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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15477
Experience:  Have owned a repair shop for 25 yrs.
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2003 chevy tahoe flex fuel 5.3 engine. I have a p0306 code

Customer Question

2003 chevy tahoe flex fuel 5.3 engine. I have a p0306 code or a p3000 code depending on how i access the machine through my scanner. misfire indicator confirms a constant miss on cylinder number 6. I have checked a few things and I have a scope and a power probe 4. For me to type what I have already checked is quite lengthy. I will start listing all that in the next email.
Submitted: 9 months ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 9 months ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you.

what all have you checked/replaced?

Expert:  Tim's Auto Repair replied 9 months ago.

do you feel the missfire?

Customer: replied 9 months ago.
Thank you Tim
This job was originially taken to a shop. They installed a new intake manifold gasket swapped coils new spark plug and and swapped an injector. I have checked fuel pressure i have 41 psi. I disconnect the fuel pressure regulator and now have 49 psi. I checked cylinder pressure and it is at 150. I pulled the spark before i started and checked it. It had a small tan spot on the insulater other wise it looked ok but it was not the same as the others. I checked it again after i checked everything with a scope and messing with the fuel pressure regulator. The spark plug was black like it was running too rich. I compared it to the others on the same bank and it was the only one different. I checked the shops work with a smoke machine i found no leaks on the intake manifold. I installed one new spark plug that is a correct ac delco part number. the rest of the spark plugs is an auto lite. I have checked the spark with an adjustable gap. I have over 30 kv. I checked the computer signal to the signal from the ecm to the coil with my power probe 4. i have 6 hertz. i checked the same signal with a scope. the signal is evenly spaced. i did not see any missing impulses from the computer I have checked the spark with my scope the burn time is 1.5 ms. i compared it to cylinder number 2 at idle the burn time is 1.10 to 1.3.ms the burn time is fluctuting on cylinder number 2. The burn time at idle on cylinder 8 is 1.8 ms at idle. I did a snap throtle test on all cylinders and everything looks good escept number 6. at idle u can hear a chug with a very small amount of engine shake. when u rev the engine up the engine will start to really miss. I can witness the miss on the scope and i can see that number 6 is the only one that acts like this. i have done more but i am running out of space to tell you.....
Expert:  Tim's Auto Repair replied 9 months ago.

ok..your fuel pressure is way too low,,these should have no less than 55psi at all times,,i would think that your fuel pump is too weak and may need to be replaced

Expert:  Tim's Auto Repair replied 9 months ago.
Customer: replied 9 months ago.
This is a flex fuel engine. I believe u are giving me the values for the non flex fuel engine? I did google it and i believe there is a diference between the two or did i look at the wrong infomation on my side?
Expert:  Tim's Auto Repair replied 9 months ago.

stand by

Expert:  Tim's Auto Repair replied 9 months ago.

i didnt know it was a flex,,but even being a flex the fuel pressure is too low,,it should never drop below 48psi at anytime

Expert:  Tim's Auto Repair replied 9 months ago.

Fuel pressure ......................................... 335-375 kPa (48-54 psi)

Customer: replied 9 months ago.
i have 49 with fuel pressure regulater disconnected. Will that cause a one cylinder misfire at idle?
Customer: replied 9 months ago.
The pressure regulater is stepping it down to 41 psi?
Expert:  Tim's Auto Repair replied 9 months ago.

it should have 48psi + regulated

Expert:  Tim's Auto Repair replied 9 months ago.

i think your pressure is way too low

Expert:  Tim's Auto Repair replied 9 months ago.

it may be the regulator if the pressure is over the max pressure with it disconnected 54psi+

Customer: replied 9 months ago.
I didnt do a flow test. i did release fuel pressure with the pump running. I did notice a lot of foam in the fuel that i thaught was very odd. I can see with my low amprobe that my injector pulses are not equally spaced on cylinder number 6. It looks like there are impulses missing. I can do a snap throtle test and cause other cylinders to misfire a few times for no aparent reason.....I got another question for u tomorrow that goese with this.. the fuel filter has not been changed since he owned it. i will do that first. but i should never see foam in fuel correct?
Expert:  Tim's Auto Repair replied 9 months ago.

how does it run in a pull at wot?

Customer: replied 9 months ago.
It does not have any drivability issues no other cylinder is misfiring at idle. i did a cylinder drop test and at idle the rpm changed very little. so i can see its not contributin properly. going down the road the misfire goese away but when u let off of the throtle number six cylinder just start counting away. and only number six He says it runs good down the road. it runs good going down the road but the fuel trims are not correct. it is running rich and not equally rich on either side
Expert:  Tim's Auto Repair replied 9 months ago.

ok,,lets try something fairly cheap[sense it is running rich]..replace the ect[engine coolant temperature] sensor..

the ect can cause the engine to get too much or too little fuel at times and may not give a code for it

Customer: replied 9 months ago.
Thanks for the help i will have a few more things to ask u tomorrow moring. its getting late and i will just ask u tomorrow. Thank you
Expert:  Tim's Auto Repair replied 9 months ago.

ok

thanks

Customer: replied 9 months ago.
just to carify this?
key on engine off fuel pressure vacume line connected is what psi?
key on engine on fue pressure regulator vacum line connected is what psi
key on engine running without fuel pressure regualtor vacum line connected psi
what is the flow specs for the pump for one minute?and which pump is best to get to avoid problems. he will be taking this on a big road trip in august
Customer: replied 9 months ago.
can u send me the wiring diagrams for the injection circuit. I seen something i when i was checking the circuits out that i need to ask you about.
Expert:  Tim's Auto Repair replied 9 months ago.

the pressure should never drop below 48psi it doesnt matter if it is running,not running,vacyuum or no vacuum,,itshould never drop below 48psi.

it really doesnt matter the brand of pump,,i have seen bad one in all brands,,though im going to tell you to use ac delco

Expert:  Tim's Auto Repair replied 9 months ago.

stand by,i will upload the diagrams

Expert:  Tim's Auto Repair replied 9 months ago.

here you go

Expert:  Tim's Auto Repair replied 9 months ago.
Customer: replied 9 months ago.
Thank you i will let my neighbor know. When i was checkig the injector power and grounds i had voltage fuctuations going with key off engine off. I did a feed test to see the ohms and it was going between 999 and 125 ohms on my power probe 4 on the injector power the voltage fluctuation was going from 0 to .5 or .7 volts this was on injector 6 and 2 was all i checked costumer complained he lost all power at one point in time.... i dont see what can cause voltage fluctuations on circuit. this is worth more then 20 bucks now and thank u for your help
Expert:  Tim's Auto Repair replied 9 months ago.

you are very welcome

thanks

Customer: replied 9 months ago.
can u send me more wiring diagrams, I wanna check all grounds going to ecm etc just send me what u got for all wiring diagrams for the vehicle. I will be looking at that problem closer tonight thank you
Expert:  Tim's Auto Repair replied 9 months ago.

what diagrams?,,for the fuel pump?

Expert:  Tim's Auto Repair replied 9 months ago.

i need to know what you need a diagram for

Expert:  Tim's Auto Repair replied 9 months ago.

i will give you all the powertrain diagrams

PLEASE COPY AND PASTE the link below to your browser, I have uploaded more info on this there please copy and paste the link below to your main browser[INTERNET EXPLORER or FIREFOX]

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https://www.dropbox.com/s/3xcer23b464o7ut/0302-tahoe-Engine%20Controls%20Schematics.doc?dl=0

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if the link doesn’t work that way, try it this way

thanks

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www.dropbox.com/s/3xcer23b464o7ut/0302-tahoe-Engine%20Controls%20Schematics.doc?dl=0

.

If you are satisfied with my answer, Please Rate my answer by clicking the rating button so I can get credit for my work. I’m not always going to be giving you good news, so please don't let this stand in the way of you accepting my answer. .it does not cost you more money and we will still be able to communicate, ,.please understand, i can not see, hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated.. if you are not satisfied with my answer, please do not leave bad feed back ,i will gladly opt out and let another expert handle the question. .if i have sent any diagrams, please print them. .sometimes you may need to right click the image [,then save picture as]to save it to your computer so you can open it with your picture program...Please ask if you need more help

Customer: replied 8 months ago.
I just got the pump in the mail. would like to install it first and then see what happens. I am happy with your service i am just not sure if i will have more questions or not
Expert:  Tim's Auto Repair replied 8 months ago.

be sure you checked the pressure before just replacing the pump

thanks

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