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mralexc
mralexc, ASE Certified Technician
Category: Car
Satisfied Customers: 25
Experience:  ASE certified Master Automotive Technician, Vocational Degree in Advanced Automotive Technology, Nissan dealership training,
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Hummer H3: Anyone have an idea what is going on. I have an

Customer Question

Anyone have an idea what is going on. I have an H3 2006 with 106k. Recently we had a P0128 code and changed the thermostat and coolant sensor. A p0300 code came up with this one. Since that time, the p0128 is now gone with the replacement of the above mentioned parts, but the 0300 is still there. We have done the following: changed spark plugs, 2 cans of seafoam in tge gas tank, replaced the crank case PCV hose (it was cracked) cleaned the maf & throttle body. Those didn't work, so we took it to the shop. They did an engine flush, due to sludge build up. Shop says it's not the coils or the head. After the flush, CEL light stayed off for about 3 days. Haven't taken it back there yet, wanted to see what you guys thought.

Light comes on & flashes when with car hits 1500rpms at 44 mph. You can feel the car bucking during this load. Light will stop flashing, but stay on once you speed up or slow down. No miss fires at other speeds or rpms.
Here is the freeze frame from the code:

P0300
fuel sys1 OL, fault
fuel sys2 n/a
calc load % 58.8
coolant 90
st ftrm1% 0.0
lt ftrm1% 0.0
Map 67
engine rpm 1478
vhe speed (km/h) 68
ign avd (deg) 25
iat (c) 22
maf (gm/sec) 21.640
abslt tps % 30.5

I have no idea what these things mean honestly. You're input is greatly apprecitiated.
Submitted: 1 year ago.
Category: Car
Expert:  mralexc replied 1 year ago.

mralexc :

hello my name is XXXXX XXXXX have a question was the vehicle warmed up when this happens

Customer: It usually starts flashing after we drive 2 miles. Anytime we keep the rpms at approx. 1500 at 45mph it will start. Usually takes 10 miles off this going off and on to set. Sometimes it may take a few days to set the code.
mralexc :

interesting that would explain the coolant temp

mralexc :

ok sorry i type slowly

mralexc :

ok how is your maintainance you said it was sludged so do you change the oil regularly?

Customer: Yes, in the past we waited for the oil change light to come on. Now we do it every 5k since the flush
mralexc :

well it is starting to sound like your EGR valve is sticking

Customer: So that would explain why this only happens at 1500rpm. Driving the car now and just set the code again. Do you need that freeze frame reading
Customer: New freeze:
Customer: p0300
Customer: fuel sys1 cl, using h02s
Customer: fuel sys2 n/a
Customer: calc load 48.2
Customer: coolant 90
Customer: st ftrm18.1
Customer: lt ftrm1 0.7
Customer: map (kpa) 65
Customer: engine rpm 1576
Customer: veh speed km/h 72
Customer: ign adv (deg) 31.0
mralexc :

the freeze frame narrows a little it could also be clogged injectors or a vacuum leak but being that it only happens at 1500 rpm i would tend to think its carbon deposits in the EGR system i would try cleaning the carbon out with a little carb cleaner and a toothbrush and put it back to see if it helps first

Customer: iat 17
Customer: maf 19.5
Customer: abslt GPS 29.8
Customer: Ok. I'm going try this tomorrow. If this doesn't work. Any other thoughts?
mralexc :

give me a min to think

mralexc :

if you had a oscilloscope you could test the secondary ignition system, the gap on the plugs could be off. causing it but it would be unusual in such a narrow rpm range i am really wanting to say its carbon buildup

Customer: Cool. Peobably do this tonight. Thanks again
mralexc :

my best advice is to perform an air induction cleaning, and clean or replace the EGR and see, past that

mralexc :

its going to take some research

mralexc :

glad to help if you need any further help dont be afraid to ask

Customer: Bad news. No egr on a hummer. System has a vvt.
Expert:  mralexc replied 1 year ago.
got you i am looking it up now on mitchell
Expert:  mralexc replied 1 year ago.

ok p0300 is a common problem with the vvt motors in an h3 it can be caused by alot of things most commonly soft seats on the valves that allow the pressure to leak by, other issues can be fowled spark plugs, fowled fuel injectors the cam phaser losing oil pressure due to sludge a cam to crank shaft issue phase issue, leaking cylindars, a bad cam or crank sensor a bad coil , etc... the p0300 is a hard code when it is flashing that means you can be causing catastrophic catalist failure. which in itself a restricted exhaust can cause a misfire, the first step is to find which cylindar is misfiring by attaching a scan tool and watching the misfire data, unfortunately there is no easy fix for this you can try the easy stuff and see if the plugs are fowled etc however to diagnose the cylinder misfire you need some specialized equipment.

 

I am going to opt out and see if anyone else has any ideas for you to try sorry i couldnt be more help

mralexc, ASE Certified Technician
Category: Car
Satisfied Customers: 25
Experience: ASE certified Master Automotive Technician, Vocational Degree in Advanced Automotive Technology, Nissan dealership training,
mralexc and 13 other Car Specialists are ready to help you
Expert:  Tom replied 1 year ago.
Different expert here did you still need help?
Customer: replied 1 year ago.
Yes
Expert:  Tom replied 1 year ago.
You have paid the other expert already would you like to be refunded and then I can assist you with your issue or a I will let him continue since he was paid. Let me know thanks.
Customer: replied 1 year ago.
Yep. Am in need of your help. Do you have any idea what is causing this.
Expert:  Tom replied 1 year ago.
Has the VVT solenoid been checked?
Customer: replied 1 year ago.
Yes. It is fully operational. Screen are without blockage and is firing correctly.
Expert:  Tom replied 1 year ago.
Ok so with the scanner hooked up its working properly?
Customer: replied 1 year ago.
According to my husband it is. He said that the shop put a new one in after the engine flush
Expert:  Tom replied 1 year ago.
Ok just need to be sure. That Maf sensor reading is off which very well can be the issue. You need to have them test that next. I can post the test for you if you would like? Remember that I'm here if you need any further assistance just let me know. Hoped this helped.Please rate excellent service so I can get Credit for my help thanks. Bonuses greatly appreciated.
Customer: replied 1 year ago.
Sure. You think the maf sensor is bad? We have just cleaned that peace off
Expert:  Tom replied 1 year ago.
Yes from those readings. I would have that checked next for this issue. Remember that I'm here if you need any further assistance just let me know. Please rate excellent service so I can get credit for my help thanks. Bonuses greatly appreciated.

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mralexc
mralexc
Master Automotive Technician
22 Satisfied Customers
ASE certified Master Automotive Technician, Vocational Degree in Advanced Automotive Technology, Nissan dealership training,