Undercar: The Science Behind Traction And Braking
Let’s look at an intermittent poor-run, hard-start complaint on a 2012 Hyundai Sonata. This car came into the shop by way of a body shop with which we work closely. One thing you learn quickly is that body shop clients can be harder to please than on the mechanical side. It might be that they don’t remember what the car did or felt like before the accident, or they’re thinking the insurance company is covering it, so they should get as much out of the repair as they can. And, of course, many times there is a mechanical issue that comes up as a result of the accident, and we are usually more experienced and better equipped to diagnose and perform the repair.
Back to the Sonata at hand. We received a call from the body shop that this car had been delivered back to the client a couple of weeks before. All was going well for a couple of days, when they received a call that the car was hard starting and running poorly. With it back in their shop, as you would expect, it ran and started well with the only sign of a problem being a check engine light with a P0087 code indicating the Fuel Rail/System Pressure was low. They cleared the code, drove it for a couple of days without a problem, and gave it back to the customer. Of course, it acted up again for the customer, and they were absolutely certain that the problem was the result of the accident. Needless to say, our friends were feeling the pressure.
Gasoline Direct Injection System
When they started looking at data, there was some confusion about what they were seeing, so they decided to ask us for advice. Before we go much further, we should talk about the Gasoline Direct Injection (GDI) system with which this car is equipped. Hyundai has really embraced GDI for all the right reasons — with increased performance, mileage and lower emissions, why wouldn’t they? You already know that direct injection moves the injector from the intake tract to the cylinder. With better injector location, atomization and electronic control, the cylinder runs cooler, allowing a more aggressive compression ratio and ignition timing strategy. This results in more performance without an increase in displacement.
With the injectors and coils being paired (cyls 1 & 4 and 2 & 3), the lower emissions are the result of getting the cat up to operating temperature sooner with a burn event during valve overlap.
With the GDI setup, the fuel pressure has to be increased so the fuel can overcome the cylinder pressure. In the case of our Hyundai, the fuel pressure was 580 PSI at idle, climbing to 1,400 PSI at 1,500 RPM, and peaking at 1,850 PSI. To make this kind of pressure, Hyundai uses a low-pressure electric pump in the tank to feed the high-pressure mechanical pump, driven by a camshaft lobe with four high points. The pressure is controlled by rpm and the pressure regulator mounted on the high-pressure pump. The powertrain control module (PCM) sends a square signal to both wires on the regulator to ensure the pressure is correct for the engine’s demands.
One important thing to keep in mind is that when there is a code set that puts the car in limp mode, it will stay in limp until the code is cleared.
That means the PCM will stop controlling the high-pressure pump and the car will run on the low 62 PSI pressure pump to (hopefully) make it back for service, although sometimes these have to be towed in.
We still hadn’t seen the Sonata, although we suspected a problem with the high-pressure pump based on the symptoms of the recurring code and the information we picked up about the problem from trusted technician websites. The first thing we discussed was the car’s mileage. At 120,000 miles, it was off the liberal Hyundai powertrain warranty. There was also the concern about how the shop would convince the insurance company that the fuel pump failure was related to a rear-end collision; thankfully, that was their problem. All we had to worry about was helping to fix the car.
A big part of the problem was they weren’t able to look at the data when the vehicle was acting up; it was in limp mode when they got it and would run well after the code was cleared.
Value of Scan Data
We never got an opportunity to look at the data on the body shop’s car. However, I did get a photo of scan data from a GDI-equipped Veloster that shared the same data. Looking at the fuel-related parameters in display (PID) (see image below), you can see the top one indicates that the high-pressure pump is under the control of the PCM. The second parameter shows the actual pressure in Megapascals (MPa). The third indicates the pressure sensor voltage. This voltage will increase along with the pressure, then you have the set point or commanded pressure.
The next two PIDs indicate the activity of the pressure regulator showing the dwell time in degrees and that the relief is closed (this will change with the pressure).
The first source of confusion was quickly cleared up with a conversion table. 1MPa = 10 bar: We all should know that 1 bar represents barometric pressure at 14.5, so with a little arithmetic, we come up with 145 PSI times four for 580 PSI at idle.
The voltage reading provides a more detailed look if we should be facing a diagnostic challenge. We came up empty looking for specs to indicate what the timing should be on the regulator. I suspect it’s dependent on how much dwell time is needed to maintain the commanded pressure.
That’s the value of having an enhanced scanner. We can look at this data and see what the PCM is seeing and how it’s controlling the fuel pressure. In this case, it’s doing what was expected.
The body shop got approval for the high-pressure pump on the Sonata and went to work to replace it. It was an easy job as far as accessibility and level of skill required, but we did go over a couple of things before they dove in. The first was the warning about the high pressure in the system and how important it is to relieve the pressure before cracking the fuel line loose. Just remove the fuel pump relay and run the engine until it stops. Be sure to clear the low-pressure code that will set as the pressure goes away.
The next tip involved turning the engine to get as little pressure on the pump as possible. When removing the pump, remove the bolts a half turn at a time to not put too much stress on one side or the other as the pump comes loose. If you feel there is a lot of pressure pushing the pump out of the head, turn the crankshaft slowly in the direction of rotation (clockwise) until you feel the pressure going away, as the cam follower comes off one of the four high points and goes on the base circle of the lobe.
Pump Installation Tips
When installing the new pump, it’s not a bad idea to remove the roller tappet and inspect it for damage. Lubricate it and its bore and make sure it’s installed correctly with the pin on the tappet in the groove in the bore keeping the roller in line with the camshaft. Lastly, be sure there are no fuel leaks and all the lines are properly connected.
I haven’t mentioned the low-pressure pump for a couple of reasons: The first is that this Sonata always ran in limp when the problem occurred, so we knew that the low-pressure pump was running.
Historically, there have been more problems with the high-pressure side than there has been with the low. When it comes to diagnosing the low side, there is nothing new, other than they are looking for a little more pressure (69-75 PSI) than we are used to seeing on a port-injected system. Your fuel pressure gauge set should have the proper adapters to tap into the inlet line at the high-pressure pump.
From there, command the pump on with the scan tool, jumping the relay or turning the key. If you should find yourself removing the in-tank fuel pump module, check your service info for the procedure. You don’t have to remove the tank, but it will have to be lowered to facilitate removal.
So, at the end of the day, we were able to help the body shop repair the Sonata. Both the shop and its customer were happy, and we were pleased that we learned more about GDI.
Article adapted from Import Car.