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Discussion Starter #1
So my girlfriends dad had this TB in his backyard and just out of curiosity I asked him why it was parked. Well he said it just died one day and he never checked it out. He tells me that I can have it for free!!
So I get a new battery and start testing it. The OBDII system brings up a few codes for the APPS and the TPS. I figure out that the fuel pump is running but there is no pressure. I put in a new fuel pump and now I get it to start but it's running horribly. It will only start with the accelerator pedal pushed half way and it will rev up to about 3400 rpm if you let off the pedal the SES light starts to blink and it idles really badly for about 7 seconds before shutting down. I'm going to pull coils and plugs to see how things look. The PO also said that he thought he might have gapped the plugs wrong but I don't think you are supposed to gap iridium plugs right?? If there is anything else I should check let me know. I do have a scanner with live feed so any parameters that I should be looking at please let me know
 

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Pour a couple of bottle of Techron complete into the gas tank to take care of any varnish or dirt that might have built up on the fuel injectors and fill up with some Top Tier gasoline.

Also, make sure the spark plugs are all ACDelco 41-103's. If they are not, install new ACDelco 41-103 plugs (just don't purchase them off of ebay - too many counterfeit Delco plugs there). You are right about not regaping iridium plugs (99% of the time).

Disconnect the negative battery cable and clean the throttle body. Be very careful and do not 1) immerse it in cleaner, and 2) do not move the butterfly valve. These throttle bodies are electronically controlled and you can seriously damage the motors and electronics by immersing them in liquid and by moving the butterfly valve. There are many threads here on how to properly clean an electronic throttle body.

One final thought, check the fuel pressure regulator for integrity/proper operation. You can do a quick test by hooking a length of vacuum tubing to it and sucking on it to see if it holds vacuum. If it does, great. If not, the diaphragm is shot.

Good luck!
 

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So I had a very eventful day working on my TB. I followed the advice of a diagnostician and found quite a few problems that could be causing the random misfire. And probably the definite reason for the misfire is 4 of the 6 coils are bad. Is it still possible for the truck to start and run on only 2 cylinders?? I checked the coils by starting the TB and unplugging each of them listening for a change in the RPM's and the engine to big. Well only two that I unplugged made the trucks engine bog. The other 4 didn't seem to make any difference either plugged or unplugged. I even unplugged each one a number of times just to make sure. It doesn't seem like the engine should even start with only 2 working coils. And when I unplugged one of the working coils I don't understand how it could have stayed running on 1 CYLINDER!!! Another surprise was the number 4 spark plug. It looked like something bit the end of the negative electrode and opened the gap and took a chunk of electrode with it. Here's a picture of the plug. Also the plugs were Bosch Double Platinum so I figure that is probably why the number 4 spark plug got like that. The gaps were way too big on all of the plugs too. The diagnostician had me checking the throttle body cause I had a code. So that got removed fully cleaned. He also wanted me to take the MAP sensor and test it and it was fine. When I hooked up the scanner and pulled the live data I thought the throttle position sensor was for sure the issue. I did the throttle body before troubleshooting the coils and plugs. The readings said 18% open with the accelerator pedal up. And it said 87% open with the accelerator pedal to the floor. I figured they should be at 0 and 100 with the pedal fully up and fully down. And when I started the engine the throttle wouldn't go past 38% with the pedal to the floor. I was already looking for a throttle body to buy when he said that the figures were within spec. So I started on the coils and plugs. And now here I am waiting for my ACDelco coils and plugs. I also went ahead and ordered the transmission fluid and filter. I found it cheaper online cause it came with 2 gallons of Dextron VI and the filter kit. Is Rotella T6 ok to use in this engine? I've used it in everything I own so far and I've had no issues but with this vehicle it seems that there are specific products that can destroy this engine such as spark plugs!!😛
 

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Discussion Starter #4
My questions-
Should the engine start with only 2 good coils?
Can it even run on 1 cylinder? It stayed running "barely" when I unplugged one of the good coils but picked up when I plugged it back in.
What could have caused the spark plug damage on the number 4 cylinder? I don't see any damage in the cylinder.
Should I run a compression test on the engine just to make sure that cylinder is ok?
Is there a way to put an o-ring on the coil bolt to keep the plug hole dry? It looks like the coil bolt is where moisture is able to seep in and collect. I couldn't find anywhere else the moisture could be getting in through. The coil gaskets were all intact and doing their sealing job and I didn't see anywhere on the gasket where moisture had been getting through.
How much blow by should be coming through the crankcase vent? I saw a little oil vapor streaming out while I was checking the coils with the engine running but it didn't seem excessive but the throttle body was covered in oil residue.
 

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Well, just sitting there it just might be possible to run on 2 cylinders. Not sure about running on 1 cylinder.

Glad you are doing diagnostics before jumping on the parts swapping train. Not sure what caused the damage to the #4 spark plug - possibly pre-ignition?

OK on getting ACDelco plugs and coils. While you are at it get a tube of dielectric compound (about $7 for a large tube at most part stores). Before you mount the ignition coils to the spark plugs, take a q-tip and get a pea sized dallop of dielectric compound on it and stick it inside the coil boot and coat the inside of the boot with the dielectric compound. That will help to keep the boot from heat bonding to the spark plug insulator. Also, spread a decent amount of the dielectric compound around the rubber seal (engine side) of the ignition coil. That will effectively seal out any water intrusion into the spark plug well eliminating the need for an o-ring on the coil hold down bolt.

I can't give any insight on the amount of blow by. However, for an engine that has been sitting without being run for as long as you mentioned, it might just be normal.

I would hold off on the compression test until you've gotten the engine running normal and do an oil change or two - unless there is an obvious problem after you replace the coils and spark plugs, used some Techron enriched Top Tier gas to clean up the injectors, etc.

Regarding the Rotella T6, go right ahead and use it especially if it's the 5w30 flavor. The one thing with the 4.2L I6 engines is that they require regular oil changes of a good quality (like the T6) motor oil in order to keep the Variable Valve Timing Solenoid (also called a CPAS) clean and functioning properly.
 

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Just my 2 cents but have you checked that the Dead ignition coils electrical connector
that its getting the 10 to 12 Volts Feed ?
Also is it supplying activation signals ?
Also the Grounds good ?
Just check before condemning the coils
 

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When I checked the coils I also checked the wiring. I also rearranged the coils to see if anything changed and the bad coils didn't work anywhere I put them. So 2 coils were completely dead no spark at all. 2 had weak orange sparks and the other 2 had nice blue sparks. I'm figuring that the two that had weak spark were still working somewhat and that's how the engine was able to start and run. I'm still in the diagnosis phase but I can't go any further until I install the new parts. I have got a throttle body code on 3 different occasions so if I'm still having issues after the new parts that will be the next system I'll check.
That's where I was looking to begin with but when I found the plugs to be Bosch Double Platinum and then found the coils to be bad I had to stop and get the right plugs and replace the coils. The diagnostician was looking at the throttle by wire system too thinking that was the cause of my misfire but when I pulled the spark plug that was trashed he said we needed to get that taken care of before we can go any further with the diagnosis. I'm really hoping the coils and plugs fix it. While testing the ACC sensor I found a ohm spec out of range but it functions as it should so once I get the parts installed we will see if that fixes it. The throttle plate opens fully and closes fully. I recorded the throttle opening with my phone and recorded the live data feed from my scanner on my go pro. When played simultaneously everything seems to function smoothly and as it should. So we will see next week how things go and I'll post my results.
 

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Today I was checking the coils again so that I could mark the good coils and toss the bad coils. Then the good coils can be kept as spares just in case. Well only one coil didn't spark today (#4 the damaged plug cylinder) the connection has power and ground so it must be the coil. It probably went bad from the plug gap being 1/3". I also noticed that the heat sink is smashed so it really does need replacing. The other 5 coils sparked but the spark was orange and it seemed erratic. Normally when checking spark I get a nice even rhythm of spark. It seemed that these were bouncing around. It would spark like 3 times evenly then it seemed to spark at different intervals not evenly. I even pulled a plug on my truck to see how it sparked and it was a nice even rhythm. Should I be checking the cam position sensor? Or crankshaft position sensor? Or maybe I'm just being paranoid and I need to stop reading horror stories of not being able to fix the issue. Tell me what you think 🤪
 

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Wait until you get the new plugs and coils installed, then let the TrailBlazer tell you what is or is not going on by reading the PCM for any codes. If either the camshaft or crankshaft sensor is flaky, a code or codes will be set and then go from there. By the way, if you have to change the crankshaft sensor, a relearning procedure will need to be done in order for the engine to run properly. Also, the relearning procedure requires the use of a high end bidirectional scanner like a GM Tech II or equivalent.

Yes, stop reading horror stories otherwise you'll wind up replacing a whole lot of parts unnecessarily.
 

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plscolla thank you I just needed some reassurance. It's puzzling though how yesterday I had 2 coils with no spark 2 with orange sparks and 2 had blue spark. Today 1 has no spark 4 have orange spark and 1 has blue spark. I'm not going to worry anymore until I get the coils and plugs done. I think the plugs being gapped wrong killed the coils. The #4 especially. That's the cylinder that hasn't had spark ever and had the damaged plug with a 1/3" gap. I'm sure a 16 year old coil can't last long trying to produce enough power to jump the spark through that large of a gap.
 

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I think you are demonstrating to yourself that the coils are indeed bad by their erratic behavior when you are testing them day to day.
 

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Ok my girlfriend killed my phone in Pecos river so I haven't been able to give an update cause I let my phone keep all my passwords and usernames. I guess I need a different way to keep the information! 😰
So this is Dieseldog the original poster. I've received all the parts and I've installed them. This is what I've done so far-
Installed a new battery
Replaced the fuel pump
Plastic-welded the fuel tank filler neck
Replaced the fuel filter
I had to make a fuel line cause I broke the line from the filter to the engine 😭
Replaced the ignition switch
Replaced all the spark plugs with ACDelco
Replaced all the coils with ACDelco
Cleaned the throttle body and reset the PCM by disconnecting the battery for an hour
Ran a can of Gumout through the crankcase and changed the oil after about 15 minutes of idling (misfiring the whole time)
Ran 1/2 a can of Gumout through the intake and heatsoaked for 20 minutes then restarted it for a few minutes to clear the carbon
New air filter and cleaned the hoses and resonator
Removed and cleaned the CPAS then soaked it in B12 then reinstalled it without testing it
Checked wiring for the coils and tested for voltage, ground and signal and checked for continuity through the connectors
Changed the transmission fluid and filter

I'm still getting a misfire P0300 and flashing CEL when I drive it. I haven't driven it very much cause the light flashing in my face the whole time doesn't sit well with me. Originally I said I had found a damaged Bosch platinum spark plug in the #4 cylinder but it is actually in the #5 cylinder and after I installed the new plugs I figured since I used ACDelco iridium I would be good.....
I am thinking the Bosch plugs somehow caused internal damage to the #5 cylinder cause I still have the misfire and when I decided to pull the new plugs, to see if I saw any indication of lean/rich conditions that could point to the misfire, I found the #5 spark plug damaged exactly the same as the Bosch plug- opened gap and what appeared to be little bites taken out of the negative electrode. I regapped it and sanded the negative electrode where it was trashed but stayed away from the positive electrode iridium. I reinstalled it and the TB started easily and idled for about 2 minutes before the misfire started again. I have no clue what is going on in the #5 cylinder or how the plug could sustain that sort of damage!?! Who ever did the plugs last seemed to know what they were doing other than installing Bosch plugs
because there was anti-seize compound on the threads of the plugs and coil bolts and what appeared to be di-electric grease on the boots but this could be from past work and not the recent work. So my theory now is a valve issue such as broken spring or worn guides maybe even a bent valve. So my next job is a compression and leak down test. What else is there I should be checking other than the compression and leak down? I'm leaning towards valves so what's best- rebuild my head or just purchase a rebuilt unit? I can do the rebuild but the machining and valve seats will have to be done by a shop so it seems like maybe a rebuilt unit is better? Can I hand lap the valves if they are leaking and causing the misfire? Can I replace just the valve spring if I find a broken one? If you have had valve issues that caused random misfiring, please let me know what you did to fix it. I have done a head gasket on an Isuzu Ascender before and it was a PITA!! Took me 12 days!! I only broke 1 head bolt and it didn't completely break! It kinda stretched and the threads looked unraveled but it stayed complete and came all the way out. I hit all the bolts with an air chisel in the bolt head for like 5 minutes each but I got impatient with the last bolt and it almost broke. I wish I had a pic cause it was amazing lol!
What else should I do while the head is off?
Thanks for your time and help with my Trailblazer!
No matter what I have to do to get this going I will get it done. I'm not in this for a whole lot of cash yet cause the Trailblazer was given to me so if I need an entire engine I'm going to get one lol
 

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Well, you certainly have done quite a bit. I think the next step is to see if you can get a boroscope and get a peak at the piston in the #5 cylinder to see if there is or is not any damage. Then, do a compression test of all the cylinders, not just the #5 cylinder. If you can get a hold of a cylinder leak down setup, you might consider doing that as well. Then decide if you want to pull the head and either install a new remanufactured head or have yours rebuilt.

I can't give you any guidance on whether or not hand lapping a valve or two would be worthwhile.

If you find a broken broken valve spring I say go ahead and replace it.

Good Luck!
 

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I got the compression tester but it doesn't have the capability of a leak down. I had an idea about the spark plug in #5. I went out and got a plug that's 1/8" shorter so whatever is grabbing the electrode can't reach it anymore. But even though I haven't done the leak down I'm pretty sure it is the valves on the #5. I can hear the compression loss through the exhaust. I got the plug just for S&G. I'll let you know tomorrow the pressures I find in the compression test.
 

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I didn't even get to try the new plug there is no compression in cylinder#5. Zero. Didn't even move the needle on the gauge. Cylinder #1 160 psi
#2 165 #3 160 #4 155 #5 000 #6 175
I'm in the process of removing the valve cover to assess the situation. I'll let you know what I find. I read somewhere that an 06 head is an upgrade does this sound right?
 

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Good lord, those are some awful and mismatched plugs!

OK on cylinder 5 having zero pressure. I do not know about the 06 head being an "upgrade". The guys at GMTNation would likely know.
 
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