January 24, 2021

How To Diagnose a Hot Start Problem- By [SPOOLIGAN]

I figured I would do this write up to help the large amount of people with this issue or who may have this issue in the future. This is just a simple FAQ that will hopefully solve/find the culprit for your hot start problem.

1) EGR Valve- Sometimes the EGR Valve will fail on our DSM’s. When this happens, you may encounter a hot start problem. Think of this as a great opportunity to do something you may have wanted to do but have continuously put it off. I am talking about the EGR valve block-off plate. Remove your EGR valve and install the block-off plate. If your EGR valve was bad, this may fix your hot start problem. If not, at least you will never have to worry about having a dirty throttle body anymore. Which brings me to number two.

To find out where to get an EGR block-off plate, reply to this thread.

2) Clean Your Throttle Body- After you have installed your new block-off plate, clean your throttle body with carburetor cleaner and some rags. Be sure to open the throttle plate and clean it when cleaning the TB so you can make sure you get her all spic and span.

3) Fuel Pressure Solenoid- The FPS, is designed specifically for hot starts. It raises the fuel pressure during hot starts to make it easier to fire up the engine. If your FPS is bad, this may be your problem. Replace it. You could also unplug the vacuum line that runs to it to check and see if it is your problem.

To do this, drive your car enough for it to get warmed up. Come home, turn the car off. Try to start it. If it will not start, unplug the vacuum line to the FPS, then try to start it. If it does start, then that could be your problem.

Most of the time when people upgrade and mod their cars using a AFPR (adjustable fuel pressure regulator), they remove the FPS to clean up the engine bay and free up some space. You can re-install the FPS by running the vacuum line from the intake manifold, to your FPS, then to your FPR.

4) Other Vacuum Lines- Change all of your vacuum lines. One of them could be split and causing a leak.

5) Change Your Plug Wires- You don’t need to run out and get some new NGK plug wires. You can if you want, but it’s not necessary. You could purchase either OEM wires or Magnacore wires (Magnacore wires are the cheapest). You will probably only be using them just to see if it fixes your problem.

6) Spark Plugs- If you are at the parts store buying new plugs, you might as well spend the $5 for new NGK spark plugs.

7) Clean Intercooler- You should also clean out your intercooler. Over time, alot of stuff can get in there as well as build-up of blow-by. To clean it, remove it from the car. Dump some gasoline in it, shake it really well, then dump it. The gasoline should look pretty nasty after you dump it the first time. Continue this process until the gasoline comes out very clean.

8. Coolant Temp Sensor- This is one of the most common reasons for a hot start issue. There are a few different coolant temp sensors. You want to change the one that tells the ECU what the temperature of the coolant is. It is under the thermostat housing, to the left of the sensor for the temperature gauge. It has two prongs.

9) Thermostat- In order to replace the coolant temp sensor, you have to drain the coolant. While you do this, you should go ahead and spend the $8 to replace the thermostat.

10) Radiator Cap- You should replace the radiator cap as well when doing the CTS and thermostat. Your old one may not be sealing properly.

If you have done all 10 of these steps and still have the problem, you are going to have to keep looking. Most of the time, hot start problems will be fixed by following these steps. But there are the unlucky amount of people who have to resort to checking other things.

Here is a short list of other things you could check/replace:
-Fuel Pump
-Fuel Rail
-Fuel Injectors
-Fuel Injector Clips
-Fuel Injector Resistor Pack
-Coil Pack

If you have done everything mentioned in this thread and you are still having problems, it is time to make a new thread so you can get more help to figure out your problem.