92 Chevy G20 Van, help!

[Bill P]

Okay, I'll try to make this as clear as possible, so some of you nice people can help me with this. I have a 1992 Chevy G20 conversion van, that I recently purchased. When I got it, it didn't pass emissions, the HC levels were too high. I had the engine tuned up completely, IE: plugs, wires, cap, rotor, air filter, fuel filter, still din't pass emissions. This van starts smooth, idles smooth, and doesn't smoke. It has 124,000 miles, and is in great shape all around, but......... Here's the only real problem, and I think it's related to the emissions failure. When I'm driving along, the van seems to have a "bucking" or surging feeling between 30 and 45 mph. The engine seems to run a little cold, according to the gauge. My regular mechanic, and myself seem to think that this problem is causing the failure, but he admits that emissions are not his specialty, and suggested taking it to someone who's more familiar with them. I have had people saying that it's probably an 02 sensor,or an egr valve that's causing the surging, and possibly the emissions too. I thought it might be the tranny, but it doesn't seem to slip at takeoff, and doesn't hesitate to go in to gear. It really only does it, when I'm barely giving it any gas (cruising), not during acceleration, and I can't notice it at speeds over 50 either. Please help me to narrow down this problem, so I don't spend a fortune.

[RABarrett]

First, get the engine back up to operating temps. If it does not, it will ignore all of the other "emission" sensors. I suspect a defective O2 sensor, but if the engine is running cool, the ECM will ignore it until at least 120 degrees. Ray

[CD Smalley]

Running cold would cause this RABarret. My guess is it's a combination of things.


Any SES light or codes?

Next let's look at the temps. If the van is running cold, it probably has the wrong temp thermostat installed. Make sure it's a 195* unit. Even if that means installing a new one. They're less than $5.

After that a bad CTS, coolant temp sensor, would make the van THINK it was running cold, and force it into open loop mode. Which means it dumps more fuel, etc....

Then I'd look at the O2 sensor and the EGR valve. The chugging at speed would indicate an EGR failure to me. If you replace either of there parts, save yourself the trouble and buy a GM part. My experiences over the years with aftermarket versions of these parts has been less than satisfactory.

[Bill P]

Thanks for the responses. No, I'm not getting the check engine light, and I haven't gotten it thrown on a diagnostic yet, but soon.
I just replaced the thermostat, and that didn't seem to help with the temp.
I'm wondering if the sensor that reads the temp, and sends it to the gauge is messed up. The stock gauge doesn't give temps, just little dashes, and it''s usually halfway between the first, and second dash, I think there are five.
I think I remember my old k5 Blazer, running a little warmer, like closer to the middle of the gauge (same engine) Did I mention that it's a 5.7 (350) throttle body injected? If that matters.

How expensive is it to replace an egr valve, or an 02 sensor? What exactly do both of them do?

[CD Smalley]

There are two temps sensors. One for the gauge and one for the ECM.

The o2 sensor mounts into the exhaust, probably directly into the left exhaust manifold on your van.

The EGR is mounted to the intake manifold. Two bolts should be all that holds it down. You will have to take the dog house off to get to it. But from there it should be very easy to replace.

Both parts should run under $50 each.

[Bill P]

It was the EGR valve, it passed emissions, and the surging has stopped.