e-bay.

Good.

Leaking as in; allowing exhaust into the intake manifold when it shouldn't, or over active. the first being an idle concern, the second being a cruise concern.

(and thus

The PCM -controls- the timing, but that control is only as good as how accurately the base timing is set.

Should only take an hour.

Good. FWIW, I've pulled fresh Cardone brand re-builts out of the box with cracked pole piece magnets. cracked pole piece magnets can trick the PCM into reading higher RPMs than what the engine is actually turning.

I'm very suspicious of after market catalytic convertors. If you have to replace it, don't go by the catalog recommendation, fit the largest cat that you can find, with the correct pipe size of course.

Reply to
aarcuda69062

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.