Misfire and rough running 98 k2500 5.7

[jaxcob]

So my new Delco cap and Delphi rotor came in. Like the old cap that I replaced a couple months ago, this Delco one has aluminum terminals. The one I put on has brass terminals. Small confusion

 

[stutaeng]

I'm not sure why you were suspecting MAF, if you saw good change on your scanner. Maybe I missed something? There's a rule if thumb for what the MAF readings should be at idle based on engine displacement. I can't remember off the top of my head. But generally, a smooth reading with increasing RPM tells you it's good. You can also even check it with DVOM with Hertz capability.

That high fuel trim on bank 2...what does that number do when you rev up your engine?

 

[jaxcob]

I'm not sure why you were suspecting MAF, if you saw good change on your scanner. Maybe I missed something? There's a rule if thumb for what the MAF readings should be at idle based on engine displacement. I can't remember off the top of my head. But generally, a smooth reading with increasing RPM tells you it's good. You can also even check it with DVOM with Hertz capability.

That high fuel trim on bank 2...what does that number do when you rev up your engine?

So the new maf has better values on the scanner than the old one. While it might not been the issue, it probably needed changed. I cycled the fuel pump a couple times and checked the Schrader valve and there was barely any flow. So I tore it down and changed regulator out with the old one off the poppet system. Checked the Schrader valve again and it had pressure in it. Set up towels to check the injectors and all 8 worked. So took a chance and put things back together after cleaning some of the carbon sludge and all. Threw my new cap and rotor in as well. And the misfire situation is fixed. I know I didn't test everything to the extent I should have but wasn't loosing anything but time by just checking things like I did. Now I do have fuel leaking around the fuel lines but the misfire and rough running is completely gone now. And that makes me happy.

 

[wirlybird]

So the new maf has better values on the scanner than the old one. While it might not been the issue, it probably needed changed. I cycled the fuel pump a couple times and checked the Schrader valve and there was barely any flow. So I tore it down and changed regulator out with the old one off the poppet system. Checked the Schrader valve again and it had pressure in it. Set up towels to check the injectors and all 8 worked. So took a chance and put things back together after cleaning some of the carbon sludge and all. Threw my new cap and rotor in as well. And the misfire situation is fixed. I know I didn't test everything to the extent I should have but wasn't loosing anything but time by just checking things like I did. Now I do have fuel leaking around the fuel lines but the misfire and rough running is completely gone now. And that makes me happy.

I bet it does!!! Congrats and good work.

 

[Toenail]

Check your distributor gear for wear. The engines with roller lifters will wear the distributor gear due to mis-matched materials running together. The engine timing will show a shift also.

 

[DavidAlan]

I know this will be funny, with all your work, did you do anything simple first? Did you by chance buy bad gas? did you fill your truck as a fuel tanker was filling at same time? or could be the one thing people over look all the time, Change your Fuel filter ,lately? the one thing that can block and give a false reading to all your hard work.

 

[asinclado]

You said at the beginning it needed 2 quarts of oil. how long before that you checked the oil? I am new to chevy trucks and have a 97 k2500, but I would say 2 quarts of oil is a lot for any car (40% of total capacity for a 5.7) With that mileage, I would do a compression test. after all, you dont know how that engine was cared for by previous owners. The engine in it might be a used replacement they already threw in it with unknown mileage.

 

[jaxcob]

I changed the filter a couple months ago with a wix. I'm changing the pcv valve as soon as that gets in. I check the oil at least once a week and this is the first time I've ever seen it use oil. I don't fuel up if the tanker is there and always had good luck with Sam's fuel.

 

[asinclado]

never mind. i miss the part when you got it taken care of. Good Work.

 

[75lemans]

I’ve been having almost the same exact problem with my 98 k2500 5.7. Started out as a miss just at idle and slowly got to a very bad miss all the time and spits and sputters when you try to speed up. Just did the MPFI a couple months ago and ran awesome. I just put a new distributor in with no change. Have 58 psi of fuel pressure with engine off and 52 psi with it on. Cleaned the MAF too with no change. No codes at all either. What would be the next thing to check?