CEL's...thoughts...ideas???

Well I finally got around to fixing all the rattles and the truck rewarded me with a CEL on for 3 days straight.

So off to a buddy with a MAC scan tool to pull some codes and scan. Pulled codes P0128 and the dreaded (from what I have read) P0300 code. When at Idle motor would miss on Cyl #1 consistently, occasionally on #2 and very rarely on #6 (twice in five minutes). Once accelerated under load all misfires went away, however when accelerated without load the truck would still misfire occasionally (far better than Idle, cannot even feel a stumble anywhere off Idle –well I can’t anyway). Guy says the miss on idle is obvious but I recall this motor always having a bit of a rough idle since new (possible just getting slowly worse enough to not notice it). So we really only talked about the p0600 code and he suggested a full tune up. The truck is a 2005 zr2 with 78000 Km, only oil changes and air filter change…….so far. He suggested a full tune-up plugs, wires, cap, rotor, pcv, fuel filter. As far as recent on-road performance I have noticed an increase in fuel consumption (aprox 75-100 km less per tank), an intermittent highway stumble occasionally feels like a miss on aprox ¼ throttle its especially prevalent when going on a slight upgrade. Also the truck does not get up to op temp- runs at aprox 70-80c (I say aprox as the gauge reads 40 low 100 mid 125 high (GM math?)

Took it to GM to talk it over with a tech for a second opinion. (not to pay a tech $90 an hour to look at it no thanks…………………well not without a fight!!) He suggested first the t-stat to try and alleviate the p0128 code and get the motor back up to temp. He then suggested I should switch the number 4 wire for the #1 wire and try to “chase the miss around”. Next he suggested bringing her into the dark garage and mist the wires with gasoline……………….no water (I always forget), in an attempt to find arcing. Ultimately he ended up saying it was probably best to do a full tune-up which SHOULD get rid of it. Want a good laugh price out some tune up parts at a Canadian GM dealer $209 for wires, $17.99 for A spark plug!!!…. although I think they will be getting my money for the cap and rotor, both guys stay stick with A.C. for that part.

Now the problem with well…. The problem. I have seen too many threads about the p0300 that start out with…….well first I did a full tune up, still had the problem then I replaced the (insert crap part here) and it still did it, then I replaced the (same here) and no change etc etc. I don’t mind doing a tune-up if it needs it but it’s just the stuff afterwards. And I still need to service the tranny, T-case and diffs before the end of the year!!

Here is the plan of attack. I’ll stop once it is fixed

1) T-Stat replaced. (and possible new stant cap)
2) Swap #4 wire for #1 wire and rescan
3) Spray water check for arcing.
4) Plugs, Wires, Cap, Rotor, PCV, fuel filter (and maybe fuel pressure check?)
5) Lucas (or similar) injector cleaner – theory is if it even gets even a little better I may be looking at an injector problem.
6) Check Coil – replace?
7) Clean EGR valve
8) Place car in drive facing lake…… place brick on accelerator……. and walk away.

Thanks if you took the time to read this rant let alone reply!!

Also looking to score the aforementioned parts relatively inexpensive, any help where to find some deals in Southern Ontario would be also be of great help.

What engine?


Yes
You need to.
Replace the stat.
Clear codes and see what returns first.

Code 300 is a missfire code.
Go threw the repair chart for that code.
Has the camshaft retard retard reading been checked or adjusted?
What is it reading?
What is the fuel pressure doing?
Does it have good hot blue spark to the missing cylinder?
What is the code P0600 number?
600 or up P06--?

You are seeig the results of the P0128 which means your t-stat is stuck open causing the engine to run rich which will cause the occasional misfire as the cylinders start to carbon up a bit.

If you haven't done a tuneup lately, Now is the time as well. This would explain the higher fuel economy, the truck can't go into closed loop anymore seeing the engine is running too cold.

Update: Thanks for the replies gents. Swapped the t-stat, poured a little lucas injector cleaner and cleared the codes truck is now getting up to temp and running a little better. Noticed some brown deposits on the t-stat and old rad cap and a slight brown "film" in the overflow and when looking in the rad............. not good I would assume......and probably time for a flush. No CEL post repair, Idle still not the best but as previously stated it never really was all that great. Tommorow fuel filter, plugs, wires, cap, rotor, pcv and maybe price out coolent flush (already????) Cheers

I don't think a flush is needed. With the good rad cap (I hope you used a stant and no acdelco), things will clear up.

I think the truck comes with platinum plugs so plugs really don't need to be changed. I would avoid changing them or the wires. Just change the cap and rotor, replace the air filter, pcv valve and the fuel filter and it will be fine.

Wires and plugs will last a lot more than 3 years and are not even close to being worn out. The cap and rotor is the weak spot that causes most of the idle problems and should be changed yearly.

Lt: I replaced the cap with a prestone from c-tire, (looked for a stant at 5 different places- got frustrated and ended up just buying the prestone cap - hope its ok- if not I'll spend the extra $10 and find a stant) I am still a little concerned about the brown in the coolent especially after doing some internet reading re DEXCOOL (class action lawsuits!!!) and brown sludge and was hoping on some insight on how it should "clear up" without a flush.


As for the tune up I got OEM plugs but settled ona bosch wire set - I already opened the plug packaging to check the gap so I'll just keep them around until its time and may return the bosch wires until I need it (and go OEM?).

FYI the cap, rotor, ff, air filter and pvc are all OEM a.c. parts.

So based on your imput tommorow I will be replacing the parts you suggested, run it back to my friends shop and do a quick scope to see if the #1 and occational #2 & 6 miss are gone > If its still missing would you then suggest plugs and wires or start looking elsewhere? I was still contemplating the "water spray in the dark" to test for arcing as there is a trace of white efferecence <sp? on the #1 spark plug wire boot > where the wire attaches / enters the boot.

fella I might already owe you a beer or two as you saved me some serious $$$ on that front end clunk and now if you can buy me some time on the plugs (especially that PITA #3) and wires......well I'll owe you a case!!

Prestone cap is fine and dont' worry about the mud. The dexcool problem was solved a long time ago and the cap was the issue most of the time, not the coolant. so don't worry about it.

There is no way in hell your plugs are bad with platinums at 78000kms. Wires will be fine as well. I can guarantee it. They are good till 160,000kms easily.

Get some torx screw drivers handy for the cap seeing that is what you will need to remove them.

Remember to remove one wire at a time and transfer them over to the new cap. All of them don't directly correlate to the cylinder fire. One at a time to be safe. All my misses were from the cap and rotor and nothing else.

It might have never been tuned up. Which is why I do that with any new car I get regardless.

stuff like this has me a littlew concerned
http://www.sancarlosradiator.com/dex-cool.htm

Last night replaced fule filter. Installed, started truck, checked for leaks, no leaks no CEL's, engine still had slight miss on idle (no suprise). Moved on to cap and rotor, took my time, applied dielectrode grease to dist end boots and dab on each connection > (I also applied a VERY small coating to the lip of the cap that "seals" with the distributor > was this wrong?) Cap and plug wires are numbered and all hooked up the same as before and triple checked, rotor was replaced in the EXCACT location as removed (I think the only way to screw this up is to install it 180 deg. backwards). When removing the wires off the old cap I made sure I pulled from the boots and not the wires (not a complete idiot). Then replaced air filter, then attempted to replace PCV....well not happening there... removed hose behind air snorkle on valve cover leading to TB found a non removable PCV? on valve cover, looked down "PCV" in valve cover and saw a small hole, no valve, no "click" when I tapped it and it did not look like the replacement pcv I had bought> read on a forum regarding a "new style" PCV with no moving parts and am wondering if this is what I have???.

So hooked everything back up (again triple checked all hoses and connections) started it up..... got a CEL right away and noticed the Idle appeared worse however once off Idle the truck appeared fine except a little low on power (NOT my driving style at all but it would not break the high KM BFG's loose turning from a stop in the rain, In the past I can recall the truck having enough jam to do this). Disconnected battery ground, satfor 20min hooked back up, CEL on from start up.

Spray bottle, blacked out garage no arcing from anywhere.

No time to get the codes read again and see what I have done till monday so for now we are really only guessing but what the Hell did I do?

Some of my uneducated guesses,

1) Although I applied very little dielectrode grease possably got too much on the contact points causing short (not very likely)

2) Even with pulling the Boot and not the wire I still broke or damaged a wire that was already on the way out. (hoping this is it)

3) broke the seal of the pcv, hose was loose when reapplying creating partial vac leak (don't even know if it would)

4) when replacing air filter I pullled the top of the cover too far up, partilaly disconnecting or breaking connection to MAF? (never looked yet)

5) somehow installed Cap/Rotor wrong > again I triple checked all conections and TOOK MY TIME to ensure everything was hooked up corectly.

6) Wrong or faulty Fuel filter, looked the same, same connections, no problems, CEL's or Leaks after installation.

Thanks for your imput.

Did you take each wire off the old cap and put them immediately on the new cap or did you yank them all off and put them all on the same time on the new cap?

for one, there are two hoses going to either valve cover. One is the fresh air intake and the other has the PCV valve. The PCV valve is in one of the valve covers. And I don't know why you forced it and broke it.

Plug wires need to be changed I guess now. Try to get the stock wires from the dealer, avoid aftermarket, they never seem to pan out.

Why did you potentially do damage to the MAF and never checked it out?

Cap wires replaced one at a time, even if i crossed a wire i would figure the idle and drivability would be much worse, I don't think the firing order is that close that I wouldn't notice if I switched wires. Did'nt break the PCV hose just was stating its easier to remove now and possibly not a good seal around the top of the "PCV". Again the peice on the drivers side valve cover looks nothing like the replacement "PCV" I got and is non removable (other than removing the valve cover). A internet search reveals that I cannot order or find a 2005 PCV valve for the truck.......Weird.

CEL came OFF yesterday and has remained off, Truck drives ok, idles with a miss and is getting poor fuel economy (140 km from from full to 1/2 tank mixed city/hwy...........)

Thanks for the heads up on wires, I'll take the bosch set back and source some A.C. delco's

The piece on the driver's side valve cover is the fresh air intake, not the PCV valve. I don't know about the '05 models, but on mine, the PCV is on the passenger side valve cover.

Cap wires replaced one at a time, even if i crossed a wire i would figure the idle and drivability would be much worse, I don't think the firing order is that close that I wouldn't notice if I switched wires. Did'nt break the PCV hose just was stating its easier to remove now and possibly not a good seal around the top of the "PCV". Again the peice on the drivers side valve cover looks nothing like the replacement "PCV" I got and is non removable (other than removing the valve cover). A internet search reveals that I cannot order or find a 2005 PCV valve for the truck.......Weird.

CEL came OFF yesterday and has remained off, Truck drives ok, idles with a miss and is getting poor fuel economy (140 km from from full to 1/2 tank mixed city/hwy...........)

Thanks for the heads up on wires, I'll take the bosch set back and source some A.C. delco's

You damaged the MAF sensor i think and why are you not looking into that when you said you damaged it.

2005 and up do not have the type of PCV valves that are interchangeable/replaceable as a regular one. They can look the same, but are in fact more or less permanent. They usually have a little metal flange thats rivited to the valve cover.

It would be a good idea to check the MAF and make sure its clean and not damaged or not performing poorly.

Generally, 78K's on the wires and plugs is about halfway through their estimated lifespan, they should be good, but that may not always be the case. For the p0300, if your ignition system is good and a full tune up has been done(like you have done), you should take a look at the fuel pressure and make sure its at spec.

If you have a weak fuel pump, or poor regulator, you could have low fuel pressure. At low fuel pressure, the injectors may not be firing properly, causing misfires and poor engine performance.

If it holds at spec with and without engine running, then I would be looking at the injectors for sure. The injectors/pintles on these trucks have had a nack of clogging and performing poorly, causing random misfires. An updated fuel injection spider has been made which relocates the injectors and dramatically improves the reliability of the system and virtually eliminates fuel injector problems.

Hope this gives you some help, and an idea.

Blazer LT : It's possible that when I lifted the upper airbox to change the Air filter that I lifted a little too aggressively and put stress on the connection to the MAF. I have since check the connection and all seems good. Other than checking the connection and inspecting/ cleaning the wire I don't think I can trouble shoot it anymore. One thought is to disconnect the maf (which will probably throw a code and make it run worse) and if my idle miss goes away the problem lies in the MAF??? My miss (prior to changing the fuel filter, cap,rotor and air filter which has seemed to make it worse) was mostly on #1 cylinder with occasional misses on #2 and # 6. Logically I would think a MAF problem would create misses "across the board"?

Keep in mind that we are really only guessing until I get the motor hooked back up my buddies scanner next Tuesday and see where the miss is now. The plan is if it’s still mostly #1 cyl I will swap some wires around to try and isolate it, if still on number #1 I will swap #1 plug, if resolved new plugs and wires all around, if not I think I may have to consider a fuel related problem.

My very uneducated guess……… a partially clogged #1 injector, some debris when changing the fuel filter made its way upstream and clogged the injector a little worse making my idle a little worse.

Blazes 9395 : Thanks for clearing up my PCV problem, very frustrating trying to replace a non replaceable part, HA!!! The "parts pro" must have used an old part # from a 200? And figured there has been no change so "here ya go".

Sorry for the confusion I have only so far replaced the cap, rotor, fuel filter and air filter and have NOT replaced the plugs and wires yet for a few reasons 1) Most state they should still be good 2) no time to yet 3) not very mechanically inclined (can you tell LOL) and have big mitts so I am not looking forward to that #3 plug.

Once I can safely remove ignition as my problem then I think your right on that I should start looking at fuel related causes (read more $$$$). So on Tuesday I will be playing with plugs and wires and once I can safely rule out ignition (coil as well???) then I will be doing a fuel pressure check (for which I have no idea how to do, I wouldn’t think it's rocket science a quick Google search should have me on my way).

If ignition and fuel pressure are ok I am wondering how you would confirm the injector was bad. Would it be just a process of elimination? I would hate to be replacing $$ parts like this only to find out I had sticking valves or some other internal engine problem. I am trying to avoid being part of the "lets just put parts on it till it works" crowd, which seems to be a big crowd when it comes to blazers!!!

Some reading info on the revised spider and any related TSB’s would also be helpful.

Thanks again guys for your input, have a good weekend I will post back on Tuesday.

You know what I would try, go to the parts place and get a replacement MAF. Plug it in and start the engine to see if things smooth out. Then return it if it doesn't.

I had 5 guys I helped that had a bad MAF that causes the misfire as well. Try it, you can take it back after if it doesn't work.

There is no what you have a plugged injector. You have a fuel filter that takes care of that and stops any debris.

Update: Re-installed cap and rotor, replaced #1 plug and gently cleaned maf > truck is now running well and returning good MPG..... Thanks for all that helped.