the68

Lately my 1993 Chevy G20 6cyl 4.3l sportvan has started sputtering at low RPM, low throttle. It has no trouble at all starting up, and the fuel pump primes well. The first thing I replaced was the fuel filter, which looked as though it hadn't been changed in years by the rust. No dice. The fuel pump was replaced in 2009, but I figured I should drop the tank and see what was going on in there since my gauge had been working only sporadically. Turns out the gas tank baffle had come loose and was swimming around under the float, causing the gauge to fail. The hose that connects the pump to the hanger also had a disconnected clamp on it, likely resulting in some of the fuel being pumped right back into the tank rather than to the throttle body. There was no indentation in the hose beneath the disconnected clamp which leads me to assume it was never snapped down to begin with. I bolted the baffle back down to the bottom of the tank, snapped the clamp, and hooked the tank back up. The gauge worked but the engine still sputtered at low RPM, low throttle. So off comes the turtle shell. I find that one of the new spark plugs I installed earlier this year had come apart and was rattling around loose, so I replaced that and checked the others. This didn't change anything, so I checked the EGR which seems to be working properly upon testing. I then replaced the distributor cap and rotor, and upon inspecting the engine at night I noticed a short around the main coil so I replaced that too, along with new spark plug wires. The engine definitely seems to be running better after all of that, but I still have that low RPM, low throttle sputter.

I'm glad I started having this problem, as it's led to a few discoveries that definitely needed attention. I'm not sure where to go from here though. I'm wondering if maybe the fuel filter failed or something and sent a bunch of crap that can't be touched by fuel injector cleaner up into the throttle body, which is what I'm going to check out next. If anyone has any ideas as to where I can go next that would be great; sensors to check, etc. This is my only vehicle other than my bike (working on the slave clutch on that one, and as much rain as we've been getting here in the NE it hasn't been much practical use anyway) so it'd definitely be nice to have my wheels back before I move on to the next construction job.

canucklehead

Vaccum leak? Try the propane test.
Could maybe be and o2 sensor.....
What about gas cap not venting?

the68

Whoa, that's a possibility. Whenever I take the gas cap off there is a bit of a sucking noise. I'm going to check that out, thanks!

edit; no dice. There still is the issue of that sucking noise, though. I thought it was normal.

the68

Well, I said I checked the EGR valve which consisted of removing the vacuum line, manually depressing the valve with my fingers, holding my thumb over the vacuum inlet, and letting go of the valve to see if it stays in. It passed. However, I read somewhere if the EGR gets hot quickly that it could be a sign of carbon buildup. I started the engine and the valve gets hot almost immediately. So I guess I'm going to remove it and see if there is any carbon buildup in there. If anyone else has any more suggestions they'd be greatly appreciated!

the68

I took the EGR off this morning, it was carbed up but it didn't look bad enough to cause it to stay open. I've checked my vacuum hoses again and they all seem to check out, but I'm probably going to end up doing the propane test on them. At this point I'm also starting to suspect the injectors. All I gotta say is I'm glad I finally got my bike up and running, because it's looking like this is going to be an ongoing project.

the68

Okay, I think I found the problem. The passenger side injector is splattering fuel whereas the driver side injector is spraying as it should be. Does anyone know how many volts it takes to fully open the injectors? I'm thinking about saving myself a couple of bucks by taking the jets out and using a variable power supply to open them up and see if I can blow the garbage out the same way it came in. Does anyone know whether you can replace one injector or do you have to replace both?

canucklehead

If you have TBI.....try reversing the injectors. They are the same, but one is the regular one, and the other is the secondary and cold start. If you revers them, you may find it idles better, but maybe revs a bit slower. Then you can pick up a used injector from the wrecker....or a new one.

the68

Thanks so much for the help, canucklehead. See, that's the funny part; the engine sounds beautiful at idle. It only sounds horrible when it's at low throttle, low RPM. I'm getting ready to try to backflush the injectors this afternoon since I have off work, I will reverse them when I put them back in to see what happens. Thanks for letting me know the differences between the two, I know the 4.3 TBI have two different injectors but I didn't realize the difference or that they could be switched. I'll keep you updated, can't wait to be out doing stuff like this in it again;

the68

Just wanted to give everyone an update on my van since it's up and running like a champ again... better than ever, actually. It turned out to be the EGR unit after all. I asked some questions on a couple of youtube channels, and youtube user DoctorD907 still suspected the EGR even though it tested well. He wrote me a message suggesting that I simply unplug the EGR vacuum line and try to run the van without it connected. I didn't realize the engine would start and run without it before. So I tried this, and the sputter disappeared. As soon as I would plug the EGR back in, the sputter would return. So off to the auto parts store to get the new EGR, which cost me 50 bucks. I installed it and the van is running great now.

Canucklehead, I do have a question for you though; I did end up switching the injectors before realizing the EGR was the problem. They are still reversed from their original position, so my question is whether or not it is okay for me to leave them as they are? Or should I go back in there and change them back to their original position? Thanks for all of your help!

canucklehead

I guess if its running fine that it should not be a problem. Its just like switching the fuel pump and starter relays in that box under the hood....they are the same too.
Good to hear you sorted it out.
Saved yourself some cash for sure.