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Tool Hut
Tool Hut, ASE Certified Technician
Category: Chevy
Satisfied Customers: 494
Experience:  Owner of a mobile diagnostics company assisting auto technicians with difficult vehicles
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I have a 1999 s10 blazer it has a p0300 code i have replaced

Customer Question

I have a 1999 s10 blazer it has a p0300 code i have replaced the plug cap rotor distributor... The fuel is running 25% long term and 50% short term on the bank 1 the new spark plugs on the drivers side have soot all over them. My fuel pressure is about 60psi and all cylinders have around 150psi bank 2 is good but when i reve it up the stft drops to 0 on bank one and on bank 2 it jumps up please help I don't know what's going on here. Also the timing on the scanner is jumping between 13-20 advanced map is 15 psi and mas is around 1lb per minute o2 are all over the place on bank 1
Submitted: 1 year ago.
Category: Chevy
Expert:  BOBBYSS replied 1 year ago.

Hello, my name is Bobby. Thank you for the question. Can you tell me if the check engine light is coming on? Does the engine run rough? If so when does it run like this?

Customer: replied 1 year ago.
it has a check engine light and it is missing really bad i bought the car with this problem i have extra parts like mass air map crank shaft sensor ...... Nothing is working any different
Expert:  BOBBYSS replied 1 year ago.

Have you scanned the computer for codes?

Customer: replied 1 year ago.
Ya thats how i got all the specs i gave in the first question. Did you even read it ?
Expert:  BOBBYSS replied 1 year ago.

Thank you. I wanted to make sure that there was nothing besides the 300 code. From what you are telling me it sounds like you have a lean condition. Most of the time on this engine this is caused by either a vacuum leak in the intake manifold, or more commonly it is a restricted fuel injection spider unit. This is the most common failure on this engine. Some shops can clean it, but most of the time it needs to be replaced. I typically prefer to pull the upper intake manifold and see how the plastic nozzles look on the engine of the injectors. Most of the time they get clogged with carbon and this occurs.

Customer: replied 1 year ago.
I did change the spider with a old one. That was the first thing i did before I even tested anything because the guy i got the car from had silicone all over the spider injection where it meets the and Plenum. I posted the vacuum pressure because im almost sure there no leek but just in case if it's abnormal you would notice
Expert:  BOBBYSS replied 1 year ago.

Did you happen to check vacuum with a vacuum gauge also?

Customer: replied 1 year ago.
No just used the bosch scanner that i have its the obd1300. The best one at O'Reillys
Expert:  BOBBYSS replied 1 year ago.

Thanks. I would like to see if you can get a manual vacuum gauge and see what it reads at idle and while holding 2500 rpm. I want to know how steady it is also. Does the misfire smooth out at higher rpm or get worse?

Customer: replied 1 year ago.
The thing that gets me is the soot on the 3 new plugs on the drivers side but the other side is supper clean. Any thoughts on that ?
Customer: replied 1 year ago.
It gets smoother but dosnt go away by any means
Customer: replied 1 year ago.
I don't have a vacuum gage anymore but i can test it by changing the map with a extra one i have
Expert:  BOBBYSS replied 1 year ago.

The thing that gets me is that it is affecting one side of the engine only. The only other thing it would possibly be is the O2 sensor or possibly a computer issue, but that is not too common on this vehicle. Have you replaced the O2 sensor?

Customer: replied 1 year ago.
I swapped them and its still the same bank 2 work the way it should but bank 1 is crap
Expert:  BOBBYSS replied 1 year ago.

Thank you. Either you have a computer failure or you have a wiring issue. It is common for that injector harness to fail and cause this if it is keeping the injectors open for too long. Does the truck run any differently if you move the harness around while it is idling?

Customer: replied 1 year ago.
I checked the injection harness its all working i did find a bad injector and change it now it runs smoother in the top rpm's but it still has the miss and is kinda backfiring when i give it gas from idle it has no power and sounds like it's running off time
Customer: replied 1 year ago.
The vacuum is 13 1/2 psi at idle and 14 1/2 psi at 2500 rpms
Expert:  BOBBYSS replied 1 year ago.

Your vacuum should be higher than that at 2500 rpm. It should be above 20 HG. You either have a timing issue like a bad distributor, a restriction in the exhaust, or a stretched timing chain.

Customer: replied 1 year ago.
Its not the distributor thays brand new and exhaust is under 1/2 psi at any rpm. I'm thinking its the timing chain but i wont have time to check it tell Friday I'll keep you updated
Expert:  BOBBYSS replied 1 year ago.

Keep me posted and we can continue from there is needed.

Expert:  Tool Hut replied 1 year ago.

Hi, My Name is***** have over 20 years experience repairing vehicles. I am a ASE Certified Master Auto Technician. I am confident we can resolve your problem together.Please remember I don't know your skill level. I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies to get to a satisfactory resolution.I also try to give all of the information you may need expecting a positive rating. If there is any reason I cannot get a positive rating please let me know.

I am not real sure why he opted out. Are these long term and short term fuel trims + ? Have you checked for a vacuum leak. These are kind of common for a plenum leak

Customer: replied 1 year ago.
they are + and the o2's are all over the place and I did check for a vacuum leak with starting fluid I didn't find any
Expert:  BOBBYSS replied 1 year ago.

I have not opted out of the question, but would be more than happy to opt out if you would like Samuel to help you instead. Please let me know.

Expert:  Tool Hut replied 1 year ago.

I agree with BobbySS that the fuel injector spider is suspect. You definitely have a lean condition caused either by vacuum leak or plugged fuel injector spider, Both are very common on this vehicle

Customer: replied 1 year ago.
I checked the fuel injectors there all spraying. I checked the timing chain its was all lined up I replaced the chain just to b safe the motor is still running exactly the same
Expert:  Tool Hut replied 1 year ago.

What is the bank 2 sensor 2 reading?

Expert:  Tool Hut replied 1 year ago.

Oxygen sensor reading

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