P0171 and P0303

[thebat]

I have 05 Trailblazer LT, 4.2.
I've had rough idle and CEL on/off for a year. I changed air filter, fuel pump assembly, plugs and cleaned throttle body completely. I moved coil from #3 to #2 to determine if coil was bad if code followed swap.
The rough idle has improved but CEL just came back, 0171 and 0303. So it's not coil, plugs, air filter, throttle body, fuel pump.
I'd like advice on what to look at next. Thanks!

 

[Sparky]

Misfire on #3, system too lean.

What did the plugs look like on the various cylinders, especially #3 compared to the others?

Things that can cause too lean conditions are a bad O2 sensor or a leaky intake gasket, loose/bad/disconnected vacuum line, or even a bad enough exhaust leak near the manifold O2 sensor can trigger it to think there is a lean condition and cause other issues. If it thinks it is too lean it will be dumping fuel into the system, that could then be leading to a rough idle as it is actually pigging out on fuel.

 

[thebat]

Misfire on #3, system too lean.

What did the plugs look like on the various cylinders, especially #3 compared to the others?

Things that can cause too lean conditions are a bad O2 sensor or a leaky intake gasket, loose/bad/disconnected vacuum line, or even a bad enough exhaust leak near the manifold O2 sensor can trigger it to think there is a lean condition and cause other issues. If it thinks it is too lean it will be dumping fuel into the system, that could then be leading to a rough idle as it is actually pigging out on fuel.

My MPGs have been going down for the last year or so too.

 

[Sparky]

Does it seem to idle and run OK until the engine warms up, or is it rough regardless?

 

[thebat]

Cold idle is always good. Rough idle is only when truck is warmed up. Sometimes it will idle at 1000RPM and it is smooth. Mostly, around 600 and rough. I just cleaned throttle body today and it seems improved though. Let me run it awhile more today and give you more accurate response.

 

[Sparky]

Alright. If it seems like it is fine until it is fully warmed up then the problems only start when hitting closed loop. Last time I ran into that, the upstream O2 sensor was shot and was feeding bad data.

 

[Mooseman]

BTW, you did disconnect the battery at least 30 min. while you cleaned the throttle body? Have to do that to reset the fuel parameters as it may think you're still on a dirty TB.

Do a compression test. If that passes, check for intake leaks by spraying a little carb cleaner around the intake gaskets and fuel injectors and listen for a change in RPM. After that, only thing left really is a dead injector or bad wiring to it. Check that power is getting to it with a noid light (basically a 12V LED). Way to confirm that the injector is dead is to find a shop with a Tech 2 or at the dealer and have an injector balance test done. This checks each injector as to how much fuel it dispenses.

 

[jeffro312]

just my 2 cents but when i had a p0171 it was related to the sais pump. Not sur if 05 trailblazers have them. With mine the hose connection on the pump under driver seat broke off and also the valvle on engine side didnt work. my fix was to delete the sais send my ecu to get reprogrammed and program out the code and bought a block off plate from dealership installed and all was good.

i did drive it without fixing it for over 2 years only issue was when check engine light came on idle would jump from 600 to around 1k

goodluck

also you used acdelco 41-103 plugs when changing spark plugs? the only time i ever got a misfire code was when coils went bad. But i also changed plugs way to often.

 

[Sparky]

It is more the particular truck than the year more than anything. Seems to be no rhyme or reason to what results in a particular truck getting SAIS.

 

[thebat]

Alright. If it seems like it is fine until it is fully warmed up then the problems only start when hitting closed loop. Last time I ran into that, the upstream O2 sensor was shot and was feeding bad data.

I drove it awhile tonight. Idle stayed at 900 RPM cold and warm. No rough idle, truck purrs like a kitten. But, today is the first day of the season that the temp is over 70. It's been very cool here. I'm wondering if ambient temperature is involved somehow.

Alright. If it seems like it is fine until it is fully warmed up then the problems only start when hitting closed loop. Last time I ran into that, the upstream O2 sensor was shot and was feeding bad data.

BTW, you did disconnect the battery at least 30 min. while you cleaned the throttle body? Have to do that to reset the fuel parameters as it may think you're still on a dirty TB.

I did pull neg battery cable when I started job. The PCM reset fine I think. Truck ran great after starting with coil swap and clean tb.

 

[Mooseman]

Please use the edit and/or the +quote button instead of posting consecutively. Thanks.

900 RPM is too high. Normal is ~650 RPM. It may be in open loop (cold mode) for an extended time. If that's the case, you might kill your cat. You still getting codes? Have you looked at the suggestions above?

 

[thebat]

Please use the edit and/or the +quote button instead of posting consecutively. Thanks.

900 RPM is too high. Normal is ~650 RPM. It may be in open loop (cold mode) for an extended time. If that's the case, you might kill your cat. You still getting codes? Have you looked at the suggestions above?

Is this something I can see with OBDII reader? Truck is still cold and I can test now and after warm up.

 

[Sparky]

Depends on the reader. With Torque and an OBDII dongle I can gather live data.

 

[thebat]

Is this something I can see with OBDII reader? Truck is still cold and I can test now and after warm up.

Depends on the reader. With Torque and an OBDII dongle I can gather live data.

I can gather live data with this one. Or freeze frame. I/M readiness. Problem is I don't know what the labels mean mostly. If you tell me what you are looking for, I will relay it to you.

 

[Sparky]

It should tell you whether it is is open or closed loop for starters. Once engine is fully up to temp (210).

If it is fully up to temp, closed loop, and idle is still high, that's a very good indicator of a vacuum leak.

 

[thebat]

It should tell you whether it is is open or closed loop for starters. Once engine is fully up to temp (210).

If it is fully up to temp, closed loop, and idle is still high, that's a very good indicator of a vacuum leak.

Yoiu are referring to FUELSYS1? It is always CL even if engine is cold. At start up it is OL, but quickly changes to CL as soon as I accelerate. Then it stays CL until I shut off engine.
The idle speed has returned to @600. Pretty consistent now. A little rough but not as bad as before cleaning tb.
Another development: CEL returns quickly after I erase. CEL on, I erase, run car for 10-15 minutes, CEL turns on. I erase, it turns on in 10,15 minutes. But now it is just misfire code, not lean code. That is true of pending code too, it is P0303.

I am going to run car with scanner on in 'live' mode for a couple of 10 mile trips. I will watch idle speed and fuelsys1. I'll let you know.

 

[Mooseman]

At this point, I'm thinking either a leaking intake manifold on #3 runner or a dead/weak injector but only after a compression test.

 

[thebat]

OK, thanks. I will do compression test ASAP, probably Friday. If I take off air box to access coils/plugs can I see all the bolts on intake manifold? I would like to tighten them then just to try to be efficient. Or does more stuff have to be removed to access bolts?

 

[Mooseman]

Nope. They're on the driver side of the engine, below the PCM, behind the alternator. Can be a to get at.

 

[thebat]

Nope. They're on the driver side of the engine, below the PCM, behind the alternator. Can be a to get at.

I wonder what I was tightening on the passenger side. Valve cover?

 

[Mooseman]

Probably.

 

[thebat]

Probably.

One last thing, you mentioned wobbly sockets. I need to buy 1/4 inch, 10mm and 13mm? Or are all the bolts 10mm? And 10 inch extension?

 

[Mooseman]

Just 10mm. Maybe a 2" and a 10" extension should do. It's been a while since I've done it so not sure of what extensions will work.

Here's a pic of the manifold with the bolts for reference. One is hidden under the PCV hose.

 

[thebat]

I'm not sure where to post this so I am putting it here. Regarding the throttler body. There is a hard plastic tube that connects to the metal tube of the throttle body. I believe it is fuel intake? Well, the hard plastic part connects to a fabric (?) tube that heads for the front of the engine. My fabric tube is worn and frayed. It looks as if there was a clamp on this at some time but now there is not. So the hard plastic part fits into this rather loosely. I'm wondering if this could be a vacuum leak? Should I just put a clamp on it? I have seen no mention of this part in any of the throttle body threads. I find that odd.

 

[Tiggerr]

Not sure what it's for either but off the top of my head I'm pretty sure there's vacuum there... could be a leak..

 

[Mooseman]

Definitely not fuel but it is some sort of vacuum. Can't remember what it's for. You could get another at a pick-a-part rather than the dealer which will likely charge $$$, just like fuel lines. Another option could be to cut the connector off and use a rubber hose spliced to the plastic tube.

 

[thebat]

OK, I'm doing compression test and intake manifold bolt tightening. I'm looking over the various posts about these procedures and I have a couple questions.
Is it difficult to remove the electrical connectors to the PCM? Is there some trick to that?
Can I just pull the brake booster hose from the firewall side.
The small hose in the way that is supposed to be a PIA. If I destroy it is it easy to replace? It sure doesn't look like much. I wouldn't mind paying a few bucks to get another.

Regarding compression test, what relay do I pull to stop fuel pump?

TIA

 

[Mooseman]

PCM connectors are easy. Just unscrew each (7mm IIRC) and pull off.

Yes for the booster hose.

That small PCV hose should just pull off, no issues. Haven't heard of these breaking. They are molded so you might either need a new one from the dealer or just use a longer regular hose. I've pulled mine lots of time, never an issue.

Don't remember the relay for fuel pump but should be in the cover. Same for the fuse.

 

[thebat]

I'm on my to AutoZone to pick up a compression tester and torgue wrench. The ABS warning light came on and CEL was throwing codes P0122, P0123, P0223. Something about throttle/pedal circuit low/high circuit A and B. WTF! Should I continue with compression test and tighten manifold bolts assuming that the new codes are not related to old misfire/lean codes?
I don't want to remove the same parts again.

BTW, kudos to AutoZone for letting me borrrow tools, no charge. That's a great program.

 

[Mooseman]

You're also getting a reduced engine power too I'll bet. And the ABS? All this happened at the same time? Sounds like an electrical issue. Try unplugging the fan clutch as it is known to sometimes mess up the throttle circuit. Another possibility is the ignition switch.

These new codes are not likely related so you should continue.

 

[thebat]

I did the compression test, 1=195, 2=195, 3=60, 4=165. I only did those four. I guess the consistent misfire code 303 is a result of low compression. As I was doing the test I noticed a coating of oil on each plug I pulled.

I tried to tighten up the intake manifold bolts but I couldn't do it. After a couple of hours I only got to two and they were the easy ones. I had to give that up.
The two were pretty tight, maybe a quarter of one rotation each.

So, with the new codes, P0122, P0123, PO223, and the ABS light, I may have to bring this truck to a real mechanic.

You're also getting a reduced engine power too I'll bet. And the ABS? All this happened at the same time? Sounds like an electrical issue. Try unplugging the fan clutch as it is known to sometimes mess up the throttle circuit. Another possibility is the ignition switch.

These new codes are not likely related so you should continue.

Sorry, I didn't see your post before I posted results of compression test. I check those things.

 

[Mooseman]

Don't bother. At a compression of 60, you have a serious mechanical issue with your engine so everything else is now a moot point. You would have to do further investigation to find out exactly what the problem is but suffice to say, it will be a big and/or expensive job.

Sorry to be the bearer of bad news.

 

[thebat]

Yep, it's time to break out the check book. I will have the trouble diagnosed and decide what to do from there. I might just keep driving it the way it is, the truck runs good!

Thanks for all your help.

 

[thebat]

Is there a thread that discusses buying used/rebuilt engines for TBs? I've searched but I can't find anything.

 

[djthumper]

Not that I recall. Try http://car-part.com/ it may point you to a local resource.

 

[Mooseman]

I do believe there is one or two threads on swapability between years in the 4.2L FAQ.

 

[5xBuckman]

Is there a thread that discusses buying used/rebuilt engines for TBs? I've searched but I can't find anything.

I just bought an 05 with a bad #3 cylinder. I'm pretty sure it needs a valve job, but after looking at the amount of working involved with pulling the head, I opted for a salvage motor. I found a 05 with 112k miles for $715. then I paid an additional $75 for a 3 year parts warranty.

I just started to pull the engine, mine happens to be a 2wd, so it's easier....but, it's a LOT of work. A close quarter battle.

 

[thebat]

I just bought an 05 with a bad #3 cylinder. I'm pretty sure it needs a valve job, but after looking at the amount of working involved with pulling the head, I opted for a salvage motor. I found a 05 with 112k miles for $715. then I paid an additional $75 for a 3 year parts warranty.

I just started to pull the engine, mine happens to be a 2wd, so it's easier....but, it's a LOT of work. A close quarter battle.

Well, you're certainly saving a lot of money. I was quoted $1500 to remove and replace engine. I need a valve job too and that is going to set me back $1300. Since they are doing manifold gaskets and machine work I'm going that route.
Good luck and let us know how it turns out.

 

[Mooseman]

Another member had no compression in a cylinder and wound up being a valve spring. Relatively easy fix. Before condemning the engine, take the valve cover off and check the works.
http://gmtnation.com/forums/threads/p0301-then-p0300-please-help.17094/

 

[5xBuckman]

I'm just getting ready to pull it....but, I will pop the VC and have a look.