Ready to pull hair out.

[jistincase]

I have a 2003 TB that i have been chasing a problem for over 3 years now. It is getting worse over the course of that time but when it started it was very intermitent. What happens is when you are cruising at a steady speed especially in the highway it will all of the sudden jolt and buck. Sometimes it is like someone turned off the key or the fuel. It has started to do it around town now and sometimes it will stall out at a light. When it does this it there are no codes or cel lights that come on. One time it did throw a code about bank 1 lean and the idle went up to about 1000rpms for a bit and then went away. Today I was doing about 35 under very light accelleration and it took a nose dive like you turned it off and then came back. At one point I thought it might stall completely. It has over 100,000 miles on it and has the oil changed every 3000 because I have the lifetime oil change through the dealer.

I have replaced the cam sensor, o2 upstream sensor, MAP, new plugs from delco, all coil packs, fuel filter and fuel pump along with a new alternator just because. O and a new pressure regulator. This is not like a little loss of power it is a total loss of power and then back on again. I do mostly highway miles with it as I travel a lot taking my daughter to BMX races around the country. I even pulled the cam positioning sensor out to see it the screens were clean and they are spotless. It does have a little oil around the electrical unit though. One thing that I do notice is when I am on the highway it seems like it has a lean miss all the time. My hearing isn't that good anymore but I seem to hear it popping in the exhaust and you can feel it slightly surging. It also only seems to do it when it has reached operating temp and when it is hot out it is worse.

I do have a scanner and did a live recording the other day and did notice when it did its thing that the throttle position went from like 39% to 12% and them back to 39% all the while holding the pedal steady. Could this be a pedal switch problem as I use crusie a lot or am holding it at a steady speed a lot? If anyone has an idea where to look I would appreciate it immensely. If there is any other data that I could provide that would help I can try to provide that.

 

[BlazingTrails]

Have you checked into your ignition switch? What you have described has characteristics of that being the problem.

Edit: The surging and "popping" while cruising the highway is likely a vacuum leak.

 

[gmcman]

Also if you have not changed your fuel filter in awhile I would put a new one in. Just to rule it out.

 

[dmanns67]

It would appear that he has replaced the fuel filter and the fuel pump within the last 3 years.

 

[jistincase]

I forgot to mention that I did a new ig switch and the fuel filter and pump are less than 2 months old.

 

[gmcman]

It would appear that he has replaced the fuel filter and the fuel pump within the last 3 years.

That's what I got out of it but didn't know if it was 3 years or 3 weeks.

Good that he replaced it recently.

 

[Mooseman]

The CPAS (cam solenoid) with oil in the connector is indicative of failure or coming failure and should be replaced.

Have you cleaned the throttle body and disconnect the battery for 30 minutes? I know this is usually for idle issues but it's someplace to start.

The ignition switch is also usually suspected with electrical gremlins. It's a cheap fix and worth trying.

Now that blip you had with the TPS, if it would have been a real issue, would have thrown it into REP with a code but that hasn't happened. If the TPS doesn't jive with the pedal sensor would trip that safety.

 

[Wooluf1952]

Welcome

In case you haven't heard:
http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/

IMHO, Mooseman has the first things to check.

 

[gmcman]

Also, take a look around the engine bay for any loose ground wires. Try to move the battery connections with your hand, they should not move at all. Check the ground wire at the firewall and I don't know off hand if there's a ground strap to the cylinder head but if so make sure it's not corroded. I'm not near my Envoy for a few more days so I can't look. I don't remember if the coils ground through the electrical connection or the cylinder head. Just an easy quick check though.

 

[jistincase]

okay, so I took it in to a shop with a good rep to try and find the solution. They could not pin it down specifically but they did pull a u1301 code which is a class 2 data circuit from what I am told. The check engine light did also come on for them on the first start of the day which was p0013 and p0014. They cleared those and they did not come back. He seems to think that the pcm needs to be updated and it could be a communication problem betwee the pcm and other modules. The software version on mine is 12579356. He said that is an old version. The thing that makes me mad about that is I took it to the dealer to have the latest updates done only about a month ago. I also am going to replace the cam solenoid as it has some oil in it. Everything else that I replaced he said checked out fine and that all those were known problems. Any thoughts?

 

[Mooseman]

U1301 gave me this:

DTC B1327 not set as a current code, the ignition switch position requires serial data communication to occur, no valid messages were detected on the Class 2 serial data circuit, or the voltage level detected on the Class 2 serial data circuit is high for 3 seconds

Could be pointing to a bad ignition switch but you said you replaced it. What brand did you use? There could also be a short to battery + somewhere in the data bus circuit.

P0013 and P0014, both are related to the CPAS. Replace it with an ACDelco or Delphi, no Dorman crap.

Do this first before going into the PCM.

 

[RedRocketZ28]

No one think's it could be something with the throttle body or pedal assembly? Going from 39% to 12% TPS while holding steady does not jive. Also, when my foot is off the pedal mine shows around %15 (would need to check to make 100% sure) which is what most electronic TB's will show.

 

[triz]

Did you clean the TB? How are your fuel injectors?

If that has not been done. Clean the TB, thoroughly. Drop a bottle of concentrated Techron, or PI Performance. Fill with 93 Octane and run it.

 

[Mooseman]

One way or another, the CPAS has to be replaced. You replace one part at a time and re-assess. If it's really borked, it could be affecting the 5V reference.

 

[jistincase]

Got one at the house and will put it on this weekend and see what happens. I don't have a connector so I am just going to clean the heck out of it and hope that works. I will post back after a few days to see if my problems changed at all.

 

[jbwi112]

the consensus is the second 02 sensor is only to make sure the cat is working correctly. However I had Fiero that would randomly cut out while cruising. I replaced plugs, wires, distributor, rotor, fuel pump and filter, and a ton of other parts.

Before taking to the junk yard I replaced the 02 sensor, and wanted to cry, it ran beautiful.

Maybe its the other 02 sensor

throttle body and gas pedal swap from local boneyard would be my next step

 

[gmcman]

Have you tried a new ignition switch yet??

These are known failure items, they just don't turn off the motor, they're more elaborate.

You have a situation that doesn't make any sense to continue chasing the problem without trying a new ignition switch.

I would change it just because, and especially since they have been so problematic with these platforms.

 

[jistincase]

Okay so I changed the cpas and cleaned the connector out and for the first 4 or so key starts it ran great. After that it started the same thing all over again and this time it set a p0171 code which according to the reader I have is bank 1 lean. The idle came up to about 1000 but strangely it didn't do the cutting out after the code set. After a couple of starts no more pending code and it is running fine at the moment. Ambient temp seems to have some affect on this whole thing. I am starting to wonder if the pcm is bad and after the relearn process from taking the battery cable off it relearns all the bad things once again. Just grasping at straws here. I also replaced the ignition switch a while back for those asking about that. I can say though that the frequency and intensity of it acting up is getting worse all the time. The other day when it was acting up I was wondering if it was going to stall going down the freeway. If something would just crap out it would make things a whole lot easier I am really starting to think that there is a bad connection some where but do not have an idea where to look first. Is it a possibility that a failing pcm could do all this and not set a code?

 

[Mounce]

Did it go back to running good after replacing the cpas? What brand did you get? Reason I ask is that like many other things, it prefers the ACDelco brand but I'm not sure I'd tell you to buy another unless it throws a p0014 with the new one.

The pcm is supposed to set a code if it itself messes up but it doesn't always throw it.

 

[Mooseman]

I would disconnect the battery again for 30 minutes and clean the throttle body. It does through a relearn process but it shouldn't throw a code. Try this first and we'll go from there.

If after that it's still acting up and giving a P0171, record the rpm along with the STFT and LTFT.

 

[jistincase]

I have cleaned the throttle body so many times I could do it blindfolded. I did that not more than 3 weeks ago and it wasnt even that bad at the time that I did it. Could the evap system have anything to do with all this?

 

[Mooseman]

It could but I'd would think that it would throw a code specific to that. What about the O2 sensor? Did you replace that?

 

[jistincase]

Okay here is a list of what has been replaced within the last 3 months. O2 sensor, fuel pump, fuel pressure reg, CPAS, cam sensor, all coil packs and delco plugs, fuel filter, alternator, ignition switch and had the pcm flashed with the newest updates but another shop said that the build version was an old one according to the data base that they connect to. I have also cleaned the TB twice within that period. And I had the Cat replaced also.

 

[Blckshdw]

... Ambient temp seems to have some affect on this whole thing...

Can you elaborate on this part? Does the truck seem to run better when it's cooler and/or been sitting for a long period, and run worse when the engine is hot, or it's been sitting in the sun? If so, you could also suspect the intake air temp sensor.

When unplugged, real time data shows the temp as -40. I doubt the PCM is actually factoring in sub freezing temps into it's equation for AFR, but since warmer air has less O2, that could explain why you're AFR is reading on the lean side if your IAT sensor is starting to go bad and feed the PCM lower numbers than what it actually is.

 

[jistincase]

When it has been sitting in the sun for a while it will act up more often. Today I thought i was going to stall in the intersection after it had sat for the afternoon in the sun. It quit a few times and had to do a neutral drop to get it going. Farted and missed for a little while and then when I made it back home was running fine. No codes or pending codes at all. I tugged and pulled on as many wires as I could get my hands on and nothing. In the morning or when it is cool it runs fine with hardly ever a problem. I have ran it a few times since it stalled out on me and seems to be fine at the moment. About ready to have an accidental fire with this thing. I was also noticing that the stft was going from -8 all the way to +3 is this normal?

 

[BlazingTrails]

I also replaced the ignition switch a while back for those asking about that.

What brand did you use? The reason I ask is because the dorman units are known to have failures sometimes right out of the box. I get OEM ac delco units on eBay for $32 with shipping. I think it would be in your best interest to order one regardless.

AC Delco ignition switch.

 

[gmcman]

Have you followed all you ground wires and ensured the contacts were clean? Just for future reference...try not to rev it and engage the trans, that will likely crack the sunshell then you will have a rebuild on your hands.

I would go over every ground and positive cable and I would also check the battery leads under the boots. Warm them with a hair dryer if stiff but they will generally slip down so you can see them.

Sounds like you may have a loose wire, at least the symptoms point to that.

 

[gmcman]

Check under the fuse box also, I think I remember one member finding a loose connection under there.

I think there is a ground down by the trans also or rear if the block.

These are easy things to check and rule out. Don't just tug on the wires, remove them and go over with some fine sandpaper if necessary.

 

[Harpo]

Could the evap system have anything to do with all this?

I had some temp related stalls before.
Had a P1441 randomly but also the lean code you talked about one or two times.

It turned out to be the purge valve.

If you don't mind, would you try to remove your gas cap while the engine is idling. Wait a couple of minutes and check for stuttering and rough idle.


If you get those symptoms you probably got a bad purge valve.

 

[jistincase]

I replaced the IAT sensor this weekend and things at the moment seem to be fine. We will see how it acts in the next week or so. If it turns out to be the 20 dollar part and not any of the others I will be upset. I was thinking that a bad purge valve could be involved also so I will check that also.

 

[nozzleman]

FWIW, had a Suzuki Sidekick that would randomly quit. Wait about 5 minutes and would run again. Not predictable when it would quit. It never threw a code but it was the Manifold Air Temp sensor, shutting off the fuel. Took 6 mos to find it. Could only troubleshoot when it quit.

 

[forrestnummy]

I had kinda the same issues as jistincase. I replaced the variable timing solenoid tonight and the trailblazer, seems to be driving great again. I had already replaced the CAT and the muffler. (flowmaster super 50, and flowmaster CAT) I kept getting a drag, sluggish feeling. Accelerating out of a turn or a slow roll, took so much out of the car. Sometimes, I would just have to floor it, for it to go. Even on a mile long, 45 mph, road, it just felt like the brakes were being pumped, slowly, non stop. I replaced so many parts on this beast, she is almost new again. Every sensor. A/C comp, and system, power steering pump, new alt, new pulley, new water pump, new fan clutch, new computer, Entire new EVAP system and charcoal canister, new fuel pump, fuel filter, gas tank neck, new fuel injectors, new spark plugs, all new coils, new EGR, and pump, new sensors in the tranny and filter, used dexron VI, flushed and drained the rear with royal purple and filled with royal purple,, all new suspension, sway bar links and bushings, all new bushings around the whole car, new lower and upper ball joints, new hubs and ABS sensors, new valve cover gasket, plug seals, intake manifold, intake gasket, new fuel pressure regulator, new throttle body. Im sure there is more, but I would have to check my book. lol.
@ jistincase, if that MAP sensor doesn't solve your issue, please focus on that variable timing solenoid. VVT. You already said that you had oil in the plug and I know someone else on here mentioned the same part to you. That little guy works on hydraulic pressure. ( My lack of a better way to explain it) SO, the fact that your seal has failed and is pushing oil back into the plug, says 2 things. There will not be a good electrical connection with the oil and sludge, in there. And, with that seal broken, it cannot build the pressure that it needs to do its job correctly. Bad thing is, you may never throw a code with this guy. Most people, look right over this thing, and it does so much more than it is given credit. I am guessing that you take the same VVT as mine. Here is the Dorman part#. 917-010. You will have to take your belt off and then take the 3 bolts out of the power steering pump and just let the pump move back and down and bit. Then you will have enough room, to pull the, VVT, all the way out. You may want to get a can of electrical connector spray from the store, to clean out the other end of that plug. Throw a little oil on the new, VVT o-ring, and put it back into the car. Just a hint. It is a very tight fit. Getting the old one out was hard and getting the new one in is hard. I just twisted it back and forth until it came out and I did the same in reverse, to install it. THERE IS JUST 1 BOLT THAT HOLDS IT IN. Put everything back together and take it for a drive. You should start to notice a change pretty quick.

 

[jistincase]

Okay so the problem that i am having is getting more constant and I keep getting the p071 code for bank one lean. When it does it the idle goes up to about 1000. I can erase the code and it will return to normal only if the car is at a stand still and out of gear. I have checked for vacuum leaks and i did as one person suggested and left the cap off the gas tank to see if it started running rough and it did not seem to affect it. I did notice one day when I was wiggling the map sensor around that it would stutter and miss for a second. I just think that it was getting and air leak around the seal.

 

[gmcman]

Have you checked ALL your intake manifold bolts? Use a 1/4" drive, universal joint and short extension....just past snug, don't crank them down....I believe they are 89 inch pounds....verify that though.

This is the bolt pattern.

 

[gmcman]

Update? Did the manifold bolts check out?

 

[jistincase]

Well I think that it is finally fixed. The other day I was under the hood and was wiggling the map sensor and it died. I repetedly did that and it would die almost every time. The next day I went and got a new sensor and pigtail and replaced them and it has not missed a beat since. The thing that seemed to throw me off was it never set a code indicating a map sensor other than the lean code and I had replaced it prior a couple of years ago. I am hoping that this is it but since replacing them it runs and sounds totally different. Thanks for all the hints and help and if anything changes I will post again.

 

[Mooseman]

Excellent. Glad it worked out.

 

[bennys602]

Hopefully this helps someone else. I have a 2007 chevy trailblazer that got a CEL. I did a scan and got the P0171 code only. I noticed that my STFT was fluctuating between -3% and +5 while my LTFT was at 29%. After reading a lot of different websites, I cleaned my K&N oil filter, changed my MAF sensor, cleaned my throttle body, change the secondary air injection check valve. After changing all these components, it made my STFT almost stay a 0% and lowered my LTFT by 2%. My check engine light came back on two trips later. I then climbed up on a ladder on the side of the motor and heard what sounded like a small hissing noise. I then went over to my air filter and heard what sounded like an increase sucking of air. Since I have no time right now to work on the vehicle, I am taking it to the dealership to have the change the gasket and check for any cracks in the manifold. I think I will have the change out the tubing while they are working on it. I'll post if this fixes the problem after the work is done.