Dillon93dillon

So i have a 2000 chevy 5.3l, swapped into my 79 chevy 4x4.

runs about 50-60 psi depending on the vacuum of the engine.

I just recently started having a missfire, not bad enough to throw the check engine light on, (sometimes it will flash like a missfire should)

today i hooked up efi live, and see that cylinder 5 has 100 missfire counts, so i check volts at the coil pack and at the injector.. both 14.2v
try swapping plug wires, and plugs around and it stays there.

I even swapped coil packs but cylinder 5 still holds that missfire.....
I CAN ONLY THINK A BAD CAM OR CRANK SENSOR..
anyone have any better ideas than i have?

crainholio

iTrader: (2)

Swap the injector next, see if the misfire follows it.

After that, compression test #5 as well as a few others for comparison.

Dillon93dillon

i swapped a coil from a good cylinder, and it didnt follow. i see 14 volts to the injector and the coil. i wonder if the ground is gone on one of them? where does the ground go?

i can only think its a ECM problem. because if i had compression missfire i think it would be alot worse than it is.

crainholio

iTrader: (2)

I'd say it's time to put down the tools, stop posting for a bit, and do a lot of reading.

Old Geezer

iTrader: (3)

And put the post in the correct forum.....

Ethan[ws6]

iTrader: (13)

I would still swap the injector and see if it follows. I had this same issue on Tuesday with a Camaro I did for a guy. Put a noid light on the injector and it showed signal and checked voltage. Switched injectors around and my misfire moved.

Dillon93dillon

ill swap it around, but i put another set of injectors in and the issue was still there.

i did a compression check and it shot to 150psi almost as soon as it turned over

t5munoz

Ill tell you what i had the same problem and it turned out to be the upstream o2 sensor

SVTconfused

do a leak down test...

Dillon93dillon

even only one cylinder was missing? i got like .03% on one bank and it alters some of course. and 13% on the other bank. forgot which was which tho

Dillon93dillon

Havent done one before. whats the consist of? pressurizing cylinder and seeing how long it holds?

Dillon93dillon

i dont have a leak down gauge, and no one i know has one haha. i will never use one again after this so i dont wanna buy one

SVTconfused

pretty much what you do is bring the cylinder up to TDC and the "gauge" has a hose with a set of threads that screw in like a spark plug... you hook the gauge up and zero it out with out having the hose into the cylinder attached... then you hook it up and it will show you the % of leakdown...

Dillon93dillon

yeah i dont have that. best i got is the compression tester.

i would think if it built 150psi i wouldnt have much leakdown.. but am i wrong?

SVTconfused

my motor for instance 2000 ls1 had 165 iirc compression on cylinder 6... it would miss at idle and low rpms...under 1200... once it got above that magic number the miss would stop and she ran good...

turns out i either had a bad seat or bent valve... when i filled the port( cant remember if it was intake or exhaust) with the heads off the motor water leaked thru into what would be the combustion chamber. none of the other valves did that...

so to answer your question... you may have leakdown... I didnt own a leakdown gauge at the time of me diagnoseing my car...


now onto another thought... is this only at idle? or will it occur only under load or is it random?

Dillon93dillon

it is noticable more at lower rpm. but you can still hear it and tell through the exhaust.

i can try leakdown if i can come up with a gauge.. but this was just a all the sudden deal. didnt start over time or anything. one day came to start it and had that issue.

Dillon93dillon

also, sometimes my ecm wont even pick up a missfire... even if the wire is disconnected on the coil and injector.. but sometimes it will and will flash as well. which is weird.

even unplug a good running cylinder and it wont pick it up sometimes. swapped crank sensor and still the same

Dillon93dillon

hopefully this helps some.

idk what else to do besides maybe a bad ecm

crainholio

iTrader: (2)

LTFT for bank 1 is high @ 19%. Can you re-scan and get LTFT for bank 2 as well?

SVTconfused

i also have to ask if your 02 sensors are fluctuating correctly...