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Discussion Starter #61
I guess I should. But no offense I don’t trust any main stream shops or dealers to properly diagnose. I need to find a EricTheCarGuy type..
 

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I agree, at this point I see no reason to remove the heads.
 

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So, thinking about your problem, a couple of questions.

When you checked the intake for leaks, do you do it with a cold engine,
Reason, a warm engine expands and can seal a leak.
When you checked for leaks did you use a vacuum gauge?
 

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Discussion Starter #64
Morning..

actually I think the leak testing with propene was done after warmed up to op temp. It may have been after a short drive.. so not sure...

I did not have a vacuum gauge attached. I was monitoring the STFT and LTFT for any change. No change..

I can retest cold and with a gauge attached. But let me ask what is best place for gauge. There is not a lot of choices... I have usually used the manifold port where the head cover vent feeds back to intake. This is a non EGR vehicle.. thoughts..
 

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Discussion Starter #65
I have read a lot of blogs where lots of people have had misfire issues. I found a couple where the eventual fix was having the ECU re-imaged.. This seems frightening of why it was needed? But it’s basically the only thing I have not done yet.. but I still have to replace injectors back to my original injectors..
 

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Discussion Starter #66
I have addressed everything in this article except:

1. Replacing Valves
2. Timing chain or belt skipped tooth? Does anyone know an easy way to determine if timing is off?

 

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Hi glennst ,
I'm not sure if you are aware that you can get a O2 sensor thread cleaning tool , I always use it after removing & before installing ?
 

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Discussion Starter #68
Thanks for info. I was not aware. Hopefully I will never have to replace them again on this vehicle..
 

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Discussion Starter #69
UPDATE:
I just completed a Block Test. I was not aware of this test but learned of it on YouTube. Basically a chemical test to determine if any combustion gases are getting into coolant system. Tests for a blown head gasket, cracked head, etc. Loaner tool from autozone.

The results were good. Blue fluid remained blue with no color change after 3 minutes of bulbing air into tube..
 

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Discussion Starter #70
For those following my issue I am now battling a misfire code P300 or P301 depending on what day it is.. mostly at idle and not while at higher speeds. Compression testing good, new fuel pump, filter, injectors. New MAP, Crank CPS, CAM CPS, Regulator, Throttle Body / TPS, new plugs, plug wires, new O2 sensors, no exhaust leaks, fuel trims look good below 10 combined and LTFT +/- 5. STFT +/- 6. Coils good and any moving of parts to new position does not follow. Issue always stays. Vacuum perfect passed smoke test.


UPDATE: 01/11/2020

I just tested the fuel injectors. I tested resistance of injector as well as the pressure drop flow rate (or whatever it’s called)…

Remember I am getting a P301 or P300 code and am seeing most misses at idle on 1 and a few on 2.

Resistance in ohms. I did notice I would get .1 ohms movement depending on how firm or where on probe tip I held wire. I tried to record the peak number seen on meter that was stable.

#1 = 13.6 #2 = 13.4
#3 = 13.5 #4 = 13.4
#5 = 13.5 #6 = 13.4
#7 = 13.5 #8 = 13.4

Below are the pressure readings when using the OLLOSUN EM267 pulse meter. Setting on mode 2 medium pulse. Before each test I turned on pump to maximize pressure on rail. In most all instances starting pressure was 45 PSI.

#1 Start 45, End 24, Drop = 21
#3 Start 45, End 24, Drop = 21
#5 Start 45, End 25, Drop = 20
#7 Start 45, End 25, Drop = 20

#2 Start 45, End 22, Drop = 23
#4 Start 45, End 23, Drop = 22
#6 Start 46, End 24, Drop = 22
#8 Start 46, End 24, Drop = 22

Attached of pic. I won’t let me prove video…
 

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The ohms readings are good. The flow drop/rate is consistant across all injectors which makes me think they are ok. Not sure why pressure is at 45 PSI but all the flows are the same. I wonder if there is a wiring issue back to the ecm or the ecm itself.
 

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Discussion Starter #72 (Edited)
Your reading my mind. I have been thinking ECU also but before going there wanted to discuss other issue.

1. Do I need to retest injectors? I ask because I heard they should all be within 1.5 psi? Could a slightly rich condition (1psi more) on #2 cause it to misfire on occasion? Or am I stretching? I know anything is possible but is it logical?

2. I am not sure about the 45 psi start. When I turn on key and/or short pump relay pins and it comes on the pressure jumps to 50 psi but then drops to 46 psi when pump stops. Also if I let it sit that way for 20 minutes the pressure drops down to 42-43 range. It’s a new pump and new filter. The regulator is not leaking and 1 year old. When idle it runs at 43-44 spec and removing the regulator vacuum line it jumps to 50 which it should. Thoughts? BTW my emissions Evap is never passing or getting to ready but I have no Evap codes. I am replacing the gas cap because it’s 15 years old. But could a evap issue cause the slight pressure drop?

3. Spark Tester - I placed an in-line spark tester between the coil and plug on #1.
It lights up when spark occurs. I notice that the light blanks out on occasion and seems to be in sequence with my ears hearing the misfire but to be honest my skills are not honed enough to be sure. What is for certain is the firing is not consistent and blanks on occasion. So after thinking about it is below thought correct?

a. The coil firing is between coil and ECU and a good wire and spark plug. Regardless if fuel/air mixture combusts in chamber I should never see a spark blank out. Correct?

b. If true then it appears the misfire (spark blanking out) is caused by the coil not firing on occasion. The coil appears good since I have swapped it with other coils. The same for plugs and cable. So I need to figure out why is the firing blanking out? If not coil it has to be the firing/ignitor signal correct? How can I test? Can I use T-pins and another test light to see if the ignitor signal is blanking out on the #1 ignitor input signal?

c. Noting I have a new bank coil harness that splits to each coil and attached to main bank connector and that has been eliminated.

d. What is more logical? A intermittent continuity problem on 1 wire? Or an ECU that is failing to fire properly?

thoughts on next steps?
 

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Your fuel pressure is too low.

Key on should read 55 to 62
 

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Discussion Starter #74
No for my vehicle it’s correct. I have been through this many times. Not sure why but for 5.3 Z Flex engines it’s 50 key on, 43 at idle. This is published in the AllData for my vehicle (2004 Tahoe 5.3 Z Flex). It is odd because most other vehicles are higher but it’s correct.

I also have a 2007 Silverado with 4.8L and It is 62 key on, and around 55 idle. Today I did the same test where I turn on key ( no crank) and pressure jumped to 62. I turned key off and over about 30 minutes the pressure slowly dropped down to 40. My truck runs great with no issues. Thus it must be normal for fuel pressure to slowly slip down when key is not on...
 

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Discussion Starter #75
My next step is to connect T pins to coil input signal and see if it will light a test light? I think the ignitor signal from ECU is a 5v circuit (not sure) so it may not light? If it does I want to film it to se if it blanks out and misses on the input side of coil like it does on output side..

Ultimately if I cannot locate the problem I will consider an ECU swap.
 

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The next gen Tahoes use different pumps for flex and for non-flex engines. I don't know if it's because pressure is different.
However, your flex fuel 5.3 uses the same pump as the non-flex fuel 5.3. Does this mean the pressure is the same for both engines?
I don't know!
Usually the reason parts are different is because E85 needs different rubber and plastic components.
 

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My next step is to connect T pins to coil input signal and see if it will light a test light? I think the ignitor signal from ECU is a 5v circuit (not sure) so it may not light? If it does I want to film it to se if it blanks out and misses on the input side of coil like it does on output side..

Ultimately if I cannot locate the problem I will consider an ECU swap.
At idle, the engine runs at 550 to 600 rpm, that means the coil flashes the plug at 35 times a minute, your not likely to see a single miss using a light.
 

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Discussion Starter #78
Just to share the pump was ordered from Rock Auto. I think I it is same for both but I always order parts for the Flex. They always list them specifically.

Yea it seems you could not see it but I can see it go dark for 1 second.. actually it looks like it’s firing more than every 2 seconds.. doesn't each cylinder fire once every 2 rotations? Or 600/2 = 300 times per minute?
 

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600/2/8 = 37.5
 

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Discussion Starter #80
600/2/8 = 37.5
I only ask because I tried to research this before and I always found feedback indicated in a 4 stroke each cylinder always fires 50% of crankshaft rotation (RPM). Below are things I found in different links.

Regardless I am able to see the blank out. Actually because i think is firing 300 times a minute (5 times per second) so it looks like the light is always present, or flickering like a candle, but when it blanks out and goes dark it stands out.

Below are info found about the firing...

No matter how many cylinders you have, every cylinder fires once for every two rotations of the engine's crankshaft. So if a four-cylinder engine and an eight-cylinderengine both are idling at 800 rpm, in one minute, every cylinder will fire 400 times.

or



1 RPM is one revolution of the crankshaft per minute.

A two cycle engine fires once per revolution (per cylinder)

A four cycle engine fires once per two revolutions (per cylinder)

So at 1,000 RPM
  • a 2 stroke does 1,000 firings
  • a 4 stroke does 500 firings.

Or

That means in a four stroke engine the shaft rotates twice (two revolutions) for every four stroke cycle, which means one power stoke for every two revolutions of the crank. So, if the crank is turning 1000 times per minute, that would be 500 power strokes (firing of the spark plug) on each cylinder in that one minute.
 
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