Burnt twice .....

Same vehicle, same problem, same day.  Ouch!

A 1989 Chevrolet Van with a 4.3L engine came towed in for a crank, no start condition.  The engine cover and air filter was already removed by the customer.  The customer mentioned that there was no fuel spraying out of the injector.  Sure enough, the customer was correct.  There was no fuel spraying out of the injector.  I decided to look at the fuel pump current first.  Why?   Fuel pumps are the most common failures and there is no test port for checking the fuel pressure.

My suspicions were correct.........                                      After replacing the pump

Bad pump

After replacing the fuel pump the injectors still didn't spray any fuel.   Further checking revealed a bad fuel injector fuse. I'm thinking "no problem" the customer tried to do his own diagnosis  and blew the injector fuse.   I put another fuse in and the engine starts up but it barely runs.  Now the left injector isn't spraying any fuel.  I hooked Vantage up to the control side of the injector and it appears that the ECM isn't pulsing the injector.

Left injector                                                                  Right injector

I included the primary ignition so a relationship could be established.   The injector signal test point was taken at the ECM.

I'm thinking that the customer must have somehow shorted the injector driver in the ECM.  I guess some of you have already guessed that replacing the ECM didn't repair the problem of the injector not spraying  fuel.  The problem ended up being a shorted injector.  The bad injector measured 0 ohms and the good injector measured 1.3 ohms.  Confused?  Read on.

Both of the images were captured on the injector that wasn't spraying any fuel.  If you look at the left image you would think that this couldn't be possible.   There is current draw but no indication of the voltage being pulled to ground.   If you look closely (right image) you can see the ECM does try to pull the voltage low but terminates as soon as current limit has been achieved.

Here is a comparison of a good injector voltage and current during the peak period.  Notice the difference in the duration of the peak period between the good and shorted injector.

I think there may be a few lessons to learn here.... I will think about it when the pain goes away.

If you are interested in posting an article or case study on this site, please feel free to contact Jim Wilson.