I need a smart GM mechanic's help

[jlbota]

Re: I need a smart GM mechanic\'s help

One thing you may want to check or just change is the Coolant Temperature Sensor. Not the one that controls your temp gauge or light...But the one that your computer reads from so it knows whether to be in open or closed loop.

That little sensor being bad will cause more problems than I can count and most of the time you never get any kind of a specific code from it other than residual codes from other problems it is causing...like fueling problems etc...

Your engine will start out running in open loop when cold running off the basic perimeters set in the computer for a cold start situation...as your engine heats up to about 100 degrees or so...your computer picks up on this from the CTS and then scans all of your sensors and switches to closed loop and your computer will actually then take readings from your sensors and adjust accordingly to keep a proper running engine.....Usually at closed loop is when you see your first codes come up.
So basically what happens is that you may be running an engine that is say 180 degrees but your computer thinks its 60 or just the opposite it thinks its hot when its cold....
Just a thought as I have replaced alot of these on the 4.3 engine and is a common problem on most GM vehicles.
Let us know what you find.

 

[CTyler]

Re: I need a smart GM mechanic\'s help

</font><font color="blue" class="small">( There are no code faults in regards to the miss. I do have a secondary air fault. That is the air pump which only works when the motor is cold. The pump is frozen. Plugging the EGR wire back on makes the truck run crappy again.. )</font>

Did I miss something? Your first post said "The engine light is back on again now for the same reason, misfiring."

 

[texbaylea]

Re: I need a smart GM mechanic\'s help

JimR

Autotap is powerful software. I have a copy and am just learning how to use it. I bought it to help me select a replacement for my 1990 Suburban that had finally become unreliable after 15 years of service. I found a nice clean one owner 2002 Suburban that checked out well. I had it for a full day of driving of which I logged about 2 hrs on the computer. Replay convinced me that it was in good shape.

The other thing I always do for my vehicles is to buy the complete set of factory manuals. I feel that the $100 or so is well worth it since I do most of my own maintenance. I always do my own diagnosis in any case.

Vernon

 

[CTyler]

Re: I need a smart GM mechanic\'s help

Looks like decent software. The one thing that jumps out at me is I did not see bi-derectional comminication. However it is only needed if you intend to command sensors. I went with Autoenginuity for that reason. Just depends on what your needs are.

To add....

The factory manuals are definately the way to go. I used to get Chiltons or Hayes back in the early 80's. Then went to the factory manuals about 86 and never looked back.

 

[ericinmich]

Re: I need a smart GM mechanic\'s help

Just some comments.

If there is a SES light, there must have been a code. It may not now be an active code, but it will be in history for 40 key cycles. If a code doesn't show up, than there is likely something wrong with the scan tool (or it's operator /forums/images/graemlins/smile.gif ).

The info. on that autotap site is very good (look at how-to articles). They are some of the most accurate write ups of problem solving of engine control systems... (coming from a guy that has been in this business for 20+ years for an OEM).

- Eric

 

[JimR]

Re: I need a smart GM mechanic\'s help

I goofed on the light issue. The light comes back on due to the secondary air system fault. There was no code listed for the misfiring. The scan tool showed intermitten misfires. I watched the scan tool as the guy used it. The misifres go away when the EGR valve is disconnected. This morning I was messing around again with the truck. I didn't find a short in the white ground wire to the EGR valve. Then my son informed us that he had to get back to D.C. for school tonight. The truck is gone and will have to wait to get fixed. I disconnected the EGR valve and he is on his way back to D.C. So the dealer stuck me for $120.00 as I didn't get a chance to get back over there either. They will be getting a nice letter from me today. Just a note on manuals. I also have the 3 set GM manuals on my Blazer. They are full of all types of great info if you can understand it all. I am by no means an electronics type of person. But give me something mechanical to fix or build and I will breeze through it.

 

[JimR]

Re: I need a smart GM mechanic\'s help

Here is a letter that I just sent to the Chevy dealer
To whom it may concern,

On Monday I visited your dealership for diagnostic work for a poor running condition on my 2000 Blazer. You charged me $120.00 for diagnostic work to tell me that I had a plugged Catalytic Converter. This was fine as I know time is money. Yesterday I had this converter changed. The converter is in fact not plugged up at all. There are no plugged screens and it is completely free of any obstructions or burnt out material. The problem with the vehicle is in the EGR system keeping the EGR valve in an open position. I am truly upset that a supposedly trained mechanic couldn't find this out by test driving the vehicle to see that it was misfiring on hills as I told you when I dropped the truck off. You got me for $120.00. But the bad publicity I spread about your dealership will cost you much more than that. I'm just glad that I didn't fall for the $1000.00 new catalytic converter that your service department quoted me. How would you have gone about explaining that charge to me when the truck would have run the same afterwards as it did when I brought it in. A simple unplugging of the EGR valve has made this truck run like new again. Shame on you folks for failing such a simple test. I was going to bring the truck back yesterday afternoon to have you test the EGR system. My wife said no friggin way. Today my son left for college as he couldn't hang around any longer. He will have the truck checked out down there by more qualified people.

A very unhappy first and last time customer.
James Robert

 

[Bird]

Re: I need a smart GM mechanic\'s help

Jim, I guess sending a letter like that may make you feel better, but will it get you a refund? I don't know. You've already told them you won't be back and intend to try to spread the word and give them bad publicity. That doesn't leave much incentive for them to refund your money. Personally, I'd have tried a nicer approach first to see if they wanted to correct their mistake (who among us has not made a mistake?). And then if they refused, I'd have sent the letter to the Better Business Bureau with a copy to the dealership. /forums/images/graemlins/wink.gif Just my personal preference for the way to handle a situation like this; may or may not be any better than your way.

 

[KAB]

Re: I need a smart GM mechanic\'s help

I have to agree with Bird. You originally took the Blazer to a parts store to have the code checked and they said to replace the O2 sensor. Did it fix the problem? No... So you take it to a dealer where their computer said it was a bad converter. You replaced it, it was not clogged and then you found the problem with the EGR valve after you tried replacing a bunch of other parts.

Now, I am not trying to blame you or anybody else for your problems but think about what has been done. The COMPUTER told you what was not wrong the first time. And I would have to assume that the COMPUTER told the mechanic what was not wrong the second time. I have looked at some of GM's trouble shooting guides and at times based on what is seen in a computer (or not in the computer) you can be sent looking for a problem in the wrong area. (same as home computers) As others have mentioned here before, there is a good possibility there is a problem in the wiring system. With all of the rain the east coast has had over the last few weeks, the moisture could be causing a problem at one of the connections. (could still be a bad EGR or VCM) When I worked in a GM parts department MANY years ago, we would harass the mechanics as being parts changers as it was the easiest way to determine if the part was bad or not.

I would call and talk to the service manager, let him know that the converter was replaced, that the old was not plugged, and that by chance you disconnected EGR valve and the problem went away. Ask if he can diagnose the exact cause of this problem, for no additional cost. Then if they find the problem, if the cost is reasonable, let them fix it. Keep in mind that most dealers will roll the diagnostic time into the repair as the make money on the parts in addition to labor. I.e.. You do the repair yourself - 1hr diagnostic = $60.00. If the dealer diagnose and then repair - 1hr diagnostic = $0 but the diagnostic labor get rolled into the repair time (should be the same as the repair for just replacing the part, this is the dealers way to make some money on the part).

You also need to realize that they would have used a factory converter as compared to a universal fit converter. This does add up to big money. Even different universal fit converters can vary in price by hundreds of dollars.

Remember "You can catch more flies with honey than vinagar".

Kurt

 

[CTyler]

Re: I need a smart GM mechanic\'s help

My first thoughts would be about the same as what you wrote. However Birds example is more usefull.

The dealer made a huge mistake. You don't just make a quote like that with out checking to see if its really plugged.

Kinda like the dealer telling my wife She needs a new tranny at $2400 for our 99 blazer. However there is a known problem with the valve body and the PWM solenoid that is easily fixed. Insert expletives here _________ ________.

I understand the dealer or anyone for that matter may not get it right the first time. The OBD can only do so much but to jump to expensive conclusions is NOT acceptable.