Mechanics

ENGINE SHUTS OFF

1999 Jeep Grand Cherokee

Engine Mechanical problem
1999 Jeep Grand Cherokee 4 cyl All Wheel Drive Automatic 127, 00 miles

engine would shut off and then restart, over a period of time engine shuts off and would take several hours or next day to start. Sometime it will only run 10 minutes then shut off, sometimes over an hour and shuts off. Not throwing code. Has factory defect on PCM and replaced with sheet metal screws. Replaced Coil packs, new spark plugs, radiator cap and fuel engine cleaner. Per auto shop costing $748. For it to do the same thing, the only difference this time shut off headlights and started again. Fuel pump is working perfect, camshaft relay working, postioning sensor working. Have been working on this for 5 months with no answers. Single mother and I do most of my repairs to my ability and knowledge. In need of good advice
Avatar
Deana mathers
November 5, 2010.



All " crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.

Wrenchtech
Nov 5, 2010.