Here is one 2004 Toyota Tacoma 2.4 liter with 145,763 miles on the clock. Vehicle was towed in as a crank no start. On Motormouth radio the hosts were asking me about "Drivers seat diagnostics". I wanted to use this vehicle as an example of what can be done exclusively from the drivers seat in short order. Remember, in my job I need to diagnose accurately and quickly. The first thing I do is crank the engine over and verify it is a no start. I also listen to make sure we have an even cranking speed. It is indeed a no start and cranking speed is nice and even. Time elapsed-2 minutes. Next step is to hook up the scantool to look at some data parameters while cranking.
So here is a screenshot from my Ottotest. I am looking at engine rpm, fuel pump relay activation, injector pulse, and mass air flow sensor grams per second. The screen is 25 seconds worth of cranking data captured. Including scantool boot up we are up to approximately 5 minutes. Lets zoom in and add some cursors.
Ok, now we are rolling. We have 209 rpm, fuel pump relay is being activated, 12ms of injector pulse, and the mass air flow sensor is reporting 4 grams per second. So what does this all tell us. To me the injector pulse and fuel pump relay activation tells me we do not have an anti theft issue causing the no start. Most manufacturers turn off injector pulse and fuel pump operation when in theft prevention mode. The 209 rpm tells me that my crankshaft sensor is working. The 4 grams per second cranking tells me this engine is mechanically sound. If there was an issue with valve timing/compression it would affect our cranking engine vacuum and therefore we would have lower MAF data cranking. Also, remember our cranking speed was even in our very first step. Time elapsed now-7 minutes. Let's move the cursor.
Wow. We went from 12ms to 33ms of injector pulse. This is something I see all the time with Asian import vehicles. If the car doesn't start with the base injector pulse lets double or even triple it. At this point if this vehicle was dumping this much fuel there would be two things happening. Number one I would smell fuel and number two the engine would crank over faster due to washed down cylinders. Cranking speed did not increase either by scantool values or my ears. I also do not smell any fuel. Time elapsed-8 minutes. Keep moving.
I look at a wiring diagram and locater for the fuel pump relay and break out the low amp probe. The next shot gives you an idea where it is.
I told you this was "Drivers seat diagnostics". At this point I am at the 10 minute mark into my diagnosis. Checking actual fuel pressure on a Toyota product is asking yourself to be tortured. Typically, you have to break the pressure line open and piggyback an adaptor and get a reading. Put it back together and pray it doesn't leak. I would rather look at an amp pattern and see if I can decipher something from there.
This is a nice even pattern. However, the amperage is way too low and the fuel pump RPM (revolutions per minute) is 7741rpm which is too high. Most fuel pumps have eight bars or sections. The way that we figure rpm is identify the eight segments and then setup cursors to time one complete revolution of the fuel pump. Which in this case was 7.75ms. We then take this time measurement and divide into 60,000. This gives us our fuel pump speed. Using amperage, pattern, and fuel pump speed we can determine if our issue is fuel pump related. While there are no hard and fast rules for amperage and speed. I use this as a guideline. Most fuel injected pumps draw between 5-7 amps and 5,000-6,000 rpm is the norm. Now, there are exceptions. One that comes to my mind is GM vortec fuel pumps that draw 9 amps all day long on a healthy pump. Back to our Toyota. Low amperage and higher than normal rpm tells me we are out of gas in the tank or the pump is freespinning. I wrap on the tank and there is fuel in there. So that leaves the pump is freespinning. To verify all of this I pop the hood and give a spritz of carburetor spray into the air duct and the vehicle starts and runs until the carburetor spray is gone. The tank has to come down. Time elapsed-12 minutes.
There it is fresh out of the tank. We have a fuel pump that become dislodged from the rubber hose that connects it to the vehicle's fuel system. So we had a fuel pump pumping fuel back into the tank instead of to the fuel system.
Here is another shot. The squeeze clamp that holds the fuel pump output tube to the rubber hose seemed to be in fine shape. I have seen this once before on a Toyota pickup truck that was used for heavy off roading and I theorized the jostling around caused it. But, this is a street vehicle. With well over 100k miles on it a new pump was installed with all new attaching parts.
New pump and the vehicle starts and runs.That is more like it. The amperage is back to normal at just under 8 amps. But, wait the rpm is still high. If you figure the rpm it is at 8915rpm and the pattern is not exactly textbook. This is just a cheap aftermarket pump. It is an issue that is rampant in our business unfortunately. I feel a rant coming on. However, the focus of this case study was to show how "Drivers seat diagnostics" can work. So, in just over 12 minutes without getting our hands "dirty" this vehicle was diagnosed. Now, remember there are a couple of items you need to have for this to work. One is faith in your scantool and the other is a working understanding of the make and model you are working on.
