2011 Express Van Injector Codes After Engine Install
A customer called me in to program a new computer for them on an Express Van that they were having problems with. They had changed spark plugs and bank one injectors. I programmed the PCM and reset the immobilizer. After starting the engine I could tell something was not right. I pulled the codes and found injector circuit codes on all four of the left bank injectors.
From that point I decided to look at the wiring diagram for a common connection point. All of the odd cylinder injectors go through fuse 65 and all the even cylinder injectors go through fuse 79. I told the technician about the fuse and started putting away my gear. Not so fast, the fuse is good. Off comes the doghouse. Check voltage on bank one. 12.5 volts. Hmm, we have voltage here. Each injector has it's own wire to the PCM for the signal. How could all of that bank be effected? I looked for any PCM grounds that could be a problem. This PCM has a common ground.
The customer had told me that he replaced the injectors with aftermarket ones. Could all the injectors be bad? How could the exact same problem exist replacing 4 injectors? I decided to get out my handy Steelman Scope. I like pictures to explain things. I took a scope trace of cylinder 7,5,3,1. They all looked the same. They did not look right. Notice along with the extra pull to ground the inductive kick is lower than the next picture.
There were multiple square waves along with the expected injector pulse. I took a scope trace of cylinder 8 and it was just as expected.
What is going on here? Next test was to check each signal wire for continuity, short to power and short to ground. All the wires were clean. We stripped back the tape and convoluted tubing from the wires. Each wire was separated to make sure there was no crosstalk of the the signal wires. (Short to each other) All the wires were separated successfully. Some were stuck together from the high engine temps but no evidence of shorts.
So the injector circuits were all failing on Bank 1, there is voltage, the drivers are pulling to ground however the driver circuit trace does not look right. Normally, one would lean toward the PCM for a faulty driver. Since this PCM was not the original and the same problem exists, it must be something else. While running I decided to measure the voltage on both banks to see if there was a difference. Bank 2, 14.2 Volts. Bank 1, 12.5 Volts. So somewhere in the power circuit for Bank 1 previous to the 4 wire split, there is a voltage drop. The extra resistance is causing the circuit to misbehave. A jumper wire was supplied to the power side of one of the injectors. Boom! the car quit and would not restart. Nope, not this time. The left bank woke up and the engine started running on all 8 cylinders.
In the scope trace there is still an artifact although not pronounced. Something in the wiring on the power side is cross-talking. Not enough to prevent operation. (Note that the voltage scale is not the same in all the traces.) I left it to the technician to solve from there. He told me that he would look at the fuse box and run a new wire to the 4 wire splice from the fuse box to the injector power leads. The lesson learned here is when things are not making sense, change the approach and retest. We spend too much effort in beating ourselves up finding these issues. Sometimes the problem is caused by a subtle difference in voltage. At the end of the day the problem is found and the vehicle can be delivered.
I read this before work today, Mike, and it reminded me of something I have been thinking about for a while. It is VERY easy to miss a pulsed ground not going to zero or a feed not quite at B+ when we are looking for pattern glitches. It is not this first time I have seen something like that happen. Anyway, your story prompted me to finally reveal my new ScopeMeter to the world. I promised…