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Roy
Roy, import/domestic specialest
Category: Chevy
Satisfied Customers: 5733
Experience:  ASE master tech for 40 years
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My 96 suburban with 5.7l vortec is getting a code saying #7

Customer Question

My 96 suburban with 5.7l vortec is getting a code saying #7 is misfiring. I did a full tune up and it didn't fix it so it replaced the injectors and its still there. I checked the fuel pressure and im getting 58# ***** on and 50# ***** idle. is that enough pressure and could that be the problem?
Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.

the only code number it is setting is P0307 ?

Customer: replied 1 year ago.
let me check real quick
Expert:  Gary replied 1 year ago.

ok

do you feel it skipping or just that one cylinder is dead like at idle if you pull off the # ***** wire the engines idle stays the same and any other wire you pull off the idle gets worse ?

Customer: replied 1 year ago.
Stored codes
po307
OEM codes
po300
po141
po1380
Expert:  Gary replied 1 year ago.

is just # ***** dead at idle where you pull the wire off of # ***** and the idle does not change at all but all other wires do change the idle when pulled off the cap ?

Customer: replied 1 year ago.
ill check give me 5 min
Expert:  Gary replied 1 year ago.

ok

Customer: replied 1 year ago.
doesn't change when pulling #7 and only changes slightly when pulling 3 and 5. when I pulled 1 it changed a lot. didn't pull any others I have a 3 year old im chasing while I do this
Expert:  Gary replied 1 year ago.

is the cap and rotor brand new ?

do you see spark jumping out of the # ***** off the cap where the # ***** wire goes into the cap ?

Customer: replied 1 year ago.
its getting spark and its new cap rotor plugs and wires
Expert:  Gary replied 1 year ago.

if you do a compression test on that bank of cylinders of 1 3 5 7 what do all 4 read for compression ?

Customer: replied 1 year ago.
ill have to go get one real quick mine broke. ill let you know in about 45min
Expert:  Gary replied 1 year ago.

ok if # ***** is 0 or very low pull the valve cover and see if any rockets fell off or if a push rod or lifter broke and crank it over watching those rockers v/s the others and also check for a broken valve spring

Customer: replied 1 year ago.
will do. on my way to get a compression testor
Expert:  Gary replied 1 year ago.

ok

that cylinder just needs spark fuel and compression to fire

Customer: replied 1 year ago.
I only tested 1,3, and 7. #1 was 60psi, #3 was 65psi, and 7 was 60psi.
I noticed that while it was running I could hear the fuel pump running non stop and it was noticeably loud. I don't think its been like that before
Expert:  Gary replied 1 year ago.

that low for PSI ?

a bad fuel pump would effect all the cylinders not just one cylinder

Customer: replied 1 year ago.
Maybe I am doing it wrong. do you start it and take that reading or release the pressure and take that reading. its been a long time since I've done it and I'm an idiot. cuz otherwise 1 was 92, 3 was 95 and 7 was around 100
Expert:  Gary replied 1 year ago.

no pull the coil wire off and just crank it over like 5 or 6 times with the starter to get the reading

then release the valve on the tool and do it again to be sure

Customer: replied 1 year ago.
that's right dang it. im an idiot
Expert:  Gary replied 1 year ago.

try it gain

calm down..no worrys

Customer: replied 1 year ago.
I'll go check again. b back in 30
Expert:  Gary replied 1 year ago.

ok

if all 4 of those cylinders are above 120 ish then compression is not the issue

Customer: replied 1 year ago.
1 is 135, 3 is 135, 5 is 125, 7 is 128
Expert:  Gary replied 1 year ago.

the compression is good

the 7 wire is in the cap correctly and where 7 should go and there is spark at the plug wire where it connects to the 7 spark plug and swapping 7 plug with 3 plug the skip is still 7 cylinder ?

Customer: replied 1 year ago.
ill give it a shot
Expert:  Gary replied 1 year ago.

ok

with a new injection unit and the compression good we are getting down to a bad crank sensor or possibly a cam shaft issue

Customer: replied 1 year ago.
swapped 3 and 7 and seemed to run slightly worse and gave a po300 code. there is a low buzzing noise coming from the passenger kick panel. almost a buzzing crackle. its never done that before this issue
Expert:  Gary replied 1 year ago.

swapped 3 and 7 spark plugs only and it did this ?

Customer: replied 1 year ago.
did what
Expert:  Roy replied 1 year ago.

good evening my name is ***** ***** I will assist

from the previous conversation, you have covered all the basics. the only possibilities that are left are valve train issues. you may have a broken valve spring or a camshaft or lifter failure.

Roy

Customer: replied 1 year ago.
ok that's not good. where do I start. And what could the buzzing be that's coming from the passenger kick panel. I was hoping it could be some kind of electronic problem that's causing the issue. I had a similar problem with my moms buick and it was the computer. not sure where its at on the suburban though. The weird thing is that for a while I was tripping a po306 intermittently on and off for about 6 months, then it hasn't happened for at least 2 months and now its tripping po307 and running slightly worse than when it was tripping a po307 code. And now that noise is there which is definitely load enough to be annoying. Thanks Roy
Expert:  Roy replied 1 year ago.

you said you have spar, fuel from the injector, and good compression. with all that, it leaves a mechanical issue. if the pcm was the failure, then you would be missing injector pulse to the cylinder.

Roy

please dont forget to rate me as it is the only way I get paid for my efforts

Roy

Customer: replied 1 year ago.
I don't know if im getting fuel to the injector. how do I check that
Expert:  Roy replied 1 year ago.

you need to do a fuel pressure test. you can rent a tester from a parts store

Customer: replied 1 year ago.
key on 58psi
at idle 50psi
doesn't change when revving or holding at 2000 rpm
Expert:  Roy replied 1 year ago.

ok, spec is 58-62 while running. the pump is not working correctly. you have low fuel pressure which could cause the issue as well.

Roy

Customer: replied 1 year ago.
That's what I was thinking and shouldn't the pump turn off at some point at idle because standing outside with the motor running, the pump is screaming non stop.
Expert:  Roy replied 1 year ago.

no, as long as the motor is running, the pump is on. it should never make any noise what so ever

Roy

Customer: replied 1 year ago.
I can definitely hear it buzzing almost as loud as the exhaust.
Expert:  Roy replied 1 year ago.

you definitely need to replace the pump.

Roy

Customer: replied 1 year ago.
I'll give that a shot and get back to you in a couple days or I'll send a revue.
Expert:  Roy replied 1 year ago.

please dont forget to rate me as it is the only way I get paid for my efforts

Roy

Customer: replied 1 year ago.
Will do
Expert:  Roy replied 1 year ago.

thanks