The purpose of this Case Study is to show you how to test the ignition system in a NO START Condition. You should be able to see that:
- These tests do not require expensive tools or testing equipment.
- That they are very easy to perform.
- An actual application of the theory learned in the article: How Does An Ignition Coil Work?
You can find this tutorial in Spanish here: Estudio De Caso: Volvo 740 Arranca Pero No Prende (at: autotecnico-online.com).
How It All Started
Alright, lets begin the tale...
Towards closing time, the Volvo 740 GLE station wagon rolled off of the tow truck. As Oscar (the owner of the Auto Repair Shop where I work at) walked by my service area, he mentioned that this job was for me. And that all it needed was a tune-up and the customer had already bought her own parts. They were in the vehicle.
A Tune Up solving a NO START? That sounded kinda' strange to me. It's very rare for a tune-up to solve a no start condition. But it has happened before.
Ok, the following morning I got the key and went out to take a look at it. I got in and cranked it up. It started! I was surprised. Well, as I was backing out of the parking space, it stalled. And from that point forward till it was in my service area, it would not re-start.
Ok, I walked away to go and get the rest of the guys to help me to push it into my service area. I decided to have Oscar call the customer and approve a Diagnostic. Which the customer did. The testing would be starting soon.
Once in the bay, it started one more time, as a tease I guess. This worried me because as long as it starts, there's nothing to check. Intermittent problems are always a tremendous pain in the neck to diagnose. For the most part the vehicle HAS TO BE DOING the problem to find its solution.
This particular Volvo does not have self-diagnostics. No way to hook up a scan tool and check for codes.
This reminded me of how it used to be back in the late eighties when most vehicles still hadn't jumped on the bandwagon of self diagnostics, especially all of the European vehicles (so much for European Engineering). You would have to check system by system to find the problem without any help from a scan tool or diagnostic codes.
Anyway, this vehicle brought back memories of the way things used to be. The basic flow of testing that I took on this Volvo 740 stationwagon was the following:
- Check for Spark.
- Check for Fuel. By this I mean Fuel Pump Pressure.
- Check that the Fuel Injector Computer is pulsing the fuel injectors.
From these basic tests, I or you should be able to get a starting point.
The very first thing I did was to check for spark (it's always the easiest thing to do). Also, I didn't think it was a Fuel Pressure issue since I could already smell gas coming out of the tail pipe from all of the previous attempts to get the Volvo started.
Testing For Spark At The Spark Plug
I removed one of the spark plug wires (ignition cable) from its spark plug and attached my HEI Spark Tester. I had my buddy crank the Volvo over. No Spark was the result.
Just to make sure, I removed one more spark plug wire and attached the HEI Spark Tester and redid the test. No Spark.
Whenever I get NO SPARK at the spark plug wire I know then that I MUST check that the distributor cap is indeed receiving the SPARK (if there's any).
It could be that the spark is indeed being created and delivered to the Distributor Cap and Rotor but if they're bad, the Spark won't leave to the Spark Plugs. To check for this, I'll hook the Spark Tester to the ignition cable that feeds the Cap the Spark.