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Fuel Injection Mysteries

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posted on Dec, 31 2006 @ 12:21 PM
Back in the good ol' days, cars had carborators. These were relatively simple fuel air mixers. Troubleshooting and repair was fairly cheap and inexpensive for backyard mechanics.

Then they went to fuel injection, supposedly to get better performance and mileage. Looking at todays car mileage doesn't seem to show any improvement though. The only thing it really did was make it more difficult for backyard mechanics.

Until recently I refused to purchase a vehicle with fuel injection because I didn't know how to work on them. That all changed with a $450.00 Buick Regal I found. After fixing most of the problems, it ran great for a while.

A few months later it started to die out of the blue. Sometimes while going down the highway, and sometimes at a stop. It would always start right back up though. Then one day it wouldn't start back up, and I was stuck in the middle of an intersection.

The tow driver took it to a mechanic shop I knew. They said that it could be this, or could be that, and they would like to start by changing some parts for $675.00, but they weren't sure that would fix it.

Forget that! The car didn't cost that much.
I put it on a dolly and took it home. I started researching the problem and found out that there are so many things that could cause it I didn't know where to start fixing it.

I compiled a list of what could be wrong, and hit the junkyards for cheap parts. It turned out to be flakey injectors, which I replaced all 6 from the junkyard for $50.00, but it made me want to start a thread about troubleshooting fuel injection to help others.

I dont have the time to lay this out more professionally, but perhaps it will help someone. Please feel free to add to this troubleshooting list for fuel injection systems.

First, I make the assumption that you have some basic mechanical skills and tools. Second, I assume that you dont want to take it to a mechanic. (what fun would that be?)

Here is a link to a basic diagram of fuel injection systems for your review.

The basic checks are:

Fuel pump/cell operation.
Fuel pump/cell pressure.
Fuel pump/cell volume.
Fuel injector voltage/amps input.
Fuel injector ohms.
Fuel injector operation.

There are many other things to check like the crank sensor, cam sensor, MAP sensor, etc. but I dont have time to go into those. Please feel free to add them in.

Here is a bit more in-depth list.

1. Start with the fuel. Is there water in the fuel? Did your wife put diesel in the gas tank by accident? Mine did once!

2. Is the fuel pump/cell functioning? Turn the key on and listen for the whir sound of the fuel pump. These pumps are mostly inside the gas tank nowadays, so they are no fun to change, but it can be done.

It is good to remember that some cars are made with a kill switch for the fuel pump in case of accidents. This can also be triggered by towing, or even a hard bump in the road. The reset button is usually in the trunk of the car.

3. Is there enough fuel pressure? On the engine follow the fuel line to where it comes into the fuel rail. At the fuel rail there should be a threaded nozzle, just like the one for air on your tire. Rent or borrow a pressure guage and test the pressure.

Use the web to find out the proper pressure for your vehicle. I sometimes like to use the Auto Zone site for some of these specifications. It allows you to choose your vehicle, then you can look up some of the repair info for some of the items.

4. If the pressure is low, it can cause the injectors to malfunction. Troubleshooting this can consist of replacing the fuel pump/cell, physically checking the screen on the fuel pump/cell. It can get clogged from rust in the tank. Also, the fuel filter may be clogged, (about $4 part). If these are ok, it may be the fuel pressure regulator, (another cheap fix). You will have to pull the plenum and fuel rail to replace the regulator generally.

That is kind of scary the first time because it looks complex, but it's not. Basic steps are; remove the plenum cover if it exists. Disconnect the airflow hose, unbolt the plenum, disconnect the vacuum lines, electrical cables and throttle cable. Unbolt the fuel line from the fuel rail, (release the pressure first), and viola.

If the pressure is ok at first, then drops dramatically it could be a bad/stuck injector. We'll get to that later.

5. If the fuel pressure is ok, the problem could still the fuel pump. You need to check the volume of fuel the pump is putting out. I have heard of the pressure being fine, but there is still not enough volume of fuel for the car to run at mid to high speeds.

6. If the pressure and volume is ok, check the voltage on the cables at each of the fuel injectors using a digital multimeter or a noid light.

7. If the voltage appears ok, the inector could be bad or weak and misfire once hot. So check the ohm on the injectors while hot if possible. Use the web to find out the appropriate ohm for your type of injector.

These basic 7 steps seem to take care of 90% of fuel injection problems. Thats all I have time for now. Hope it helps some of you backyard mechanics.

Best of Luck

[edit on 12/31/06 by makeitso]

posted on Jan, 12 2007 @ 03:38 PM
great writeup makeitso. Really good info.


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