Hello all,

Last week I changed out the fuel pump, relay and filter due to the pump failing...pump was dead. It drove great for a week and now I have a strong pump and no start. I checked for pressure at the rail...just pressed the valve and gas just dribbled out. I swapped around relays just to make sure the new relay did not go bad and still no joy. Any ideas? (If I put this in the wrong forum, I apologize).

Christopher

 

Moved to OEM TECH:

Do you know if you have power going to the pump?
I've seen new pumps fail.

 

Could be a bad crank Position Sensor, check and make sure you have spark. If you have spark, that's not it. Then, do you hear the pump kick on at all? With a new pump, your check valve should keep the line pressurized for awhile, so drain the pressure with the valve, then hit the key to the on position, you should hear a slight hum which is your pump priming the line. If you don't hear it, unplug it and check for voltage. Harbor freight sells a cheap multitester (like $10) that is a great investment for a Jeep. Not the best quality, but small and works in a pinch. my snap on tester was like $250 so you could spend alot on one too if you plan on using it alot. Anyway, back to the pump, if you have voltage, it's a bad new pump, not unheard of. If not, check your fuses. there are like 2 or 3 that will kill power to the fuel pump. One of them is the big 30 amp that is also your engine control, the other is a mini fuse. there may be one in the fuse box inside too, I don't have my book in front of me anymore to look and be 100% certain. If all those are good, then check wiring. Again that multi tester will work great to check continuity. Another something that will kill power is the auto kill switch, but I only know of it's existance and not how to test it off hand. Hope this helps.

 

It is not a fuel problem anymore. I replaced a few hose clamps that I had problems with, now I have plenty of pressure at the rail. It turns over strong, fuel pump running, but will not start. I pulled one of the plugs and it had fuel on it...I am alone right now so I can't check for spark. It was running great, for five days, now no start.

Christopher

 

I went out and found the CPS and it is reading 4 Mohms. It is cold out, but I think that is a bit high. I still have not checked for spark, but it looks like a replacement is in order.

Christopher

 

Typically, a bad CPS will kill both gas and spark, not one or the other. 4 ohms is not right at all. I just went and tested mine and the correct reading on my tester is OL. I would retest it to make sure that's it.

 

Last night in the cold, it read 4 Megaohms (Mohms). The sensor probably has a couple of diodes in it, so you may need to swap the leads around. The manual said that it is supposed to read 125-275 ohms on a hot engine. I was an aircraft electrician for many years and am using a Fluke meter...I understand how crazy electronic components can behave...it might just start up if I go and try it right now because it is warmer today. The plugs may have had some fuel on them because it did make a very short rumble of a start before it died comletely. I still have not gotten a chance to check for spark yet. Thanks for all the suggestions thus far . I will keep plugging away at it.

Christopher

 

I finally got out to check for spark...nice blue spark is what I have. I have plenty of fuel pressure, but nothing this time on the plug. I read for the .5VAC-.8VAC from the sensor as the engine cranked and got nothing. Looks like the sensor is dead.

Christopher

 

Swap out the CPS and that should solve your trouble. you may want to also check the cam sensor in the distributor as well, just a thought.

 

If you have a strong, blue snapping spark, the crankshaft position sensor is unlikely to be your problem.

When they fail, you have NO SPARK.