Diagnostic Tech: 1992 Ford Tempo (originally posted Oct 11, 2007)

 Thursday, October 11, 2007

Diagnostic Tech: '92 Ford Tempo EECIV

We're going to need to set the Wayback Machine for 1992. Ford was using Electronic Engine Control System IV, or EECIV. By today's standards EECIV lacks sophistication but in its day it certainly performed its tasks very dependably.
On the plate today is a 1992 Ford Tempo w/2.3 engine and automatic transmission. The complaint is an intermittent Service Engine Soon light on and a high idle speed at that time. This system does store trouble codes in memory but should only turn the SES light while a code setting condition is present. In this case it just seemed to me that a test drive to verify the complaint was in order.
Initially the car ran fine. No light came on and even though I was driving in stop and go traffic there were no idle speed problems. I decided to return to the shop and just run the EECIV self-tests. When I pulled into the driveway the SES light came on. The idle speed was fine until I stopped and put the car's shifter into park position. The idle speed went to around 2000 rpm and stayed there for about three seconds before slowing back to normal. I had just verified the complaint. Time for the EECIV checks.
The car's test connector is at the left shock tower, near the battery. Technically there are two connectors. One is a single wire called the self-test input connector.
I'm going to mention that there are alternatives to retrieving codes. You don't have to use a scan tool. That being said, you will find the scan tool method more reliable with less chance of misreading a code number or accidentally clearing memory codes.
It is important to understand EECIV self-tests before using them to find a problem. Ford has the car's computer run specific tests and report back areas that failed the tests. The failures are reported as trouble codes. Running the tests improperly can give you misleading results.
A quick warmup cycle for the engine and I'll get started.
After connecting the scan tool to the test connector and entering the car data I want to start with "Quick Tests" and the Key On Engine Off tests. If a sensor fails the KOEO test then it should be repaired. You'll need a "Pass" or a no fault found condition in the KOEO self-test before any KOER (Key On Engine Running) tests can be reliably done.
The KOEO running test results are called "On Demand" codes. In this case I get a Pass code 111 which means no problems were found. After the On Demand codes are displayed the Keep Alive continuous memory codes will be displayed. The Keep Alive, or continuous codes are codes from the car's computer memory. Codes that have set in the past. This car has a 332 in memory. A 332 indicates insufficient EGR flow. I don't think a problem with the exhaust gas recirculation system it going to be related to the high idle or even the SES on at that time. An EGR not flowing should not cause the idle speed to be higher and since the EGR is not supposed to be flowing at idle anyway I don't think it would turn the light on at that time. I'm going to move on to the KOER tests because that test should be done before getting too involved with Continuous codes. The KOER test will reveal any sensor failures that happen during the test.
The KOER test codes indicate a 332 again. This time I know the EGR failed a test in real time and currently has a problem. Again though, I don't think it is related to the idle speed problem. Two more codes do indicate a problem with idle speed control, a 412 and 411. These codes indicate the car's computer not being able to control the idle speed. These codes do not store to memory so without running KOER tests we would not see them. If you think that was a lot of trouble to find that something is wrong with the idle speed you have a point. What was learned though is that the several sensors that contribute to the computer choosing an appropriate idle speed do pass self-tests. That means I should start by concentrating my efforts in testing the computer's ability to control the idle speed. In other words, I've learned that the inputs to the computer are likely to be fine but there is a problem with the idle control output circuit.
It's a good idea, I think, at this point to check the base idle and minimum air adjustment. Before any throttle adjustments are made I want to be sure I have a clean throttle plate. I'll remove the air intake hose, the MAF and the air cleaner cover as a unit. The throttle plate actually doesn't look too bad. It's pretty clean on the air cleaner side. The air filter looks good and the air cleaner housing was properly fastened.

When I open the throttle fully and look past the plate I can see major carbon buildup. I can even see why the EGR flow is low. The EGR passages are just behind the throttle body and fully plugged with carbon. The best thing to do here is remove the throttle body, remove the EGR valve and do some cleaning.

While we are in the neighborhood, this is a good time to remove the Idle Air Control (or Air Bypass Valve) and clean that passage as well. The engine computer uses this valve to control the amount of air that bypasses the throttle plate. The amount of air allowed controls the engine idle speed.

Once everything is clean and reinstalled it is a good idea to clean the MAF sensor or at least see if it needs cleaning. Two tamper proof screws hold the MAF to the MAF housing. A torx T20H will fit the screw heads. Carefully remove the MAF from the housing. With a magnifying glass and a good light you can look for dirt on the two tiny wires at the bottom of the sensor. If you see dirt, carefully clean it. These days there are spray MAF cleaners on the market. That wasn't always the case so I still use the same Berryman Spray Carb Cleaner that I always did. For stubborn spots I use a Q-tip as well.

This particular MAF looked pretty clean so after reinstalling it I let the engine warm up again. I know that I now have a clean throttle, a clean MAF, a clean IAC and a clean EGR passage but what I don't know is if I've fixed any of the complaints. It's time to run the KOER test again.

After getting the same results with the KOER self-test as before all this work, I decided to see just what was happening at the Idle Air Control as far as the computer control was concerned. The voltage at the IAC signal wire should roughly match the position being commanded by the computer. A command to open the valve 34% would have 3.4 volts. As a load is placed on the engine the command would increase, so a voltmeter could be used to check the command to see if the computer is trying to slow the idle speed during the high idle problem. Another method would be to disconnect the IAC wire connector from the valve and see if the engine slows. You see, the valve is spring loaded to return to minimum air position without a voltage command to the contrary. In fact, it is by disconnecting the IAC and adjusting the throttle position stop screw that minimum idle air is adjusted. All I have to do is wait for the high idle problem to appear. After a few minutes of running time the engine idle speed begins to race. When I disconnect the Idle Air Control the rpms do not change. The IAC valve is bad. I suspect a vacuum leak within the valve is the problem.

After replacing the IAC valve I now have no more racing idle and no more idle control related fault codes. One thing very good about the EECIV testing method is that I can rerun the test after a repair to verify the problem is fixed. The idle problem is fixed! BUT the EGR problem remains. I still have a 332 fault code in the KOER test.

During the KOER self-test the ECM will open the EGR vacuum regulator solenoid very briefly. This allows manifold vacuum to pass through the solenoid to the EGR valve. The vacuum should open the EGR valve. The pressure in the exhaust tube that runs to the EGR valve is measured by the PFE sensor. If the ECM has commanded the EGR solenoid to open yet does not see the PFE sensor voltage indicate a pressure change the ECM will assume the EGR is not working and will set the 332 fault code.

For testing purposes I like to use a length of vacuum hose and bypass the solenoid, feeding the vacuum directly to the EGR valve with the engine running at idle. If the engine nearly stalls then the valve is passing plenty of exhaust flow.

I started to do that here but noticed that the hose that feeds pressure from the EGR exhaust tube to the PFE sensor was broken. With a broken hose the PFE sensor would not be able to monitor the exhaust tube pressure change and would indeed set the 332 code. A replacement hose and another KOER test and this time the repairs were done! A complete system pass. No more light, no more high idle, no more codes!

Kenny@GGAuto.repair

Diagnostic Tech: 2000 Dodge Dakota (original post February 2008)

 Sunday, February 17, 2008

Diagnostic Tech: '00 Dodge Dakota

A 2000 Dodge Dakota SLT, 4.7N engine and automatic transmission came in with a complaint of stalling at idle. It was a few days before I could schedule the job but the truck was left anyway because the owner said he could not drive it with the stalling condition. Shuffling the truck in and out of the shop each day it was easy to see that the truck would stall if the accelerator was released but would remain running if the accelerator was applied slightly. By the time I got around to checking the truck the symptom was gone and the truck would idle without stalling.

Idle control is sometimes a numbers game and even though the truck no longer stalled I could still take a look at some numbers and see what may have caused the problem. There are some important numbers for idle control on this truck. The throttle position sensor voltage is best at 0.65-0.90 volt range and the idle air control counts should be between 10 and 24. These numbers are easy to check with a scan tool. Warm the engine fully and note the readings.

When I checked this truck I found a tps signal at 0.61 and an iac count of 125! The higher the iac count, the harder the idle control is working to maintain the rpm. In this case the iac was being commanded very high just to be able to maintain an idle of 608 rpm.

From the clues, it was likely the throttle bore would need cleaning and some slight throttle adjustment to bring the tps into range. I cleaned the throttle body first and let the engine warm before taking a look at the iac counts again. I want you to see a picture of the throttle before a cleanup. Notice how little carbon buildup it takes to limit minimum airflow and cause an idle problem.

After simply cleaning the throttle bore with some spray carburetor cleaner and a shop rag the iac counts dropped to 38. So now the iac was finding it much easier to maintain 608 rpm. The tps was still slightly low. When I adjust the minimum throttle opening it will raise the tps voltage and the iac counts should drop to compensate because the iac will have to close slightly to drop back to 608 rpm. I ended up with everything right, by the numbers!

Kenneth Hayes

G&G Auto Repair

Diagnostic Tech: 2011 Toyota RAV4

 The complaint here was that several warning lights were on. The "check engine", "traction control" and "4x4" were on steady as I drove it in. 

The customer said the lights all came on at the same time. Any engine performance fault seen by the system would also turn on the other lights so I expected to see an engine performance problem, perhaps a misfire. Warning lights turn on when a computer has seen a problem that warrants attention. A trouble code related to the fault should be stored and you will need that code if you want to know what the computer is trying to have you check. I did find an engine performance related code, actually two. 

 The P0171 means the fuel mixture was too lean, not enough fuel or too much air. P0101 means the measured airflow at the mass air flow sensor doesn't match what the computer expects to see based on other inputs. C1201 is an empathy code. It means the engine control fault has placed these other systems into fail-safe. They will revert from fail-safe once the performance problem is repaired. The problem appeared soon after a service/maintenance job so it seemed a good idea to look around for something related to that before getting more involved, and there it was. A small breather tube had been left disconnected from the air intake hose. 

That open hole allowed air to enter the engine downstream of the air flow sensor. The extra air was setting the lean code and the air flow code. Now you can't just do a fix and be done. Eventually the computer would figure out the problem was fixed and turn the warnings off but that could take quite some time. It would have to see the monitors run and see that the same problem did not occur for several cycles. (On that note, never disconnect your battery to clear codes. Never.) You have to tell the computer the problem is fixed. Clear the stored codes with the scan tool. The computer will still run tests and will still watch for faults but the lights will be off until there is a problem. Many cars now store the codes in a memory called "permanent" codes that can't be cleared until the computer verifies the fix and clears them on its own even though the lights are now out. 

Before clearing codes though, I want to show you that more than codes are stored in the system. The conditions at the time of the failure are stored as a frame of sensor data. Once the codes are cleared the data is gone as well so lets look now before we clear. 

Given the conditions if I didn't know the air flow was incorrect I might suspect a fuel delivery problem. The point though is that there are several ways the computer can store and aid in your diagnostic journey. Use them. 

I cleared the system and all is good. 

Thanks for reading!

Kenny@ggauto.repair