I know this isn't about a Fiero, but its about a GM vehicle and I registered on the S10 forum and can't post. I've been a Fiero owner in the past and the Fiero community has always been very knowledgeable about tech in general.

I just got a Chevy '97 S-10 with the 4.3 and have been having a couple issues. When I got it, it was showing a P0420 code, the O2 after the cat was reading the same as the other O2 sensors (indicates there's no cat). Replaced the cat, turns out the previous owner had hollowed it out. Also broke the wiring on the O2 sensor and replaced it. No more P0420 code!

Now it has a code for P0151. Low voltage from the 1st O2 on bank 2, indicating it running lean. I've searched and searched on the S10 forum and every instance of it someone has always had other codes. Especially the other bank running lean, which points to a vacuum leak, fuel pump, or MAF issues. Since mine isn't throwing the code for the other bank, I can rule all that out? What're the chances its the O2 sensor actually being bad? I've read on there about even the battery having a bad cell causing this kinda issue, or grounds needed to be cleaned. Could it be a bad injector? Injector needing to be cleaned? etc?

I'd like to know what's going on before attempting to change this O2 sensor, the one downstream from the cat was almost impossible to get out (screwed in so tight). This 1 appears to be on the manifold tucked in tight in the engine bay and doesn't look fun. Would like to avoid changing it if its some other issue, something simple hopefully?

[This message has been edited by sdgdf (edited 05-10-2019).]

If one bank is running leaner than the other, it isn't going to be a fuel pump or MAF issue.

Bank 1 is the driver side of the engine.
O2 sensor on that side could be bad - check the signal wire for continuity and swap the 1st position O2s from side to side to see if the issue switches sides.
Check for any exhaust manifold leaks on that side as well.
The EGR tube connects to that side as well, so it could have a cracked tube (exhaust leak) or an EGR issue.
Ignition components on that side (plugs, wires, caps) could be causing a mis-fire (but you should be getting a code for that.
Injector spider is also suspect. There could be a partially plugged injector, a cracked poly line between the injector and poppet valve, or a sticking/plugged poppet valve.

[This message has been edited by fieroguru (edited 05-11-2019).]

Did you mean first position O² sensor, rather than MAF?

quote Originally posted by fieroguru: If one bank is running leaner than the other, it isn't going to be a fuel pump or MAF issue. Bank 1 is the driver side of the engine. O2 sensor on that side could be bad - check the signal wire for continuity and swap the 1st position MAFs from side to side to see if the issue switches sides. Check for any exhaust manifold leaks on that side as well. The EGR tube connects to that side as well, so it could have a cracked tube (exhaust leak) or an EGR issue. Ignition components on that side (plugs, wires, caps) could be causing a mis-fire (but you should be getting a code for that. Injector spider is also suspect. There could be a partially plugged injector, a cracked poly line between the injector and poppet valve, or a sticking/plugged poppet valve.

Thanks for the ideas! That all sounds like possible issues.

I posted here before going to bed and wasn't very clear, P0151 appears to be bank 2. Does that mean EGR isn't on this side?

Any advice for dealing with the injector spider? Get an injector and change them around to see if 1 is bad? Run an injector leakdown test? Use a scantool and look at fuel trims as its running or something? I've never believed in injector/fuel system cleaners or services but maybe that could help?

Also, are you saying there's 2 or more MAFs? There's just 1 intake, and a V6 Fiero only has 1 MAP sensor??? This might have more?

If they have the same connectors and you have enough cable length, swapping the upstream and down stream should also work to test. It is pretty rare for only one bank to be running lean on pretty much any engine I've every worked, so even if you can't swap it for some reason, I'd still throw the o2 sensor at it, they have a finite life span anyway.

quote Originally posted by sdgdf: Thanks for the ideas! That all sounds like possible issues. I posted here before going to bed and wasn't very clear, P0151 appears to be bank 2. Does that mean EGR isn't on this side? Any advice for dealing with the injector spider? Get an injector and change them around to see if 1 is bad? Run an injector leakdown test? Use a scantool and look at fuel trims as its running or something? I've never believed in injector/fuel system cleaners or services but maybe that could help? Also, are you saying there's 2 or more MAFs? There's just 1 intake, and a V6 Fiero only has 1 MAP sensor??? This might have more?

I have had several 4.3s (1 even in a Fiero) and a L31 Vortec 350 for about 9 years... so I know these engine quite well.

EGR tube connects to Bank 1 (cylinders 1, 3, 5), so if the issue is Bank 2 it won't be EGR tube related. Here is a pic from one of my engine way back when. This shows the EGR tube running down the intake and connecting to the driver side (Bank 1) exhaust manifold.


It isn't MAF, MAP or Fuel pressure related as all of those are single components and support both banks. Only seeing the issue on one bank, means it is something specific to that individual bank. I fixed my typo as I meant to say swap the upstream O2s not MAFs.

Fuel trims are only bank specific, so the scan tool will only show Bank 2 being very lean, which you already know. That is pretty much the extent that computer diagnostics will get you unless it is also saving an individual cylinder misfire code.

Beyond that, you will have to do physical troubleshooting.
O2 sensors can be swapped from bank to bank (you should have 4 O2 sensors, 2 per bank, with 1 before the catalytic converter and 1 after). You would want to swap the O2 sensors that are in front of the cats.
O2 sensors signal wire should be checked for continuity and resistance.
Exhaust leaks you can normally hear and normally show a carbon dust pattern near the leak.
Vacuum leaks can also be heard with an automotive stethoscope or hose to ear technique.
Ignition components on Bank 2 should be checked - plugs, plug wires, distributor cap etc...

The best way to check the Injector spider is to pull the upper intake off. Most of the inside surfaces should be black from carbon build up. If one of the poly lines is cracked or leaking, the fuel spray will make a clean spot on the intake surface. Disconnect the coil wire to the distributor, remove 1 poppet valve at a time and have a friend crank the engine over. You want to verify clean spay and once the engine is off, no dripping. Do this for all 6 and try to notice if one is spraying less fuel than the other. This test sprays fuel into the air, so no flames, sparks, or smoking while doing this.

If you find an issue with the injector spider, or it hasn't been replaced in the last 5 years, it would we good to replace it and upgrade it to the newer version that moves the injector bodies to the poppet valve locations and eliminates the poppet valves. The upgraded version looks like this, but isn't cheap.

[This message has been edited by fieroguru (edited 05-11-2019).]