[FIXED] 1998 Chev K1500 with vortec MPFI spider fuel injection

Greetings All,

Have a misfire code on my 1998 Chev K1500 with vortec ( this is not the LS ) - definitely missing and I can smell gas in the exhaust. I rebuilt this engine had about 6 K trouble free miles and then we had a cold snap into the 20's and this miss occurred. Other facts: I replaced the failure prone plastic distributor with a chinese one off amazon - going to check gear backlash this morning.

Question - how best to trouble shoot ? I was thinking either ignition, distributor or a stuck open MPFI fuel injector - this has had the conversion from poppet to the delphi electronic about 10-15K ago . I am going to 1) check distributor cap and rotor, 2) check distributor gear for backlash 3) do a cylinder balance test by unplugging each plug one at a time trying to isolate it. 4) I have a pocket chinese DSO and a Hantek spark plug wire sensor - was trying to look at the spark pattern but the thing was so small was having trouble getting it framed right - didnt look like the classic spark plug secondary pattern. Any thoughts appreciated

REM wrote:

3) do a cylinder balance test by unplugging each plug one at a time trying to isolate it.

I think this is going to be the important part of your testing. Once you can isolate the miss to one or more cylinders, you can start doing pinpoint testing (spark strength, ignition pattern, ect.). Is the miss at idle only, or all the time?

Do you have a scan tool available? Fault codes and fuel trim may not be necessary for your diagnosis, but could help give you a better idea of what's going on.

misses all the time - not sure if this computer has fuel trim - I think these are batch fired injectors - P0300 - multiple misfire detected

REM wrote:

misses all the time - not sure if this computer has fuel trim - I think these are batch fired injectors

Miss all the time makes this much easier to diagnose.

It has fuel trims, but it may be in the old Integrator/Block Learn format.

My scan tool reads factory codes - but not seeing fuel trims - I believe these MPFI are batch fired VS sequential - so not sure you would have individual fuel trims that would show a difference cylinder to cylinder

Fuel trims won't reveal cylinder specific corrections or events on this car. Nonetheless, they may point to an ignition or fuel related problem.

juergen.scholl wrote:

Fuel trims won't reveal cylinder specific corrections or events on this car. Nonetheless, they may point to an ignition or fuel related problem.

Exactly what I was thinking. The amount and direction of trim can sometimes give us clues.

Still, if the miss is constant, then a manual power balance test will probably be more revealing.

Problem Solved - was listening to the engine both during normal running and on startup - I notice that the motor was cross firing - like firing against itself both during crank and normal running - IE a detonation without the rap - did a cylinder balance test and the misfires where random - the alkyd cap looked good - but I noticed the manufactures date code on the cap was 3//5/12 - ten years ago - so I replaced it - and problem disappeared. Thanks for the comments gentlemen.