S10 rough engine

Possible causes: Intake air leaks, Faulty front heated oxygen sensor, Ignition misfiring, Faulty fuel injectors, Exhaust gas leaks, Incorrect fuel pressure, Lack of fuel, Faulty Mass Air Flow (MAF) sensor, Incorrect Positive Crankcase Ventilation (PCV) hose connection...If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced. The P0174 code could also be caused may be caused by one or more of the following: debris on MAF sensor causing an incorrect reading, improper oil level, low or high fuel pressure or Engine Control Temperature (ECT) Sensor reading inaccurate.

Is it really possible that all the possible causes only influence bank 2? Bank 1 is working correct according the Live Data from my code reader and from what I can see on the spark plugs. P0174 is the only code I have. A faulty MAF sensor I think will influence both bank 1 and bank 2. My next step will be to remove the upper intake manifold to look more on the injectors.

When I removed the upper intake manifold I saw that the intake for cylinders 2 and 4 was much more sooty than the others. My code reader says nothing about misfiring. What is the best next step for me?

Good morning. I had to work yesterday sorry I didn't get back. So that is an indication of leaking injectors, or fuel regulator, the sooty look under the plenum. This must be a 4.8L engine? This is a common problem, leaking spider injection assembly. To verify, you would want to do a fuel bleed down test. This would fit the po174 code. Let me know where you are at with this, I don't have to work today, but have some things to get done. I'll be around.

Thank you for your comments Rowefast. My S10 has a 4.3 V6 engine. I made a fuel pressure test today with the upper manifold removed. Key on gave 64 psi during about 2 sec then down to 58. After 5 min it was 56 and after 10 min it was 55. No fuel was possible to see at the spider. Even if I can't see any fuel leakage it can be some problem with the spider and the poppets. For me the fuel pressure seems okey. Do you agree? I shall think a little more about it then I think it's time to order a conversion kit from CSFI to MPFI. Do you think that is the right thing to do?

Fuel pressure itself is good, but it is bleeding down indicating a problem with the spider injection. Fuel pressure should be 56 to 63 lbs. Any time fuel pressure starts getting 55 and below, you have a hard start situation until it gets down to 52 and below, a no start condition. The fuel pressure should not have dropped down more than 5 lbs. in 3 minutes. So there is a problem developing with the spider injection, and should be changed out. When everything is good, fuel pressure would drop down some, but hold for hrs. Do you have a sight that I could look at for what you are looking at for a conversion kit? On the spider injection, that is a Multi Port Fuel Injection system. When buying a new assembly, it has be upgraded, made better than original. Also, re-torque the intake manifold to 15 ft. lbs.

Rowefast: I agree of all your comments and will start to find a MPFI injection for my S10. I am living in Sweden so I think it's hard to find this here. I have to order it from US I think, but that is no problem it just take some time. Thank you again for your comments.

Check this out, maybe you can order from these guys, this is what you need.... https://www.carid.com/1997-chevy-s-10-pickup-fuel-delivery-parts/delphi-replacement-fuel-injectors-277592159.html

Rowefast: With a new updated MPFI spider the engine work as a new car. Thank you for your comments.

That is always good to hear! Glad I was able to help. Thank you for the follow up!