re: OT Mechanics- car won't fire

Burn it , technically it will fire

From the description I would bet Fuel Pump. Same symptoms on my Blazer and the wife's car when hers died. Also, with the Blazer, the gas gauge issues were resolved with the pump replacement because the little rivet holding the float arm wore out.

On the Grand Prix there is an access panel in the trunk so there is no need to drop the tank to access. It would be a quick job. If you have someone do it, spend the money on an AC Delco pump, the Airtex ones are crap and you will more than likely be replacing within 2 years

I wrote this to someone in the past via email trying to help them. I think it might apply here as well.


Most people (mechanics included) don’t truly understand how simple the internal combustion engine is. There are a few things required for a motor to run.

1. Compression – You need compression in the cylinder of an internal combustion engine for the “power stroke” to occur. The compression happens when the piston moves upward in a cylinder. The other conditions that must happen for compression to occur is that both the intake and exhaust valve must be closed to create a closed area for the piston to compress against.

a. Since these things are either ok or broken and your engine does run, I’ll say your compression is ok.

2. Fuel – This is pretty self explanatory. You need fuel in proper quantities delivered to the cylinder at the stroke before the compression stroke.

3. Air – You need the appropriate amount of air to have efficient combustion in the combustion chamber before the power stroke on an internal combustion motor.

4. Spark – You need the spark plug to deliver a spark sufficient to ignite the fuel air mixture in the combustion chamber.

If you have all four of the things listed above at the same time the motor WILL RUN. It might not run great but it WILL RUN, NO MATTER WHAT.

All four stroke engines are functionally the same. The introduction of complex control systems found on today’s cars only ensure the most efficient delivery of items 2-4.

The reason for highlighting the steps is to simply trouble shooting. At its core, all we are doing is checking for which one of the four are missing. Here is where I would start.

1. Compression – as discussed before, the chances that you have in intermittent compression problem are almost zero. I’ve seen it once in my life and it was on my wife’s vehicle. When you lose compression it’s typically a catastrophic event.

2. Fuel – Your vehicle has an electric fuel pump.

a. Typically these have a check valve in them to ensure that the residual pressure that is in the fuel line from the previous drive remains there for the next start. I’m not sure if the Rav4 has this feature. One test to see if this is an issue is to turn the key into the “ON” position and leave it there for 10 seconds before starting the car. Modern cars typically will run the fuel pump for a few seconds to “prime” the fuel system. This will ensure the fuel line is pressured up.
i. If your fuel pump is failing fuel delivery can be a problem.
ii. Your fuel regulator could be a problem
iii. The electrical relay that controls your fuel pump could be flaking out and not providing power to the fuel pump constantly.
iv. Your fuel injectors may not be opening to allow fuel into the cylinder. There is a light you can hook into the electrical connector for each fuel injector that will light up when the signal is sent to the fuel injector to validate it works. For the record, fuel injectors failing are rare in my experience. It will most likely be electrical.

b. The thing to note about all of these things is they will typically not “throw a code”. The reason is that running out of gas will cause the same symptoms and I’m pretty sure running out of gas doesn’t cause a check engine light.

c. All of these items can be validated by running a pressure test on the fuel system. I’m not sure how Toyota does this but I’m sure it’s not difficult.

3. Air – I’m pretty sure your car has a mechanical “flapper” controlled by the gas pedal.

a. If your air filter is clean and your flapper is working, you have air.

b. You may not have the proper ratio of air to fuel but you should have air and it should run.

c. If your air ratio is wrong or isn’t being properly measured there are a couple of things to note.
i. You have a Vacuum leak

1. Internal combustion engines create a “vacuum” in the intake manifold due to the intake stroke on each cylinder. This pulls the air fuel mixture into the cylinder.

2. If you have an air leak between where your air is measured (Mass air flow sensor) and your cylinder, the wrong air/fuel ratio will enter the cylinder.

3. You can find a vacuum leak by getting a can of “starting fluid” and spraying it around the engine lightly while it’s running.

a. The premise is that the engine will pull the combustible vapor in the leak path and the engine will rev up.

4. I found a leak on my wife’s vehicle when I did some work. It presented itself early on as a loss in MPG. The engine control system was sufficient to compensate for it but my mileage suffered. I would take note if your mileage has gone down recently.

4. Spark – This is the interesting one. There are many, many things that control the spark delivery on your car. To understand how the system works is important. At its base, battery voltage is “amplified” by a coil and “stored” until it’s needed. At the appropriate time, something tells the coil to discharge and the electrical energy is sent down the spark plug wire to the spark plug. There is a “short” that occurs at the end of the spark plug creating the spark. This causes us to break our spark up into two separate systems.

a. Power- This is where the energy that is applied to create combustion comes from. There are typically a few components involved.
i. Coil- This is where the power is “amplified” before delivery to the spark plug. These are pretty easy to check and a simple electrical test with a meter. Check manufacturer spec’s on what the resistance readings should be. If it doesn’t fall within tolerance it should be changed even if it’s REALLY close. (I learned this the hard way).
ii. Trigger system – This is what tells the coil to “discharge” and send spark to the plug. This is where it gets “fun”. There are a multitude of things that can command the engine to stop firing but… we are going to dissect this very simply.

1. Ignition module – This is the interface between your ECM (electronic control module) and your coil. It basically takes the low voltage signal from the ECM and does something with it to discharge the coil.

a. These are easy to check and can be done with a meter.

2. ECM – This commands the Ignition module to fire the spark plugs.

a. There are a LOT of things that can effect this but knowing which of these is or isn’t working is important.

b. We need to see if the ECM is sending the signal to the ignition module when required.
i. If it’s not, that’s another issue.
1. Some other item is commanding the ECM not to fire.
2. The ECM is failing.
3. The wiring harness is damaged.
4. The ECM is not receiving sufficient power
5. The ECM doesn’t have a sufficient ground.