Codes p0304 and p0440, intermittent loss of power?

1998 CHEVROLET S-10
230,000 MILES • 2.2L • 4 CYL • 2WD • MANUAL
Avatar
CHEVYGAL85
  • MEMBER
  • 1 POST
Hi there,

At first, it was throwing a p0304 and p0440 code. Misfiring very badly and the CEL would flash at times, especially at high speeds. I changed the plugs, wires, coil, and module. Needed to be done anyway, but no change from any of that. Cleared the codes and they came right back. Then I changed the fuel filter and injectors. It ran Perfect for about a week. I cleared the codes, and they didn't come back. After that week I had a loss of power going about 70 MPH. Flashing CEL. This time code P0303. Drove it like this for a few days. Flashed again and threw a Po325 knock sensor also. Cleared codes and have not seen the p0325 since, only p0303. I did a compression test, perfect compression. But the spark plugs were bridged. I had gapped them to the Chilton .06. Saw later engine bay says .05. I put a new set gapped correctly. Did a fuel pressure test at rail. Good at prime and idle. But I do notice a whine coming from my gas tank so I'm suspecting my pump may be acting up intermittently and causing misfires. Any suggestions for further diagnostics? Can a failing pump cause a one-off knock sensor?
Dec 17, 2022 at 6:49 PM
Advertisement
Avatar
STRAILER
  • Experienced Mechanic
  • 55,256 POSTS
Yep, weak fuel is common on these vehicles. To be sure this is the problem let's do a fuel pressure test which you can rent a gauge for cheap or free at the auto parts store. Here is a guide to help walk you through the process and I have included the fuel pressure specs and how to change the pump out just in case you need it.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Pressure 55-60 PSI
Open Throttle 66 PSI

Check out the images (below). Please let us know what you find. We are interested to see what it is.
Dec 19, 2022 at 1:37 AM
Join 2CarPros for free, one of the most advanced car repair communities on the internet. From first-time drivers to seasoned mechanics, everyone is welcome to reply, share details, and get better answers. You can add a temporary image or video first; uploads are limited to 20 MB.
Ask a Free Question
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.