Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

1997 Chevy Burb 5.7 w/P0303 misfire

1 year 1 week ago #58253 by PTDFlorida
This burb survived a tornado in my cousins barn - mostly repaired but had a bad idle when it was picked up to transport back to home state. It then sat for three years as I moved with my company. I did a bit of prep - full tank of non-ethanol gas with a quart of stabil, synthetic oil, topped up coolant and it was stored in a storage facility.

After I moved back I found a good YT video with about 15 steps on what to do to make sure you don't mess up your vehicle by just getting in it and cranking it up. After about a have day of working off that plan and with the battery mostly charged (and the crank was able to be turned by hand) I turned it over. First time - no joy. Second time it came to life.

Drove it to the self-clean and went to town cleaning it. Looked decent after that. Still needs a good bit of body/paint work but focusing on the mechanicals for now.

I am an ok DIY but usually need help when I get into the weeds on a more complex problem.

Tests completed so far -
1 Good spark on cyl 3 plug with a spark tester - all other cyls are running smoothly and no codes on them
2 Close ohms reading for suspect plug and two others
3 Close ohms for 3 plug wires
4 Compression test on #3 @ 150 psi - no leak down
5 Fuel rail pressure test @ 58

I have the BlueDriver OBD unit and am seeing several different readings but not sure how to interpret them. This is where my ask for help comes in.

The engine starts right up, runs well except for the #3 misfire, will rev up high in fairly quick manner, does not stall, and when idling the mis is almost not noticeable.

I did search and found this thread which closely matches my issue but it sort of just stops without finding out what happened - Notice: Undefined variable: target in /home/i81rb962hx44/public_html/components/com_kunena/template/aurelia/layouts/bbcode/url/default.php on line 32

It came with the old style spider CPI system and was updated to the MPI when the shop had it last.

I am leaning toward a clogged or malfunctioning #3 injector but those are just possibilities that seem to fit all the data at this point.

I can supply the sensor data and answer other questions that you may have to further the diagnosis.

Sorry for the long post but I figured it's best to provide as much info as possible up front to help eliminate dead ends.

Looking forward to discussing this with everyone

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1 year 6 days ago #58290 by 70monte
First thing that came to mind was the possibility of a intake manifold leak near cylinder 3. These vortec engines are famous for them. I have a 98 K1500 truck with this same engine and I'm on my third intake manifold gasket.

What are your fuel trims like? You seem to have addressed most of the other things that could cause a misfire. It's possible that you have a malfunctioning injector since it sat for a while. Try running the Chevron Techron concentrate in the gas tank.

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1 year 6 days ago #58292 by PTDFlorida
70Monte - thank you for your reply. I did a quick ear check around the cyl 3 for any hissing sounds but didn't hear any. I thought that my compression test would suffice and I kept it under compression for 15 minutes and since it held I went on to other areas.

I did plug in my OBD scanner and saw quite a bit of data but have not sure how to interpret it. I will post some of the info.

I put two bottles of the Techron in a half full tank and thought if it was a dirty injector that may clean it out.

I bought an injector tester and was able to do some checking
I ran a medium pulse count on cyl 3 and didn't hear anything. It was a little noisy and thought I may have not been able to hear it. So, I decided to check another cylinder or two and was able to hear them pulse just fine. I tried cyl 3 one more time and there was no pulse noise.

I have concluded that cyl 3 injector is not firing so I ordered a replacement for #3 and gaskets (just in case). I should get it in the next few days and will install it right away.

I'll post once I'm done installing it with an update. Thanks again for your reply.

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1 year 6 days ago #58293 by 70monte
You are welcome. A leaking intake manifold gasket will not affect the compression so having good compression in that cylinder is not an indication that your intake gasket is good.

sounds like you might be on the right track with the injector so hopefully that will fix the problem.

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