Lean Fuel Mix

1998 Mazda B4000 with a "check engine" light on. Since the light is on there should be trouble code(s) stored. Let's take a look. The Mazda is basically the same as a Ford Ranger, so the self-tests for EEC-V Ford systems are available if we use the OEM (original equipment manufacturer) access. What we want initially though is just to see what trouble codes are stored in memory.

Our stored codes are P0171 and P0174. These are fuel system lean codes for each bank of cylinders on the engine. The fuel mixture was too little fuel or too much air to set the codes and the problem affected both the right and left banks (banks 1 and 2). 

Now we are in the OEM diagnostic system but let's exit that and go into OBDII briefly to take a look at some data related to the problem. OBDII is the government mandated onboard diagnostic system and while it does have more limited diagnostic abilities in some aspects, it also has a lot of useful data if you know where to look. Mode 2 would be "freeze-frame" data related to the time the code set.

The freeze frame for P0171 indicates then engine was at idle and cold. The engine has to be warm enough for the fuel control system to go into closed loop or the sensor readings will be ignored. Closed loop puts the computer in control of responses to sensor inputs. So, while 161 F isn't completely cold it is below normal operating temperature for the engine. Fuel trim shows the computer adding fuel. The freeze frame shows us a car that is sitting still, at idle, and warming from a cold start. Lean fuel under those conditions would usually be a vacuum leak. Remember, lean is either not enough fuel or too much air. Engine vacuum is strongest at low rpm and little fuel is needed to run the engine. If the freeze frame indicated lean fuel under a heavy load we would suspect a fuel delivery problem. If we consider that the vacuum leak is under cold idle conditions then it is likely to be a leak under the upper intake or plenum. Very common on these engines. 

The next step is to verify the leak. We want to set the scan data to monitor short term fuel trim. Then we'll spray my good friend Berryman's spray carb cleaner at the base of the upper intake. If the fuel trims respond to the cleaner then we have verified the leak is at the upper intake gasket. 

We need to let the cold engine warm just enough that we can see fuel trim start to be controlled by the computer. That would be the shark fin waves on the left of the scan waveforms. When the carb cleaner is sprayed about half way into the event you can see it is picked up by the engine vacuum leak. The computer sees it as fuel and starts commanding lean. That's our solid test result. A leaking upper intake gasket. 

As always, thanks for reading!

Kenneth Hayes

G&G Auto Repair

Chevy Truck Misfire Quick Check

The 2010 Chevy Silverado had a misfire complaint. There was no misfire on starting to drive into the shop but the MIL (malfunction indicator lamp) was on so some sort of trouble code was stored. I could go drive the truck under different conditions and try to recreate a misfire but if it did miss I still wouldn't know why and the engine would need to cool for awhile before I could test. First thing then was check for stored trouble codes. P0300 is a misfire code and it does mean the engine was running badly at some point but it isn't especially helpful in diagnosing the problem. But suppose there was a misfire on a specific cylinder that just hasn't yet set a code. On the GM I could access stored misfire history and look for a problem.

Cylinder #7 has logged 2,116 misfires. All the others, 0. Looked like I should start with a look at #7 spark plug. Original plugs, 94000 miles. I replaced spark plugs and plug wires.

Thanks!

Kenneth Hayes

G&G Auto Repair

Battery Checks

The complaint on this Chrysler Sebring was that the battery would not stay charged. It was dropped off after-hours and sure enough the battery was dead next morning. A jumpstart was needed and I tested the alternator voltage while the car was running. The alternator was working.

In theory my tester can check a discharged battery. It works best to disconnect the cables from the battery since there could be interference from the car's electrical system. I put the memory saver in to keep settings and system memories alive before disconnecting the battery. The battery tested bad. Now sometimes I can get a *bad* reading testing a battery that is very low that turns into *good* after an overnight trickle charge. I put the charger on the battery for the slow charge and installed a known good battery on the car to use for further testing in the meantime. 

At this point I had tested battery and alternator. I needed to see if there was something on the car draining the battery. With the good battery on the car and with the memory saver removed I tested the battery draw. I wanted to see less than 50mA. Battery draw was good. 

To wrap things up, the battery never came to full charge and would lose what charge it did have very quickly. Bad battery. 

Thanks!

Kenneth Hayes

G&G Auto Repair

Diagnostic Tools: Amazing What You Can Do With A Cellphone cont.

The Lincoln Navigator I had used for an example in the first part of this article had no trouble codes stored, which was fine for my purposes. I just wanted to introduce you to the cellphone possibilities. I also had a Ford Explorer which did have a pending code stored. When a car with OBDII system sees a fault that it is programmed to notice, it stores that as a pending code. Based on programming as well it can move that code to current if it is noticed again. Usually three logged faults and the code will set as current, or hard and the light will come on. I won't go further down that road in this article but did want to briefly explain what a pending code is.
I scanned the Explorer for codes and found P1443. The definition information shows the code is pending and is listed as Evaporative Emission Purge Valve Malfunction. The U-Scan app has a *smart* link as well called code connect. Code Connect will let you in on the most common repair for the problem. In this case, the most common fix for a code P1443 is to replace the EVAP canister purge valve. Now, exactly because I always stress there is no machine to tell you what is wrong with your car, let me stress that we don't know what is wrong with this car. <vbg> We have a pending code for a fault that is often caused by a bad purge valve.

That is information we can use though. If I were going to go further in diagnosis I'd have a place to begin testing. What I did further with the cellphone though is input the vin to the OReilly store where I could get a price and availability of the purge valve. With that I could make an estimate on a likely cost range and get an ok to go further with tests. Yes, very useful. 

Time for a phone call and coincidentally the phone was in my hand. 

Thanks!

Kenneth Hayes

G&G Auto Repair

Diagnostic Tools: Amazing What You Can Do With A Cell Phone

It is actually very amazing to me how far technology has come in my own lifetime. Modern cars are like computers on wheels. The testing equipment used to work on cars has changed at a pace that is truly dizzying. The old Sun Engine Analyzer was a fond memory of days gone by.

found at http://bambam.gmu.edu/sun/

http://bambam.gmu.edu/sun/ has a very interesting collection of old testing equipment. Very much worth a look. 

Time marched on and the tools now look very different from then. Some aren't what you would think of immediately when working on your car but can be helpful to do just that. Let's start with something very common. 

I'm not going to pretend that I use my cellphone a lot when testing cars. I don't. I have other equipment that is arguably better for most things. That doesn't mean the phone can't be useful or even downright impressive in its possible uses for car repair. Let's walk through a scenario. I have installed on my phone a scantool app called Actron U-Scan. There are lots of similar apps out there. I can't comment on those or compare them. U-Scan works for me and I have it on both an iPad and the Samsung phone. 

A wireless bluetooth connector plugs into the diagnostic lead on the car. After linking the connector to the phone I can do a scan of the system. Just how comprehensive a scan or how many modules can be accessed depends on the particular car. I can read or erase codes, access datastreams, graph data, or even share information from the app online. 

Now, I want to jump from the scan app discussion to talk about another app. This particular app is from O'Reilly Auto Parts. There are of course, other apps like this but as with the U-Scan, I only know the one I'm using. 

I can scan the vin or type it in. The scan feature is great when the car allows it. Many cars don't have a scannable vin. 

Once the vin is entered I have access to more information about the vehicle such as sub-model and engine size. When the vehicle is validated the vin and vehicle information is stored in the apps "garage" along with other cars and can be pulled up later or deleted when no longer needed. 

The validated VIN information is also sent to the OReilly online site. If I go to the store's online site the car will already be entered and I just have to navigate to what I want to see that is related. All being done with the phone. Repair information is available onsite. It isn't parts only. 

Amazing stuff! All packaged together in a small handheld device. Since you also have the power of the internet you can google, email and access other data based sites. We'll do a walk through of initial diagnostics using the things I've mentioned in the next part of this series. 

Thanks!

They Die In Threes part 3

In part 1 the Impala was repaired with a new starter. In part 2 the Mazda got new spark plugs and an ignition coil. Part 3 is the Buick that usually needs a jumpstart of the battery. The reason I had to let the car sit for a length of time before testing for battery draw is that there are several module/computers on a car that don't shut down immediately just because you have turned the key off. They do timeout or go to sleep mode after enough time has passed if the car isn't disturbed. I had opened the hood prior to waiting so that I wouldn't have to open a door to pop the hood later and start the cycle over again. If a circuit is disturbed it will wake a system so I use an amp clamp that goes around the battery cable and doesn't require a connector to be removed. The battery ground cable on this car had two leads so the clamp had to be placed on each, one at a time. The rule of thumb is that I want to see less than 50mA of parasitic draw on the battery with a sleeping system. 

Both leads show acceptable draw. I started the car again and it cranked normally. I put a voltmeter on the battery with the engine running and noticed slightly high charge. That is a sign of a low battery voltage. 

I shut the car off with the meter still connected to see what the battery voltage was. It was just under 13 volts *but* when I turned the lights on and key on it took about 4 seconds to drop to under 6 volts and kill the battery. The connections were tight. Bad battery. 

Tools to diagnose:

Thanks!

G&G Auto Repair

They Die In Threes part 2

In part 1 I walked you through the diagnostics and repair of an Impala with a bad starter. I still had the other two cars to work with. The Buick with potential battery drain still needed to sit so I could be sure the computers were timed out. I hadn't been able to get a misfire from the Mazda but a scan for codes showed it had been missing on cylinder #1. The car had 130,000 miles and it wouldn't be a crazy idea to check the spark plugs. An easy way to see if a car needs spark plugs is to pull one out and look at it. Well, sometimes easy. 

It wouldn't be easy to remove the actual #1 cylinder spark plug. It's buried pretty well under the upper intake or plenum. 

You know what though? All I really needed to do at this point was find out if the car needed spark plugs. The front bank ignition coils were not hidden. I said I like to go for easy if the car lets me. 

Pulled one of the spark plugs from the front bank and yes it had worn spark plugs. Original plugs with 130,000 miles. 

The customer gave the go-ahead and I went after even those hard to reach spark plugs. The car got new plugs and a new coil on #1 cylinder. I know #1 was misfiring even if I couldn't re-create the problem. Driving with worn spark plugs causes damage to ignition coils and you really don't want to put that same coil from a misfiring cylinder back in that hole. 

Tools to diagnose:

Tools to repair:

Thanks!

G&G Auto Repair