For this month's edition of Tech to Tech, I'll share another “unusual” repair adventure, this one involving a 1985 Nissan Stanza that wouldn't start. As I write this, my second year of Advanced Auto students, all seniors in high school, have finished the Electrical/ Electronics, Engine Performance curriculum. When a vehicle rolls into our shop on the hook, as this Stanza did, I force myself to not lift the hood or begin a diagnosis. Instead, I gather a group of these young “techs-in-training,” give them the vehicle history just as a customer would, and let them formulate their own repair process. Would you have approached this repair in the same manner?

Figure 1 is what faced Dan and his group: the gaping mouth of a no-start Nissan. Dan cranked the car to verify what the customer had experienced the previous day; all crank, but no fire. Figure 2 shows the noid light and spark tester the team attached to check fuel and spark. Both were present, so a fuel pressure gauge was brought into play. The team was disappointed (as we all would be) to find there was no quick fuel tap on the fuel rail. So we grabbed the two tackle boxes full of adapters and spliced into the fuel line on the inlet side of the fuel filter, on the lower side of the firewall. Cranking the car showed 0 psi; Dan and his team now had a tangible lead.

The next question facing the team: Is there a no-start chart, similar to the General Motors “A-3 No-Start” chart? Our electronic information system had individual component tests listed below the section on “watch the LEDs blink to see if there's a code in memory,” but no flow chart. “So what,” I said. “Create your own based on the components involved.” I had the team pull a wiring schematic for the EFI control system, including the fuel pump, relay and any other pertinent circuit information. Figure 3 shows the comprehensive diagram for this injection system. It doesn't get any more basic than this; a perfect system for the team to diagnose without getting overwhelmed with a cluttered wiring diagram.

The team wondered where the fuel pump was (thinking it was probably in the tank) and, after a visual search, found it on the frame rail in front of the tank. Dan grabbed a digital volt/ohm meter (DVOM), hooked it to a clean ground, and checked for B+ at the wire for the pump. It was fine. This is one step where I made sure the team didn't lose its way, so I asked, “How's your ground back there?” Testing the B+ and ground right at the fuel pump connector revealed no voltage, indicating that we had no ground reaching the pump (Figure 4).

With wiring schematic in hand, the team searched out the fuel pump relay, finding it only after looking in the component locator and verifying the wire colors. Figure 5 shows the condition of the relay, but, could a defective relay cause the B+ to be lost at the tank? A critical look at the power circuit for the pump revealed that the ignition switch supplies constant B+ when in the run position. So, if we're getting power back at the pump with the key on, regardless of how rusty the relay looks, it has to be “OK.”

The team began the search for the missing ground by looking up the strategy for the fuel pump operation. The information said: “The EFI unit operates the electric fuel pump. When the ignition switch is turned to the 'on' or 'start' position, the fuel pump operates. It will operate for 16.7 seconds before engine is cranked before shutting off.”

The first thing I saw was: 16.7 seconds. Why not 17? Oh well, at least we knew that with the key “on” for a short period of time, there should be ground activation of the fuel pump by the EFI control unit.

Next, the team pulled out the rear seat in search of a broken ground wire. They figured that it might have rubbed under the front or rear seats, so they began tracing the ground, and I just let them go on their search. Figure 6 is a connector that was under the right front seat. Thinking it was a perfect place to lose a signal, the team probed for a fuel pump ground with the key “on” and found none.

After establishing that the wires now wrapped up over the top of the dash, I urged the team to go directly to the EFI control unit to look for a signal. Figure 7 is what they found after removing the left kick-panel and dropping the EFI unit down. Now we had a new question: Why does this car have a used EFI control unit? Is this a recurring problem? Turns out that the customer bought this car two weeks earlier, so they probably inherited the issue.

Once the team had the unit in-hand, they searched the schematic for the exact wire that grounds the fuel pump; a white wire that terminates at terminal “O.”

A check of this wire revealed the signal wasn't even leaving the control unit! Now what? I told Dan that since our testing indicated that the EFI controller could be our culprit, we first had to determine if it was getting all of its B+, ground and critical sensor inputs in order to send a "give me fuel pressure" signal to the fuel pump. I also pointed out that a short-circuited component, such as a relay, could have killed a circuit in the EFI unit. The team went to work checking for all of the critical signals and possible short-circuits in output devices, but found all was in order.

“Can we open it up?” asked Dan, as he stared at the EFI controller on the bench. I was so proud. I love it when students have that extra curiosity that compels them to look for the “why” in the broken car equation. Figure 8 shows Dan opening the computer to discover a clean, shiny circuit board. He traced terminal “O” down to the printed circuit, where he saw it go through the board. Everything looked in order.

As a last look, he pulled four more screws that hold the printed circuit to its case, and there it was: an ugly, corroded solder joint, right at the lead coming from terminal “O”! The team was excited. Dan posed an excellent question: “What now?”

I asked them what could have caused the terminal in Figure 9 to lose contact with the printed circuit board. Here's the list we came up with:

• The used EFI control unit came that way, damaged by its old car.
• The used EFI control unit was installed to fix another problem, and this car broke the fuel pump circuit.
• This car damaged the same circuit in both the old, and new, EFI control units.

The next order of business was to find out if this car melted the circuit in the control unit. We installed the controller back into the car, hooked an ammeter in series with the fuel pump ground wire, completed the ground, then activated the key. Figure 10 shows the current draw from the Stanza after running for a long period of time. The amperage never exceeded three amps; not enough, in my opinion, to melt that connection in the control unit.

Faced with the prospect of paying several hundred dollars for a new controller, we decided to try soldering the terminal in the control unit. Once soldered, the current draw remained the same, and the connection has not failed in the weeks since. So, what do you think caused the connection to fail? Did we perform a reasonable repair after giving the customer a choice? Would you have not even offered this option to your customer and installed a new EFI control unit instead?

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