92 G20 van (camper van, but without the high roof)
5.7L L05 engine
Van has 157k miles, but the engine was replaced with a used on around 120k (or so I was told by the PO).
2WD
Auto

My teenage son bought this van and we took it in for a general safety check (this was a "post-sale" check).
The shop let us know that the van wouldn't pass emissions due to high hydrocarbons (they only said it was over 1000 ppm), but otherwise, no major issues.

The van was idling high and tugging a bit when at a stop with the transmissions in drive.

So we started poking around a bit to see what might be causing the high hydrocarbons. I should note that I'm trying to help my son to not just throw money at the problem, but to approach things in a methodical way. Which for him, means try the cheapest things first, especially if they are things he should or will likely need to do at some point anyway.

We replaced the distributor cap and rotor and put new gaskets in the injector pod including the one that goes on top of the throttle body. We did not pull the throttle body itself and replace the base gasket. There were no signs of any leaks, so we decided not to mess with it yet.

Changed the oil and put in a new air filter.

We also noticed what I believe to be a cruise control actuator attached to the throttle linkage. It was a bit bent/stuck and seemed to be holding the idle high, so I removed the linkage and the idle dropped considerably to waht sounds "normal." I haven't put a tach on it yet.

Since it sounded so much better, he took it for an emissions test. Here's what the results were:
HC = 1558 (limit is 220)
CO = .358 (limit is 1)
CO2 = (limit isn't specified, but CO + CO2 has a limit of 6, so I assume this is high)

I should say the engine seems to run great. very smooth and seems to have plenty of power.
Exhaust doesn't smell obviously rich.

We plan to do the plugs, 195 thermostat, and replace all the vacuum lines next. The plug wires look fine (no cracks), but I'll check the resistance and replace if necessary.

I'll do my best to check the timing, but it look a little hard to do on the van. I'll post for tips in the van forum, but if anyone here has any, please share.

I think this engine has only one O2 sensor on the left side header, but maybe there's two. The SES light is not on (does light with the key turned to Run), but I can't be sure it is hooked up correctly since the engine was replaced. Does the fact that it lights when I turn the key mean it's hooked up correctly to the ECU? The shop said the scanned for codes, but didn't find any. Not sure if that verifies anything, though, due to the engine replacement. So, not sure if we should try new O2 sensors yet.

I can check and clean the EGR and bench test the MAP sensor.

The shop also indicated that the speed sensor in the tranny is soaked in oil and leaking a bit. Does that have anything to do with the emissions control?

I've read that misfiring is the most common cause for high HC. The engine doesn't feel like it's missing, but maybe it is? Or maybe just an inefficient burn?

I'll also read that the cat can be the cause. I'm sure it's toast and likely part of the problem, but can that cause such a big spike?He is budgeting for a new cat, but we'd like to make sure we aren't going to ruin it by not fixing other causes first. My though here is that cat can only clean up so much, and 1300 ppm is probably over it's capability. Ideally, we'd see some good improvement before putting on a new cat. For all I know, the one on there has been gutted. In any case, there's no sulfur smell or rattling.

What about the injectors? Can they be tested? They seem to spray fine, but I can't tell if they leak. Is there a simple bench test I can do? Given new ones are $80 each, I'm not sure if it's worth taking them to a shop. non Ac-Delco ones are cheaper still, but I'd probably avoid that route.

So, did I miss anything? Can the things I listed account for such a high HC measurement? Any recommendations on how to proceed?

We are in a bit of a chicken and egg situation. My son doesn't want to spend too much money on the van as he is concerned he may not be able to get it to pass emissions and may have to flip it at a loss. But if he can get it to pass, or at least to a point were we start seeing improvement and feel like it's promising, then he's more willing to spend money on it. It's a pretty cool van, and except for the emissions issue, in good shape. I'm willing to help him a bit (I paid for the inspection), but also want him to learn to be smart about his money and responsible for his own decisions.

Thanks,

James

 

The cat is supposed to neutralize unburned hydrocarbons (such as fuel). But you don't want too much going in there or it will burn out in short order.

Things I would check are the EGR and PCV systems. Not sure if it has a MAF or not, but inspect anything fuel metering related. general carbon building in the engine/intake/valves, and maybe a compression test. After that you'd be looking at more involved things like valve seals.