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Discussion Starter · #1 ·
A while ago, when I bought the truck, mother and I went on a road trip. We quickly found out it would not take gas, so we took it to a shop. Ya know, being 460 miles from home and not being able to get gas, a little scary. Long story short they disconnected the EVAP system. It started taking fuel again. Now, many months later, having had the check in engine light on for a long time since the EVAP was disconnected, I thought nothing of the light. Last night I started it up and all of a sudden it starts "hiccupping" and my friend tells me to use his scanner to look at my codes. I do, and I found all the codes mentioned in the title;

PO455 (This showed up twice, it came up first and then after all the other codes on the list it also showed up last)

PO526

PO300

I continued through the scanner and it told me what the codes meant, and that is what is in my title. Now, we cleared the codes and he told me to go drive it and let the light come back and see if we can get it to maybe pinpoint the issues better. I started driving, it was still hiccupping, but nonetheless was accelerating fine. I came upon a hill and bam, 2 cylinders stopped working. I knew this sound as my old Corolla did this. I pulled into the nearest driveway and turned around, all the while it was intermittently reactivating and deactivating cylinders. Then, it stopped doing so and went back to "normal" with all of its hiccups. I decided not to go back to the friend's garage but instead continue. I then accerlated down my home road and right as I hit the speed limit I let off the gas. The engine sputtered, turned off then turned back on again. All was fine afterwards. The truck does sound like a Diesel, and it has plenty of muffler explosions too. Almost sounds like a very quiet rally car pop.

I've given it over 4 hours runtime since then and the check engine light has not come back on, yet it still continues to hiccup and warble when holding speed.
 

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Discussion Starter · #2 ·
Also, probably extremely important. I changed the spark plugs a few weeks ago. I gapped them to manufacturer spec, and torqued them to spec too. It had been running completely fine and normal until last night when I started it and the misfires began.

I was at my friend's garage to install some lights onto my car. 4 LED amber parking lights for the grille, make the thing look spiffier I guess. I connected them to the parking light wires, positive and negative on the passenger side headlight. After I was done and about to leave, I started it up and the misfires started. I thought "Oh- shoot, maybe I grounded something by accident..." But I turned all lights off and yet it still misfired with all of its hiccups.
 

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I do not know about the other codes but please hear my warning REPLACE THE FAN. I got that code and kept putting it off. Next thing I know I'm driving on the interstate and the fan got so fast that it exploded sending shrapnel throughout the system.
 

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Discussion Starter · #4 ·
I do not know about the other codes but please hear my warning REPLACE THE FAN. I got that code and kept putting it off. Next thing I know I'm driving on the interstate and the fan got so fast that it exploded sending shrapnel throughout the system.
DARN OKAY- NOTED: Replace fan clutch
 

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SilverShadow, what spark plugs did you use to replace the ones that were already in the engine?

When you say you gapped them, did you jut check the gap, or did you actually bend the electrode on the spark plug? If you did bend the electrode, what kind of tool did you use?

Before you replace the fan clutch, verify that the wiring to the fan clutch is in good repair and not frayed, almost falling out of the connector, etc. The P0526 code is telling you that there is a problem with the fan clutch speed sensing circuit. It does not say you fan clutch is bad. A big difference. It might be a bad fan clutch or it could be a poor electrical connection somewhere in the circuit. Diagnose first then repair the problem. Don't just throw parts at a problem because it might not fix the problem.

Good Luck!
 

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Discussion Starter · #6 ·
SilverShadow, what spark plugs did you use to replace the ones that were already in the engine?

When you say you gapped them, did you jut check the gap, or did you actually bend the electrode on the spark plug? If you did bend the electrode, what kind of tool did you use?

Before you replace the fan clutch, verify that the wiring to the fan clutch is in good repair and not frayed, almost falling out of the connector, etc. The P0526 code is telling you that there is a problem with the fan clutch speed sensing circuit. It does not say you fan clutch is bad. A big difference. It might be a bad fan clutch or it could be a poor electrical connection somewhere in the circuit. Diagnose first then repair the problem. Don't just throw parts at a problem because it might not fix the problem.

Good Luck!
We replaced them with the factory AC Delco spark plugs, I forget the number but we had AutoZone make sure the numbers were right. We checked the gaps with a gapping tool, then bent the electrodes with the tool itself.

I checked the fan clutch wire harness for frays, none were found. My radiator shroud has been missing forever, so the fan clutch wires ar just sitting out in the open and I thought maybe they'd have been nicked by the fan. But nope. The fan clutch wire was wrapped around itself to keep it away from the fan, so it wouldn't get frayed.
 

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OK on using ACDelco plugs - you likely used 41-103 plugs. OK on checking the gap, but I'm cringing that you regapped them. They are pregapped from the factory and should not need regapping, and regapping them is risky because the gapper itself can damage the fragile iridium plating on the electrodes.

Now having said that, how far off from the alleged factory gap of 0.043" were the gaps. NOTE, I am assuming you have the 4.2 L I6 engine. Also, what year is your vehicle?

If the gaps were really off, I would take them back to Autozone and have them replace them because they could be counterfeit plugs. Genuine ACDelco 41-103 Iridium plugs come pre-gapped from the factory and do not require gapping. If you look at the Autozone website's page for the ACDelco 41-103 spark plug, it too says that the plug comes pre-gapped from the factor and not to re-gap.

OK on the fan clutch wiring.
 

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Discussion Starter · #8 ·
OK on using ACDelco plugs - you likely used 41-103 plugs. OK on checking the gap, but I'm cringing that you regapped them. They are pregapped from the factory and should not need regapping, and regapping them is risky because the gapper itself can damage the fragile iridium plating on the electrodes.

Now having said that, how far off from the alleged factory gap of 0.043" were the gaps. NOTE, I am assuming you have the 4.2 L I6 engine. Also, what year is your vehicle?

If the gaps were really off, I would take them back to Autozone and have them replace them because they could be counterfeit plugs. Genuine ACDelco 41-103 Iridium plugs come pre-gapped from the factory and do not require gapping. If you look at the Autozone website's page for the ACDelco 41-103 spark plug, it too says that the plug comes pre-gapped from the factor and not to re-gap.

OK on the fan clutch wiring.
Well, 3 of the 6 plugs on my 2004 TB were a bit off, within .10 of whatever the measurements were... The AutoZone I got them from did not tell me not to gap them. In fact they suggested to check the gaps because it may not be correct from factory. Which is contrary to what you said. I'm not sure who to believe here.
 

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Do you mean the gaps were off by as much as 1/10 of an inch (0.10) or do you mean 1/100 of an inch (0.01)? 0.10" is way too much to be off and to be a genuine plug.

A far as who is correct, check out the plug listings on rockauto.com, autozone.com, oreillyauto.com, advanceautoparts.com. They all state that the ACDelco 41-103 plugs are pre-gapped at the factory and not to regap them. I would have cited the ACDelco website, but it is too difficult to find their recommendation.
 
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