2005 Colorado Too Lean, continued

At this point the truck is confirmed to be running too lean, but why is it too lean? This could be a fuel quality issue, fuel pressure problem, injector problem or it could be a base calculation error. The more that can be ruled out with scan data, the less physical testing that needs to be done to prove what is wrong.  Some of the things to think about are what information the PCM uses to make its base fuel calculation. GM uses a mass airflow sensor (MAF), and the software takes that MAF value and calculates the engine load and from there what the injector pulse width should be under those conditions to provide the engine with the right amount of fuel.  While on a road test the accuracy of the MAF can be checked by watching that engine load calculation in scan data. During a wide open throttle acceleration a snapshot of the engine data can be captured and then later played back so that the engine load pid can be examined to see if the MAF sensor reported.

During the road test it was easy to get the MAF to report 100% engine load.  So the PCM should have been calculating the correct base pulse width and turning the injectors on long enough for the engine to get the right amount of fuel. However it was still very lean under all phases of operation and the fuel trims were adding 40-45% to the injector pulse width. One note-able observation was that during a hard acceleration where the PCM commands an open loop enrichment to provide full power, all four O2 sensors reported over .88 volts, and then on a closed throttle deceleration they all fell to 0volts showing good amplitude and reaction. At this point it’s back to the shop for the last phase of testing.

Once back in the shop the fuel pressure was confirmed to be at 63 psi, with enough fuel pressure and fuel volume that mean the only two things left that could be causing the problem were fuel composition/quality or restricted injectors. With the vehicle otherwise operating reasonably well there was an option on how to proceed and its one that the customer chose to try. Instead of doing specific fuel quality testing and manually cleaning the injectors, he was to go fill up at a Top Tier fuel station, and add a very specific fuel injector cleaner, Chevron Techron to the tank.  His travel plans included one immediate trip of about 250 miles to start the injector cleaning process and run all of the old fuel out of the tank. Then we would check the fuel trims and see if anything changed after he refilled the tank.

To be continued…

Fuel trim Issue 2005 Chevrolet Colorado

A few years ago a fellow showed up with a 2005 Chevrolet Colorado with a 4.2l 6cyl. It had a misfire at idle that was proven to be valve seat failure which was common for those engines. We didn’t get to do the repair because of a special policy set up by the manufacturer.

Just this past week the customer came back to us after numerous attempts at other shops to have a check engine light issue repaired. The vehicle couldn’t even have its emissions test run because of two incomplete monitors, the catalyst and the evaporative emissions systems.

When dealing with one of these the first step is to retrieve and write down any codes, check and capture freeze frame and failure record data and then get a good road test in so that you have a good baseline on how the emissions system on the car is functioning.

There was a P0171 set in the computer’s memory, that’s a lean air/fuel ratio code. Checking the freeze frame the code set at 25% engine load and 33 mph, that’s a light throttle condition. Now the question that has to be asked yet is whether this is the only time that the engine is too lean or not. The answer to that is easy, start the engine and get the truck into closed loop. Check the fuel trims at idle, no load and what I saw was the long term trim at +25%, and the short term trim +20%, that’s a total correction of 45% which is a very lean condition. The next step is to try and determine if this is a vacuum leak or some other fuel issue. To do that the engine speed is increased to 2500 rpm while again monitoring the fuel trims. They were still +25% long term and +20% short term just like the no load idle. Generally if the problem is a vacuum leak there will be a smaller correction at the higher speed because there is less time for the leak to impact the air/fuel ratio. The next step is to put the car into gear against the brakes and speed the engine up to around 1500rpm. Now there is almost no manifold vacuum, and a vacuum leak would be nullified if that was the cause of the problem.  The trims were still a total correction in the 40% range.

This is information that is gathered before the car ever moved from the spot the customer parked it at. Think about what the next step should be, and what the possible causes are. I’ll post the next part of this vehicle in a few days.

Just good people who do a difficult job

A couple years ago NBC news, Jeff Rossen, did a "sting" on auto repair shops using a defective AC relay. Like most of those attempts they found some things that really are bad about the repair trade. The caught some dishonest people and most techs want nothing more than to have people like that out of our trade. At the same time they also found things that are actually bad that they praised!. In the end they really only succeeded in exposing some people who were giving all shops and techs a bad name, but did nothing about the underlying causes for the behavior.

I've made it a point to be a thorn in the side of one of the groups that participated in that sting. They are portrayed as experts and sat in judgment of shops and techs and routinely were giving advice to consumers that was flat out wrong. I always made it clear why I was there, but the individuals who were involved in the sting refused to subject themselves directly to my scrutiny. That was a wise move on their part, they really didn't have anything to gain,  and besides they didn't have the expertise at auto repair that they claimed and I would have made that very evident.

Well this week Jeff Rossen came out with this "sting". It speaks for itself and while not perfect its good enough and for my part I'll steal a line from Harry Potter. Mischief Managed. Maybe the pressure that I brought had something to do with this, maybe it didn't. But it's about time the public gets to see real techs doing what they do everyday, and that's their best to try and take care of their customers.

http://www.today.com/news/could-little-dashboard-light-cost-you-big-bucks-2D11603387

I could ony advise the techs to find new jobs as fast as they could.

Another technician wrote a post about a dealership who has restructured their service department so that they have some techs who only do diagnostics, and then they pass the cars onto other techs to do the actual repair. The real kicker is that they take two productive hours off of the regular techs each day to make a pool from which to pay the diagnostic techs. I can only wonder how people who know so little about being a technician get into a management position over them where they get to make these kinds of decisions.

 

I could see myself as potentially one of the diagnostic guys. What I can't see is handing the work off to someone else once the diagnostics are completed. Fixing the car means also doing the actual repair  because that serves to reinforce the intuitive side of a technicians knowledge and experience. As one of the other posters noted anytime the process doesn't work and a car isn't repaired, who do you point the finger at? IMO, the moment you have to start pointing fingers you have all the proof that you needed to prove that this wasn't a good idea to start with.

 

Getting good at diagnostics requires just plain getting good at fixing cars, plus a whole lot of hard work on top of that studying and developing as Jim Garrido says a good game plan. I think most of the top techs will agree with me that there were a lot of mistakes on the way to figuring out their game plans, and most of the lessons taught by those mistakes were (and occasionally still are) learned the hard way. One of the toughest hurdles was to learn to take a patient disciplined approach, especially when the store only wants to pay pennies no matter how much time needed to be spent doing diagnostics. I have 1999 Jaguar XK8 in the shop right now that makes for a good analog.

 

A week ago a shop sent it to me for a P1646 which his information showed to be fuel pump #2 relay control circuit issue. Except that the #2 pump is only used on the super charged cars, so right away he had no idea what was going on with this car. It took some researching and it turned out that P1646 is for the heater circuit upstream sensor bank A. But instead of having me go through the steps to prove what the failure was and complete the repair the shop stopped the diagnostics and took it back to their place to just throw a sensor in it. In the process of doing that they bought a "very inexpensive one" compared to the O.E. that I would have recommended and to install it they had to splice the connector from the original sensor. Two key starts later, the light was back on and the code had reset, so now they wanted it tested completely.

 

If you are able to look at that paragraph and see quite a few miss-steps, from not fully diagnosing the problem at any time, to them having inadequate service information, and then using questionable parts and repair habits you see how a lot of shops run. By the numbers, however 95% of the time they were going to get the final outcome correct by just slamming that sensor if they had only used a quality part so one can argue there is a potential reward for that approach. However instead of fixing the car, they added yet another variable to the problem and that has both of us further away from fixing the car than they were a week ago. At least they broke tradition at this point and are going to let me prove what is going on before they just slam another O2 sensor even if it is the correct part this time.

 

The real problem isn't whether what that dealer is trying to do is legal or not, it's how many things will go wrong with it because management hasn't thought it out completely.

The above scenario where some techs are doing the diagnostics and while others are replacing the parts are going to create a lot of Jaguars, and when they slam the parts and get it right they will turn around and feel that the lower level tech was all they needed. While if they still rush it at all they will defeat the whole idea of having the diagnostic techs in the first place and that's when the finger pointing will start. One of the worst parts of this is they have just added a glass ceiling to the career path for the next generation of techs who should be learning to be their diagnostic techs of the future, and they are taking two hours off of them each day  to pay for all of this. To me that shows that they don't care about technician retention nor does the management understand the long term technician career path.

Getting your car ready for winter

Times have changed and so have the cars here are a few tips.

Rotating your tires is still a routine exercise but today your car may require the TPMS (Tire Pressure Monitoring System) to be retrained after you rotate the tires so that the dash reports the correct pressures and tire locations. Putting the system into training mode can be as easy as one GM system where having the key on and holding the lock and unlock buttons on your key fob until the horn sounds two times. Then you can first go to the left front tire and let out some air from the tire and the horn will beep one time. The horn beeps when the system receives the tire pressure sensors signal which goes into a fast update when the tire pressure changes rapidly. Continue the retraining by going around the car to the right front and repeat the step of letting some air out, then onto the right rear tire and finally the left rear tire. When the last tire is trained the horn will beep twice again instead of just once.  If you only get one beep at each wheel you may have to access the spare tire as well. The last step is to then reset all of your tires to the proper specification which will be on a label on the driver’s door or its frame. This was just one example, there are a lot of different systems out there so consult service information or your local shop for your model.

Time to change your oil?

There was a time that the only thing you needed to know was the SAE grade and to look for the API and ILSAC ratings. Today even the simple oil change is much more complicated. Specifications like GM’s dexos1, Chrysler’s MS6395R, Ford’s WSS-M2C930-A all greatly exceed the current API SN and ILSAC GF5 ratings. The engine oil life monitor systems on today’s cars countdown start-ups, mileage driven, temperature conditions and will alert the driver once it’s time to have the oil and filter changed. While conventional oils may last the 6000 miles that Honda and other Asian manufacturers require, they often do not last long enough for Ford and GM vehicles which can call for serices to be done in the 7000 to 10,000 mile range while a manufacturer like BMW may reach 15000 miles.

Is it time to replace your battery?

For many people replacing a battery when it gets to be five years old is simply about buying the peace of mind that they know the car will start once the bad weather really hits. For others they will make that battery to go until they know that it needs to be replaced. Either way there is more to it than just dropping in a new one. One step is to attach a memory minder so that the car doesn’t get completely depowered while the battery is replaced. That’s pretty convenient for not needing to reset your clock and the radio stations but it also keeps the other memories on important computer systems from being cleared which can have some unpleasant surprises. Another important issue is today the charging systems are computer controlled and it has been adjusting to that older battery and that will cause it to charge the new one incorrectly if that isn’t reset. Many techs associate that with manufacturers like BMW, when in fact just about every manufacturer has this function. Once again consult service information for specific details about your car.

Engine Coolant, Antifreeze

Beware of claims of universal antifreeze, there is no one size fits all specification. Some manufacturers require silicates, while others ban them. The same goes for phosphates, and borates which are all good for some things that may be used in a car’s cooling system and can be bad for others. When you go to the parts store to buy new antifreeze consider buying it pre-mixed where you don’t add water. That saves you an important step that most don’t realize. Antifreeze isn’t designed to be used with tap water, if you buy concentrate you are supposed to mix it with distilled water.

Did your doors freeze and get stuck closed last year?

A little silicone spray on the rubber door seals will displace the moisture that can freeze and make it difficult to open the door in the morning.

Do you need to use dry gas or injector cleaner?

Gasoline today is up to 10% ethanol which is an alcohol. “Dry gas” is normally isopropyl alcohol, and a common property of each is they like to be in solution with water more than they do gasoline. Dry gas never took water out of fuel, it simply helps prevent any water in the system from freezing, so no,  you really shouldn’t need to use a dry gas additive anymore  but injector cleaner is different. Using an extra injector cleaner additive can help keep your car running better and a good rule of thumb is use it once a year or every 25,000 miles. Manufactures like GM recommend Chevron Techron especially if you normally don’t purchase a Top Tier fuel. That’s a subject you should Google, Top Tier Fuel, there is a difference in gasolines that you can run in your car.  

 

Not Ready For Testing

Not Ready For Testing.

This is a common problem that we deal with a couple times each week ,  usually the story goes something like this.

The car was due for inspection and the check engine light was on so it failed the emissions test. During the course of the repairs the codes get cleared and then the owner is told that they have to drive the vehicle for a while to try and get the car ready for its emissions test but it keeps coming up not ready. 

The OBDII emissions test is really carried out by the car every time that it is driven, all the states emission test does is collect the cars data as it reports if it passes or fails. When someone clears the codes they also clear all of the test results that make up the monitors that the state needs to see completed in order to know if the car is operating correctly or not. If all of the tests that make up a given monitor didn’t get to complete, then that monitor won’t be set to ready. When we have to deal with one of these situations, understanding what it takes to get given tests to run is very important because tests can be stopped from running because of the car’s operating environment failing to meet certain minimum criteria. One example of that could be if the ambient temperature was too low or too high or if the engine coolant temperature did not stay within the programming limits. Both of those would be considered blocking conditions where the tests are prevented from running because the results would be too unpredictable. There are other times where the vehicle might not have been driven long enough to ensure full system operating temperatures. Some of those aren’t even directly measured but are inferred by operating conditions such as the catalytic convertor temperature. The engineers use modeling to try and predict how hot the catalyst would be based on the way the vehicle was driven, then with a catalyst at that temperature, they measure the oxygen storage capability of the catalyst and write the testing tables for the vehicle’s computer to run.

Once we have confirmed that no blocking conditions are occurring, we then have to make sure that each test enable criteria is met. This is easy to do in some cases with a scripted drive cycle that most manufacturers publish, or it can be done with a scan tool as in Chrysler’s case where the scan tool displays the parameter limits and the vehicle just has to be driven within them for a period of time.

If a test fails and it’s a two trip test, you will find a trouble code but it is set in global mode seven and those are known as pending codes.  They have to fail twice in a row to turn into a confirmed code and cause the check engine light to come on.

2002 Rendevous won't shift

This vehicle just had a used transmission installed and it wont shift correctly. When in drive it starts out in third gear, and once up to about 30mph it shifts into second. Then at forty it shifts to third for a few seconds and then goes into limp in mode, which is back to second gear. Reverse operates normally. Typically the limp in or failsafe modes for an electronically controlled transmission will give you one forward gear, which is what ever gear both shift solenoids turned on creates, and you will have reverse, neutral and park. All of these are commanded by the manual valve which is directly linked to the shifter cable. The computer in the car was setting a P1875 for the pressure control solenoid circuit open.

To test for the cause of that code, the technician needs to access the PCM which is inside the air cleaner housing. On connector #2 pins 44 light blue / white, and 45 red / black provide the feed power to the solenoid and the ground return to the PCM. By unplugging the connector at the PCM the resistance of the circuit can be measured and the circuit was open. The next step is to find out where and why the circuit is open and then plan to do the repair. One of the easiest things to do is to remove the connector at the transmission and jumper the two pins together and then ground one at the PCM connector and provide power through a small lamp. In this case something that draws 1.5 to 2 amps such as a brake lamp bulb. The lamp lit up confirming that the wiring was OK, and that means that the problem is inside the transmission or with the connector itself.


The following two pictures are screen shots captured with my bore scope.

The red arrows point out the damaged pins, note the second one on the top, right hand row and the fourth one are pushed out of place, while the third is bent up out of line.

Most of the time when a connector is damaged like this it isn't a big deal to disassemble and repair it. Unfortunately with the way this connector for the transmission harness is assembled, that's going to mean that the transmission will have to come apart to access the other side of the connector.